I have designed adapter boards for replacing original relays found in APT Holman preamplifiers. These relays (IDEC and Aromat) are now about 40 years old; replacements are difficult to find at best, and are not optimal for low-signal usage - they were general purpose relays. Owners of these preamps know by now that one of the most common failures in these otherwise excellent units is the relay. Relays are a maintenance item, and when they are decades old, replacement/upgrade is a good idea. We're fortunate to have really high-quality relays available in small sizes like this Omron. I've installed and tested them in my 3 APT Holman preamps, and they look and function great. Total height is much lower, since the new Omron relays are really tiny compared to the original relays. Link to Omron relay datasheet: Omron G6S

My adapter boards are extremely compact - just barely larger than the original relay footprint. They utilize a top-quality, low-signal current production relay - Omron G6S-2-Y - that has very low current draw, very low contact resistance, and very high cyclic life. They are used in expensive, high-quality audio equipment by major manufacturers, and I've used dozens and dozens of them in my multi-relay input selector boards. Their performance is excellent, even with very low MC phono signals, as well as line-level output signals.

These are sold as completed and tested (on a jig with a flyback diode connected to my lab power supply) assemblies so you don't have to solder the pins or relay. The boards use header pins to connect to the original APT main preamp board. Just desolder your old relay, and pop in the new relay board assembly and resolder. I recommend you seat the pins only deep enough to solder properly so you don't have to trim the pins - there is no need to seat the adapter board against the PCB.

For the Aromat adapter board, I've revised the design to includes pads for the flyback diode closely across the power supply pads of the new Omron relay, rather than an inch or so away on the main PCB. If you want to keep your original layout, just ignore the new diode pads on the adapter board, but if you want the revised layout, let me know when you order and I'll solder in a 1N4148 for free - you will then remove the flyback diode on the Apt PCB when you replace your Aromat relay with the new board assembly.

Assemblies will be shipped by USPS in a padded envelope, with additional protection around each relay assembly. Postage costs me between $5.50 and $6.50 per envelope which costs more than $1 each, so total price is very reasonable - $34.00 for either version including shipping and PP fees (Continental US only) if using Good and Services, or $32.00 if using Friends and Family.

I've installed and tested them in my 3 APT Holman preamps, and they look and function great. Total height is much lower, since the new Omron relays are really tiny compared to the original relays.

Link to Omron relay datasheet:
Omron G6S




I've had a couple of questions about how to access the relay, and how to determine which factory relay is installed.
There is a bottom panel held on with Phillips head screws that are easily removed. The relay will be readily visible - you can take a photo of your relay and if you have either the Aromat or IDEC I'll let you know which one of my boards is correct.

Here are the Aromat (left) and IDEC (right) original relays. Pinouts are completely different, so the adapter boards are specific. Additionally, please read the voltage markings on your relay so we are sure your unit uses a 24VDC part.

Hi everyone,
I bought this Nemesis as is and the output Mosfets were annihilated. All 10 were destroyed. On the botton side there was 5 IRF3205'and naturally I assumed that the top would be the same. After further troubleshooting I noticed that they were not all the same. The top side had only two as pictured, PLUS a MUR2020CT and 2 goofy ones marked 01A. I feel like that is incorrect. Any inputs you guys are really appreciated.
Preview attachment IMG_2569.jpg
https://mail.google.com/mail/u/0?ui...attid=006C07E4-A75D-4FBE-9EAA-7B3B41B2B92F&zw
https://mail.google.com/mail/u/0?ui...attid=006C07E4-A75D-4FBE-9EAA-7B3B41B2B92F&zw


Preview attachment IMG_2570.jpg



Preview attachment IMG_2571.jpg




IMG_2571.jpg
4.7 MB


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IMG_2573.jpg
5.4 MB

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4.8 MB

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4.5 MB

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3.6 MB

Some might call me a glutton for punishment, but I have taken on one of these that’s sickly and that has even had modification attempts! I’m nearly at the point of digging into the power supply. It’s great to have schematics available online, but I’m struggling with identifying ZD12. It‘s labelled as a ZD20, but I’m clueless at exactly what that specific Zener is. Would anyone know?

Over the next few months, I'll be building the DynakitParts ST-35 with their bias control upgrade and choke. I also will be doing some other simple and inexpensive upgrades, whether "necessary" or not. I have opted not to use "enhanced fixed bias" circuitry, choosing instead the bias kit from DynakitParts that allows adjusting each tube individually.

It's a very nice kit, complete with everything needed except tools, solder, and tubes. It even comes with a free Dynakit ball cap. https://www.dynakitparts.com/shop/st-35-kit-120-vac/



I did purchase the optional tube cage as shown above, but I doubt that I will ever use it. Some future owner might though. I might open up the solid sheet metal sides and install matching perforated metal if I can get a small quantity of it.

A discussion of tube lifespan and possible power supply mods is here: https://www.diyaudio.com/community/threads/dynakitparts-st-35-power-supply-mods.398189/

The first "upgrade" was to purchase a 14/3 power cord. The kit comes with an adequate 18/3 power cord with inline rocker switch, but I will be installing a switch on the chassis instead, ideally a rocker switch on the front panel if I can find one that will fit.

Today I mounted four larger rubber feet to the bottom of the chassis. The ones that come with it are very, very small, making it hard to lift or move the amplifier because you can't get your fingers under it. I just happened to have four new rubber feet from some other project in my parts box and some screws and washers that fit, so that worked out great.

The two power supply diodes look a bit skimpy by today's standards, so I'll order a couple of 3A diodes if I don't have any in my parts box.

The four coupling caps (C4 and C5) that came with the kit probably are fine, but I'll upgrade those with something a little nicer like the ones shown in the video at the bottom of this post. I'm not sure what those are though. What's a good cap to use without busting the budget and given the obvious space contraints? If Mouser sells something good, I'll be placing an order from them anyway so I could save on shipping charges.

I can't stand silver audio components, so everything is now satin black, including the choke and the quad cap. I have decided for a variety of reasons to stuff different capacitor values into a quad cap can that I emptied out, rather than use the included 60/40/20 uF 450VDC 100uF 25VDC quad cap. The 100uF section isn't used with the bias upgrade kit, so I only need three caps not four. I have retained the terminals and locking tabs unused and undamaged. I bought a cap that had a sticker on it instead of stamped values on the can so I can make a decal to show the values that I actually put inside along with the date.




I have completed the artwork for a new set of white decals to go on the satin black chassis. I haven't had them printed yet because I may use triple binding posts for the speakers instead of just the 8 ohm outputs, and I may be able to fit a power switch on the front.




My first technical question is, with modern equipment, C1 is no longer necessary, correct?




I'll be ordering some 6P14P-EV or 6P14P-ER tubes for it. The ST-35 runs the tubes quite hard, and those military ruggedized versions of the EL84 can handle it.

I'm not sure if there is any real need for the CL-90 inrush current limiter, but it seems to be a popular option.




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Update: here is the final schematic as-built. Parts in red indicate additions/changes vs. the kit.

I currently am running a pair of k402MEHs as a 3 way with a pair of f20 subs. I just picked up a Yamaha sp2060 and it offers a 2 way + sub configuration and a 3 way configuration. I like having the full range for my stereo setup (my MEHs will dom20hz to 20k, but I am pushing the M3H 15"Celestion woofers too hard..hence using as a 3 way now).
What is the difference, and what would the advantages and disadvantages be. I am using a Denafrips Athena 2 channel preamp for my stereo setup and feed my Marantz av8805a into one input on the Athena for movies.

I would like to introduce AST Conductors, a new company in the market, but with
a history of several years of advanced R&D. We have been passionate
audiophiles and DIYers forever and we also happen to include in our team accomplished
metallurgists with connections to the research community.
For several years we were discussing ways to develop the best possible silver
conductor, as there were products in the market which indicated that there is some
upside there,
Having rewired several amps and other equipment (both DIY or not) we knew very well
the importance of the hookup wire quality and, of course, the material used in cables.
So we embarked on this R&D journey and invested in some pretty high-tech equipment
for the production of silver wires.
We managed to achieve a purity of 6N+ measured by a very specialised independent lab in
France.
The sonic results were very positive from the beginning and, as we were improving our
processes and lab results, they were becoming really impressive.
Ultrapure silver, when correctly processed, sounds extremely detailed and balanced,
very harmonically rich and smooth sounding. Maybe its most important characteristic
is its naturalness. It does not have any of the typical silver \glare' and aggressiveness.
Even a short piece makes a clear difference in a system's sound quality.

We are getting excellent feedback from our customers, which include DIYers and
audio manufacturers.

Having sent some samples around we were pleasantly surprised to have our first
Youtube review by channel iiWi.
You can see it here:

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And you can read more at www.astconductors.com

SInce the start of this year our products are for sale and we are preparing a proper
webshop. Currently we receive our orders by email.

So, we are very happy to present ourselves to the community here (which in the past has included
members of our team) and answer any questions or enquiries.
Nick Mesimeris, General Manager AST Conductors

under
Schiit Audio: Audio Products Designed and Built in California
I read this:

Choose Magni 3+ for the ultimate expression of an affordable all-discrete current-feedback headphone amp. It’s now seriously like a mini speaker amp, right down to the driver stage and Vbe multiplier. Magni 3+ is in our traditional silver and gray chassis.

but in post #130 under
Review and Measurements of Topping A30 and Schiit Magni 3 Headphone Amps | Page 7 | Audio Science Review (ASR) Forum
and
Schiit Magni 3 abgefackelt - Verstarker, Lautsprecher, Zubehor - Analogue Audio Association
so as in the attachment (first both images) you will find versions with destroyed output stages.

