Hi,

I'm about to test some speakers at home with a measuring mic etc. On the one hand it would be useful to see how the speakers perform in a "typical" domestic setting but as a reference (and out of curiosity) I'd really like to know how the perform under anechoic conditions.

I remember seeing a web page that showed an alternative method: a very short burst of noise is played through the speaker and recorded. The burst is so short that the recording only contains the direct output of the speaker i.e. the recording time wasn't long enough to contain any reflections from the room boundaries, therefore anechoic.

Does anyone know what this method is called or have any links? Are there any draw backs with this approach?

Thanx in advance,
Dean.

Hi everyone! After building numerous chipamps now i'm heading towards discrete amplifiers. I know very little about discrete designs & still learning. It'll take time i believe but despite that i've no dearth of enthusiasm!

Anyway my question is how much power i can get from two pair of mjl 93/94 into 4ohm & 8ohm load(real world use)? Driver transistor recommendation? Actually still i'm struggling to understand SOA. Please help me 🙂

I'm toying around with a Nakamichi tape deck that has separate knobs for R/L recording levels and I'd like to make a test jig for matching the levels (the meters are not accurate enough).

The most basic idea could be a LED that is fed by the voltage difference between both channels, when it is dimmest it is matched (although resolution might not be great)
Or a row of LEDs that is centered when balanced and lit on either side depending on whether the voltage difference is positive or negative.
Also open to a display/voltmeter module but seems like it would be more complex.

I don't know where to start on how to design such a schematic, any help or suggestions would be appreciated.

Hey folks, if you bought one of the kits and haven't built it or built it but want to move on to something else, please see my posting in the Marketplace/Swapmeet. Thanks! Jim

just taking an idea from sonus faber lilium, it has a tuned mass damper insde the cabinet to reduce cabinet virbation

Login to view embedded media
now compare to taiwan101 tower it put a mass damper on the top of the building instead using the total length of the cabinet

Which one it the proper implementation ? to me it seems the tower is the proper implemntation becasue it also take account of the horizontal and vertical virbation.

Now we put this mass damper design into a vented box, shall we creat a seperate enclousre on top of the box so we can eliminate the accoustic sound the mass damper created ?

Hello,
I just got this amplifier and when power it on the relay does not click.
The two power transistors on the left side has +41/-41V (collector pins) and 0V (base and emitter pins).
The two power transistors on the right side has +41/-41V (collector pins) and +6V (base and emitter pins).

Any troubleshooting?

One pair in cotton and switchcraft rca conectors.
40 euro plus 7,90 shipping inside EU.

Hello,
I am planning to make a CRC PSU for Class A (Jean Hiraga), which can also be used for class AB.
The PCB layout is made in 2 styles.
I have made 2 layouts and wish to know which one is the recommended one.
Attached are the schematic, Layout A, and Layout B.
Thanks and regards,
Sumesh

Hi there,

I ve been looking for a Horn project since long ago.
i think I got lucky this time, a friend is giving me a pair of JBL 2360A for free.
i am worried by the size but i annot let pass this oportunity.
i am in Chile so importing these horns from usa would be imposible so here i am.

I am very ignorant about horns, but have seen a few projects with 2360A that alwais appealed to me a lot.

here some data to work with:

Room: 8mt width x 7mt long

dac: Buffalo IiI with balanced and single end output. can use both outpus if neccesary to feed two amplifiers

Amplifier: japanese SET 45 with Tango Irons (great stuff) 8ohms output only. not a lot of power so impedance should math.
i have also a SS 41hz.com 100W amplifier, i want to avoid it as much as possible, but I will use it with woofer if really really needed. At the moment I have a 97db woofer, so seems it will be necesary to match horns sensitivity.

tweeter: thinking to buy a jbl 2405h on ebay (because i love everest d55000 and fell in love with these tweeters)

mid: horn JBL 2360a, looking for good and cheap CD to go from 350-500hz to 6khz-8khz

bass: reaching quality 40hz-50hz should be ok for me. i already have a Eminence omega ori 18a with me and want to use it in the beggining to save cash, can get a 100db woofer later...

Crossover: I would rather passive, since I like my DAC and like my 45 SET amp, want to avoid touching sound as much as possible, but want a bunch more of sensitivity to drive my amp better.

Current speakers: 94db open baffle Saba green cones with 18inch woofer. first order passive crossover. i like it but is the weak link now for my System. mids are great but I lack detail and dynamics, I want more high end stuff.

so my questions:
1) does it sound good project, something to finish your speaker building career?
2) looking for a 2inch driver that can do the job, with quality sound. Buying in chile would be much cheaper, but only optons at the moment seems to be here:
Selenium d3305ti
Eminence PSD 3006-8ohm
rcf n850 (more expensive, more power, dont know if better in Sound Quality)
the selenium is cheap at 200usd in Chile, and i tend to think it will sound good.
3) lots of CDs are 16ohms, my woofer is 8ohms, whats better to end up with a 8ohms load to the amplifier? 8 or 16ohms CD?


So your help and experience will be invaluable to make the right choices.
best,
Carlos

Hi,
I have created an amp based on IRS2452 which is design-wise very similar to IRS2092 (has differential inputs).
It is based on IRAUDAMP23 (schematics attached). The MOSFETs in schematics have been replaced by IPP530N15N3GXKSA1 which have much lower Gate capacitance.


I have a problem with shoot-through when the high-side MOSFET turns off (and low-side MOSFET turns on).

Although I have gate buffers installed, the driver inside the IRS first seems to slowly discharge to VBoost and then discharges the gate(or the gate buffer transistors) faster. Due to this slow discharge, I get a shoot-through.
See attached photos taken between R1409 and R1408(yellow) and R1419 and R1424(blue).



Any idea what could be the root cause ?

VBoost is 45V, -VBoost -45V - the other voltages are okay as well (the amp plays well but idle current is too high).




Regards,
Beetlebuster

Hi,

I'm new here, I've read a lot of good stuff on threads here before.
I've been doing glassware amplification for about three years now, and i've come to thepoint there i'm learning how to design proper output stages.
Up till now, I've been learning all I need from education+diy. preamps, power supplies and triode power ( SE/PP) are things i can design already. at least they work😀

So, I finally decided to make an account and actually ask a question. 😱
I'ts about Pushpull Pentodes. I've already got a nice amplifier so now i'm working on an amp that doesn't only sound nice, but also looks nice- better than this: (i'm the engineer there, too)
Circuits Online - Forum - Show your projects! Part 26.


