This is the Group Buy and Build thread for the Alpha Nirvana 39W SE Class A amplifier designed by AKSA. The technical discussion thread is here:

Alpha Nirvana 39w 8ohm Class A Amp

PCBs:


Production ones will be 2mm thick, 2oz Cu, ENIG gold finish, and Blue solder mask.

Amp module looks like this assembled:


Includes helper snubber boards to allow remote mounting of MOSFETs for flexibility and ease of installation by decoupling the installation of the PCB and the MOSFETs:


Latest Schematics and BOM will be updated soon, but current version (very close to final) is below:

I recommend use of these Fairchild MOSFETs (higher power rating than IRFP's):

FQA40N25 ON Semiconductor / Fairchild | Mouser

FQA36P15 ON Semiconductor / Fairchild | Mouser

The SLB PSU is also highly recommended - proven to work with single SLB and Antek 600VA 24v (AN-6224) trafo. Should work as dual monoblock with dual SLB and Antek 300VA 24v trafos (or equivalent). Also, a ready to run (RTR) solid state relay (SSR) DC protection is highly recommended to prevent turn on thump and provide safety net for your speakers should something fail.

Also tested to work on DIYA Store Dissipante 4Ux300mm chassis. Board is UMS compliant and I did not have to drill and tap a single hole on my UMS heatsink. Chassis temp is 57C at hottest point in 20C ambient. A 5Ux400mm would be much more generous and allow higher bias current.

Pre-Orders are now being taken in my Etsy shop for the GB.

Pricing is $37ea (includes pair of snubber boards - which cost almost as much as the PCB, hence the higher price). Thus, a stereo pair requires two boards. Free shipping in USA. Etsy calculated shipping elsewhere - circa $23 via tracked and insured USPS First Class mail.

If you place a pre-order, please add your name to a running list below with name, qnty, country. Thanks!

A huge thank you to Hugh (AKSA) for the design and JPS64 for the superb professional layout.

Here is the schematic of my amp "AS-BUILT". These values should work and clears up any ambiguous locations where multiple values are possible.


Schematic of snubber boards:


Edit Dec 26, 2019: AndyR has put together a nicely annotated BOM for both the 8ohm and 4ohm versions here:
Alpha Nirvana 39w 8ohm Class A Amp

Edit June 13, 2020: note that the feedback resistor R126 and R124 could 1% metal thin film or hand-matched carbon film as 1% not available at reasonable price. This needs to be done to get the same gain from left and right channel. It’s more important that they are matched left and right and not for absolute value. Also note that metal oxide thick film should not be used (dominant H3 and high THD). Do not use carbon composition - that is an error in the BOM. Sorry about that. Carbon film will have a slightly higher THD but more H2 vs H3. Metal thin film will have lower THD but relative H3 will be closer to H2 but H2 still dominant. Safest bet is use 0.5% metal thin film for these 2 resistors. But I personally like the carbon vs metal thin film.

Edit Feb 7, 2020: Pin diagram for Molex quick connects to MOSFETs


Edit Mar 11. 2020: helpful pin diagram for MOSFETs


Edit Apr 24, 2020 - Dual Monoblock Connection Diagram if using SLB PSU's:

What Type of Capacitor is This? Can/should this be replaced with a film cap in the speaker crossover? I'm unable to find anything that looks like it on google.

AC
TSI-8044
PXB25LR50
25uF-50VA* (* last character is obscured, assumed to be 'C')

The cap looks like this with the above markings (pic borrowed from a diyAudio post from 2011).


As used in my crossover:

Hi everyone

after years of lurking on DIYAudio I've decided to step out of the shadows and join the conversations.

After many years of being an audiofool and buying too many systems I thought it was time to design and build my own. How hard can it be?
Pretty bloody hard as I found out!

I'm interested in distributed audio, active loudspeakers and horns - a match made in theoretical heaven but practical hell. The upside of each brings great benefits but the downside is its really hard to do and hence the motivation to join diyAudio and discuss the challenges with people far more knowledgeable and experienced than me.

Currently I have a pair of Kii3 active loudspeakers that I love but am looking to replace them with my own design and build active, three-way using horns and distributed audio.

Anyway, enough about me - I'm off to the forums.

PrinceArnold

Posting the schematic of my tube preamp:

Sounds ok but when breaks up, the overdrive is too thick.

Swapped the cathode bypass caps from 22uf to 2.2uf but can't notice any difference.
Swapped the cathode resistors from 820 to 2k4 (should be towards less gain and cold/ asymmetrical clipping).

Could it be the MOSFET follower that alters the signal spectrum in a way?
F.ex. input capacitance, how it AC loads the valve, changing the harmonic distortion (f.ex. odd vs even order harmonics)
I put it so that it buffers the valve output, thus preserving all the top end and harmonics..

I want the overdriven sound not that thick and with more chime on the top end.

There is a 220k audio pot between both stages (the gain).
I think of treble bleed cap (some more top end) but it won't affect full gain setting and the general sound signature.

Selling a fully built and tested LR Phono by Pete Millett,
more info here: http://www.pmillett.com/LR_phono.html

Phono board and PSU board
for EU buyers, will throw in 2 12V batteries for those that want to try a battery supply.

SOLD

hi there, i joined this forum mostly just to post one technical question, but ill probably still stick around. i don't know too much about audio but my house has a fairly old surround sound system (yahama ns-ap1600s and yst-sw011) and i'd like to figure out how to troubleshoot/fix some of the issues i encounter. 🙂

Hi guys,
I got a high quality 23uf cap but not the 22 uf that the schematic asks for. Would this pose a problem or only be of minor concern?
Position C2

Hello, just joined and hoping to learn, maybe contribute. Even I am in US, English is not my first language so sometimes I may not be best at communicating. That being said, now about me, I have EE degree but in electrical devices, more like electronic drives, control, typical industrial stuff. I was working as electronic engineer /designer, developing power supplies and protection circuits but have no experience in audio and zero knowledge of tubes. I have basic test equipment (scopes, bench power supplies, multimeters) can read schematics so I should be able to participate in discussion. I am looking to dive deep and start tube amplifier build, will post in proper forum soon.

I have 1.6s now. Owned them for 25 years. I would like to find a used pair of 3.6s, but was thinking about new 2.7i. Anyone here own the 2.7i or the 3.7i? My local dealer, which is not very local, is no longer open on Saturdays. I know if I want a serious audition, I need to book an appointment.

General complaints now... Why is the dealer not open Saturday?!?!?!? Probably too many tire kickers. The price of 3.7s is way too much for me at this point. And don't even get me started on the X upgrade. Also, why are all the 1.7, 2.7, 3.7 models not bi-amp / bi-wire capable? I would want the crossovers external like the 3.6s. I know, these are rhetorical questions because it comes down to cost and marketing. I really want to listen to Diptyque speakers. Nothing close by and probably out of my price range. But reviewers say great things about them.

Rant finished.

I am a hobbyist based in North DFW and want to learn a thing or two about speaker cabinetry, drivers, and crossovers.

I currently have a pair of Tekton Double Impacts I am trying to "clean up" and customize for my listening space.