A headphone friend I know well wanted to hear my opinion on this device because he is playing with the idea of getting this device.
But after checking the web I found the above mentioned (I was shocked), so that I strongly advise against buying it.

Nevertheless I want to know the reason for that or at least the schematic, which isn't online for download.

Hello All!

I just built two Elekit TU-8888 monoblock amps. One is working fine I have issues with the second. Look forward to discussing. I built a TU-8200 using Sophia Electric EL34 several years ago.

Full meaning the whole thing.....

I last listenend to my BEST OF MOUNTAIN record 🙂

Hi ! It is something about impedance matching or what else ? Capacitors value are so small that my multimeter shows 0.01nF that propably be an error, but it measures values about 5-10nF very well...

Hello Audio Enthusiasts! Some of you may know my work on www.audiocircuit.com, where for many years I have been helping to advise Acoustat owners. I was an engineer and manager with Acoustat, starting when the David Hafler Co bought Acoustat out of bankruptcy, right up to the very end of US production under Rockford Corp ownership (sad day that was!). So I thought I'd lend a hand here, too, because I LOVE Acoustats and want to help as many owners as possible to keep their Acoustats running for many years to come. I don't sell parts or do repairs, but my advice is FREE! So let me know how I can help YOU with your ACOUSTAT's! (And this being a DYI crowd, I don't mind discussing modifications to the speakers.)

Andy Szabo

stay safe my friends!

here are some projects i am working on at home

first i got some old vifa midranges back from a friend, and I got small dayton amt to mate them with
vifa 13wh-00-08 is somewhat special midrange, free of the breakup grunge, even the ones i got are old, they still measure nice

here are some pics from the build, work in progress

may go active!

I've used easyEDA to create an EF2 Blameless-style amp schematic and find it easy to use, but up to a point. After 14 months of reading Netflag breaks/errors and fixing these only to Save and Refresh and see rework dissapear or flags reappear, I've decided to swallow my pride ask for help.

My aim is to sell PCBs to raise money for a Social Enterprise [OneDollarGlasses] and local charity [SeeScape] - both support people with vision issues. Should anyone have an interest in assisting me please reply. Once the amp is soak tested, I'll make the Gerber available to those of a like mind who may wish to sell PCBs in their region and donate profits to a charity of their choice. Using easyEDA isn't imperative should someone wish use a different tool. The schematic attached has fuses and some protection diodes to get placed in.

There are plenty of cool pictures in the photo gallery threads posted in the other forums, so it only seems right that there be such a place to post your amp photos in the class d forum as well.

It doesn't matter whether you've got a prototype working on the breadboard, an amp jerry rigged on the table, or an electronic masterpiece in a case; post your stuff here for everyone to check out. It's a good way to share ideas and may even give someone a little bit of inspiration to tackle that project they've been wanting to do 🙂

Hey Guys

So the other day I picked up a used set of Martin Logan Aerius i ESL's in great shape and I have been really enjoying them. I was thinking it might be a good idea to think about replacing the 20+ year old electrolytic caps in the crossovers with something better such as Clarity caps. I'm fairly new to this but know this is popular with conventional style loudspeakers. I'm comfortable working through parts values but I'm not really 100% sure where my time and money would be best spent so I'm here to take in any info offered.

Martin Logan has proved to be extremely helpful and provided me with crossover schematics and a detailed electrical print on the whole speaker. I have not opened these up yet to take a look for myself but plan on doing so this week at some point. I've attached all the electrical info for everyone's viewing pleasure.

Hey everyone,

Hope you're all having a great day.

I've been locked into Troels Gravesen’s designs for the past 6 months, obsessing over which model to build. But recently, I decided it’s time to get out of my comfort zone and explore other options, and Lautsprechershop.de came up with some really interesting kits.

That said, I have a couple of concerns:

1. The website looks like something my grandmother used to browse on her dial-up modem, so I’m wondering, has anyone here actually ordered from them? How was the experience?
2. Some of the designs seem a bit under-documented, missing cabinet drawings and detailed build guides.

Would love to hear your experiences before I pull the trigger.

Thanks a lot!
Awni

Hi Forum

Warning: there is no such thing as "the beste (NOT, as in limited LF) full range Speaker in the world".
But the title sounds nice as a follow up of the previous thread. And like my previous design it is all about what compromises you want to make.

It has been over 6 years ago that I build that big 3 way speaker, together with my friend Joost who made the small two way that I also build as surrounds with Atmos upfiring section
"building the best 3-way full range speaker"
Earlier this year we did a big renovation of the living room with attached kitchen and when this was done, I found the speakers a big too massive.
Maybe it is my age and the testosterone is diminishing but the speakers always were big.

So I am starting a new design, with 20% smaller footprint and 30% less volume.
Still a large speaker but a bit better suited to the room and in this thread I would like to share this journey with you.

What did I do so far.

Wel in this design I want to be capable of simulating and measuring better to help tweak the end result with less trial and error.
For enclosure simulation and filter design I will use VituixCAD (with a well deserved donation when it all works as displayed)
For measurements most likely Arta

And to make sure that what we measure is accurate I bought an EarthWorks M23R and built a nice mic stand that should be close to the ideal setup.
The stand is described here:
The Ultimate Speaker Measurement Setup

A smaller speaker will be more limited in its LF performance, and that means a dual 8" instead of the original dual 10"
An 8" woofer will cross better to a 5" midrange then the previous 6" and also can live in a smaller enclosure.
The tweeter is to me still a beauty so it remains the same but might be crossed a bit higher
So the following units are selected and ordered:

• Dual Audio Technology Flex unit 8 H 77 20 06 SDKA
• Dual Audio Technology C-Quenze 15 H 52 06 13 SDKA-LR (so without the M surround as this one has a lower Fs)
• Scan Speak D29080714000

The smaller woofers allow for a smaller baffle and that will influence the way the speakers are perceived from a size point of view.
The underhung magnet construction should improve linearity and the smaller lighter cone will improve speed compared to the 18 H 52 17 06 SDKA that I used in the big speaker. the later was ordered with an Re of 7,5 ohm as was the 10" 10 C 77 25 10 KAP I used in the big design.

This selection comes with a few new design challenges.

• The midrange with its underhung motor cannot be ordered with a higher Re, so the two units in parallel will have an Re of around 2,7 Ohm
• These midranges have a higher efficiency and I want to use that to make the end result a >92dB @ 2.83V
• The tweeters low end will match that but the design will most likely have a slight roll off above 10k what in practice is also a normal design criteria
• The woofers will have a hard time catchup up with the MF/HF set so it will be powered by a Hypex module with DSP section

Using a (modified) class D plate-amp for the LF section has a few massive advantages:

• You can tweak the volume to keep up with the very efficient MF units
• You can add room correction without the risk to ruin your high end frontend (DAC/Phono/Pre/Power) as the important MF HF section does not need to pass a low cost ADC/DAC that is part of the plate-amp.
• The big impedance peak at 15Hz and and mainly the one at 60Hz (enclosure tuned at 30Hz) of about 20 Ohm would make a passive low pass filter complex and bulky. This all is not needed with the DSP filter section that is only used for the woofers
• The cost of serious LF filter parts is also substantial and I think the plate amp will be only mildly more expensive
• The Re of 2,7 ohm is fine for this nCore based amp with still 400 Watt @ 2 Ohm

The enclosure will have a similar construction and look and feel as that is what fits nice in our house.
multi layers of MDF and HDF, and for now a baffle milled out of a solid 40mm thick aluminum slab 🙂
10 pieces metal 8 mm rods that span the baffle with the rear to remove all fibrations by adding a tension on the total enclosure.
This is all copy and paste from something that worked very well.

The next challenge is to learn a 3D program (Fusion360) a I need a .step file so the CNC company can cut the front panel to the right size with the right diffraction preventing curves.
So I do not expect an update soon.

Cheers,
Peter

Hi guys,
Is it possible to change this buffer to have about 12db gain without sacrificing sonics.
One channel shown.

Hi everyone,

For years, I have been reading the various DIY turntable threads on this website, hoping to get some ideas for a design of my own. It seems that everything imaginable has been tried, and the only variations from turntable to turntable are visual rather than technical. The one area of interest to me is the design of the turntable main bearing.

No matter how precise the shaft and the sleeve bearings are made, there has to be even the smallest clearance and that clearance causes the shaft and platter assembly to wobble in a counter-clockwise direction. I have learned that quite recently. So, I set out to design my own “Zero clearance” main bearing.

My bearing design is based on a principle that was discovered hundreds of years ago, but to my knowledge, has never been used in the design of a turntable main bearing.

I am not ready to disclose how the bearing is going to function, for fear that I’ll fall flat on my face if it doesn’t.

Because of that uncertainty, and because I don’t have the money to build “iffy” turntables, I am going to build a no-cost test model, just to test the bearing principle.

So, I looked around my shed and discovered a discarded disk brake rotor, left over from a brake job I did on my pick-up truck some time ago. The rotor weighs 24 LBS. and is about 12” in diameter. I machined a spindle for it from aluminum pieces lying around my shop, and I made a base from ¾” hardwood plywood also lying around my shop. And then my CAD computer crashed. That was in December 2021.

I used to do all of my design work on a drawing board many years ago, and around 1994 I switched to CAD, and there is no going back! Luckily, I paid off my mortgage in January of 2022 and I was able to build a new computer. Three weeks ago I finally got it set up and running.