I was aiming for a mercury rectifier, a nice glowing regulatortube such as OA3 to 0D3. that's all settled and fine. For output tube i'd like a nice topcap tube, but not too expensive. the budget is limited🙄

Ive been loking around and my eyes fell on 2E26 tubes. I really like the looks ( and the price tag) on them. the datasheet mosty supplies data for Eg >0 but I dont want to go there.

The aim is a 15W amplifier. with my calculations I can get nowhere near there. but it should be easily possible with htis tube! i heard someone calling "14W SE" but that must be a little on the high side.

So, what i'd like to know, what kind of values to expect. Ra~a, Vb+, Eg, Iadc.
There 'll be a big electro market soon and i'd like to go shopping 😀

my guess is something like Pda +/- 7W, Va = 250 to 350V, but then I don't know what Ra~a i should choose.i've no experience with these tubes.


I'll gladly hear your thoughts on this! ( & please tell me whenI'm doing things wrong)

My Yamahas have had a hard life. Getting married and kids relegated them to the garage for a few years, then into the workshop where the angle grinder gets used quite a lot. As part of my recent workshop upgrade, I thought I would upgrade my sound system and the Yamahas didn't sound like I remembered. Inspection revealed one tweeter was dead, and one mid was distorting badly.
A friend pointed me at this Login to view embedded media which is an encouraging demo of a simple fix to the tweeter.
I didn't really have anything to lose so I thought I would try what I previously thought impossible - fix the drive units.

My tweeter was in a much worse condition than the youtube vid. The Copper Clad Aluminum ribbon had corroded for about 1/3 of a turn (turned to white aluminium oxide powder) which meant nothing to solder on to, and the coil had become detached for that area.
Nothing to lose now! so I unpicked the epoxy hoding the coil on This shows the state of the coil and dome just after freeing the coil:



During clean-up I broke the negative tail of the coil as well 🙁.

Next challenge is to get something to solder on to. I unwound a bit of the negative tail, and unwound almost a full turn of the positive tail. CCA is incredibly fragile and this is probably the most challenging part. I used magnification, a scalpel, time, and a lot of tea breaks. That left me with a long positive tail, and just enough on the negative to lay flat across the coil and solder an extension. Note these Yamahas use a single layer coil so the negative is glued flat across the coil to get it back to the bottom of the coil. the smallest drop of superglue stuck it back to the coil. Here we are with long tails:

I was very wary about soldering the CCA so stopped as soon as I had electrical contact. This does not look nice!

The coil is now out of round 🙁

Coincidentally, a cigar tube happened to be just the right diameter, so I put the coil on this and placed on the cleaned-up dome (I picked off all the old glue with a scalpel and lots of tea again).


I spend a while getting this centred by eye. Then I tacked in place with small dots of superglue.

Ease out the cigar-tube coil former and tack with superglue on the inside:


Then solder it up. I broke the negative tail again so had another go at soldering - what a mess! I'm using a bit of transformer winding for the extension.

Super glue the tails in troughs cut out in the surround. Then glue all around inside and out with thinned 2 part epoxy:


Carefully screw it back together. OMG! It only flipping works!
It sounds perfect to me - but I'm old (I've had these Yamahas for over 35 years).

I wonder if that incredible beryllium dome midrange can be bought back to life?! .... watch this space.

Over the past 12 months, I have built a pair of GM-70 monoblocks. During this process, I sourced many of the transformers (filament, power, chokes) from J&K Audio Design. I can say, without a doubt, that in my experience, these transformers are first rate. Excellent build quality. Reasonable prices for a custom transformer supplier.

By comparison, using other brand transformers, I continually experienced mechanical vibration and hum. With the J&K Audio Design transformers, there was absolutely no mechanical vibration nor hum. Dead quiet. Silence. Rock solid.

Additionally, the engineer at J&K Audio Design (Jolin) is very helpful and willing to educate this newbie.

Highly recommended.

J&K Audio Design

Pat

I want to buy a kit or a finished Salas DCSTB for dual mono, preferably from EU.

Hi everyone.

I thought I'd pick up some misc small signals for repairs and playing around. I found kits with typical used transistors on Ebay/Banggood for almost no money.
But I am worried they are fakes, because almost all transistors have the same datecode/batchno "331" even when they are very different types. Also, i do not see any manufactorer markings.
I bought some 2n5551/2n5401 that also have this same marking. Unfortunately I noticed this too late.

Should I be worried, or is there an explanation for this. Please see the attached picture ( from banggood )

Regards
Jørgen

as above. Thanks in advance.

So, I'm fiddling with the surround sound option on my old AVR.

I know this won't sound great... will using a 6" 2way and 6" midrange in series for each Left and Right channel (all 4ohm). Going to sound too terrible to try?

I have a single large 3 way 8ohm for the center. and a pair really low end 4" full range for the rear.

I was looking for a simple tube preamp schematic and found in one
old Italian electronics magazine an amp with this circuit
tube input, which they call CASCODE, so it would be
the classic SRPP.
But this pattern is totally different from the others I've seen
and it is not a printing error because the connections are also in the PCB
they are the same, so that's it.
So what is the TRUE CASCODE / SRPP ??

Sorry for any google translate errors...

As per title, I have a Cyrus smartpower that makes 'thump' when powering on or off heard through both speakers. This is occurs when the mains cable is plugged in, and the main switch at the back is turned on or off. There is a much quieter click when the front switch is pressed on, but not when off, which I can live with.

I have the service manual that shows the circcuit diagram but have to admit it is beyone me to where to start looking. I am planning to replace the electrolytic capacitors although none of them look bad (bulged or split). Examination of the board shows no damage e.g. burnt or discoloured resistors, components or pcb.

In the manual there is this - hence why I am looking to replace the capacitors.

Any help/advice appreciated.

Hi all, first post here! Looking for help properly sourcing a replacement part I need to repair my amp.

I have a PrimaLuna Evolution 400 Tube Integrated Amplifier that is out of warranty, and I have taken it upon myself to repair it.

The issue is that the volume control on the remote control does not work -- the volume knob itself does work when you turn it manually. It has a motorized potentiometer that should react to the remote but doesn't.

To diagnose, I took off the bottom cover, located the potentiometer's motor terminals, and hooked up a multimeter. Saw +2.5 V when pushing volume up on the remote, and -2.5 V when pushing volume down. So, it would appear that the potentiometer motor itself is dead, and I'm hoping that replacing it solves my problem.