I am quite happy with them as is, but since I am a tinkerer and can't sit idling for more than 5 minutes, I figured I would take them on and upgrade the cabinet finish and crossover components and wiring.

I intend on beginning with a baseline of measurements and going from there. I look forward to chatting with y'all and learning a few things.

Cheers

My kids are begging me to help get them going in car stereo.

Does anyone know where to find obsolete parts, such as the balance pot on this preamp? Having issues with lost right channel and scratchiness in balance pot. Cannot restore right channel after multiple cleanings with deoxit. I think the pot is junk, feels very rough and center detent is a bit out of whack, if that makes any sense. It seems as though there are several "detents". Not sure what that means. Is it possible to match it up with a different pot as this one seems to be obsolete. I have searched everywhere and cannot find an exact match. It may be an Alps piece but not sure and if so, they don't seem to make it anymore. Any help would be appreciated. Thanks,
Bill

New member from Kansas City. Former sole broadcast/transmitter engineer for a 100Kilowatt FM College station (CE without the title) then moved on to producing and recording syndicated radio music programs for a religious world headquarters. Annual Handel's Messiah recording and broadcast (Large orchestra, 300 voice choir, 4 soloists). Hundreds of hours recording classical pipe organ. Opened RBW Records in 1990 and was self employed recording around the country, operating a struggling little e-commerce record label and designing and installing in-house video systems for call centers for data and powerpoint. Also designed custom 3 and 4 way mic transformer mic splitters for a Colorado Acoustic Design Firm that put my gear in a half dozen opera houses around the world. Also served as an RF and support tech for Arrowhead Stadium game day production from 1993 till 2005. Not great years for Chiefs football but most games were a lot of fun. Am now moving into collecting some vintage audio equipment, restoring them as necessary. Selling a few and maybe putting together a small analog/digital hybrid composition and recording home studio. I love my late 50s/early 60s Altec A7s, vintage Crown D60, D150 and D300 amps. A dozen or more great mics (Schoeps to Shure to AKG and EV), a vintage AKG BX20 reverb, various outboard gear and mic pre's. I look forward to tapping the knowledge on this list as I make my final years of life journey finding and experiencing great audio.

Hi!
Its time to change drivers in my ML-TQWT boxes. So,after looking for new drivers,im not sure wich is best choice.
So please,share your opinion. Fostex 167 with bad cone and all other problems perform very well in this boxes,and as owner od dallas II horns with fostex fe206en inside,i have faith in fostex ff165wk that will perform well. Markaudio looks better on paper,specialy PLUVIA model,but i know it not always beter sounding what looks better on paper.
So im open for sugestion and your opinion.

Looks like fun forum. Thanks.

Hello,


For my two (or three) way speaker, I have search for a 12" driver with a sensibility of 95 dB / W / M for a boxe around 100L.

Actually my design is :
- Faital Pro 12PR320, 12" drivers : 0 to 500 Hz inside 110L
- Fostex FE208EZ : 500 Hz to 20 kHz with corrective RLC inside ~8L

I have "found" the Faital Pro 12PR320 drivers, release in 2017, so relatively new. Is there any one tried it ? did you know any review or test ?

Importants datas was for me :
- sensitivity
- Fs : 42 Hz
- Mmms (low mobile stuff) : 51.4 g
- Xmax : 7.37 mm
- Vas : 98.4 L

The link : FaitalPRO | LF Loudspeakers | 12PR320

And the response from the manufacturer :

Hello!

I'm new to this forum and looking for some help with my Sennheiser PC360 headset.

The potentiometer makes a crackling sound and I've read something about bypassing the volumeknob.

I know how to solder but I don't know which wires to solder. I've included a photo of the backside of the potentiometer. I really hope anyone can help me with this 🙂

Thanks in advance 🙂

Hi,
I've attached the section of a project that converts speaker lever audio to line level.
It's similar to many I've seen on the net except for one detail (which I got from a schematic I also found on the net): it includes a 1uF series capacitor.
Would someone tell me why the cap is there?

Can you help me. I want to build a 2 wire version of Buck Converter to go from 24V 4amps to 17V 4a

Hi I have a Pass Labs X1 preamp, and I’m currently facing an issue where, at volume level 3, the left channel suddenly goes to maximum loudness. During troubleshooting, I swapped the volume control board with the right channel, and the problem followed the board. This confirmed that the issue lies with the volume control board.





After further testing, I identified that Q3 on the board is the faulty component. It’s marked as “8F” and comes in an SOT-23 package. However, I haven’t been able to find much information about it. Could you help identify the exact part number for this component?

I'm offering a pair of Hartley 224 HS. They are in very nice condition, original boxed and spec sheets, only used for testing. $1250 / pair + shipping, they do not weigh too much, less than 20 lbs each, shipping shouldn't cost too much. I'm in Los Angeles. ( they are huge!)

Geoffrey

Hi everyone,

I'm just making an account to say thanks in a 10 year old post, which seems to keep being necroed ever few years due to the issue still being an issue.

Cmon sennheiser, spend the extra 3 cents...

Selling 1x pair of Lie Belin P13564 input transformers.

Lie Belin is a famous French designer and company, that made a lot of equipment and transformers for the ORTF, the French broadcasting company.

These can be used in a ratio of 1:2 or 1:4, as an input transformer for a preamp or power amplifier.
Nice sound and bandwidth, and pretty rare

SOLD

I thought I had posted to this site years ago, but since it’s asking me to first make an introduction, I guess not.

I got into “audiophile” equipment years ago after my Sherwood receiver (c. 1981) gave up the ghost and I went to a nearby stereo repair shop that happened to also be a high-end audio dealer. While I was arranging to have my Sherwood repaired, I was offered an opportunity to audition a pair of Soundlab A1s powered by VTL monoblocks, VTL preamp, and Wadia CD player (the old BIG boxes.) I was blown away to say the least.

Since I was just a poor, 1 year out of college student, I immediately read every issue of Stereophile, Absolute Sound, and happened across a small DIY electronics print newsletter (before the internet) that walked people through the process of recapping old amps from the 60’s and making them better. I found a Lafayette KT-600, and so began my journey to better audio to listen to music the way the musician wanted you to hear it. I eventually acquired an Eico HF-89 and rebuilt it, then added another HF-89 a few years after that. My soldering iron became my favorite tool. Along with learning about different caps, culminating in my discovery of Black Gate caps, as well as a hundred other components and their good/better/best rankings inside the 80/20 rule.

I had an Aleph 5 for a few years coupled to a Classe and some other “high-end” preamp I can’t recall. I sold all of them, but a day before I was supposed to ship out my Aleph, I received my VTL 5.5 in the mail and hooked it up to the Aleph. I cryed. I should have backed out of the sale, but it was already sold, so I packed it up and shipped it out. God I miss that amp. Stupid preamps were getting in the way of magnificence.

OK, enough boring history stuff, I’ve had a pair of LX521s since 2013 and have made several upgrades along the way and now have the LX521.4 Mg ASP setup that is currently in storage. I’ve decided to sell the Genelecs I’m currently using and replace them with a pair of LXMinis, starting with building a balanced (XLR) version of the Nelson Pass ASP.