So, in this first post I’ll show you the beginning of my test model, and in subsequent posts I’ll show you the proposed design of my turntable that I will build, if my initial tests work out.

The build might take the rest of 2022 because I have yet to establish sources for the various components of my turntable.

Sincerely,

Ralf

�-��m�

Hi all, extremely keen on building a tiny tiny listening bar. I’m a visual artist and intend to transform a tiny self built pavilion into a listening bar.
The purpose: set up the bar in exhibition spaces, collaborate with artists, dj’s to concoct weird drinks menus and musical explorations.

The place is already built: 18mm plywood room (floor and walls) with a paper/wood cassette ceiling, dimensions 220x330x230 cm LWH.

It will feature a bar and 4 fixed stools, and a booth for 2. (See plan sketch)

What isn’t there: the bar, sound system, drinks&vinyl shelves etc.

My skills: sculpting, wood.
My interest: building speakers (I like large speakers in a tiny room!), to set up a weird but also nice experience for visitors. Afterwards also building some more if it turns out well.

The speakers could be built into the wall, since there is space around the pavilion, like backpacks hanging from the wall exteriors.
Almost no budget, so looking for diy or assembled parts to build with.

Curious!

Having build the very capable F6 I was left wondering (more like fantasizing) about how I could improve this magnificent amplifier.
Fortunately I'm not the first one here having this crazy ambition, so I soon gathered a list of improvement candidates.
This is where my problems started. I am educated in the field of software so i quickly realized that I am in over my head when it comes to electronics.
However, this has never stopped me when creating software so I quickly decided that I'm not going to let it stop me this time either.
Having considered the options I have chosen to start with the power supply.
After gathering tips and suggestions from this forum I have settled on a dual mono power supply in a separate box.

So far I have gathered:
Two sets of Nelson's Bipolar Power Supply
Two Toroidy transformers
A soft start board from the DIY Audio Store
A Pesante 2U from Modushop

I have attached a picture of the layout I'm considering.
I welcome suggestions to this setup and anything that might make it better will be considered.
Thanks in advance.

Oh, by the way, I could use a suggestion for a nice power button for the front.

At long last, I have completed the LX-mini Analog Crossover and posted
in in the Article section of FIRST WATT

It will serve as the documentation and assembly manual for the kit which
will soon be available in the diyAudio store.

Enjoy.

Hi,

I'm about to add a subwoofer output to a 6SN7 driver stage (Williamson style). U1a is the amplifier; U2b is the phase inverter.
Too keep things simple I added a STP8NM60 MOSFET (or similar) as source follower. My idea is that the MOSFET will lot add a lot of load to the first triode (U1a),

According to LTSpice this seems to work OK. With only 1.1 mA and approx. 300 VDC across the MOSFET the dissipation is only 0.33 Watt.



Note: The original 100K plate resistor for U1a was split into 2 resistors of 85K and 15K. Adding C5 creates a short for AC. The reason for this change is to lower the gain without changing the DC settings.

Any additional suggestions will be welcome.

Regards, Gerrit

DCX is taken.

I have a dcx2496 that was damaged with a power surge when we recently had an outage.
The unit is cosmetically perfect and can pass for new. It’s free plus actual shipping if you want to try to repair it.

US lower 48 only please.

Hello, i m andrea and i m from italy.
I just joined the forum to get some help with my projects.
I build tube amplifiers, guitars and cabinets.

Why is there such a big price difference between the two TDAs?
TDA7294V 2.9$
TDA7294HV 12.8$

Hi everyone!

This is my first post, so I hope everything abides by the rules and you get something out of it! This project was a long time coming for me and I would like to share it here.
I want to make a headphone amplifier, as I think it is a perfect "beginner project". Not too much power, not many unnecessary features, just a simple but performant amp. Going back to the basics if you will 😉
In this first post I will go over the background, some decisions I made for now and share the schematic I came up with.

Thank you all a lot in advance! I am really looking forward to your comments 🙂

Background and Goal
This amp is meant to deliver the best possible performance with the least amount of complexity and cost. Power efficiency is not a primary concern, as it is "just" a headphone amplifier, so naturally I chose a class A topology. The amplifier is meant to be built up entirely of through-hole components. While this makes it a lot nicer to build up for me as a hobbyist, it will also make the amp last a lot longer, as it will be easily repairable - especially as I am using only main-stream components (standard BJTs, standard values and packaging for resistors and capacitors). Furthermore, it is intended to feel premium and make a statement design-wise - audio gear has to look and feel premium as well imo. While the design is still a work in progress, I have some features in mind that I really want to implement. I want to show off certain parts of the electronics as a design-feature; more specifically, the power transistors in a TO-3 package. Therefore, the output-stage is designed in a way that there is only one high-power transistor - a MJ2955 BJT. That transistor was specifically chosen for its good availability and the TO-3 case available in a configuration with the collector connected to the case. The emitter-follower configuration of the output stage in combination with the grounded collector allows the case of the power-transistor to be grounded, which makes it possible to safely display it on the outside of the amp's case. I have always found old TO-3 packages to be really cool to look at and wanted a way to display them safely. I think this will be a really cool design-feature in the later amp!

Schematic
Following the philosophy of simplicity and fully discrete design, the preamp-stage of the amplifier is kept relatively simple as well. The input stage consists of a long-tailed pair. The constant current source is set to a current of approx. 620 uA for a high input impedance (roughly 100 kOhm) of the two input transistors. This stage is followed by a common-emitter voltage amplification stage biased to roughly 2.6 mA. Finally, the power-stage is made up of a PNP-darlington pair in a common collector configuration. The amp is designed for a single voltage rail of roughly 20 V, so a bias-current of roughly 500 mA will flow through the output stage (with the DC-component of the output signal at half the supply voltage). The output is coupled with a large bipolar capacitor (how large exactly will be determined as well by some factors of the final design, but it will be somewhere between 3.3 and 10 mF; the simulations are done with the "best case" of 10 mF). This makes it possible to use a simple power-brick as a supply and therefore circumvent a lot of the headaches with regulation and safety when it comes to the higher grid-voltages. I plan on using a 24 V power-supply with a barrel connector (easy to get, cheap and safe) and filter the supply heavily to get a smooth 20V supply for the amplifier.

Projected Performance
The simulations done for now show a power output of >500 mW into 32 Ohms. The distortion is low (simulations show <0.0001% THD at 1 Vrms into 32 Ohms and <0.0005% THD at 0.5 W into 32 Ohms - both at 1 kHz). The simulated bode-plot shows plenty of phase margin and a flat gain curve (to within 1 dB) from 1.5 Hz to >200 kHz. The clipping behavior and power dissipation of the components seem decent. I am really happy with the schematic so far. To be clear: I know that simulations are just the first step and I fully expect the real-world performance to be worse, but the results encourage me to go further at least. I am curious to see what the real circuit can do!

Outlook
The next steps now are to build up a prototype and - if that works - design and order PCBs to populate. In parallel I am designing a suitable case. This will be a long project, so bear with me; I really want to push this amp to the best possible outcome. To this end, I would love feedback if you have some! I know some parts of this project may seem weird, but I really want to keep the single-PNP-output stage and just keep the whole thing simple and easy to build. I guess the spirit of this forum is to try new stuff after all 🙂

What do you guys think?

I did some measurements of this circuit with some changes. The VAS stage is loaded by 1k to just show how it works together with the current mirror and the input stage.




The table over the measurements.
Measurement 1: No current mirror just 1,92k instead to get the same current in T1 and T5.
2: Now we have a current mirror and it raises the gain of the circuit 44,4dB.
3: The VAS has now 2x BC548B. 1 mA In the driver and 6 mA in the VAS output as usual. 5 dB more gain
4: With the resistors in the current mirror increased to 470 ohm the current mirror shows its potential.
5: 2N7002 as VAS and back to 47 ohm mirror resistors.
6: We are back at 470 ohm. No difference at 100kHz but at 1.
7; Increased current in the input transistors. Max gain of the test at 1kHz.
8: BC 558B as input transistors and no current mirror. We lost 58dB gain.
9: Current mirror shines.
10: Now lower current in the input transistor but no great change.
11: 2N5401 is a popular input transistor especially at high voltages. No gain change.
12: 2N5551 as current mirror is a tick give as a tick less gain.
13: 0,5 mA for the input transistors doesn´t change much.

Input noise: BC557B and the BSS84 has both good noice figures but with the 2N5401 care in the planning is needed especially if you use the amp with a volume control at the input.

The BSS84 and the BC 557B has different strong sides so the actual amplifier topology decides wich one will fit the best.
The MOSfet might give lower RFI with higher current and the gate not rectifying. Maybe a tick lower distortion. Maybe higher ripple rejection.
The BC gives lower offset voltage and price + you find it everywhere.

Hello. I built this serial fx loop as drawing below. It work very well with two small issues: First it raise a bit of noise - very extremely slight but still here when 5ft. patch cables connects.(I can pass that). Second it slightly pops when I engage any pedals I have ( not any external noise, just popping when engage the foot switch). All my pedals are supplied from mains from 9V independent smps adapter supplies. Please help how I can cure the popping noise when pedals engage please ? Thanks.


The level of noise is dependent by 100k pot position. More loud as the pot is more open. Should I isolate the recovery stage input with a cap please ?