The potentiometer is a blue motorized ALPS potentiometer, and it has a sticker on it that says "848G 100KAX2". Googling shows me that this part seems to come in many flavors (motorized vs non-motorized, KAX2, KAX4, KAX6...).

I have not found anywhere selling something labeled "848G 100KAX2" exactly.

Partsconnexion has this one simply labeled 100k: https://www.partsconnexion.com/ALPS-71668.html

Aliexpress has this one which doesn't exactly look like mine but says it is 100KAX2: https://www.aliexpress.com/item/2255800877149088.html?gatewayAdapt=4itemAdapt

Is the "848G" part of the designation important? Or is it just the 100KAX2 part? Is the one simply referred to as "100k" on partsconnexion the right part? Are the ones on Aliexpress authentic?

I don't need to find the cheapest price or anything, I just want to find exactly the right part and get it here 🙂 Any advice here is appreciated!!

Hi all,
is it still software worth considering?
Do any of you know of an alternative to this redrockacoustics software?

Regards

Given the shortages of 36.864Mhz oscilators.. I’m looking at cunning options..

The normal ways of clocking on the RPI/STM are:

Software GPIO toggling (including interrupt) - slow and inefficient
DMA pin set - works but uses bus (more efficient than software) but unreliable.
Hardware PWM - maxes out in the low MHz
Timer with force - with a 480Mhz chip this maxes out at 1/2 system clock (200+Mhz) this could be configured 1:13 and you’d get a 36.864MHz clock
HDMI TDMS - configuring the right screen pixel resolution, bits/pixel and fps means you can get a 36.864MHz pixel clock on the TDMS clock pin.

Anyone tried the last two?

Allright, admittedly a bit of a clickbait title as there was strictly no blood involved and the explosiveness of the power supply caps is only assumed at this stage - but I could really use some help over here since this is my first repair attempt.

I purchased this Armstrong 626 amplifier (S/N: 613377, seems to be a rather early series) yersteday from a guy whose brother-in-law, an audiophile collector, recently passed. When said guy plugged the amp without load after an undetermined amount of time without use it very briefly turned on before he heard a "schplat" and everything went dark.

According to what I have read from Jim Lesurf's excellent Armstrong part of his website, and Mike Solomon's Armstrong Repair shop's site it appears as though "The power supply capacitor can fail, spraying corrosive fluid onto a circuit board, causing massive damage."



I am leaning toward this lead since some wires appear to have suffered from corrosion that "ate" the plastic cover and exposed the metal shielding (or is it the wire?).





But I canno't grasp how the toroidal transformer can be that drenched in what seems to be an oily fluid seeing how little are the leaks from the power supply caps, and also the fact most of the wetted area seems to be directed toward the back of the unit where no capacitor are present?



Unfortunately I haven't figured out how to remove the plastic underside yet so I couldn't check what's happening backstage. It looks as though a sleeved cable is also drenched in fluid under what I beleive to be the speaker output capacitor (which has a visible tiny "leakage sprout" as well and reads 4.130 mF instead of 3300 uF, so surprisingly almost still within spec! If not accounting for spraying crap all over the place of course).



So my questions are: is it salvageable without having to replace the transformer? Is the fluid dangerous for the skin (cap reference: KA3174AGT 74, 100vDC / 3300 uF) and will it dry out eventually? Should I try to clean it or remove/replace the draping on the transformer?

My only tools are a digital multimeter and soldering iron, I have no audio-specific machinery. The fuse seen in the picture has current continuity, the damaged 47kOhms metal resistor is still perfectly on spec. Here are the schematics in case it could help.

I did some loopback testing on my Xonar U7 (non-MKII) to determine the optimal signal level to drive the ADC with, when I noticed that the right channel has a lot more noise than the left channel.


94dB vs 70dB is quite dramatic. Of course I switched cables and flipped the L and R signals driving the ADC around. The problem still persists.

With no signal present you'd think everything is okay:


Does anyone else here have a U7 that does this? Did I break mine? Can this be fixed? I'd love to hear what you folks think as I really like this interface otherwise.

Hello,
I would like to buy at least n.10 Gento SP99023A 2 "Paper Cone Full-Range. They are available on Ebay, Jameco, Baycreators but the shipping costs in Italy from shops is really very high. Can someone in the USA help me to realize my project and save money?
Thanks for your help.
Regards
Guglielm

A few years ago I made a replacement cover for my turntable from acrylic glass using pure DCM as a solvent. It looked nice in the beginning but after few months the net of cracks started to develop in joints. Basically the joint itself, the very thin layer of dissolved polymer, started to shrink. What did I do wrong? Can it be attributed to the quality of the material? Can adding a small amount of acrylic to the solvent prevent this? I want to redo it.

Hi,

When I connect the LINE OUT of my piano to my smartphone mic (TRRS) to record me playing the piano everything works fine, but there is a very annoying buzz at the background. The only way I managed to make this buzz to go away is to touch with my bare hands at the same time the GND of the LINE OUT and the smartphone surface at the same time (I discovered this by accident / trial and error).

I tried using my wife smartphone, I tried another cable... and the problem is exactly the same: the buzz always goes away when touching both the smartphone and the GND of the LINE OUT with the bare hands.

So I ask you: how can I simulate this "touching" without really touching the LINE OUT and the smarphone? Maybe using some capacitor in series or in parallel some where (maybe between GND of LINE OUT and signal?)... Unfortunatelly I cant ask a person to keep touching my smartphone while I play the piano to record it... Is there some "hack" circuit that I can build and attach to the cable? I have basic electronics knowledge and I am confortable soldering capacitors, resistors... so if you tell me to solder something I can do that!

I recorded a video so you can see this weird behaviour happening:

https://photos.app.goo.gl/DSrusHy5JCDAVyXC8

NOTE: I know that mic level voltage is not the same as line level, however I know many smartphones accept line level at the sleeve of the TRRS including mine smartphone. So using line level at the sleeve of TRRS is not the problem here, also because the recording is really really good when I am touching the GND of LINE OUT and the smartphone.

Hello,

I'm just "cleaning out" again and I came across a project that I hadn't finished ... PASS Aleph J Clone from Zen Mod!

However, without using the gold dust and with IRFP150 as power transistors (practically 2x IRFP240).
If the power of an Aleph J is not enough, you can use the expansion boards and then have 3 x IRFP150 power transistors .... do the math ;-)
Only assembled, not tested, ... and then put away

Article on diyaudio.com: https://www.diyaudio.com/community/threads/about-possible-babelfish-j-interest.273318/#post-4300905

At that time I had taken the "complete" package + the additional boards (18€) and thus had paid 98€.