Bottom line, I love building cool things.
Mark

There have been multiple conversations on many threads about the potential benefits of removing source resistors from the AC current flow;
Nelson write in the F5Turbo article about the application of diodes for the purpose but more recently in several threads there are discussions regarding the potential use of supercapacitors for bypassing the source resistors:
F5 - `Update on Pa's new F5?', some comments in a tread on the F5m.
And of course most recently in the ACA Mini - the article itself

After some searching and reading I am curious why they are not used more often and I am hoping I could gain some enlightenment on the subject from the great and wise?

I have been reworking a germanium amplifier, and I understand the circuit below is an emitter follower (besides just the schematic saying so ), but there are some oddities about this circuit that I do not understand. I don't know anything about the transistor beyond it is germanium, obviously PNP. A pox on Magnavox for using internal numbering, and I don't have the photofact for the Magnavox A531 to look up an equivalent or whether it is even listed. Questions below . . .



Questions:

I understand R17 and R16 set the -7.2V bias voltage, but why are R15, C10 needed? Input impedance? Would not the emitter follow the base without them?

Why are R18 and C31 necessary? I'm guessing this transistor maybe cannot handle -19V on the collector, so R18 reduces the voltage drop across the transistor while C31 maintains an AC ground? But C31 (0.001uF) seems awfully small to be a bypass capacitor- maybe it is involved in a filter from the collector side somehow?

Thanks for your help!

Howdy folks! I have here a Pioneer SX-1980 receiver. The problem is that I only have one AUX input to spare, and I need another input for my Rose streamer. Since there aren’t two AUX inputs available, can I use one of the TAPE-1 & TAPE-2 for the streamer without causing any harm to the receiver? Please let me know if this is a safe alternative. 🤔

Very sought after American High-End DAC, that normally is sold out because they are not able to deliver to the high demand ... And this one has been further
upgraded in 2 important areas (Analog output and PSU).

As the name suggests this is the newest model with an AKM 4483S DAC chip, and it is about 3 months old.

It is default delivered with OPA1656 op-amps in sockets in the analog outputs. They sound good, but not nearly as good as Sparkos discrete SS2590 Pro opamps,
that in mine and many others opinion are the best op-amps on the market. The SS2590 type are originally developed for expensive studio equipment, but Sparkos
delivers adapters, so that they can be installed in 8-pin DIP sockets, and therefore also can be used in consumer equipment. But be aware that Geshelli do NOT
deliver these types from the factory. They only deliver the cheaper model SS3602 - so this is a unique offering.

As it is configured right now, it is only the RCA outputs that are running, because I have uninstalled the op-amps for the balanced outputs. But they can of course
be re-installed, if necessary.

The Sparkos SS2590 op-amps gave a large quality improvement, and the next improvement appeared by installing a powerful and noiseless linear power supply.

So if you check out videos on YT, that generally are super positive, remember to add those 2 important upgrades to the evaluation.

The DAC will be delivered in original packaging, with the upgraded PSU, and the standard PSU and 2 OPA1656 for the balanced outputs.

White alu housing with see thru plexi front and back plates. Measures: DAC: H5 x W16 x D12 cm., PSU: H5,5 x W10 x D21 cm.

The switch on the cable is installed because the linear PSU starts very slowly, and the DAC will not accept that, but will go into failure mode. But that is fixed with this switch.

The pictures might not be exceptional, but the DAC is 🙂.

It can be sold for Euro 350 with the original OPA1656 op-amps installed in i both RCA and XLR outputs, but I recommend it with the SS2590 for Euro 470. It can be sent inside
the EU with GLS for Euro 30 - contact me for pricing outside EU. Payment could be PayPal to a friend, or bank transfer.

I'm new to the construction part of this. Used to service TVs back in the 70s and early 80s, and collected/fixed tube radios and TVs after as a hobby. Retired now, recovering from a brain injury (long story!) Slowly improving, and trying to relearn electronics, as my understanding of it is not what it was. I'm thinking building a simple tube amp is just the thing to help, and should, I hope, be fun.

What is the meaning of Life?
To me it seems life has no real meaning.

What do you think?
What are your goals here in life?
Other than surfing diyaudio.com 😀

Hi all,
I am ould (58) and some of my ideas are from 40 years ago. Many changed since than and I could realize one of my favorite ideas from my youth.
I registered here, I think, some years ago to get a better impression what is possible today and to find some help if I get really stuck.

I am far from experienced if it comes to PCB design and construction. I am more someone who has a good base for get things running.

Besides the hobby I still need to work for my living. In real life I earn my money as a Software-Architect/Technical Lead. So I there is some money to spend for my hobby.

Probably I need to fix my profile a bit. But that will come later.

I have a 12v power supply and a car stereo on my bench for testing amplifiers. I would like to add a 12v battery that will feed constant power to the radio so I don't have to reset all the settings every time I turn off the power supply. I would also like the power supply to charge the battery. What do I need to do?

I admit I started to buy vfet amp years ago influenced by some "internet influencers" they make me to believe they have unique sound, like no other trasistors can compare.
So, I got Yamaha b-2, Yamaha b-1, recently a Sansui ba-1000. Sure they sound similar sweet and smooth and i am satisfied.
I also found that not all vfet amp is so sweet and smooth for example hitachi ha-500f. I haven't heard one but according to kitr's review and listened to some youtube recordings I feel it sounds a little dull maybe on par with sony ta 4650. lacks some airy and live feel of ta-8650 from videos recorded in same environment. So I feel circuit design is more important.
I wonder is that true no other transistor can achieves sound like vfet? what about mosfet, high current mosfet like uhc or lapt, SiC depletion jfet? Anyone know any non-vfet amp with similar sound?
I am also curious about how vintage vfet compare to modern lowest distortiin class ab amp(
topping la90) or a GaN fet class D?

Hi everyone,

SpicyTL is online and available for download.

SpicyTL is a simulation model, based on the electrical circuit theory, which predicts the electro-acoustic behavior of transmission line loudspeaker systems. It is the evolution of the AIRDAMP model, whose development (and the principles that allow its operation) is illustrated in the article Progettare una linea di trasmissione utilizzando SPICE (Designing a Transmission Line with SPICE), published in issues 408, 409 and 410 (April, May and June 2019) of AUDIOreview. Compared to the latter, SpicyTL has a modular structure composed of several acoustic blocks and can also simulate tapered and expanding TL's.

The model, particularly suitable to design a TL damped with polyurethane foam, allows to simulate frequency response, phase response, group delay, electrical impedance, speaker cone excursion and air velocity at the TL output.

Operating instruction and download at the following address:

SpicyTL-english – Transmission Line Speakers

An in-depth look at the software, and its use for designing the Ikigai monitors, can be found in the article Progettiamo una linea di trasmissione con SpicyTL (Designing a Transmission Line with SpicyTL) on the 427th issue (January 2021) of AUDIOreview.

Kind regards,
Andrea

I have chosen to restrict access to transmissionlinespeakers.com for users from Israel. This decision is a response to the current events and human rights violations in Palestine. I strongly oppose any form of violence and injustice, and I believe this measure is necessary to express my ethical dissent.