Late: oh no, a cap at input recovery stage did not do a difference...more, it seems it pops a bit louder than before...A capacitor from the whiper output to pedal input did not helps either...
There are not ground loops, supplies are galvanic isolated by separation transformer...just a comute regime I cannot get rid of...

Boost channel worked fine for 32 years then provided reduced output, I put in a new valve but to no effect, something on the PCB such as an opamp or diode may be culprit

Any ideas folks?

This is a very simple Bingham tilt tone control which I found here: https://www.angelfire.com/sd/paulkemble/sound4e.html

I have recalculated components values for lower impedance (= lower noise) and smaller adjustment range (+/-5dB). The original circuit gives up to 40dB variation over the audible frequency range which is a bit excessive to say the least.

Schematic:



Frequency response:



Turnover frequency is 935Hz which is close enough to 1kHz.

Worst case input impedance is ~3kOhm which can be easily driven by any modern audio opamp:

I thought why not try the 3 pole compensated blameless amplifier clone. It worked out pretty well in simulation.
All important information is on the pictures.

Hello, a bit ago the amp suddenly died when sitting at idle and not playing anything, after that when trying to power it up just pops the speakers and goes into protect.

I only have some basic knowledge of amp repair. The tools I have are a scope, multimeter, thermal probe and soldering iron.

In the amp I was able to identify 1 dead output fet (B31N20D), but I also wanna check the overall health of the amp and if everything is working like it should, as it has been repaired before by someone else.

Currently I've removed all of the output FETs for testing, it seems to power up fine, but I found that a KSP92 transistor on a card gets very hot (over 70c). Along with some other transistors on the card being about 50c.

The card:



What would be the next steps? The KSP92 isn't shorted according to the multimeter.

Some observations:
One side of the output side:
Gate: 0v (has some sort of pulses)
Drain: +64v
Source: 0v (has some sort of pulses)

The other side:
Gate: -78v
Drain: 0v (has some sort of pulses)
Source: -74v


EDIT: measuring output section without and with signal (37hz sine wave) applied
One side gate:

One side source:


Other side gate:

Other side drain:

Speaker outputs:


Edit 2:
Removed the hot KSP92, but seems there are 2 of them in parallel, so now the other one gets hot.
Measured what's going to the removed transistor:
Base and emitter: about 84v
collector: pulses

why would they be getting so hot?

offer an original Audio Buffer pcb from PMA as well as a completed power supply from PMA,
the audio buffer can also be set up as a headphone amplifier, details on Pavel Macura's website,
there are also three BUF634 which are currently available for around 20 euros per piece at Mouser are available,
ask for 70 Euros for all

Has anyone had experience with this Oldchen EL34 Valve Tube Amplifier. Thanks.

Hi, after re-igniting a decades ago interest in electronics, when I recently re-capped an old Meridian 577 power amp, I was looking for another project and came across the Wolverine amplifier. I've registered my interest and I'm looking to build a 557 replacement and learn along the way.

I expect this forum to be a mine of information of the build. 🙂

Regards
Steve

EDIT DEC 2021 - There are a huge amount of lost photos in this thread, please go to this link to see the new guide:
https://guides.diyaudio.com/Guide/WHAMMY+headphone+amplifier/3?lang=en


Wayne's
Headphone
Amplifier
Must
Make
Yourself

Yes, it's a silly name. But it's cute. And it explains a lot about it. So it stuck.


Video of Wayne talking about the Whammy at BAF 2017 -- Wayne Colburn at BAF '17

PCB available here - WHAMMY Headphone Amplifier – diyAudio Store

Given the explosion in the popularity of headphones, as well as the unbelievable amount of choice and variety in the market, it seemed that a simple and great-sounding headphone amp would be a great addition to the DIY community.

This one will drive any headphone you want to throw at it. Wayne wanted a headphone amp for his desk. This is the fruits of that idea. It’s made to be made in an afternoon or an evening and it has no adjustments, it’s going to have a high likleyhood of success for the builders. 🙂

It's an all in one PCB, just wire the AC & fuse, input and output jacks. Add a selector switch if you like.

Class-A output stage with enough current to drive anything. It also makes a good linestage with about 14db of gain.


PSU

Transformer 15VA or 25VA 15+15 to 22+22

25VA 22V+22V is best and used in this guide.

Currently the transformers that fit the board are available at Digikey
Amgis 6663, 6664 / Amveco 70053

Here's a link to a factory surplus transformer that fit the PCB will work beautifully - You will want to make R16, R22, R29, R32 15ohm if using this transformer.

70054K PC Mount Transformer 110/230V-18/36V 110V-36V 110V-18V 230V-18V 230V-36V

There are pads on the PCB for a non-PC mount transformer if you have room in your chassis. Something like an Antek AN-0220 or AN-0222 would work well. AN-0220 - 25VA 20V Transformer - AnTek Products Corp

If you use smaller transformer you may need to adjust the bias down a bit. It will still be pure class-A for 99.999999999% of all headphone listening.


The bridge is made from 1N4004 or use high speed diode if you like. Snubber capacitor C20 0.22uF 250v X-rated.

AC filtering is done in a big and effective way, utilizing a CRCRC filter with 3300uF capacitors and 5.1ohm resistors. You can use smaller resistors and caps if you like, it's a very effective filter and will work well with even 1/2 the values.

The regulators using 7815/7915 can be elevated a bit, using a red or green LED as the reference if you wish. Don’t use blue, they are noisy and they will set the regulators to too high of a voltage.

Circuit

On the input there is a dual opamp used for voltage gain. We’ve tried these with great success LM833, Muses 8820, RC4580, OPA2604, AD823, TL072.

If you want to try a different opamp, try something made for audio. Feel free to try some surface-mount opamps in a DIP adaptor if you like, there are lots of neat opamps to try.

Gain is set by R8/R12. Lower gain, make R12 bigger, unity gain, R12=10K

Potentiometer - Alps RK27 fits the PCB, feel free to use what you like. If you have room in your chassis, this is a fine place for a stepped attenuator.

After the opamp there is a Mosfet source follower for current capibility, and the feedback loop includeds the opamp. This keeps the DC offset stable as well as lowers the output impedance to a very low level, less than 1/10 of an ohm.


Output stage

The output stage is a Mosfet NP pair in source-follower configuration. Being a follower it can add no voltage to the signal but can contribute lots of current. Since the opamp os being used for gain this is not problem. It also has the advantage of adding very little sonic flavor to the signal, it's esentally transparent. The output stage is simple, powerful, will drive anything, and is self adjusting due to optocoupler and the opamp controls DC offset because the output stage is in the feedback loop. No potentiometers to adjust or voltages to read when biasing.

Output impedance is less than 1/10 ohm

The following Mosfets work well in the circuit.

Toshiba Mosfet 2SK2013 / 2SJ313
Fairchild Mosfet On Semiconductor Fairchild FQP3N30 / FQP3P20
IRF Mosfet Vishay IRF610PBF / IRF9610PBF

No matching is required.

Bias arrangement (low offset due to opamp precision)

(4) 10K resistors make a voltage divider to give lots of bias voltage to the gates; this bias will be 1/2 the rail voltage. Assuming a standard build with 17v rails this will give the Mosfets a maximum of 8.5v of bias. With no other controls his would make the output devices conduct like there’s no tomorrow, and probably let the smoke out, but the 4N35 optocoupler helps control and set the necessary bias voltage. With this it happily operates in Class-A all the time.

The 4N35 optocoupler does a few things -

The optocoupler has two sides when looking at the schematic, the diode and the transistor. They are linked optically, not electrically, so the two sides of the optocoupler can share different voltages that don't effect the other side. as the current change in the LED side of the opto it will glow brighter or dimmer, which controls how much the transistor side conducts - in this circuit the current through the LED is directly equal to the mosfet current, and as it gets brighter it controls the BJT, whereby the BJT "burns up" the excess dc bias voltage.

The optocoupler appears to be a variable resistor in parallel with the inside 10k resistors - it changes the gate bias with the collector-emitter junction as the opto coupler looks at the current through the mosfet sources. The LED part of the opto has a 1.2v constant drop, this is used in conjunction with R18 to set bias current across the source resistors. If the current is too high it will make the LED brighter, that modulates the base of the transistor, and the collector-emitter junction will decrease its apparent resistance in parallel with the inside 10k resistors, changing the ratio of rail voltage to ground, decreasing the amount of voltage on the gates, and keeping the bias stable as the load swings.

Is a simple solution - its a single part and it automatically adjusts. If there is any drift the optocoupler will compensate immediately No resistors to measure across and potentiometers to adjust

Output bias

The diode in the 4N35 gives voltage across source resistors to set current, a 1.2V reference.
Total source R is added, so 10R resistors is 1.2V/20R=60mA
Want more bias? make the resistors smaller. 4.7R = 120mA

hi fellows, have been reading the original A75 publish and got a few questions wondering if i can find consultation here.

my electrical engineering study experience went no further than high school level.
DIY audio-wise, have successfully assembled and run AMB β22 singled-ended and balanced in these past 3 years.
started reading and assembling an A75 these 2 months.
can sense my understanding for audio amplifier components and circuits growing, but still won't say i am knowledgeable a all.