For sale is what you see in the picture.


Costs: asking for 75€ or makes me a good offer - incl. parcel shipping in D without islands (tracked & insured)
Shipping outside Germany: by arrangement

Hi diyaudioers, i'm cracking my head trying to NOS a superb Sony CDP337ESD.

First i've tryed lampizator mode with no good, as soon as i feed the BCLK signal to one of the DACS it starts reading bad, and when hooking up the second DAC it just wont read anymore.

After i've tryed another method where i remove CXD1144 but leave all the resistors on the data, BCLK and LRCLK lines, this time kind of worked but really bad.

The only thing that make it behave correctly was to touch with my finger the BCLK resistor and keep it there beign careful to not touch any ground if not the cdp behaves like theres no clock at all (CD spin backwards really fast).

I've tryed a lot, from diffrent values of resistors (and a trimpot) and capacitors in the place of bclk line to making a small transitorized signal amplifier (that went into smoke).

i'm just locked here, any help is appreciated.

Thanks!

I recently bought this 11ohm amplifier designed for use on a siren system, and was wondering if there was a way to replace the sound files with new ones. Attached is the files on the board. The white things with the white wires are where the sounds are stored. Thanks!

Hello,
I was very curious to know if anyone has ever been inside one of QSC's CP line active PA speakers/monitors. Channel one on my fairly new CP8 is out. I loosely suspect that a huge POPPING issue with our digital mixer may have electrically stressed the channel one input. Channel B works fine so the power supply is still there.

If anyone can tell me what to expect when I open it up for trouble shooting that would be great. Unfortunately, I've found nothing in terms of schematics, articles, forum thread, and not even basic diagrams. I'm an electronic tech by day and have a good test bench set up at home but, no clues what to look out for once I get in this weekend. Channel fuses? Input OP amps?

Anything would be helpful.

Thank you!
Best
Phil D

Hi!
How to calculate the minimum required core cross sectional area, Afe, for a SE OPT?
I know some formulas, but all are different and gives also different results.
e.g.:
- Afe (in sq.mm) = 450 x sqrt Po
- Afe = 2*sqrt Power
- Afe = 20* sqrt (Power/Fd) fd is the lowest frequency
- Afe = 20* Power/Fd
- Afe = sqrt (power*20)
- Afe = (sqrt Power)*2
etc.

Is there any reliable formula?

Greets:
Tyimo

Greetings,

I'm currently converting a few 70-80's vintage RtR 280s to sub only duty. And I'm in need of a few 10" 2300 8ohm woofers and or repair cones, spiders, and voice coils. Apparently post secondary market support for these never really occurred, as the pro's don't have any data in their files. And from what I gather most were produced by RtR, with a small production run produced by Rola. I've scoured the available 1 1/2" voice coils and haven't located any that have the same winding height. Same for the spiders which were apparently doped differently for less stiffness for less resistance. Lastly, the cones are also special consisting of a composite of purple paper pulp with an added assortment of different fiber threads.

So if anyone happens to have any of these around collecting dust please get in touch. Plus if your into winding voice coils also get in touch as I may have to produce a few.

Thanks,
DD

Greetings,

I am somewhere between newbie and semi-experienced, just in the are where I become dangerous 🙂

I am working on a (what I thought) simple gain stage for a guitar preamp and am experiencing some unexpected drop in gain as the signal approaches 20 khz. The circuit is a traditional non-inverting opamp with a 50 kOhm pot as feedback resistor, a 2.2 kOhm resistor followed by a 47 uF bipolar capacitor from negative input to ground, as in this schematic.


The idea is that one can vary the gain from 1x to about 22x.

At the maximum value for Rf I am measuring the expected gain, but when I sweep the input signal past approx. 18 kHz the gain starts dropping, all he way down to only 10x or so at 50 khz.

I am using a 2134 and have also tried the 4562 opamp with the same result, and I wouldn't expect slew rate or GBWP to be an issue with these devices.

Does anyone have any suggestions what might cause this? Am I missing something?

Thanks!

I think, I'm not the first person doing this.

with a simple induction heater, the getter can be re-activated to improve the vacuum.

I have tried this to some very gassy tubes, and once there still a little bit mirror left, in most case, the vacuum can be restored.

it also good to heat the getter for a short moment (about 3 seconds), for those NOS tubes before first time heat up the cathode.

before getter re-heat, a lot holes on mirror.



during the process, the getter should not go too hot (no more than orange - yellow), otherwise it melt



after 5 second heating, the getter mirror become much more thick.
The glowing during (normal circuit) operation is gone. 🙂

Hey All. First post and haven’t done car audio in 30 years. I recently purchased a RAV4 non JBL and decided to upgrade everything but the head unit. New JBL Club dash and door speakers and a JPL sub, to go with the JBL amp. I’m using the Stadium BassHub (non powered) for my sub on the A5055 5 channel for the amp.

So I was going to set my gains on the sub output. For the input I had to split the rear signal between the rear input and the sub input. When I hook a DMM to the sub output and set head unit volume at 3/4 full volume I only get 19.2v out with gain at max!! That’s with the bass knob all the way to max on the remote. This can’t be right. This means I’m only getting about 100w @ 4 ohms. What am I doing wrong, or not seeing? Is my logic sound?

Hi
I am upgrading caps in my Valve/Tube pre amp to V-Cap ODAM.

Web site says this under Installation Notes

" The short lead indicates the outermost foil, and should be connected to the lowest impedance path to ground. Another way to identify outer foil is the writing on the label flows towards the outer foil. "

Is the lowest signal path, simply the way the signal is traveling though everything Preamp, Amp, Crossover?

Or is it the other way the return? or does it change and something I should test for each placement.

Would like to the work once and learn at the same time.

Eddie18

Installation Notes
https://www.v-cap.com/installation-notes.php

my diy side surround speakers

I've been trying to fix the amp on my Rel Britannia - I've replaced the relay and a few capacitors hoping to fix the problem but I'm likely over my head and my problems persist.
I was thinking of buying a new plate amp from Hypex or a chepaer amp from Dayton but I'm also wondering if instead I should cut my loses and get a more modern sub. The smaller footprint of a new Rel T7X would be nice but I can't help think the massive 100+ lb Britannia is a much better box. What do you guys think? What would you do?