I will post more projects that was made by me :
1. Volume controller / source selector for motor potentiometer ( like Alps blue velvet ) :
-schematics
-avr atmega8515 soft
-pcb
On atmega8515 you have to write only the fuse-bit named :
" Internal RC oscillator 8Mhz "

Hello all

Apologies if this is in the wrong section.

I have a Quad 99 pre amp and 99 CDP. I found it sounds best using RCA interconnects vs the Quadlink cable. Of course this disables the standby mode function, which is now missed.

Has anyone tried to alter a DB 15 cable so that only the necessary pin for bring in or out of standby is connected?

I've seen a few forum posts that state pin 7 is responsible for this function between the 99Pre and the 909 (but that would be the Ampbus connection), I need the pinout for the pre>CDP (Quadlink not Ampbus)

99 pre pinout




Does anyone know which pin i should be targeting?

Thanks in advance!

One channel of amp distorts when the volume is turned up. It's goes from clean to distorted around ½ power.

The voltages across r206, 207, and 208 are identical to the voltages across r306, 307 and 308.

Audio remains clean at c304 a and c201

Is there any real advantage to using single opamp in the DAC output stage?
Most of the equipment i see uses dual opamp in the output stage, would this be just to save cost and board size?

I am looking to build a new arrangement into existing pair of gifted cabinets of about 6-8ltrs. I want to run two identical (ideally 4 inch, wideband) drivers on each side in a (polk SDA-esque) crosstalk reduction arrangement. eg; LEFT; R-+, L+-. RIGHT; R+-, L-+ The drivers will be about 8-inches apart, horizontally, in each enclosure.
I have this arrangement set up in my room with 4 separate speakers and I love it. But the logistics of this are cumbersome, to say the least.
I will be running a sub from 100-150hz
I'm posting here simply to get tips and suggestions as I go through adapting the cabinets.
Any recommendations for good and affordable (ideally 4" to approximately fit the current cutouts) wideband drivers, bearing in mind cost of buying 4x
Also, my current set up uses two amps to achieve the "effect". Amp suggestions would also be useful.
I'm not particularly technical in terms of electronics/physics language.
I'm not particularly interested in a debate about the merits of xtc approach. Just hoping for experiences and tips.

Blaupunkt 5x8 voice coils melting tweeter post? I would think the coil would burn up before melting something. I measured the output for DC and it had .5v offset. It's a Chinese head unit with a (marked) TDA 75xx class AB chip. something strange going on here. Any ideas?

I am now embarking on a perilous journey on this DIY audio hobby. I am pushing the limits of my audio knowledge acquired here at DIYAudio. This project is an attempt to repurpose my pcb board intended for a CFP amp. LTSpice says the schematic will work, that is according to my understanding of how the circuit behaves.
The push pull VAS concept was taken from Keantoken's Aurum X amp with the output topology also being taken from Roender's FC-100 amp.
I ask you if anyone has made a similar design please comment your feedback. If this amp will turn out to be a firestarter 😄 I will not hesitate to toss the boards in the trash bin.

Thanks y'all!

Hi,

Long time lurker. I've been dabbling in guitar/guitar amp DIY'ing for ~20 years.

Stumbled upon some valve hi-fi gear recently - which I now have up and running.

Looking to get some advice on hi-fi speaker design and contruction and of course help others where i can.

Cheers

Hello fellow diyadio members🙂
My name is Lew, I am a student of engineering sciences in Germany. Normally I am hesitant to post online and like to just read along, but in this case I decided, after a few years of "passive membership" to come out of the shadows and to become part of this amazing community.
So far I have built four pairs of speakers, for friends, family and myself and two class D amplifiers out of modules. Now I would like to transition into class A amplifiers by first using one of the provided schematics from this forum. In the future I would like to be able to design something not terrible myself. Thanks in advance for helping me on my journey😉

Hi Moderation Team!

Please let me post in this forum, I have been repairing and modify my amps and speakers for 40 years.
I had already had an account here but I was inactive the last years.

Many Thanks!

René

Hello guys,
I'm new to the forum. I've built various DIY projects from time to time. Currently I´m a student doing my Bachelor of Engineering in Electronics and Communication. I´ll probably need some help from you soon regarding that topic.

There is a seller on FaceBay who has a pair of Shiva Mk3s who only wants $80- for both. I can't get to Mt Waverly but somebody please buy these before he chucks them to the tip.
PM me for the link to Facebook market place or just have a look for them yourself. A real bargain if they are really in working condition

Selling 2 kef blade coax uni-q drivers.
I do have 3rd one but tweeter is blown.
So I will include that one for free.
Price is 700 usd+shipping

I’ve built Ripols with 2 x 12” 8 ohm Dayton woofers. I believe that 1200AS2 should give enough power into 4 ohm. I want to use Mini DSP 2X4 with them as I have not built the crossovers. I have a balanced preamp and I want to implement the following setup:

Pre->MiniDSP-> 1200AS2-> Ripols.

I’m not sure if I can run 1200AS2 with single ended input, also, 2X4 mini DSP has 0.9 V output which is not enough for 1200 AS. I can get 2X4 mini DSP balanced that will solve the problem with the input but it’s output is only 2V so it is probably still not enough. Are there inexpensive buffers that I can use with ICE1200AS ?

HT12 is epic, but sold out!
https://www.diysoundgroup.com/ht-12-kit.html

Why wait for them to be back in stock when you can buy a set of seven fully assembled!

Look at how the HTM12 measure!
https://www.erinsaudiocorner.com/loudspeakers/diysg_htm12v2/

Now, HTM12 will be slightly different from HT12, HT12 is a cheaper model.
Most of the offaxis should be very similar between the two though.
Also, two of these are "HT12" kits with crossovers built by me.
The other 5 are "HT12+" with improved (much higher component count) crossovers purchased fully built by Matt Grant, mtg90.
If you have Dirac or Audyssey the improved crossover is a bit overkill, but wanted the best starting response possible. \
If you want, individual frequency traces flat on its back on my deck are available.

Why am I selling? Because I am a madman and built 6x 8' tall line array of ND91 drivers.

Hoping for a local sale in the San Francisco Bay Area, technically, I am located in Marin, near the Larkspur Equator Coffee.

Cost is $2500, equal to all the kits, crossovers, screws, terminal plates and wire.

The latest stable release KiCad 8.0.8 is out, just bug fixes.
V8 is very stable at this late stage of its life cycle.
https://www.kicad.org/blog/2025/01/KiCad-8.0.8-Release/

DAC-END 24 (AD1865 NOS DAC )

AD1865 is a dac chips with natural sound and inspiring.

ago, Andrea and I had success with DAC-end, now I have upgraded dac-end 16-bit, 24-bit up-end DAC.

it receives the input frequency of 192 KhZ- 24bit and special use Amanero to use USB audio source from your computer.

invited to view some links:
DAC End - the AD1865N-K with single ended vacuum output stage
http://www.diyaudio.com/forums/quan...287-dac-end-best-dac-ad1865-updat-2011-a.html
DAC End 2 - the AD1865N-K with single ended vacuum output stage



Description:

• Structure:

Digital input:
1 x coaxial input,
1 x Optical
1 x AES/EBU- Balance in put
1 x USB Amanero
1 x selected in put
1x AD1865
1x Cs8416
1x HQ-01 Transfomer supply: 0-6V*2
Analog output : R IV passive
Digital section : using AD1865 as digital receiver CS8416 + Amanero USB.