1. output stage circuit
   so i see in the amplifier wiring figure depicted in Part 2, it has speaker+ output connecting line coming from 'right in front of' the output stage circuit, rather than having OUT going through the output stage and then connect to speaker.
   i understand that the output stage is common drain mode in parallel, and it takes signal input from DRV+ and DRV-, right? so what would OUT be comparing to DRV? because in the complete amplifier circuit in Part 1, the OUT goes in to and through the whole output stage, and comes out as input to speaker terminal.
2. gerber drawing of power supply board
   is there an error with the section of where transformer secondary output goes into regulated circuit? R3 and R4 should definitely be between C4, C5 and AC, right?
   same thing with transformer secondary + and - marking in the wiring figure. (but probably most DIYer can make out these typo so no big deal?)
   after reading the article in these 2 months, i am 'guessing' there are minor errors with the gerber drawing but circuit diagram of amplifier and power supply are correct.

Would appreciate guidance on both A75 as well as suggestion on reading/studying direction to solve these questions.

SOLD a pair brand new never removed from packaging.

FYI they are in Singapore

Hi all, I picked up the 1908s Vox Venue 100 Lead very cheap, which has been working. Changed the power switch as the old one blew (it took out the small fuse at the mains plug so am hoping nothing else got "fried"). I notice one of the upright mid-size caps on the "first" board (the one that has the vol, tone etc. pots attached) seems loose, and is causing the classic "dry solder" popping & crackling, a fairly simple resolder fix once the board is out. Also, at the time I'll replace one or two pots as they're not responding to pot cleaner, with noisy rumbling. I have a basic hand drawn schematic from Vox but wondered if anyone has knowledge of a better one. Also, the reverb is very week, it has a dual spring built in but I'm not sure how to trace the signal amount going in and coming out, any advice would be appreciated. I thought a stronger signal sent to the reverb section by changing the resistor/diode might achieve this?

Many thanks in advance, Mark from Sydney, Australia.

Hi all, I have a 1980s Peavey Artist (100 combo with Black Widow speaker). Very weak output at volume, I think it might need new valves but have no way of testing them apart from taking them somewhere & paying for the service, which I want to avoid if possible.
Would you have any basic service or "testing "procedure I can follow to try & identify the cause of the weak output?
I am well aware of the potential high voltages stored in the capacitors but am keen to check the condition of the capacitors. I haven't had the chassis out yet to conduct a visual inspection for leaks etc. Can you suggest a setup I can make to test/drain any residual voltage in the caps? Can I use my multi meter and if yes on what setting?
Many thanks in advance, Mark from Sydney, Australia.

I'm building Scott Hinson's Multiple entry horns and one idea was to paint the primary horn flares with Musou black. The flare parts of the horn are mostly protected from direct contact, but I'm a bit concerned about long term durability and possible paint shedding due to vibrations.

Does anyone have experience with that paint, is it durable enough for this kind of application?

As we all known, theoretically, the second-order crossover requires reversing polarity of one driver to fix the 180 degrees out of phase between two drivers. However, there are many designs utilizing second-order crossovers with no reversing polarity on one driver. A simple answer (or the reason) for this performing could be the “measurements” don’t find the out of phase issue, so there’s no need any polarity reversal.

Nevertheless, that decision was based on “measurements”, what if we have no measurements, can we know when to reverse or not reverse polarity?

A study case, I found some manufacturers; ADS and Braun, made three-way speakers. It’s interesting that they use the SAME crossover topology on ALL models in the same series. That is second-order on all sections of crossover. And the most interesting thing is that the polarities of all drivers in all models seem to be FIXED; woofer(s) = positive, midrange = positive, and tweeter = negative. Or, in brief, non-reverse polarity between woofer(s) and midrange, and reverse polarity between midrange and tweeter.



I suspect if they MIGHT fix the polarities, by using the cited pattern, before setting crossover’s component values. If so, that should mean they know phase behavior before, or maybe the measurements aren’t that important, isn’t it possible? Again, if so, how can we predict phase behaviors, like them, i.e., what are criteria for reversing polarity or not without making measurements?

PS. I have no problems with measurements and I use a lot of measurements as well, but, just curious if we can shorten the procedures as there exists a thread advising how to build speakers without measurements—very good thread indeed.

U2 - Zooropa
Pink Floyd - Delicate Sound of thunder (next one up)

I bought two big horns this type, HL-1018:


46.3*24.4*21.4cm Wide*High*Deep*

and some real drivers Kenford comp50 with Titan diaphragm.
Not tried until now the classic driver for the horn but bought just for fun a Piezo screw on drivers GT-1188.

And did measure only a response down to 4khz like with the small tweeters like KSN1005 what left me puzzled


So did the real Motorola KSN1188 ever really reach down to 800 hz as pretended ? (did not find a measurement online of it).

And is the GT-1188 as a spare part (with internal step up coil) only not working on this big HL1018 horn?

I know that the piezos can never be as good as real coil drivers but is it possible that the frequency response is so far away from covering the claimed response down to under 1khz?

For sale:

A pair of step-up transformers from Sun Audio, made by Tamura.

Permalloy core

Provision for MC element with 3ohm, 20ohm or 40 ohm (i.e. gain of 34db, 26db or 23db)

3ohm and 20/40 ohm are on separate outputs, so 2 cartridges can be connected at the same time.

Only the 3ohm (Ortophon SPU) is connected to this case. If desired, one of the other connections can also be connected, or installed at an additional cost in another housing with all connections.

Asking 950€/pair or best offer, incl worldwide shipping

Here ya go guys, a place to share pictures and a brief explanation of your favorite amp or latest project. For discussion or an in-depth writeup, let's post at the Discussion Thread. Hope this will suffice- Who's gonna start things off? (again)

Selling a pair of 5998 tubes

These are labeled Chatham Electronics (Tung-Sol), and are electrically and mechanically identical to Western Electric 421a. They have about 250hr on them.

Asking 350€, incl worldwide shipping

Stereophile
Gramophone Dreams #54: DS Audio DS003 optical cartridge & EMIA, Lundahl, Koetsu, Sculpture A step-up transformers Page 2 | Stereophile.com
Amorphous Core (Lundahl)
K&K Audio's $1500 Premium Silver MC Step-Up (footnote 3) uses Lundahl's LL1931 Ag transformers, which are made with Lundahl's "finest amorphous cobalt uncut strip core" and wound with pure silver wire. According to K&K Audio's Kevin Carter, "The LL1931 provides a very open and detailed picture of the 'space' that was recorded, providing a level of detail recovery that I had never previously experienced with LPs."

My auditions confirmed Kevin's observation, but my experience with this transformer is limited, because I auditioned it with only one cartridge: the high-impedance (40 ohm) Zu Audio Zu/DL-103 Mk.II moving coil. (Lundahl's website specifically recommends the LL1931 Ag's step-up ratio for use with 40 ohm cartridges. )

I listened to the K&K + Zu-Denon (with a variety of RIAA stages) over many months. Every record testified to the mesmerizing effects of the LL1931's clarity and the goose-bumpiness of its transient bite. Bass reproduction could be thrilling, just-right tight with genuine power. The LL1931's best, most obvious trait was how specifically it rendered recorded information. Its worst trait was that, compared to Auditorium 23's mu-metal SUT (which was designed by Keith Aschenbrenner for use with the DL-103), it made the spaces between details feel empty, causing reverb tails and vibrating cathedral air to go missing or attenuated. The Lundahl transformers (footnote 4) showcased tight bass, intense detail, and a somewhat blunt clarity. The A23 showcased tone-truthfulness, rhythmic bounce, and a more refined presentation of ambience.

According to Per Lundahl, writing by email, "Choice of core material is a question of taste. Our top-of-the-line MC transformers are available with either our uncut amorphous strip core (like the LL1931) or with a conventional mu-metal lamination core (like the LL1933). As it has turned out, the amorphous-core transformer is most popular, but the mu-metal lamination transformer is still preferred by some audiophiles. In THD ... and linearity measurements, the mu-metal lamination version outperforms the amorphous core version, but in listening tests, the amorphous core usually wins."

I asked Per to explain the metallurgical differences between mu-metal, amorphous cobalt, and nanocrystalline transformer cores.

"In true amorphous material, there should not be any crystal structure. Atoms are randomly oriented, and there is no repeated structure such as you find in most solid metals. To achieve this, the melted metal is cooled so rapidly that atoms get stuck in their random positions. ... This very rapid cooling requirement is the reason why amorphous metal is only available as thin film, about 1 mil (0.025 mm) thick.

"To achieve nanocrystalline material, special amorphous iron is carefully heat treated at very controlled temperatures. In this process, very small [nano]crystals are formed."


I have 4 vesions
LL1931Ag Assembled version from Lundahl or Kit format
LL1931Cu Assembled Version from Lundahl or Kit format

This is a group buy for Amp Camp Amp (ACA) CLC Power Filter PCBs + Parts Kits.

The idea is inspired by the recent Sony VFET P-Channel amp power supply filter. The concept is a low pass filter designed to filter out any hi frequency hash/trash from the SMPS power supply.

This board is designed to be an easy retrofit/drop-in to the chassis. The mounting holes align with existing slots in the bottom of the chassis. Wiring is also simple. Add a wire from the ground "bus" wire at the back of the amp to the filter board. The red wires from the amp boards get cut. Amp board wires connect the "V+ to Amp" connections. 2 short wires from the switch connect to the "V+ from Switch".

Option A - Stereo Amp Kit - 1x PCB, 2x Inductors, 2x 1000u Caps, 1x 0.33uCap, 8x screws, 4x standoffs
Option B - Monoblock Amp Kit [Kit for 2 ACA Chassis] - 2x PCBs, 4x Inductors, 4x 1000u Caps, 2x 0.33uCap, 16x screws, 8x standoffs
Option C - 1 Board only - good for one stereo amp - you supply parts
Option D - 2 Boards only - good for 2 monoblocks - you supply parts

Group Buy Pricing for kits will be based on the volume of the buy. It's looking like:
5 Option B's (10 total boards including all parts) = $42+shipping per kit
6-24 Option B's = $36+shipping per kit
25+ Option B's = $32+shipping per kit
Divide price by 2 for Option A kits.

