gar1731 build thread

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Well-known member
Jan 27, 2005
Retired in (Amherst) Cleveland, Ohio

Had to happen sometime... The pnp BC560C has been out of production
for some time now and my current supply of NOS Fairchild BC560Cs
that I have been using for last 3 years is running very low. I will be using
the remainder of my supply for only for the matched pnp input pairs for the
garOA10 and gar918.

I knew this day was coming so I have auditioned many possibilities.
From now on I will only be using..

BC557C mouser # 637-BC557C in the following positions...

gar2520 Q6, Q9.
gar1731 Q3, Q4
garAM10 Q1,Q5,Q6,Q7
garOA10 Q2, Q3, Q5, Q7, Q9
gar918 Q3, Q4

Note that these are all on tape and will just drop in place to the silk
just like the original BC560C


This is the start of the official gar1731 build. :) :)


The BC560C is no longer being manufactured. If you can
Not source these, with lots of listening time with lots of different
PNP transistors, we have come up with suitable replacements.

gar2520 Q6 and Q9
gar1731 Q3 and Q4
garAM10 Q1, Q5, Q6, and Q7

(gar918 and the gar OA10 will have other recommended replacements)

New First Choice.. Mouser part # 637-BC557C

First choice BC32740TA Mouser Part# 512-BC32740TA
Second choice BC557BF Mouser Part# 512-BC557BTF

Note that both of these transistors have the same pinout as the BC560C
So you should be able to just drop them in place using the silk on the pcb.

If you want to experiment with other PNPs, Make shure the Vceo max
Is at least 45v. hfe is not all that important for these PNPs but above 250
Will work fine. Just be aware of pinout.

All of my kits until future notice, BC560Cs will be included in the kits.


Many questions will probably be answered in the gar1731's big brother thread...

gar2520 build thread (gar2520 build thread)

As this thread is a bit more mature at this point.

The BOMs are similar and construction techniques are the same.

I think the gar1731 assembly manual is a bit better than the gar2520 assembly manual
So the questions should be few but fire away if you got them.

1) The little bag with the Millmax pins also contains the matched Q1 and Q2. (BC550c)
and are labeled as such.
2) The little bag with 2 transistors without the pins contain Q5 & Q6. (BC550c)
and are labeled as such.
3) The tape strip with 2 transistors are Q3 & Q4 (the BC560c)
4) The little bag of 5 caps..
The tan ones are CD1, CD2.
The blue ones.. see page 2 of the assembly manual for value and page 3 for location.
5) Please meter the resistors to determine value.
6) After assembly PLEASE double check for unwanted solder bridges
on the Bottom of the PCB. and make SHURE THAT on the top of the
PCB that no component lead wires are touching each other.
7) When inserting your new DOA into the millmax sockets of
a module, Please insert straight down and not at an angle.
DO NOT push down on the component parts but use the edges
of the DOAs PCB. Remove DOAs the same way. Pull straight up
from the edges of the PCB and not at an angle.
8 ) Never insert a DOA or a module with the power on.

9) HAVE FUN !!


NOTE: Manual update ... Step 24 should read Q6 AND Q5

Note.. Murata has changed the marking on the Blue 10pf cap from 10D to 10J
These two parts are exaxctly the same. (D = +/- .5pf and J = 5%)
You may see either one of these in my kits.

Note: Dec. 7 2013


The RPE series is being replaced with the RCE series. I will be phasing these in as my RPE
Stock diminishes. I will be using either 50v or 100v based on availability. For you guys buying
Raw PCBs and sourcing your on parts here are some part numbers:

10p 50v.. RCE5C1H100J0A2H03B
10p 100v. . RCE5C2A100J0A2H03B

39p 50v.. RCE5C1H390J0A2H03B
39p 100v.. RCE5C2A390J0A2H03B

47p 50v.. RCE5C1H470J0A2H03B
47p 100v.. RCE5C2A470J0A2H03B

680p 50v.. RCE5C1H681J0A2H03B
680p 100v.. RCE5C2A681J0A2H03B

1000p 50v.. RCE5C1H102J0A2H03B
1000p 50v.. RCE5C2A102J0A2H03B

In a pinch the AVX SR15 series...
50-100v 5% with a lead spacing of 2.5mm (.1”)
Should work fine as I have tested these
Last edited:
Hey Gary,

I got a couple of kits on order. I can't wait to try those out. I never actually heard a 1731 before, but I've heard many great things about it!