• DAC kit Design construction:

1. NOS (non-oversampling) application
2. 3 x low noise, low Z-out shunt regulator
3. 2 x LT regulator for Digital + USB
4. 4 stages regulation for digital section
6. Audio grade components were used.
7. OSCON capacitors used for digital section
8. The composition resistors Vishay error of 1%,
9. 1 x Transfomer supply: 0-6V *2

PCB size 216 mm x 110 mm, 1.6 mm double sides board with gold plated.

Optional: You are welcome to ask if you have any question on the assembly and more information.
Shall not be reproduced without consent!

Hi everyone.

I was lucky to score a nice external crossover from Accuphase with fixed crossover frequencies. The crossover is equipped with modules to feed a a 4-way design. 3 frequencies modules and 4 line preamp modules. I have 4 stereo outputs.

The frequencies are 130, 350 and 5000Hz.

I am struggling to understand the configuration of drivers for such frequencies. I am not sure if I am willing to build a 4 ways speakers as I just finished a 3 ways speakers with digital crossover using minidsp. But I am curious.

Does everyone have an idea of a typical design with those frequencies? Typical driver size and configuration. Any compatible speakers where I could bypass the internal crossover and feed directly the drivers?

I asked the previous owner. No response yet.

Thanks!

Hello,

I have a pair of Altec 420A bi-flex speakers that I would love to use in a project.

They are the black-framed, "16 inch" type - refer picture. I think they are the same as the relatively common 15" white/silver 820A / 820-8As. I know they are different to the 820B.

These things have a huge Vas (~470L) and, unfortunately, large enclosures are not an option for me.

I was hoping to for some ideas as to what to do with them.

I was thinking (/hoping) that some form of open baffle or smallish ported enclosure might be acceptable. Ideally two-way with the 820A on bass and mid duty.

Any guidance appreciated.

Greetings from Singapore

Hey guys! i recently decided to build a new trunk enclosure for my 2 " Pioneer TS-W304R" powered by my brand new "AudioControl EPIC1000" amp and decided to use WinISD to try and get the most out of my enclosure before i go through all the work to build it, ill attach the screenshots below. i watched a few videos on how to use WinISD but im not quite sure on how to optimize it. thanks guys! let me know if you need any more info, im very beginner, any advice helps!

I'm looking for a pair of these in good or new condition.
thanks!

Getting prepared to do an arm tube swap with Cardas litz wire on one of my 1200s using the titanium arm tube from an M5G model. I've done this swap before, but this time I want to add some very fine lambs wool wrap around the wire.

I notice with some of the rewired arms I've done previously the top end took a slight hit in overall detail and the midrange sounded a bit peaky. I would attribute this to the stock alu arm being more lively and resonance prone in the HF.

I have an SME109 arm on one of my 1200s which was upgraded with ceramic bearings, but otherwise stock aside from wiring. This arm sounds very balanced and detailed with a VDH3 MC cart but it doesn't have the bass extension of the M5G arm with an AT-OC9/2 cart.

So my ultimate goal here is to have the new M5G arm setup along with a fluid dampener and cardas wire, so I can sell the SME along with its mounting base or use it on another custom TT built from a Corian plinth with SL1200 drive. On this one I'd like to use my magnetic bearing setup with the dynamic height adjustment. This would be the test bed for the bearing setup.

Has anyone done anything similar to their SL1200 using the magnesium or titanium arm tube? I also have a graphite powder resin composite coated arm tube which weighs about 0.3 g more than stock. This one also sounds very good but also has duller top end.

Hi Everyone,

Edit: Issue resolved. My amplifier was nowhere near sufficient enough to drive my subwoofers adequately. After strapping a Crown XLS2500 across the drivers, things are great. Cheers!



I built a dual 15" Ripole subwoofer using Dayton RSS390HF-4's. Everything works great as expected until transient bass notes hit, then it sounds similar to the suspension/coil bottoming out. The issue is that I hear this when there's only 3-4mm of excursion. My ignorance on the physics of this exact topic leaves me just with some bad feelings, as if the suspension is just not okay in this application, but I'm having a hard time identifying which parameters I should be looking at. I've measured the THD to see if there's anything obvious going on, like resonances from the slots, or significant dominance of even vs odd harmonics....etc. Nothing pops out. The THD plots are clean at 95dB 1m, generally less than 1% in the sub range.

Here's a recording of the sound.
Recording of "blatt, blatt, blatt" sound

I'm wondering if there's a slight imbalance of pressure on the cone from the cavity geometry, since the backwall of each cavity is curved (to reduce the Q of the 1/4 wave resonances), which may put an uneven load on the cone, which might be able to "rock" the cone to one side during its stroke, and maybe the coil is actually rubbing on the magnet / pole piece during these louder, transient signals? I'm somewhat convicted in this belief at the moment since the driver in free-air excurts significantly more before I start to hear the suspension doing suspension-y things.

This is the impedance sweep of the ripole.

And this is the THD measurement @ 1m of the Ripole, DSP already applied (dipole correction boost, cavity resonances reduced, 20Hz and 105Hz steep crossovers, room correction
)


And here's the THD measurement of the full integrated system measured at 2.5m, listening position:


I did a quick experiment. I "sealed" the front cavity on carpet by rotating the enclosure 90deg, leaving only the dual rear cavities open, the output changes to that of a monopole, and is expectedly more efficient. It gives the sound you would expect of a large driver in an undersized enclosure. But the strange suspension sound diminishes quite a bit, if not completely. However, since I don't have a way to directly measure the "sound" of the suspension / coil noise, I suspect I'm just experiencing a higher "signal to noise" ratio, given the expected efficiency boost of no longer being a dipole flapper.

Anyways, I am curious if others are having this issue. I am looking for help identifying root cause / physics of the issue. I would also love to be able to better select a subwoofer driver for this application. I followed all the info I knew at the time of purchase for this application, aiming for a final Qts of 0.7 in enclosure, choosing a driver with low distortion motor desgin, high excursion, and designing the enclosure cavity sizes scaled up from my previous build, where I used 4x Peerless SLS 10" subs, chambered. (they sounded good)

These are used.
I cannot remember what I removed them from but I'm sure there was nothing wrong with them. I'd have thrown them away if I thought there was an issue.

£6 the pair?

I have 10.
50p ea.
Free uk postage.

I decided it was time to open a thread to capture my experiences with this driver and the box I'm going to make for it.

It's a big driver. Until you have one in your hands, it's hard to imagine.

More about the driver here
Edit: the ferrite version is no longer available, I recommend the Super 12” Ferrite as the affordable alternative to the 15” Alnico. Also, I wouldn’t go smaller than 10”, where the Super 10 Alnico is my recommendation as the preferred option for a vented box design enclosure when smaller size is a priority.