Shipping will be appx $4 or 5 in USA. More elsewhere.
Option C = $4 + shipping
Option D = $8 + shipping

Group Buy #1 will close September 17, 2021.
Please make a running list by entering your DIYAudio username and which option(s) you would like. I'll total things up after Sept 17th and order parts.

December 2021 Updates
There was only 1 group buy. You can now get boards fabbed if you like. Gerber files are posted in posts #136 and #137.
Typo on the schematic. ACA uses a 24V PSU. No need for 50V caps. Go for 1,000uF 35V. I used the same series of caps that were called out in the store's P089ZB kit. Nichicon UHW or Kemet ESH series.

Here is a basic opamp with good performance.
JFET input and can be used with single or dual supply.
Max 30V single or +/-15V supply.

Can be used as a preamp or whatever you need.

I am looking to build a center channel and a pair of surrounds and have the following pieces...2 pairs of Emminence Alpha 15As , and 2 EV DH1A comp drivers for the surrounds. I also have a pair of Celestion 15ftr3070c woofers, and another EV DH1A comp driver for the center channel.

Now my front channels consist of a 2 k402 MEHs stacked per channel. I have a Celestion axi2050 in the top horn along with a pair of Celestion 15ftr3070c woofers. In the bottom horn I only have a pair of Celestion 15ftr3070c woofers. Now both horns per channel are run without cabinets, and I supplement the low bass with a LilMikes F20 horn per channel. I have the setup crossed over via a xilica as a 3 way, and power the f20s withheld Audio 300 plate amps. I also use 3 Fosi V3 monoblocks per channel.

Now I have been contemplating on making the center a diy wood horn (25" h x 25" wide 17") and having 2 ftr3070c woofers as in my MEH setup (with a cabinet), but if I do it the same I will need to raise the speakers up about 2 feet.

Now the 2nd option would be to make a 25x25x17 horn and run that on top of the horn with the 2 celestion drivers mounted on the sides like my MEHs and use the same port locations and size. This would get the comp driver about ear level or just below a few inches. Also if I do it this way would I just have the horn come to a point or have a 2" wide flat spot?

Now option 3 would be to make a bass horn with the woofers stacked one on top of the other in a horn configuration (with the horns mounted where the comp driver normally goes)same mouth size and depth, but about 32 inches high and then run a 25 x25 x17 horn o top of that. It would put the center of the comp driver about equal to my left and right channels. I have seen this config of the woofers stacked and they use a port in the center of the horn for about the 14" on a 15" driver. I used AI and AI said to make the port size 6.25" wide x 14" for each woofer. In the ones I have seen on line they vary from what appears to be a small gap all the way up to the full woofer.

I like the idea of stacking the woofers, but I do not know the advantages of one over the other.

The surrounds would be the same style of build except using the Emminence Alpha 15a woofers.

I have made a template of the short side of my k402 and will be using it on the sides for the woofer stack and on the woofer stack Inwould have a separator to devide the top and bottom woofers. For the top horn (where used), would comprise of the short side k402 template being used for all 4 sides of the comp driver horn. I am assuming when you have a horn with woofers close to the floor that the top and bottom should be parallel to the floor to avoid more floor bounce.

I am a novice at this and can use help.

Thank you

I built a modded Marshall 2203 guitar amp a few years back and ended up needing to do some prototyping on it to get it right.
Basically its the same schematic but with different B+ voltages and using 807 tubes (based on the advice of an old fella who has now since passed away.)
Looking back now I would have just built a pure replica with EL34 tubes, but hey this thing is unique!
My main concerns are around Bias voltages, plate voltages on preamp tubes and poor presence control.
The amplifier seems to sound OK, but I felt it did not put out as much power on the low sensitive input as the high did.
Not too sure if this is normal for this design or not, but its still pretty damn loud when cranked up full, from memory im getting closer to 200W on the high sensitivity input when overdriven.
This thing is a beast for sure.

So the mods are as follows:
B+ 400V
807 output tubes
12AT7 phase inverter
everything before the phase inverter is the same as the marshall design, I have highlighted my changes in red on the schematic.

When taking measurements, i got the feeling that the plate voltages on the preamp tubes might be high, the old guy also told me to change the resistor values on the power supply at the top (highlighted in red) changing the original 10K value didnt seem to reduce the plate voltages much, so i just left at 4.7K and 1K respectively.

Voltages measure as follows:
V1A anode to ground 280V
V1B anode to ground 335V
V2A cathode to ground 1.5V, anode to ground 191V
V2B cathode to ground 190V, anode to ground 383V, across anode to cathode 189V
Phase inverter, anode to ground 265V, across anode and cathode 168V

Do any of these voltages look too high? 335V on V1B seemed a bit too high to me.
As far as presence control goes, even the original marshalls had poor response and little to no difference in sound is observed, I dropped it down to 4.7K from 100K and it makes more of a difference to the negative feedback received, the difference in the phase inverter may also have a role to play.
As far as bias voltage goes, i think ive got it sitting around -50V from memory, Im not sure ive got this right, as a rule 10% of plate voltage should be applied, I think i went by ear mostly and left it where I felt it sounded right, but I should revisit this.
Any other feedback is appreciated, largely the amp seems to run sweet, but I just want to tidy this thing up and order some new resistors to replace the ones ive tacked on while prototyping it.

See schematic attached, modded values are marked in red.

Here is the info for the 45 amplifer from Sunvalley - SV-S1645D​

The composition of the vacuum tubes:

12AT7 x1 or 12AX7​

12AU7 X 2 ​

45 X 2 ​

274B/5U4G (tube rectifier only) ​

Output transformer Hashimoto H20-7U.​

Choke and Power Transformer 115/230V custom made​

Made and Assembled by Sunvalley Japan with 4 x VCAP ODAM (0.1 X 2 + 0.22 X 2)​

Available in February 2024 - Only 25 units for the 1st production​

Price : $2,725 ( included development fee $250 per unit charged by Sunvalley)​

[


[URL='https://flic.kr/p/2oPzp7X']



[/URL]

WE expect it will take 8-9 months to complete the following processes. Please stay tuned....

1. Circuit approval - DONE
2. Prototype production - DONE
3. Prototype Evaluation - DONE
4. Prototype approval - DONE
5. Quote Approval - DONE
6. Mass production - WIP
7. Assembly _ Sept 2023
8. Characteristics Verification
9. Shipping jAN 2024
10. SCHEDULE ARRIVED Vancouver Feb 24, 2024

Hi! I am making a mesa boggie mark II diy. I made almost parts and I already test of the pré amplifier. I made transformer of power.
So, I still missing the output transformer and inductors of EQ.

Does anyone have the specification of output transformer? I'll wind the transformer myself.

Hi I am looking for a schematic for this amp or equivalent Audison AV 5.1K. This amp has 2 494's, and I don't have no voltage on pin 12 of either of them. Maybe someone in here has had a little run in with this amp.

I have been tinkering with SPICE simulators for several weeks and I am still a dope. My options are limited because I use only Linux and can't afford a Windows license just to run one application. Most of the spicers are just for Windows. Qucs-s is interesting because it is OS independent. KiCad works on Linux and has a concept of simulation but I am no wiser after doing the beginner tutorials. I also did the NgSpice command line simulations but I could find no practical applications.

I installed Wine but it failed because of a missing ntdll.

I see interesting posts with simulations and wonder what tools were used to create them.

Hello there, I am looking for 98 Complete Sheets of JBL Paragon Plans Scans in very high resolution , high quality , grey scale and cheap as possible. I have no idea what is possible and You have tons of experience, Please shed some light on plans sources. I read 22 years old posts and telling the scans at ebay was very bad. I dont know if things changed and you found correct scans.
Thank you,
Umut
Istanbul

Hi great to be here get some advice and explore some upgrades for my system that I've had for a while looking at maybe a different turntable tho im really happy with my ERA 5055 that i got new in the box a few years back but as they say if you dont have a go you will never know.

Hi all, I picked up the 1908s Vox Venue 100 Lead very cheap, which has been working. Changed the power switch as the old one blew (it took out the small fuse at the mains plug so am hoping nothing else got "fried"). I notice one of the upright mid-size caps on the "first" board (the one that has the vol, tone etc. pots attached) seems loose, and is causing the classic "dry solder" popping & crackling, a fairly simple resolder fix once the board is out. Also, at the time I'll replace one or two pots as they're not responding to pot cleaner, with noisy rumbling. I have a basic hand drawn schematic from Vox but wondered if anyone has knowledge of a better one. Also, the reverb is very week, it has a dual spring built in but I'm not sure how to trace the signal amount going in and coming out, any advice would be appreciated. I thought a stronger signal sent to the reverb section by changing the resistor/diode might achieve this?
I have another query which I assume should go into a different topic but here it is anyway; I also have a 1908s Peavey Artist (100 combo with Black Widow speaker). Very weak output at volume, I think it might need new valves but am keen to check the condition of the capacitors. Can you suggest a setup I can make to test/drain any residual voltage in the caps? Can I use my multi meter and if yes on what setting?
Many thanks in advance, Mark from Sydney, Australia.