Hello all,

Looking for some input on the next build - a Coffee LDR Preamp - trying to decide if I should put a Buffer before / after the LDR Volume control. I have see a few of these fancy LDR units with pre / post buffers (The Truth LDR Preamp for example), and wonder if I need them...

Buffers under consideration:

• Simple 2SK170 based buffer (see attached) for Pre / Post LDR
• Opamp based Buffer with LM4562 opamp
• Tube based buffer (Music Fidelity X10 type)

This would land be between two Sources (DAC / Phono Stage) and either tube amp or SS Amps...

I am looking for a parts list for a Bogen C100 series classic amp. I have a good print, just need some component values. Specifically, I need the value of R67 thermistor. I meter it out at 31ohms, and would like to verify the value. I think this thermistor is the root of my problems with this amp

For sale some old but good pcbs from kit to build el84 tube amp. This pcbs are with ecc82 input tube and 4x el84 output tube per chanel.I bought this some years ago and used this amp for about 4 years in my second system.You only need to put your own psu with piwer trans and coupling caps and the amp will work. This pcbs are old, maybe from around 1995,but in still goid shape, there are maybe some 2 or 3 bad traces but you can repair this without a problem. I also have original output transformers from this kit from Welter. Verry good transformers good up to 50 watts. The pcbs were upgreded with Takman carbon film, metal film resistors and input resistor is from amtrans. There are on each chanel one mundorf 20uf mkp psu cap for last cap in psu for input tube. I used el84 heaters with AC and input tube with Coleman reg. Price would be 200 eu plus shipping or best offer. The output trans are verry bigg and havy. I can also put for the buyer my 4 year old el84 output tubes from JJ and a pair of input tubes from tungsram.More info ower contact. I also have original Elektor magazine in which the project is explained step by step.

as above.

I was looking at the range available in mouser and I came across a varied selection.

examples:

• some are even supposedly "designed for audio" (Nichicon LKG series)
• some are supposedly designed for switching supplies (CDE SLP series)
• and many many more

Thanks in advance.

I have a Marantz MR235 that needs the output transistors replaced
2- 2SD718
2- 2SB688
I cannot find these anywhere except the epay fake ones. Has anyone replaced these transistors and what's best to use? Any help?

I’m sharing my test results of the GRS PT6825-8 planar in a front horn. This driver responds well to horn loading providing low distortion down to 300Hz. IMD is -55dB even at 100dB SPL 1m. It’s nice to see an affordable replacement to the NEO8 become available.

Specification Sheet

Hi

I am newbie, so asking if anyone have opinions or experience in this matter.

I have understood that small wavequide for tweeter and "normal" cone type midrange fit together nicely (many commercial & diy examples),but what about dome midrange?

I am building 3 way classic speaker, TMW confiquration size about same as yamaha ns 1000.
My brother owns restored ns1000 and i really like the voices and midrange, though a bit sharp for my taste why i am going for more smoother elements.


I plan to buy bliesma t25s-6 silk dome, and I already own SBA satori tw29txn-b textreme tweeter.
T25s-6 can be used in a custom wg (i can 3d print it), do not have graph here.

tw29txn-b can be used in a jantzen wavequide:


I noticed that all the last speakers that i liked, had sort of wavequides, tannoy dimension 8 (8 inch coaxial), zu druid mkiv (tweeter in WG) so i would want to try wg for the tweeter.

I admit that i can't completely explain why i am drawn so much to dome midrange, but it works very good on ns1000 so it might be just feeling..

I am very sensitive to sibilance and too hot HF, so i need besides making careful crossover work with listening, also elements that are naturally more on the side of warm/smooth than detailed/bright.

I will make makeshift test cab to see does wg work to my taste, and i can always use tweeter normally without wg, but that bliesma middome is expensive to even resell, so..

Anyone have experience does wg work with middome?

Best
Jarkko

I bought an old Marantz receiver, you see them on eBay all the time. They look nice. Search up model '2230' on eBay for an example.

They get a good price and some models are advertized for over a grand. There seems to be some traffic in these old units. I guess there are plenty of them around.

Some folk fix them up with blue LED lights etc.

So I got one. But it sounds far from great. It's not even a nice old 70's kind of sound. It's just, bleh. The design is nothing too exciting, an old op-amp i.c. (e.g. LM391) driving some old power transistors. The preamp is probably equally dodgy. I figure I can easily improve on the unit, I just liked all those shiny controls - and that was my intention when I bought it a year ago. But would I be ruining a bit of history, do folk actually like this sound ??

SOLD!!! New in box Iqaudio PiDigiAmp+ with pigtail and standoffs. $15 with free shipping and PayPal fees included.

Connect to a Raspberry Pi and hookup directly to speakers.

Need a Pi? Add $10 and I'll throw in a Pi 1 Model B+ 512MB, also new in box.

Here's a new use for your old subs.

https://www.cnn.com/videos/tech/2015/03/27/orig-sonic-fire-extinguisher.cnn

B.

Could someone recomend the best driver transistors to use with output transistors MJL1302 and MJL3281.
These will be used in Class A and Class AB complementary power amplifiers of 50 W to 100 w output power with between 2 and 6 output transistors in parallel.
The MJL1302 and MJL3281 are fast high beta transistors and I am not sure which current transistors would make the best driver transistors.
Should I think about using these as output transistors and also as driver transistors?
Thanks
Don

Hello all,

What is your favourite driver low power transistor, or driver trannie?

I would like to find a transistor should be specified at 20W. Currently I am using 2sc4793/2sa1837 but would like to replace them due to that they are not linear hfe at 250-300mA bias. a bandwidth of 100MHz. TO220 (and not TO-3) would be nice too.

I was looking at the 2sc6200(or something close, can't remember right now) which seem really good (linear to 250mA if I could remember) but I can't find any place to source them.

Hi all
I am about to buy a powersupply for IRS2092. I have my on this board but first again wanted to run this one past the forum. Hopefully this time someone will recognise the board and chime in about fake parts and things

DLHiFi Dual DC 60V Output LLC Soft Switch 500W Switching Power Supply

I got my hands on an Ultrapath battery powered valve preamp, it's already got new batteries (the whole device is battery powered, both the heater and the plates of the ECC86) but one channel has a much lower rail voltage and audible distortion.
Things I've tried so far:

• Remove and measure C1-C5 OK
• Check all solder joints OK
• Measured all R's OK
• Measure PSU voltage without the preamp unit attached OK
• Swapped valves between the channels
• Measured coil resistance on the primary of the output transformers - identical between channels

What I find strange is that if I remove the LED in that channel, the B+ goes back to normal, roughly +25VDC, with the LED in circuit it drops to ~17V (measured without tubes).
When turning both channels on, on the working channel the LED pops right on while the defective one comes on much slower and stays dimmer.