Edit: this design eventually became an open back box with a light level of stuffing behind the driver. It's not an open baffle dipole in the traditional sense because the highs are mostly radiated from the front whizzer cone and the stuffing absorbs these frequencies behind the driver. The bass however is able to radiate backwards from what is essentially a U-frame, perhaps tending towards cardioid.

I have various SanKen transistors as follows :

2SA1215 X2
2SA1216 X2
2SC2921 X2
2SC2922 X2

I bought these a few years ago to put in my Sony 550ES but never got round to it. The Sony has now gone and these are no use to me.

The 1215's and 2921's I believe are genuine as they weigh 18-19 grams each, which is what the SanKen datasheet says.

£8 per pair

The other 2 pairs are lighter so may be fakes. I haven't looked into it much further than a quick Google and I'm not knowledgeable on the subject.

£4 per pair

Free postage in UK

I'm looking for the service manual for a Rotel RCD-970BX CD player. Not sur where its best to find one. Google seems to come up with sites that look a bit untrustworthy.

Need a little help here.
To cut a long story short.
A friend asked me to look at his headphone gear. Stax 007 and SRM-T1S headphone amp. The story is, that this
never worked as expected. And he´s right. The sound is dull, boring and nowhere near, what you would expect from STAX.
He hiself had replaced the tubes and all the elctrolytic cap´s. This made no difference.
Visited another firend, who has a set of Lambda phones and an older solid state Stax headphone amp.
On his setup, the 007´s sound perfect. A slight more laid back than the Lambda´s but totally acceptable. On the SRM-T1S far from as good.
So I´m confident, the error must be in the SRM-T1S
Can´t see or measure any faults in the circuit........... other than maybe this one..........
People write, that the bias voltage is 230V for normal and 580V for Pro.
Where to measure this??
No matter if I measure from L-, R-, L+, L- or ground to bias in the plug I end up with approx. 150V in the normal plug or 360V on the Pro.
I called the Lambda guy and asked him to measure his amp, and he got the same results....... 160V vs. 355V.
Am I on thin ice here, or is this measurement taken between "bias" and some unknown ref.??
I only have a really bad copy of the schematics, so if anyone can scan the org. service manual from Stax, it would be very much appreciated.
I found the adjustments on Headfi.org and adjustments are done within less than 1 Volt (Stax acceps +-15 or less).
Thanks in advance for any info...... and no...... I´m not gonna convert it according to the CCS mod´s 😉

Alpine SWR-12D4 Subwoofer
Bought a 1000w type r for $110 but it has a 2 inch hair line Crack on the cone.
Good thing is, it doesn't go through.
I have (on hand):
E6000 adhesive
Lepage plastic adhesive
Bondo
Gorilla glue
Do I need to worry about playing it and it getting bigger?

Just unsure how to fix this thing guys?
T.I.A.

Why not be bold again and simply reach into the component box?

No weeks of thinking, just have fun like a child. Just like in the old days, simply tinkering and listening to music. It's not quite that simple, because there's so much at the back of your mind ...

Design frame:
-Two-stage
-Voltage divider that bends back the cutting characteristic
-Gain about 40dB at signal frequency 1kHz
-One coupling capacitor at the input and one at the output
-Rebuildable, if it works
quite simple (KISS) and the hope that it doesn't noise - and above all works!

This problem has kept me up all night, being a 19 year old again. It's not easy to throw everything overboard and deliberately break some design rules.


Today:
I only listen via MCs, but if it works, I'll buy the nicest and cheapest MM my store has in stock.

Here's my idea, the simulation results are perfectly fine - if I haven't made a stupid mistake.
You never know.

😉

Always be gentle,
HBt.

Hi guys, I would like to know if anyone here tried the ClarityCap PUR version capacitors? How would you rate the PUR against the Jantzen Silver Z-Cap or Jantzen SuperiorZ-Cap?

Also there is a PUR-S version, is there any noticeable difference from the PUR version? Could not find any review information on these PUR version from the net, so any input is appreciated, thanks.

I'm curious how many people have bought or are considering buying that driver?
What kind of box have you built or intend to build for this driver?
I have tested BlueBuck and a smaller bass reflex so far.
BlueBuck is my favorite.

In the Spring, I finished the Missing Link boxes for the InDIYana 2022 xover theme with the added objective of using it for more upcoming 7" 2way type build stand-mount projects.
Most of you have likely seen the first use with the SB29RD(A)C and Dynavox LW6004HRN. This is the second one, using the Seas U18 and 27TAC Titan tweeter. The 50 Hz tuning and stuffed 15 ltr box was good for the U18. If I tuned lower, it would sound a bit anemic, but the highish tuning used supported the bottom end fairly well.

I used the first of my 2 pair of Titans in the EMP build recently in the last couple years, and this is now the second implementation of a tweeter I really enjoy a lot. What is posted here for FR and HD is prior the addition of a 1 ohm resistor after the xover on the tweeter to adjust to taste. It was flat before, but just a hair bright, so just eyeball about a -1dB tilt above 2.5k.
The xover ended up being LR2 at 2.5kHz, which is one of only a couple times I've managed that result. Because of this, the toe-in needs to be just a bit more than normal to get the image right and not shift when moving my head. I literally can look down the outer left and outer right sides of the respective channels when seated in the right spot. To get the drivers to comply at LR2 took a single coil on the woofer and an overdamped 3rd order on the tweeter with an additional Fs LCR compensation. The TAC has no ferroFluid, and this is a likely compensation circuit to add in most cases.
Some funny/interesting things that occurred over the course include;

• I heard more details in some tracks I know really well, and that is saying something. This is a VERY clean design. It has lower HD than a lot of my other builds, dominantly -50dB for the most part.
• I had some sssibilance initially when I added the second resistor, which was a MOX Lynk type. I changed to a sandcast, and the problem subsided.
• I have some very small Russian polystyrene caps of 0.002uF. I paralleled the tweeter caps with them just to hear the results and had no expectations. They are very small in value. Well- I removed them after a first listen as the tweeters sounded broken, disjointed, and distorted badly. I really thought I might have had a bad tweeter because of what I was hearing. After removal, the relaxed and detailed sound that I heard prior returned as I had left it. I'm not really sure what caused the bad interaction, but it was awful!! I am not a supporter of bypassing for the most part, but since I had them and they were doing nothing I gave them a shot.

Listening impressions? I feel they are really revealing without being harsh. That said though,they are okay with rock, jazz, country, orchestral, classical, etc; but I would not recommend them as metal speakers. Being that they reveal the flaws, the source material really needs to be clean to sound right. Those of us Metalheads know that over compressed and gritty can be quite common for the bad mixes. With well recorded metal, I would still think they'll sound quite good. Nightwish's 'Dark Passion Play' was fine for example, but Born of Osiris was not.

For the parts used, in case you're curious, I used ASC X387 poly-in-oil caps for the tweeter, and I hand wound a 16AWG air-core for the woofer that I triple-dipped in polyurethane. Sandcast resistors used throughout.

Thanks for reading my long winded intro to my 'King' Norwegian design.
Wolf

Hi,

I have for sale a lot of stuff I want to get rid off.

I sale all as one lot, as I don't have the time to ship each part in its own.

So, whats included??