Unlike 4”-6.5” cone drivers, frequency response of dome midrange drivers (1.5”-3.5” diameters) are different, i.e., 500-700Hz for the lowest frequency responses.

Anyone who has had the dome midrange drivers in your system, how do you cope with them? I mean you may not be able to build a traditional 3-way system configuration whose crossover points are of around 60-200Hz and 1.5k-7kHz.

In 3-way system, did you assign the crossover point of 8”-12” drivers at minimum 500Hz to match with those dome midranges? Or you add a (about 5”-6.5”) midbass driver to make the system 4-way?

I plan to use the ADS 1.5”-2” home audio domes because I like them when they perform at home. But I don’t know they’re still good in car. Are they decent enough, in car environment?







Please share your experiences about the dome midrange drivers in car audio system, please.

Hi Guys,

Please register your details for the Wolverine 5th Group Buy - Pre Order.​

After the success of the past four group buys and increasing demand for Wolverine boards, we are thrilled to announce another group buy for the DiyAudio community.


This time, we are offering the new and improved Wolverine V5 boards, along with supporting parts and boards:

The IPS, EF3-3, EF3-4 and EF3-5 boards will now include mirrored versions for Left and Right channels! These allow inputs at the rear of your chassis and outputs on the lower heatsink half, all while fitting the current UMS (with just 3 new holes for EF3-4, courtesy of Gianluca’s updated drill pattern). Huge thanks to Mainframe and DanielJW for prototyping, Harry for BOM review, and Jeremy for schematic checks.

1. IPS, Pre-Driver & Driver Heatsinks with Mill-Max pins installed:
   • EF3-3 (IPS, Pre-Driver & Driver)(Amp Board,Parallel or Perpendicular Mount to Main Heatsink): $27.50 USD (6 Heatsinks Total)
   • EF3-4 or EF3-5 (IPS & Pre-Driver)(Amp Board, Parallel Mount to Main Heatsink): $22.50 USD (4 Heatsinks Total)
   • EF3-4 (IPS, Pre-Driver & Driver)(Amp Board, Perpendicular Mount to Main Heatsink): $27.50 USD (6 Heatsinks Total)
   • IPS: $10.00 USD (2 Heatsinks Total)

1. 2SA1381E / 2SC3503E Transistors:
   • $6.00 USD per pair.

We are also offering the following supporting boards:







Thank you all for your support of the Wolverine project over the past 3 years. It’s incredible to think our first group buy was back in March 2022.

Registration Instructions:
We will follow the same process as the 3rd & 4th group buys to streamline processing. Board color will be determined based on order numbers; if insufficient, only one color will be ordered.

Pricing for Boards:
Wolverine V5 Special Edition IPS Board (2 boards) (Right and Left channel):


EF3-3 Boards: (270mm x 77mm)


EF3-4 Boards: (347mm x 77mm)

EF3-5 Boards: (354mm x 77mm)
I’m excited to share a fresh development for the Wolverine family: the EF3-5 output stage board! As you know, our current lineup includes the EF3-3 (3 current gain stages, 3 output transistor pairs) and the EF3-4 (3 current gain stages, 4 output pairs).

Now, we’re taking it up a notch with the EF3-5, featuring 3 current gain stages and 5 output transistor pairs for even greater power and stability.

To top it off, I’ve mirrored the EF3-5 design—just like the EF3-3 and EF3-4 in the 5th Group Buy—offering dedicated Left and Right channel versions. This keeps the inputs at the rear and outputs low on the heatsink, maintaining that clean, symmetrical layout you’ve come to love.

The EF3-5 boards are 7 mm longer and 10 mm wider than the current EF3-4 boards. All the holes still follow the UMS, except for the two at the top where the output transistors mount—they’ve moved up 10 mm. The output transistor mounting holes have also shifted up 10 mm, so some drilling and tapping will be required if you’d like to use the EF3-5.

The EF3-5 is perfect for those pushing higher currents or lower impedance's (think 2-ohm loads or beyond) with the same Wolverine Class AB finesse.

Please note.
The discount will only be applied for those members who order boards before they are ordered from the PCB Manufacturer.
If you wish to order more than 2 sets or adjust quantity, please contact us for pricing details.

Shipping: Prices exclude shipping costs. Shipping is at cost price plus $3.00 for packaging. No added handling fees. A copy of the shipping receipt will be emailed upon payment.

Each Order Includes:

1. Your ordered PCBs.
2. A3 Schematic copies for 57V and 64V versions. (Dropbox Link)
3. The Build Guide (~135-page illustrated A4 document). (Dropbox Link)
4. BOM in Excel with Mouser part numbers. (Dropbox Link)
5. Heatsink Hole Pattern DXF & PDF files. (Dropbox Link)
6. "How to Wire an Audio Amplifier" by Bonsai. (Dropbox Link)
7. Future updates will be available via Dropbox. Please provide an email for this purpose.

Payment: Through PayPal. Requests will be sent upon ready-to-ship boards.

How to Register:

1. Open the attached Excel order sheet, fill it out, and email it to: Stuartmp@internode.on.net
   • Subject: "Wolverine Project – Your DiyAudio Username"
2. If unable to open the file, please reply with:
   • Total number/type of EF3-3, EF3-4 & EF3-5 boards.
   • Name and total number of any of the supporting parts / boards on offer.
   • Full name, address (including country and postcode).
   • Phone number for tracking.
   • Your PayPal email address.
   • You Email address for Dropbox updates.

We will order boards once a sufficient number of pre-orders are reached and keep you updated throughout the process. Once received, we will calculate shipping and send payment requests. You will receive a tracking number once your order ships.

Please refrain from using my email for other inquiries; post questions on the main Wolverine Build thread or contact me via DiyAudio PM for order-related questions.

Wolverine Development Thread
For ongoing project updates and technical discussions, visit the Wolverine Development Thread on the DiyAudio forum. Engage with fellow audio enthusiasts and share your build experiences.

Wolverine Build Thread
The Wolverine Build Thread is your go-to resource for assistance with assembly tips and troubleshooting advice. Feel free to ask questions and contribute your insights.

YouTube Build Series
Explore our YouTube Build Series for visual guidance on assembling your Wolverine amplifier. Our instructional videos cover each step-in detail, ensuring a smooth build process. Thank you to @danieljw for putting this series together.

Support Contacts
Feel free to reach out to me directly through the forum's messaging system or my e-mail if you have any question related to the ordering process.

We truly value your involvement in the Wolverine project. By working together, we continue to make high-quality audio amplifiers accessible to enthusiasts worldwide. Thank you for your enthusiasm and support.

Best regards,
Stuart & the Wolverine Team

I recently purchased a used circa 2010 Fender Passport PD-500 portable PA system and while it works fine occasionally, most times it exhibits a clicking sound on the left channel with no other sound on that channel. The left channel vertical lights jump up a couple of lights at the same time. There is about one tick per 1/2 second. The right channel works fine.

Any thoughts as to what might be causing this intermittent problem?

Robert from Canada found my old thread JBL 2226H 30 hz "horn" i built and asked for plans.

I have been working on a new sub design some time now and with very little work I have incoporated the improvements in a new JBL 2226 design.

Enclosed is the 3d-drawing in step format. The cut sheet is missing, but I will make one when the design stabilizes.

The zip also includes a Hornresp record. I need to add values for the front chamber.

I can make changes to the design quite easliy. I generate the drawing from a script. The script also generates the Hornresp record.

If you want a longer horn (goes lower), just add some on the depth or hight. If you want a bigger back chamber, just add some width.

Thickness and bracing are easily changed as well.

I've been playing around with a Rolls SX45 as low pass filter into Parasound ZAmp and two Dayton Audio SUB-1000L subwoofers.

This supports the sound of the main small speakers in my small system. It sounds surprisingly good and fast. Not hugely deep, but doesn't matter, mostly I want to add some reinforcement for the small speakers.

So, now it got me... I got these little, shallow boxes standing... and they're pretty cheap. I thought about getting four or six more and building two stacks of four up front, of perhaps put two stacks of two in front and two more -phase delayed, out of phase, in the back.... sort of creating what Trinnov calls waveforming.

https://www.trinnov.com/en/subwoofer-guidelines/

WAF is not important as this is my home office and I got a door...

Getting the woofers is easy, I got the crossover and the amps... so all I will need is the delay unit.

Well.... WAF might be a factor... when she walks in and sees those woofers eight feet up on the back wall... etc...

Any ideas... have you tried this?

Good evening,

I have an SSE that is about 6 years old now. Recently it started red plating one power tube, does not take very long after turning on to blow the fuse. I have tried the obvious things such as a new tube, put in a new coupling cap, and replaced the bias resistor. Unfortunately it is difficult to get readings with the multimeter because the fuse blows pretty quick after start up, maybe 15-20 seconds if cold. Any suggestions of possible causes are greatly appreciated, thanks!

Just checking if anyone knows what i can use for a replacement for a TC4427COA that's marked C2 on a Sundown SFB 8000D?