I had repair a VTV 6sn7 line stage preamp for a friend before, he said he had a few preamps include a forplay I had epair for him long time ago, he mention he compare all line stage preamps he own the VTV he like most.
So I always want to build one for myself. Recently I had build one for fun, I also include a MM phono amp, I try to build a bottleheard phono amp but I don't have the schematic, the phono amp I use 6j32p, EF86 equivalent and half 12au7 each channel, at first I try to use 6dj8, but I found my extension power cable socket only had 3 pins, it need 4 pins to lift the filament cathode for 6dj8. This phono amp RIAA network only 3 components but it looks not bad I had check 5 points and the db not off to munch. I had pack 5 tubes inside a compact box. The power supply section I used a Textronix probe power as the housing. I used most parts I already had on hand. I am not a designer, I just try by mistake and make correction. I spent time to read and lean from internet. I hope some one interesting.

I'm working on a friends original amazings. These have 4 honey comb woofers and 2 32" ribbon tweeters in each cabinet. Each woofer is 4 ohm and I think the tweeter is also 4 ohm. These send the Carver M1.0 with MK2 mods into clipping very very early - literally like a pleasantly loud level. By contrast the Kappa 7's he has are deafening and still dont clip the amp on the same equipment.
The remedy/idea is to bi-amp them, crossing over into tweeter ~750-800 hz (currently they're at 350 hz with the original carver XO).
Has anyone done this - I am thinking of the woofer 2X2 for 4 ohm and tweeter on a 2nd amp (adcom 555 for woofer and Carver M1.0 Mk2 mod for tweeter).
Some pointers would be nice.

A pair of Jensen JT-11-EMCF 1:1 Trans for USD100, worldwide shipping with tracking included. These are going for around USD70 EACH new currently ,has a lead time for restock.
Specs from Jensen:
https://www.jensen-transformers.com/wp-content/uploads/2014/08/jt-11-emcf.pdf
These has been used to for BAL -> SE in my dac. Have since moved on to balanced inputs downstream and these have no purpose now.
Wire leads has been cut and they are around 6cm now.

Hi,
I have impossible problems to solve on this amp.
This is a 15 kHz sine wave at 500 mW. Other frequencies look the same. Offset at 200 mV… with zero offset, the signal looks totally distorted.
The second picture shows the same input at 1 W
The third photo shows the same input on the other channel.

Any thoughts?

Hello All,

Few days back I perfboarded the Threshold Sl10 PreAmp from the schematics available in this forum.
It simulated well in the LTSpice and sounded good too.

This motivated me to try the SL10 RIAA too.
But the LTspice simulation and the perfboarded circuit both failed to show a proper response.

I used BC550C NPN and BC556B PNP BJTs.
LTSpice BC550C BJT model is that of Bob Cordell.

I didn't use the DC servo in the simulation, but used it while perfboarding the circuit.

Where am I going wrong?

Please see the attached .asc files and the schematics I followed.

Best Regards

Hey chaps, anyone have a pair of these for sale? Only TLHP seem to offer them but not sure if they`re in stock at all.

Hi!
Running a prototype with 811, is doing well, but a tad too hot. So I am thinking about using the smaller 809 instead. Anyone has some units available?
Thanks! Erik

Hi

I have not much experience in modifying digital circuits so
I ask experiemnted guys. 🙂
I have an old Nakamichi CDP-2 and the laser is dead and no longer available.
This Nak has a good sound = DAC= TDA1541A.

My question: is it possible to transform the CDP-2 as external DAC?

Hope it will be possible.

They were used by quite a few hi-fi manufacturers including Plinius in the 1980s, but after that they weren't really seen.
I am trying to find out who made them.
There are no markings on them at all.
I have a few, but would like to find some more and knowing the manufacturer would help.

Hi, Trying to repair an linn powertex amplifier, two of the output transistors were blown, these are now replaced, and I have no DC leaking out on the
speaker terminals now. The white ceramic resistors are all measuring ok. I am still have a few issues, sometimes motorboating sound, Which disappear when the amplifier is turned off (and it plays for a few seconds due to power in the filter caps) So I suspect decoupling between the power supply and audio, I have it on a bulb tester and my bulb is not lighting so no shorts. Attached files, on the power lines is one supposed to be an ztx753 (pnp) and the other an ztx653 (CBE config ) (npn)? as both are labelled as pnp. Not sure If I can post the whole diagram here? it was released by Linn. My powerlines seem to be around the +25 and -25Volts (true RMS with negative on transformer negative supply - centre tap....chassis does not seem to be earthed) on the bulb tester, and do not fluctuate when the motorboat noise is there. All the electrolytic caps are fine. I have replaced the smaller ones (only a few), they did all measure ok under no load conditions. (polarity is fine, issue was there before recap) I have gone through each transistor in circuit with a diode tester and they seem ok, all diodes tested good, not sure on zenor what voltages I should have there D411 & d412 on either ends ? . Any hints what to look for, thanks in advance

Hi,

are you interest in a F3 then please add your nick here, thanks!

For conditions click me.

GB ist now closed, reached the 50 member limit!

From now on only waiting list, should someone not send me the required data in time, he will be removed from the list. After that the waiting list will be processed.

If some one would like only boards (without the LUs), please contact me.

BOM: First Watt - F3 (clone by Jeff) - Google Docs

One friend is selling a vintage McIntosh MC-2205 in superb condition.
Bias adjusted this year and all the components are original and in perfect working condition.
He is the first owner (his father in fact) and he has all the docs.
Could be shipped in a wooden box.
He is asking 2900€

Hi

If possible, i would like some advices on a transformer to bridge rectifier to filter caps PCB connections.
I have upgraded a tube amp in the past, done a Noir amplifier, now tackling a M2x and would like to check my wirings and most important my understanding (would go through a workmate who is knowledgeable but a bit too much as for him "everything is easy/super simple, just plug the damn thing" 😵).It is part of my learning process.

Attached is a PDF showing the different parts, my understanding of the connections i did, and some pictures in addition to the pdf.