The PCBs, kits and manual look great! Congrats!


gar381 said:
...7) When inserting your new DOA into the millmax sockets of
    a module, Please insert straight down and not at an angle.
    DO NOT push down on the component parts but use the edges
    of the DOAs PCB.  Remove DOAs the same way.  Pull straight up
    from the edges of the PCB and not at an angle...
Hi Gary and all,  ;)

On this same note, I have noticed that virgin sockets are quite stiff. It is sometimes a little tricky to seat an unpotted DOA in them the first time around. If you have a potted amp around, plug and unplug it 2 or 3 times to loosen up the sockets before you plug in an unpotted amp. It will then slide in much easier, IMHO.

Just something to keep from bending over the Mill-Max pins since it's easy to do and will happen before you know it.  :eek:

Oh yeah, do this with no power connected to you PCB.

Cheers, Jeff
Hi Gary,
Is this PCB is different from the one on PeterC's site?  Did you make any of the changes in the melcor thread? (IIRC one of the 10pF caps is supposed to go to the -Input, and one of the diodes is supposed to be 2 in series...) ...?
gar381 said:
Also...  rafafredd IS right !!!
yeah, I came to the same conclusion when I scoped it.  I used CorelDraw to "fix" PeterC's layout for home-etching and it worked quite nicely.  Are you using 680 or 1000pf for C1?
I got that one done a couple days ago ;D.
Haven't done any serious listening yet though.

Can't wait to find out what the Melcor sound is all about  :) :)


More hi-res shots HERE

I love the solder mask matte finish... very cool  8)

Congrats boys!

mikefatom said:
I got that one done a couple days ago ;D.
Nice looking work Mike. Very clean.  8)

Haven't done any serious listening yet though.

Can't wait to find out what the Melcor sound is all about  :) :)
Let us know what you think, once you do.

Best, Jeff
Gary I want to build some of these babies.  I think we outta meet up for a beer one of these days and I could get a bunch of pcb's while we're at it!

Nicely done!!!!  Your pics look better than my product shots.. :) :) :)

W DeMarco..

Would love to do beers sometime !!

Check out..

Classic API is the only outlet for these.  Jeff is 1st class to deal with !
My DOA kits and PCBs are Very inexpensive and fun to build.

I just finished building two gar1731 kits and tested them successfully in a pair of newish 512c's.  The difference between the gar1731 and the stock API doa (marked mar 2007) was instantly noticeable just with a couple of quick 'check checks' on a MD421.  Very smooth top end, can't wait to hear how it plays with cymbals or heavily distorted guitars.

Excellent kit Gary, many thanks to you and Jeff for making these available!

FWIW - the picture that accompanies steps 13-19 in the manual shows Q6 already installed and I like it - once all the resistors and diodes were down, free space was limited. 
A gar1731 has been murdered! While I was in the bathroom, some fiendish person snuck into my house and put the unmatched 550c's into Q1 and Q2. I desperately removed them and tried to get the matched ones in place, but alas, it was no use. This DOA with never know the joys of +/- 16V.

In short, I have learned my lesson. Take your time, check, re check, and check again before soldering. I don't have any fancy solder removal tools, so it's pretty much a one shot deal. Oh well. Over to Classic API. Again. Think I am going to get 2 kits this time just in case.
There are hardly any of these mishaps that can't be fixed with an piece of resistor lead... You should see the underside of my first DIY990....

In any case, if and when this happens again, if you can sacrifice the mistakenly installed part, you should first remove it by cutting the leads as close as possible to the PCB at which point removing the solder and whatever is left of the leads is usually easy enough.

It ain't over til the fat lady sings...

i really want to build a pair of these but i have no need for a mic pre  is there a circuit i could drop your doa's in.


Anywhere an opamp would be used.  line amp (like API 325)? makeup gain for a passive EQ would be one example (SS pultec used a 2520). Headphone amp? Summing amp?  there is an audiox EQ that has a 2520 footprint.
check out the 2520 # 2 file here:
and the 990 document on John Hardy's site for example circuits.
I tried my best to save my first one, but sadly, I just couldn't make it work. I built another one, and it sounds fabulous! Built my 312 on bob's boards, and the 1731 is paired with cinemag 75101APC and CMOQ 2L. Very smooth and rich sound. You know when you are recording distorted guitars, and the high end can get annoying? Not anymore baby! Mids are detailed, low end is tight/punchy/random adjective.

Thanks for the project Gary. Very challenging, but worth it!
Hi Insomniaclown

Glad you got one to work for you ! :)  congrats !!

The cinemags with the gar1731s do sound very nice.
I got 2 built up with the same Iron setup on some DIY 312 cards.


I really like them with Ed's Iron in Jeff's VP312 as well. Maybe even
a wee bit better.  Its all good !! ;)
Lots of really great little audio crayons to play with.

Those kits are silly cheap. $17 each? I'm tempted to buy a pair but I really must get round to building my pair of gar2520s first! :D