Company Background : Sun Valley Co., Ltd. [100% subsidiary of Toyota Industries Corporation]
Product specification
SV-S1628D Kit US$1700.00
SV-S1628D 4 X VCAP ODAM installed - Made and Assembled in Japan US$2,350.00

Type: 845/211 Single power amplifier
Input: Line 1 end with volume
Wiring specification: Hand wiring (power supply
part, BIAS adjuster, hum balancer is a circuit board)
SP impedance: 8Ω (4Ω or 16Ω setting is also available)
Vacuum tube: 845 or 211×2, 12BH7A×2, 12AU7×2
(*vacuum tubes are sold separately)
Rated output: more than 845/16W+16W
more than 211/7.5W+7.5W (8Ω, THD: 10%)
Frequency characteristic: 15Hz~60kHz(1W/8Ω/-3dB)
Gain: 845/25dB, 211/26dB (at 8Ω)
Size: W410xD275xH240(mm)
*including height of vacuum tube. No cage/cover.
Weight 15KG

Victor,

Some initial impressions….
The Sun Valley 211/845 amp is an elegant and beautifully designed audio component.
There are many things which are immediately apparent:
The materials are excellent, the finish of the Chassis is perfect and the coating is unusual, refined and almost indestructible. Very Nice.

This is s kit which has clearly gone through years of refinement and focus to obtain the highest level of performance. The circuits are designed with elegance and performance with dozens of notable features:
1. All of the passive components are very well specified and uniquely employed to provide the highest performance and durability. For example, the power supply employs very closely matched metal resistors for precis voltages while the audio path specifies carbon resistors, favored by manty including myself, for the audio path.
2. Extremely high quality multi strand internally tinned wire is supplied at various gauges optimized for the power and audio circuits.
3. The power transformer and filament filter/power supply design is VERY robust and can supply any 211/845 with stable well filtered power.
4. The main power supply board is designed to provide exceptional stability and filtration and separately address Blow voltage standby, and fixed bias reference voltages…very nice.
This build will be very different from anyone solely familiar with pre-printed circuit boards and step by step check box style instructions. The documentation is quite adequate, very precise and compact delivering all of the required information and guidelines BUT it is very important that the builder has noted all of the specifications and subcomponent relationships prior to the build… i.e. Know what the designers intended, why the approach the construction as they do and pay attention to the details.

Going through the instruction for the first few pages I made a few illustrative notes.

1. Note the sequence for construction and you will begin to get a feel for the relationship among the sub-assemblies and why, in many cases the parts specification is very specific.
2. The Parts list on page 6, describes not only the individual parts, but the subassemblies for which they were provided. Unlike many manufactures, Sun Valley does not package their components separately for each sub-assembly but has grouped them by component type. Thus for the Bias board the circuit board, potentiometers, connection block and resistors are all packaged in different locations but carefully packaged and verified by quality control (you will find an inspection sheet in the packaging to assure you receive all that is required. .
3. Note that you must know how components are coded, where they go or carefully follow the specifications on the parts index (pages 5-6) Sun valley does not print component values on the circuit boards (but does specify part designation relative to the parts list and schematic) and you need to attend to assuring that you employ the correct value, capacity and type of component. Resistor packs for example contain the resistors for several sub-assemblies in various wattages).
4. Mechanical assembly employs very high quality hardware with the capacity to make small adjustments to account for manufacturing variability in parts so you can obtain a perfect and symmetrical build. For example, there is just enough play in the M3 securing hardware for the tube sockets and bias boards to allow alignment of these assemblies in the exact center of the chassis holes for a perfect build and very attractive final product.








You are correct, the sound is incredible. Very beautiful design, excellent quality components; I made a few upgrades and small changes but basically and Very Well Designed.
Great and very specific guidelines for initial check and all measurements were within 3% of the reference voltages.
The sound is incredible and the power supply design, allowing a full warm up prior to applying B+ is exceptional.
I would love to comment on the noise floor... but I could not find any noise!!
This is a very quiet and refined component


"This was an interesting build. This amp is best built from the schematic with reference to the diagrams for component locations and wire routing suggestions ( I modified some of these to minimize hum). This amp has an awesome powers supply and with high quality components offers great flexibility for refinement. "

Theoretically, a (box) speaker can have crossover at the baffle step frequency. What would be advantages and disadvantages of such a design?

I've been testing the coverage ratios for The Wet Look speaker cone treatment from parts express.

Since I didn't see anythjng on line about it, I thought it would be a good idea to share the reults of my findings.

I used a blank sheet of standard white 8.5 x 10" ink jet printing paper to determine coverage, how much coating is needed to cover the white surface.

I used a lab scale to weigh the paper and coating bottle before and after application.

The test surface was 150 cm2, which required a min of 2.5 g liquid coating to fully cover the paper so that no white surface is visible.

The 2.5g of liquid dries to 1.3g final weight. Thats about 50% loss of mass once its dry in 20% ambient humidity.

The final added mass is 7 - 9 mg per 1 cm2 surface once the coating has dried.

For full coverage treatment of variouss diameter cone drivers this works out to be -

4.0" cone = 0.320 g added mass
4.5" cone = 0.440 g added mass
5.0" cone = 0.560 g added mass
5.5" cone = 0.760 g added mass
6.0" cone = 0.960 g added mass
6.5" cone = 1.040 g added mass
7.0" cone = 1.160 g added mass
7.5" cone = 1.300 g added mass
8.0" cone = 1.560 g added mass
9.0" cone = 1.810 g added mass
10.0" cone = 2.720 g added mass
12.0" cone = 4.000 g added mass

These are all approximate amounts.
Deduct for phase plugs and wide surrounds.
Add for deep cone profiles.
Add for "thirsty" cones

Inspired by Jeff Bagbys work on the Kairos and Paul Carmodys Tarkus.
Last month I bought an empty box and couple of old school Sansui speakers.
One set of the Sansui use a 140mm midwoofer and a 20mm tweeter and are an OK little speaker
The bigger box uses a 155mm and a 25mm tweeter; the bigger box is actually a pretty good speaker; but both use the same generic crossover with the only difference being the padding on the tweeters.
The woofer box suits a pair of 10" drivers and I've settled on a quad of the affordable Dayton drivers discussed in this thread
I think I'd like to use the Bagby crossover design as my inspiration but I can't really justify to the Boss the cost of a 150uF film capacitor at this time but given the spec of the cheap Dayton woofers I can't see them being used above 200 either.
Both the Sansui are a nominal 8R and at 200Hz are both probably at the DCR of 5.6 Ohms
So do I wait until I can afford $400- in parts or fudge it with electrolytics
200Hz is well below baffle step but I don't think that matters here and yes these could be Bi-Amped but passive can have the advantage of being able to be gifted away or sold at need
I don't have enough film caps in the stash to make up a 150uF bundle twice and I need to get 4 new film caps in 3.3uF to mod the Sansui XO as well
What is my best value supplier for film caps here at the moment if I don't use SpeakerBug??

Looking to identify Partially known/unknown transformer.
It's supposed to be a Woodward-Schumacher output transformer made for university sound. The only markings on it are stamped into the metal and are as follows; 050-7002-00 then under that is EIA-606-227. The wires are primary black-yellow-brown-green-orange, and on secondary is blue-red. I will use tone lizards process to get winding ratio, by inserting 1v ac into the secondary and measuring the voltages coming out the primary, put that into the formula which i do not know offhand(lol)
But I'm hoping someone knows something about these ie push pull, SE, or transistor transformers. I am working my way througg all the university sound schematics I can find online looking for that part number. Any and all help welcomed!

This is the beginning of a project to build an amp/radio, in 50s style, I want to have some really wacky tubes.

https://jblpro.com/en-US/products/md2

I have these waveguides with no box. If I never had to move them, I would build a similar box and brace/damp accordingly.

I would like to keep them free-standing, but increase the stiffness with minimal weight added. Maybe damp if the resonances are too noticeable.

I was thinking of gluing 1" wood strips spaced a few inches apart, then spraying some kind of thin rubberized coating. Anyone try something like this on similar devices?

Thank you for any input.

She Blinded Me With Science Bill Parsons (orig Thomas Dolby)

Sweet Jane Cowboy Junkies (orig Velvet Underground)

Any others come to mind?

(Thanks to Fred D. for bringing this to the top of my insomniac head) http://www.diyaudio.com/forums/showthread.php?s=&postid=81177

-- mirlo

TU-8400 is the Successor Model of TU-8200R.​

Available NOW​

There are three versions
1. TU-8400 with stock OPT with ALPS R27 potentiometer + Metal Knob) $885
2. TU-8400 with Lundahl LL2777B $1,175.00


TU-8400 is designed based on EL34 x 2 + 12AX7 x1. There are only two coupling caps. You can run KT170 with TU-8400
etc..

Just curious to know what other amplifier builders think about the various illuminated push button power switch options.

What LED color(s) do you prefer and why?

What action do you prefer, momentary or latching?

I've noticed a lot of manufacturers using blue, but that's not great for night time use IMO.

Hi,

my Micromega Stage 3 was not able to read any CD anymore (message "no disc").

I've replaced the laser pickup, a Philips CDM 12.4, but the only result I've got is a new "err" message.

There is perhaps a solder joint to be voided or restored?

I've looked closely at the old pickup but I don't seem to see any...

As usual, thx a lot in advance for any helping hand

Hey guys - I’m from North Alabama and buy and sell all sorts of vintage audio but joined as I have a few old stereo cabinets (console units) that I’m in the process of refurbishing.

I do have a website that I’m building out with the components that I have for sale. Www.pressrewindvintageaudio.com and I also sell LED bulbs for vintage receivers!!

I’m also about to try my luck making a few cigar box Bluetooth speakers.

Derrick

Took a while but I finally got them mostly finished, at least enough to listen. Been out of the audiophile realm for awhile but these sound damn good. Mounted them on some spalted Maple cut offs from a local slab supplier. Still need to mount some feet, just propped up for now.