Here is my main interrogation / where i need your knowledge for proper understanding.

a. I was worried that, maybe i would have connected the bridge rectifier wrongly and they could give me an inverted wave form, hence i could be cancelling out the power when connecting them to the filter cap PCB.
Different websites /Youtube videos seems to give different connections but not exactly for the same type of configs. (Youtube DIY Audio Implementers has 2 trans to feed the filter caps PCB)
Yet, come to think about it, since the rectifier redress the wave forms (no alternance anymore), it shouldn't matter. No need to care too much, just connect the transfer to any AC lug and get the "+" to the correct side of the filter cap PCB.
That's where i am a bit at loss and would like a bit of teaching/checking if possible.

b. DIY audio powersuppply PCB was out of stock when i need to order. Instead I went to a surrogate that should be equivalent to old schematics. I have seen the same on different builds.
Is there anything i should check particularly? (if one knows)

Thanks in advance if you can help a bit.
At this point, i would tend to agree to Nelson Pass mentioning that SMPS power supply were easier for "new to DIYs"! (but i wanted more powerful than ACA...😏)

Why do people put capacitors on the GND/PWR tabs of small BT amplifiers? On some of my 5-6v setups there was a suggestion to put a capacitor on the VCC/GND terminals of the small amp itself, but i have never questioned it as it appears to work better with no brown outs/restarts.

For example on using one of those CSR BT amp modules, it was suggested you put a 10v 2200uf capacitor soldered directly to the lead/terminals, yet on a recent build using similar parts it is now 10v 1000uf variant. Without it if i push the amp it will restart the BT component, but with it, it just pushes through no problem. So of course my mind starts to think what magic is this and how are they sized? These Chips also allow one to modify the on board EQ and filters, which made me wonder "could i size this capacitor and alter the EQ/Bass shelf without leading to saturation when pushed"

Its one of those items i've never questioned as it works, but currently looking for ways to refine the process, build and see what else i can do.

Am currently rebuilding a blown DS18 5k. The power supply and output section both need repair. Power supply used IRFP064N with 22ohm gate resistors and outputs are IRFP260M and I will be replacing all of the above. The PS FET driver section sustained some damage and I am unable to figure out the correct resistor values for some of the locations. Also need to know if the transistors I have on hand will work as substitutes for what is in there.

1) I need the resistance values for R128, R120, R109 and also the value for DZ5? I assume the row alongside is a mirror image and would use the same values and it also appears that the zener diodes survived but may change just to be sure.

2) The drivers used in here are C2814/A_715. The two PNP drivers are disfigured so I can't make out the whole part number, but I am unable to find the NPN, and it's pairing locally. I have on hand C2690/A1220 and B631K/D600K if either of those pairs are substitutable.

Anyone happen to have a copy of the schematics for the diamond audio/esoteric audio d7 amplifiers? Either the 4 channel or 2 channel units.

I'd like to trying practicing on them and figured the schematics would be very helpful.

Good Day. I am currently repairing a Taramps Bass1200 that came in powering up but with no audio. It was not in protect mode but there was 4.3v across the speaker terminals.

When checked, both outputs (IRFB4115) were testing as good but the 4R7 resistor at R60 was burnt open. I replaced that and then the amplifier would start and shut down repeatedly. The IRS2092S is likely damaged as it reads 192ohms between COM and LO out of the board. I have a brand new replacement but I want to make sure there isn't an errant voltage present that will damage it as soon as I put it in as these are hard to find. Below are the voltages on the pads for the IRS2092:
1: 5.2v VAA
2: 18mv GND
3: 18mv IN-
4: 2mv COMP
5: -4.8v CSD
6: -5.2v VSS
7: -3mv VREF
8: -49.5v OCSET
9: -55.9v DT
10: -55.8v COM
11: -55.6v LO
12: -43.4v VCC
13: 24mv VS
14: 24mv HO
15: 39.4v VB
16: 24mv CSH

Out of interests I thought I would post my REW plot of the Altec A7 Vott comparing the 416-8c verses the 515-8g

Couple of notes:
The 416 has a huge dip around 500hz as it naturally rolls off. The front horn really doesn't get utilized.

The 515 mated with the horn really is a match made in heaven...or at least they are engineered to work together very effectively.

The 515 makes the system at least 3db more efficient. The attenuation dial was flattened on both before testing.

Tomorrow I will test the same thing on my Onkens.



The caveat is the 416 goes lower, with more extension. The porting on the A7 was tuned to the 416 as well. A better option would be adding a sub with the 515. The A7 cabs start to sound like a cardboard box if pushed too hard as well...so another reason.

The highs are different because one is a 288-8g and the other a 288-16H

Hello there,
I have browsed through the designs in this forum to find a line stage pre-amp to place between my 500mV phono stage and my 45 SE power amp.

As per the power amp designer, the line needs a 15÷20 dB gain, which seems pretty rare around here. Maybe the only DIY solutions I have found are Ale Moglia's 2P29L or 4P1L DHTs, but I haven't gotten a confirmation on the actual gain yet, and besides those projects may be too far beyond my skills to build.

I like the JE Labs line stage but that only gives me 8x / 9dB, as most designs seem to. I am looking for a simple design that is linear, quiet and transparent without needing any exotic or very expensive parts.

Any suggestions?

Thanks.

A friend of mine has pignose amp at his vacation home, but only uses it once a year, so every year the lead battery is dead. I decided to replace it by 4 lifepo4 cells 32650 5Ah each. I added an UVLO based on a seiko voltage detector chip at 1.3uA, with a big fet, and active balancer based on the ETA300 chip, good for 2uA standby.
parts:

3.2V 32700 6500mAh LiFePO4 Battery aliexpress​

1.2A Li-ion Lifepo4 Lithium Battery Active Equalizer Balance Board 4S aliexpress​

IRFB7440PBF Nchfet 40V 120A
ABLIC (seiko) : S-80851CLY-B2-U voltage detector 5.1V mouser or digikey
TE Connectivity .250 FAST TAB various suppliers

Any thoughts on finding a reliable source for these? I'm in the US fwiw.

Need 6 from the same lot for a class d amp I'm rebuilding.

I see options on eBay and even Amazon (eesh), none of which make me feel too warm and fuzzy. Like many, I've gone down that road before and been burned with knock offs.

I've observed there are two camps in speakers area.... those who focus on cabinet models, and those who go with OB or horns/TL or a mix of OB/horns.

Examples of brands which recently (last year, few years) joined OB camp: Aries Cerat, Legacy, Jamo.

How about these TITANS of audio industry?

