gar1731 build thread

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Hello, I'm having a heck of a time getting my gar1731 up and running despite already building one that works perfectly.  :eek:

Already verified that the resistors go where they're supposed to by desoldering one leg and measuring the resistance.

Diodes are in the proper orientation.

Transistors are in their proper orientation.

I seem to be unable to find any cold solder joints.

Next step is to start measuring voltage and current from component to component but I do not have a schematic .

gar381 said:
Compare the working one to the non working one
side by side under a magnifying lamp and look for solder
bridges.  Do the shorts tests in the manual.

Best of luck.. :)


I used the reference sheet that shows where to make sure to check for shorts and no indication of continuity where there shouldn't be any.

R14, R15 start to overheat when I crank up the volts even around 6v in my OPamp test jig I ordered from fivefishaudio.

Where in the circuit should I start testing current and voltage?  I'm afraid of taking the working OPamp out with the luck I'm having tonight  :-\

Best for myself to just step away from the bench before another opamp gets hurt.

By the way if you know where I should start probing for voltage/current I should be able to figure out the rest of the values through ohm's law.    :eek:

Thanks in advance.
gar381 said:
Sounds like Q7 and Q8 are reversed and/or not turned in the correct position.


Yay!! That was it actually, it works!  :D  I had Q7 and Q8  reversed  :-[

I seriously appreciate all your help Gary, thanks.

So I have a 1731 I built a while back when my success rate with DOA kits was about 75%. This one in particular I had swapped parts out and in the process removed some solder pads. I got it back out to see if I could fix it, and went through and used the layout in the instructions and made jumpers for all of the places the where components weren't making connections. After I got that all sorted and compared DC voltages with one that was working, I moved on to trying to pass audio through it. It mostly works, but is putting out much less level than it should. I chased down the AC signal and what I found the drop in signal was right after D1 and D3 before it goes to the output. Before those diodes, the AC voltage was a little lower in some places than the working 1731, but with in reason. I had already replaced all the diodes and all the BC550C's and BC560C's, matching Hfe for Q1 and Q2. I wondering if someone here could help me understand a little better why there would be a drop in signal after these 2 Diodes but not the other ones. I've built several of these, but am not familiar enough with this circuit to know what is going on.


I have a question about the gar1731. I just started building it and I want to make that I do not have a solder bridge, but without a schematic it is hard to tell. Should the leg of CD2 closest to the V Millmax leg be passing any current?

To answer my own question, I just checked the gar2520 I haven't started and the answer is YES.

Hey Gary,
just want to thank you for your work.
The GAR1731 is such a great DOA. I love them on my kick and snare drum.
The build was pretty easy.
I also want to thank Jeff Steiger, who send me the PCBs.
I noticed that the new version of the build guides lists 1/2 watt resistors for R12 and R13. I've been building them a while according to the old build guide which listed the 1/4 watt KOA speer resistors. Should I toss those and switch to the 1/2 watt?
Actually both the Q2 V3 and the V4.1 manuals spec R12 and R13 as Mouser Part #293-8.2-RC  Xicon  8.2 ohm  1/2 watt

gar381 said:
Actually both the Q2 V3 and the V4.1 manuals spec R12 and R13 as Mouser Part #293-8.2-RC  Xicon  8.2 ohm  1/2 watt


I noticed that too -- but the manual I have, which was provided by Jeff in 2015 (before they were posted to the CAPI site) shows the KOA Speer  1/4 watt. The name of the file is 'gar1731_Assembly_Manual_V6,' and it references the Q2V3 revision... below is pasted from the document. Would you expect any issues using this part rather than the 1/2 watt?

R12        8R2        Mouser        660-MF1/4DC8R20F    Speer    1/4W 1% Metal Film
R13        8R2        Mouser        660-MF1/4DC8R20F    Speer    1/4W 1% Metal Film

I've just assembled my CAPI VP28.
I made a mistake that I fixed, and R14 and R15 of one GAR1731 are burned.
The contact points on the PCB are uprooted. I would like to handwire R14 and R15, but I don't see where there are wired.
I don't know if I'm clear...
Anybody can tell me where are they welded ?
Thank you for the answer.

Just built my first pair of 1731's . I have them on the fader booster in a vp28 with the 2520 on the input.
One works great, the other has toasted R14 and R15.
Ive checked for solder bridges, diodes are correctly oriented and transistors as well. What else should i be looking for?
Thanks for your help.

Im an absolute idiot.
I didn't realise Q7 and Q8 are actually different. I was only making sure they were facing the right way.
I suppose I had a 50% chance i would get them in the right position and thats exactly what happened!

I built a gar1731 several years ago (Q2v3 I think?) and it went great.  Installed in a CAPI VP312  I recently got another kit and it is the v4.1.  I also forgot/missed that part about Q7 and Q8 being different and I fried the first board (maybe I will try to recover it some day).  Ok, need to slow down...

So I bought another to start over.  Everything looked good, all the "check for shorts here" looked good and I went over it several times to make sure no extra solder.  I plugged it in and it was passing audio, everything looked pretty good.  I had it on for 30-60 seconds at that point.  I hit the mute switch, swapped to a condenser mic, engaged +48 and hit the mute switch again.  Now I have audio again and everything sounds great.  Then suddenly I see a whiff of smoke and crap... power it off. 

R14 and R15 are toast once again.  The only thing I see is that I may have a cold solder on R11.  not having the schematics, does anyone know if R11 was removed, would that cause the over-current for R14 and R15?  I have it installed in a CAPI VP312 that is also a new build.  I could swap components from my other  VP312 but at this point I'm afraid to burn it up too (or the other DOA) so I'm looking for some advice first...

thanks, Mike

Double and triple check for shorts between the millmax pins and R12.  A short there will make magic smoke
on R14 for shure and maybe other parts.  Fix the cold joint as well.

BTW.. the Q2V3  and the V4.1 circuits are the same.    Parts placement and millmax hole size
are somewhat different for ease of assembly...... just for your reference.. ;) 

I think I got the 2nd build going now.  Replaced R14 and R15 and double /triple checked everything.  It went for more than 5 minutes without smoke and nothing felt hot.  I had replaced all the burnt resistors and Q7/Q8 on the first build too but it smoked R14/R15 again so I think something else got damaged in the process.  Going to give up on that one.  I don't think it will allow another de-solder anyway. 

On that first build I had put a little bit of Deoxit power booster in the millmax sockets (they were really tight and no excess solder on the pins...) but I think I may have overdid it on one and when I inserted the pins it forced the excess out and well.. . its supposed to improve conductivity.  Great, unless it forms a drip on your opamp (when it was in the chassis vertically now).  At least I think that may have contributed.  Anyway, just telling that story in case anyone else gets a smart idea like that...