-. 24x ICEpower 80AM2 amps plus assorted cable set.
-. 4x untested Hypex UcD180
-. 42x PCM 5242 I2S DAC boards (see pictures for specs)
-. 1x ADAU1452 DSP (the one sold in Aliexpress por USD$70 aprox.) with the proper AD1938 CODEC board.
-. 2x extra AD1938 CODEC boards (see pictures for specs)
-. 1x USB to I2S 8 channel board
-. 1x SIGMAlink Programmer

Price for everything: USD$250 80 plus shipping. Depending on the country, shipping thru FEDEX would be around USD$50-70 80 extra.

Feel free to ask any questions.

Cheers.

I'm building a PCM1794 DAC, planing to have line-out, headphone amp, maybe fully-differential low-pass filter for balanced output, with line-out it's just datasheet low-pass filter, but headphone amp I'm planing to use TPA6120, which requires differential input, would it be a good idea to split the signal after I/V stage? if current output isn't an issue(using opa1612), one goes to opa1612 as in datasheet, one goes to TPA6120 without buffer?

what's normal way to handle multiple output?
thank you all

Hi all

I have a paor of jbl 4657a 15"

Can i have the recommwndation tweater to pair with itu? Prefer horn.

I see b&c de500. But the crossover point is 1.6k. Not good right?

Guess horn it not good option?

Regards
Erwin

I'm looking for three of these switches.
These switches are installed in an old Marantz receiver, originally from the company Toko, which has now become C&K.
I read in a forum that the C&K type F4UEE should fit - but I can't judge that.

Does anyone happen to have such 12-pin versions to give away? I would need three of them.

If you'd rather like to swap your switches, I have some good components to dive into.

New member ...trying to build protodac with Ian canada part running into no sound issue. Looking for directions

Help in choosing a potentiometer as a "Passive preamplifier"
============================================================

This is more of a guide as I already found the answers I need. To begin a potentiometer as passive preamplifier does not amplify anything. It is just a potentiometer used as a potential divider in a box between the source and the amplfier. It is really just an attenuator but becuase of its position and the box it is called a passive preamplifier.

You might think, well I have a single high voltage source with 2.1 Volts, no interest in microphones, vinyl, balance or (dread) tone controls - so I think I should just use a 10K logarithmic potentiometer to get a nice pure sound, because after all - less stuff in the signal path must be better than more stuff.

But if you try it, you may not get the sound you expect - it might exceed your expectations but could possibly sound terrible. If you ask about it, you are met with claims of high frequency attenuation, lack of dynamics, lack of top end, lack of bottom end, lack of sleep!, balance problems, changes in the sound as the volume is changed, too low volume at max and that by violating a 5 times or 10 times voodoo source and load impedance rule can make the sound gods angry and get you punished with bad sound.

Before I dispel some of these claims and explain the validity of the rest let's get some terms out of the way and see what a preamplifier actually does.

When you see the word impedance it is usually accompanied by one of the words input, output, load or source. In the case of a preamplifier the input impedance refers to the inputs where you connect your sources, for example your CD player. The output impedance refers to where you connect your amplifier.

Great now what is the load and what is the source?

Looking at the chain left to right CD > Preamplifier > Amplifier, you can say that the source impedance is the output impedance of the box to the left and the load impedance is the input impedance of the box to the right. But you have to qualify this with whose source or whose load you are actually referring to.

So the source impedance of the preamplifier is the output impedance of the CD player and the source impedance of the amplifier is the output impedance of the preamplifier.

A preamplifier serves several purposes:
1 It amplifies low voltage sources such as microphones or record players
2 It fixes that audio curve thing for record players
3 It provides a balance and (dread) tone control
4 It provides low output impedance
5 It provides a high input impedance
6 And it looks nice and impressive, gives a warm and fuzzy feeling inside, has a headphone output and a remote control too if you are lucky then some blue LEDs....

1 Low voltage sources must be amplified before sending the signal to the amp, otherwise they may not be loud enough. An amplifier has an input sensitivity value in Volts. A signal with this voltage will be amplified to the limits of the amplifier i.e. the rated power in Watts.
2 Look elsewhere for an explanation
3 I try to sit in the middle anyway and my sources are usually have a good balance,
4 The output impedance refers to the ability to drive a heavy load. A heavy load is one with a small impedance. The smaller this figure the better. More on this later.
5 The input impedance refers to the load imposed on your source by the preamplifier. The impedance should be a high as possible (= a light load) so it does stress on your source too much.
6 Look elsewhere for a warm and fuzzy feeling inside.


High frequency attenuation
Capacitance in the interconnect cable combined with the output resistance of the potentiometer make a low pass filter. There is a good explanation on the DACT website in the technical section two PDFs and also an Excel file to calculate it. This can be a problem if the output resistance of the potentiometer is high and or if your interconnect cables have a high capacitance and or are very long. If you choose a 100K potentiometer and 10 meters of high capacitance interconnect cable then you will get some high frequency attenuation and hear it too. If you have a 10K potentiometer and a short run of interconnect cable then you won't. This low pass filter problem does not affect preamplifiers as they have a very low usually 50-100 Ohm output impedance. With preamplifiers you can use meters and meters of interconnect cable and not fear this high frequency attenuation low pass filter problem. My L-25D amplifier has a 1 nano Farad capacitor connected to signal and ground as part of an optional RF Filter and the capacitance of the RCA interconnect cable is probably around 300 pico Farads. Plugging these values into the DACT Excel file shows that capacitance is not a problem. Be sure to read the PDF which describes how to use the DACT excel file.

Apparent lack of dynamics
Well if you are experiencing the attenuation above that would go some way to explaining the lack of dynamics. The rest of the way is found by calculating the load imposed on the source by your potentiometer and the input impedance of your amplifier in parallel. Let's look at how a potentiometer is wired and do the maths.

Figure01 shows how a potentionmeter is wired to make a passive preamplifier. The ground is the outside of the RCA interconnect cable and is usually connected to one of the outside pins on the potentiometer. The inside conductor in the RCA interconnect cable is the signal and is usaully connected to the other outside pin of the potentiometer. The signal for the amplfier is usually taken from the middle pin of the potentiometer. This is the wiper part of the potentiometer and its position determines the values of R1 and R2 in Figure01. The formula on Figure01 is used to calculate the output voltage from the potentiometer. This formula is used to calculate the volume curves seen in the figures of graphs seen later. Figure08 is a LTSpice file showing the simulated circuit. R1 and R2 are represented here as variables with a step to simulate the rotation of the potentiometer. Simulate the circuit using a 300K RLoad and you see that the VOut becomes very linear.

Figure03 shows that the maximum impedance seen by the source (the load imposed by the potentiometer and amplifier) is the impedance of the 10000 Ohm potentiometer. This occurs at the lowest volume setting -infinite dB.

Figure02 shows that the minimum impedance seen the by source is the impedance of the potentiometer and the amplifier in parallel which is calculated 1 / (1/Resistance of potentiometer+ 1/Impedance of amp) = 3230 Ohms. This occurs at the highest volume setting -0 dB. This is a rather heavy load for your source to deal with.