• Wilson
• Wilson Benesch
• Rockport
• Magico
• KEF
• Raidho
• Polk
• Klipsch
• Tannoy
• Monitor Audio
• ATC
• Gryphon
• B&W
• Dali
• Sonus Faber
• Focal

These are the biggest speaker brands as of now - and they ALL have ONLY non-OB models. Isnt it interesting?

So heres my little conspiracy theory! All these companies would rather want customers not to know how OB can be build, how they sound vs box speakers, etc. Guess why? $$$$$$$$$ Big fat income.

Vice versa, most famous OB makers are small: Bastanis, SoundKaos, Spatial, PureAudioProject.
Similar thing can be observed with FULL Range , single driver designs - these are mostly very small companies.

Thoughts?

sold



For sale is a Mark Johnson designed Ship of Theseus modular amplifier using all his board designs. While based on the VFET Pass amps, this amp uses Mosfets for output devices only and sounds quite nice. It puts out about 10 watts per channel into 8 ohms.

Housed in a standard 10mm silver faced 4U x 300 dissipante chassis, the amp gets Class A warm, but not hot, to the touch.

It is powered by the called out Meanwell external 4.4 amp supply, which is smoothed by the Ship of Theseus PS Filter board with variable time delay for thump prevention. This amp is totally quiet on my 96db sensitive speakers with either front end cards installed.

Two different front end card systems are included: The Missouri cards can take balanced inputs, which is a great option in my book, and seems to make the noise background even blacker, to me.

The other front end provided is the Nimitz front end, which allows the owner to use any of the M2X input cards designed by Mark, and maybe even others. Check out the M2X thread for those details. I have included a pair of Cedarburg front end cards using the wonderful AD797 opamp. That was my favourite in the M2X and it sounds great in this amp also. I have included a pair of bare IPS-7 boards you can build up and use if you wish, also.

This is a single ended input front end, so I have included rca to xlr adapters with the amp.

I can set this up with the Nimitz or Missouri front end for the new owner. You should feel comfortable with DIY if you plan to change things around or make up other front ends or M2X cards.

Overall, this is a great little amp with wonderful frequency extension and bass impact for its 10 watts. It has numerous other front end combos that one can experiment with, if you wish.

Amp and power supply are about 32 pounds, I will ship to the Continental USA only via insured ground shipping. Shipping to be determined at time of sale. You will need to supply a basic power cord for the Meanwell.

I have some old hardboard, the dark brown stuff that is smooth on one side and comes in max 1/4" thickness. This stuff is strong! It's light and seems like it would make a pretty good material if weight were a large concern. The obvious weakness is the lack of thickness to hold screws and flex over large flat areas, but some bracing would fix that. But I just built a 5" x 5" box and this thing is light and super strong even at 3/16".

I'm thinking I will make a small set of speakers and see how they handle screws and see if its good but so far with my little test box its great! Also cheap $25 for 4x8 vs $55 for 5/8 MDF.

Maybe it would make a good material to add to the 5/8th to give it more rigidity? Has anyone experimented with hardboard?

Some background. I was asked to repair this CA-1000 integrated after the current owner bought it pretty much in pieces, along with a pile full of blown output transistors. Not a good omen. 😱 He did a decent job of putting Humpty Dumpty back together again, though it's hard to say if he introduced any new issues to those that apparently already existed. Among those issues, the owner found that R626 on the left amp board was a charred ruin. He replaced it with a new 330 ohm resistor.

When I got it on my bench, I found that a fusible resistor on the power supply board had drifted very high, drastically reducing the B+ to the left channel. All the outputs tested ok. After replaced the fusible, I was able to power it up and set the bias for both Class A/B and A (this has a switch to toggle between the two), set the DC offset, and dial in what the service manual calls the Primary Stage Differential Amplification to 15V. So far, so good. As a little preventive maintenance, I recapped the power supply (but not the two main filter caps), replaced the two bias trimmers on each board, and also replaced C603 and R607 on the two amp boards as there was some glue that had turned corrosive around the cap that also affected the resistors. Powered up, rechecked and tweaked bias, DC offset, and differential amplification. All good.

Until it wasn't. All went to hell when I went to test the amp with an 8 ohm load and R626 on the right board released the magic smoke. Very spectacular As a reminder, this is the same resistor that had combusted on the left board before the amp found its way to me. Whatever caused R626 to go this time on the right board also took out a number of other components, including the outputs.

Here's what was damaged and the replacements:

• R626 (replaced with 1/4W 330 ohm)
• D602 (replaced with 1N4148)
• R628 (replaced with 1W 4.7 ohm)
• TR608 (2SA561 replaced with KSA1013Y)
• TR610 (2SA566 replaced with NTE2667--note that TR609 is still the original 2SC680 driver)
• TR611 (replaced with NTE280)
• TR612 (replaced with NTE281)

It was suggested that I test the repaired board with TR606 linked out. I did, and here are the voltages I recorded on the amp board inputs. This is with a 150W bulb in my DBT. Parens was after a few minutes. Bold is what the service manual specifies.


Right
A: -0.222 (-0.148) -0.28
B: -0.172 (-0.148) +1.15
C: -0.172 (-0.148) +1.15
S: +2.47 +3.9
-50: -50.6
+50: +50.0
-B: -49.3
+B: +49.3


It wasn't damaged by I also replaced TR606 (2SC458 with KSC1845) and the two micro switches for the Class A/B - A toggle, as my understanding is that these get damaged from arcing and can cause bias issues.

Earlier today, I powered up the amp again, this time with a 100W bulb in my DBT. TR606 no longer linked out. Bulb dimmed almost completely and the protection relay clicked. The left channel bias was low but steady, whereas the right channel bias fluctuated significantly, i.e. tens of millivolts. I didn't like what I was seeing, so I shut it down. The left channel bias voltage went to zero, but the right channel voltage did not. In fact, it starting rising to over 100mV before finally going to zero. I did a quick check of the components damaged last time, and everything seems ok, with one exception: R626 is now open.

Sorry for the long, epic post, but I figured more info is better than too little. Lacking any better ideas, I'm probably going to check every component on the right board. In the meantime, I could definitely use some input. What the hell is causing R626 to die on these boards and, left unchecked, kill outputs?

This is a very beautiful build, if you find one share these with us.

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Hello, I want to make a 2nd order low pass filter to increase the power handling and limit the excursion of a pair of small speakers . Because the space is very limited I would like to use small caps/inductors in the line level side. I would like the filter to cut below 80-75ish hz. Would a capacitor-inductor (3.6 mF, 0.6mH) work? What would the q of such a filter would be ?