Well not all sources are equal. My DAC has a bunch of NE5532 opamp chips in its output stage. These chips are rated to drive audio loads all the way down to 500 Ohms. One review tortured the output stage with a 600 Ohm load and it performance was barely affected. Your mileage may vary - it is unfortunate to say and I hate to say it depends, but it does. Some sources have highly integrated chips that also incorporate the output stage opamps and a bunch of other stuff into one chip. These are the bad guys that you want to avoid if you venture into the world of passive preamplifiers. They are not designed to drive heavy loads and likely will cause you problems.

So now you should be thinking: high Ohm potentiometer = potential low pass filter problems, low ohm potentiometer = too heavy a load for the source.

Balance problems
These are caused by poor matching of the two traces in the potentiometer for each channel. This effect is magnified in the low volume area of the potentiometer where the traces approach 0 Ohms. Here it is very difficult for the manufacturers to get good matching. The matching varies with potentiometer position. This is not really a problem with good quality pots, but might still be a problem if you have a low input sensitivity high voltage gain amplifier with high sensitivity speakers. Good quality potentiometers from TKD have a 0.1 dB usual to 0.3 dB maximum deviation for a stereo potentiometer. This corresponds to a 1 - 3.5% deviation in the levels between channels. Good luck hearing that difference.

Changes in the sound as the volume is changed
This is due one or two of the two problems explained above. It could be that at high volumes, you are stressing the output stage of your source too much. Also if you have a symmetrical source the balance problems are magnified. If you are worried about your four trace potentiometer for your symmetrical source then used a stepped type with make before break resistors.

Too low a volume at max
This is a problem of a source which has an output voltage which is too low or the input sensitivity of the amp is too high or both. Not really a problem for me with my DAC as a source with 2.1 V and an amplifier with an input sensitivity of 1.6 V

Hour of power
The next problem is not listed above but I will explain it anyway. It is the effect of turning the volume control and it stays really quiet until close to the end where all the power seems to be in the last "hour" of the volume control between 4 and 5 o'clock. The problem is the input impedance of your amplifier in relation to the value of the potentiometer and how this affects the logarithmic(ness) of the curve of the voltage output from the potential divider. Using the Excel file in the attached zip you can plug in some values and understand the problem better than I can explain in text how it manifests itself. The Excel file will show you the minimum and maximum load imposed on the source.

Figure04 shows my system, details of which can be gleaned from this text or seen in Figure01. The output Voltage of the potentiometer is on the left and the -decibels(attenuation) on the bottom. The red line represents the ideal curve and the blue line is the actual curve.

Let's try a 100 KOhm potentiometer instead in Figure05. That is just terrible, all the power is in the last hour as I mentioned above.

Let's leave my potentiometer as it is and increase the input impedance of my amplifier from 3.23 KOhms to 100 KOhms in Figure06. Much better, but I don't feel like buying another amplifier with higher input impedance and I cannot modify my amplfier to have a higher input impedance.

Let's leave the amplifier as it is and change the potentiometer to 1 KOhm in Figure07. That looks much better than my 10 KOhm potentiometer, but now I am possibly stressing my source with 764 Ohm load at maximum volume(formula is above) Most sources will have given up at this stage and be on their knees begging for mercy.

For my system a 5 KOhm potentiometer would have been better, but the 10 KOhm is quite acceptable. A 50K potentiometer or heaven forbid a 100 KOhm potentiometer would be no fun at all with the capacitance problem and the last hour of power problem explained above. With a input sensitivity of 1.6 V and a maximum power of 350 watts @40hms, a source with 2.1 V and 200 Watt 4 Ohm speakers - my maximum power is achieved @ 0.7 Volts which is at the -4.5db mark. The perfect result here would have been -9dB.

The 10 times or 5 times myth
Well this is just a general rule to keep the load impedance high - there is no real maths in there. If you read the above then you know already keep the load impedance high so as not to stress your source. You might get claims of: well your potentiometer has a output impedance of 10 KOhm and your amp has an input impedance of 20 KOhm and that this is bad because it breaks the rule!!. These people don't understand that the potentiometer is not a source. The potentiometer and the amplifier ARE THE LOAD.


I hope my little rant here is helpful to someone. Pointing out mistakes I made is welcomed, pot shots (pun intended) and hit and runs are not welcome. Claims of: "Well I tried one and it sounded terrible" without any details of the components involved and their input and output impedances are not welcome. If you read the above then you will now know that you cannot just drop in a passive preamplifier into any system and expect good results!! I tried to deal with all the factors involved and did not intend to scare people off. Armed with this knowledge you can put togehter a system with a passive preamplifier and get better sound than any preamplifier.

Because of the distance between your ears , the frequency response when listening to two loudspeakers in stereo should not be flat .

The Harman way of doing this is to simply ignore that there’s always two stereo speakers at normal listening to music , and just concentrate on one speaker in mono - with a flat response. This is correct when you listen to only one speaker in mono.

But what about stereo ?

Below you see two frequency response curves . The curve at the bottom is the ideal frequency response according to the research from Harman , without stereo compensation at listening position 3-4 meters away. We see the boost of bass needed below 100 Hz .

The upper curve in blue shows measurements 1 meters away from one stereosystem compensated loudspeaker . We see a peak centered at 1,7 kHz , Q=3. And a dip at 3,5 kHz .

If using two such speakers in a listening triangle L - R - listening position , the sound with good stereo material will be holografic , free from each speaker and very natural/real sounding .
This can easily be done using a dsp with PEQ function .

Hello,

I use a number of Differential Probes at work (like the TesTec SI9000-1 found in RS). The need to calibrate & repair them necessitated a reverse engineering exercise. Not at all easy, all ICs (and some of the 'transistors') have had their markings sanded off. However, some numbers could be made out.

I have to hand 4 of these probes, the earlier version uses through-hole components and the later models use surface mount components. Both types are revealed here:

Through-hole version of the probe:


Notes:
Guessed op-amp used for U3
Q3=Q5 (markings sanded off). Guessed this device as TL431
Q4 (markings sanded off). Guessed at BF451

Surface-mount version of the probe:


Notes:
U3 (markings sanded off) - can just about make out '74' so guessed at 741
Missing: SMPS chip. Could not make a guess at that!

------

Anyway, comments, discussion, errors, improvements etc. PLEASE! 🙂

Andy

Hello, my name is Francesco and I am interestd in power supply ,and scope measurement.
I hope in your help🙂

Hello, my nickname is Bane and I do electronic DIY stuff from microcontrollers, tube preamps and amps, analog AB amplifiers and attracted to anything electronic 🙂
Of course I know a lot but there is more that I dont know so I join this forum to help others of I can and get help if I need. Cheers!

THe inspiration came from reading a few books reading a few books about the design of musical instruments, particularly those made from wood. There is a similarity between tonearms and violines: You want to avoid high Q resonances, or "Wolf-TOnes" in the violine language. THerefore I tested the design principles on wooden pipes. Funny detail: It turned out that my SAMBUCO tonearm is made from elderwood, the same as Harry Potter's magic wand.

Geoff Husbands articles were part of my research work, and now I believe, I can contribute a chapter to the design of tonearms: www.sembuco.net will give you an introduction to my approach.