gar2520 build thread

[Claudio]

Hello everyone,

I’m currently building a number of gar2520s. I got five kits from CAPI, and all are fine – except for one. Whatever I do, the golden Millmax pins won’t go into the PCB. I tried it gently as well as with some force, and I even bent one of the pins during the process (ouch). It’s like the holes are simply too small for the pins. The same pins fit into the other four PCBs without any problems, it’s just this one PCB that won’t behave.

Perhaps I should also mention that it’s not the first time I’m building DOAs, but I never experienced something like this.

Is it possible that this PCB could just be faulty? And how can I fix the issue?

Thanks a lot,
Claudio

 

[Whoops]

Is it possible that this PCB could just be faulty? And how can I fix the issue?

Isn't that as simple as just enlarging the holes a little bit on that PCB?

 

[Claudio]

Isn't that as simple as just enlarging the holes a little bit on that PCB?

Yes, I just did that after reading that TillM had the same problem a while ago.

 

[thomasdf]

Hi all
I just inserted a newly built gar2520 v4.1 in a passive EQ makeup circuit that's working in another unit and R11 burned instantly. PSU is +/- 16VDC, clean.
transistors and diodes are correctly oriented... I am puzzled !

20k5 resistor is replaced by a 50k trim in order to adjust makeup gain.


edit : I dropped in another Gar2520 v4.1 built at the same time, everything works perfectly. Weird !

 

[AnalogPackrat]

Hi all
I just inserted a newly built gar2520 v4.1 in a passive EQ makeup circuit that's working in another unit and R11 burned instantly. PSU is +/- 16VDC, clean.
transistors and diodes are correctly oriented... I am puzzled !

20k5 resistor is replaced by a 50k trim in order to adjust makeup gain.


edit : I dropped in another Gar2520 v4.1 built at the same time, everything works perfectly. Weird !

Check for solder bridges or PCB trace shorts related to R11.

 

[Whoops]

I had a similar problem and it was 2 bridged solder pads, that should not be connected together.

The components and traces are so close to each other that it’s easy to mistakenly bridging them. Also solder the components on top of the PCB, or at least make sure the solder reaches the top.
Inspect all the solder pads and traces very well.

Re-check all the diodes and transistor orientation again anyway, it doesn’t hurt

If R11 burned a transistor might have gone dead with it also, so that should be checked

 

[thomasdf]

feedback : R11 burned, BD139-16 is dead too, and I found a cracked diode (D18)... maybe I got damaged during soldering ? Otherwise no short, no broken trace on the PCB.. I'll replace the components and give it a good clean and try.

 

[BassDude85]

Hey there,
I'm currently trying to build a VP28-ish clone. I'm using two Access312 boards per channel. One as the Preamp Stage and the other one as the Fader Booster Stage. I've atteched the Schematics I did, hoping this makes any sense. Everything is fed with +/- 16V.
I have abolutely no experience in designing a circuit. That's why I am frankensteining my way into it.

The Outputtransformers are EA2603 and as DOA I'm using gar2520.

Now my problem: In the Preampsection everythings seems to be ok. But the DOA in the Boosterstage gets extremly hot. Particularly R12 and Q8.
There is no Audiosignal running through them. Just the Supplyvoltage. I checked everything for Solderbridges or touching leads. Nothing bad to the naked eye.
Do you have any suggestions where to start finding the problem?

 

[KrIVIUM2323]

Hi,
Oscillations at very high freq? Did you check output with oscilloscope?

 

[BassDude85]

Do you mean at the DOA output?
Not yet, but will check it later.

 

[KrIVIUM2323]

I mean if the doa heat then it is 'working'. If you don't hear anything then it 'works' on something inaudible so it's either very low ( which often express it self by 'motorboating') or very high ( much more likely inaudible!).
So yes check the output of last doa and check for very high frequency with oscilloscope. Then go back the signal path: input of last doa, then output of doa in driving stage of preamp, etc,etc,...
Once you have spotted where it happen then it's time to think about the reason why and how to cure ( you mentioned using multiple boards... i would check for wiring then how ground is connected,...).

That said it might be another issue.

 

[BassDude85]

Well, so far I'm not getting any plausible readings. Or the resolution of my Oscilloscope isn't high enough...I also checked the Input of the last DOA and there is no Oscillation either.
Will check in again later, when I have more time.
I mean you're totally right. I must do something, even without audio.

Could the Q8 be faulty? But when I put this particular DOA into the first Stage, it is not getting hot...

 

[KrIVIUM2323]

This is interesting: if it doesn't get hot in first card ( do you have sound from the first 2623?) then it is either from second card or wiring issue.
If it's oscillation it can come from wiring, ground, a compensation capacitor with wrong value,...

Do you have a link to schemo ( apologize, i've got my kids screaming around... kind of lazy to search!)?

Edit: is the schematic you posted above accurate? Cause in a vp28 you've got an attenuator between the output of preamp stage and driver stage, which is the whole point of the circuit imho ( it mimics the original console architecture and gain structure, with preamp>ACA ( could be a third stage (ACA) in case you use bus on the console).

 

[BassDude85]

Yes, the schematic is what I "reverse engineered". It's just the two access 312 boards chained together. The 1k Ohm Pot in the schematic is kind of a placeholder, because I wanted a stepped Fader just like in the VP28. The Resistorvalues on the bottom of the page are just for memory purposes. Maybe this causes the issue, because the wiring is wrong?
Or maybe I missunderstood the description on the Capi-website. I mean, there's no schematics of the VP28, so it's a lot of guessing on my side.
When I am back home on Sunday I will hook up only the first stage to audio and check if at least that is working correctly by itself.

Edit: or I need to put a resistor between R4b and C6b, because there normaly would be the gainpot.

 

[BassDude85]

Hey there, I'm back home.
Made a few tests.
First I checked only the preamp stage and it works fine. I also checked all for DOA's in it. They're all perfectly working.
Second I checked the booster stage. When I disconnect ground the DOA doesn't get hot, but the Signal is distortin really bad.
Will check the wiring for shorts to ground. Maybe this is why the DOA gets so hot...

 

[BassDude85]

Hey

KrIVIUM2323.​

Hope I'm not bothering you. I might have I found the Problem why the DOA on the Booster Stage gets hot. But I'm not sure.
I first measured all slots for the DOA. Everythings normal. But as soon as I put in the DOA and measure the output pin of the DOA it shows a DC Voltage.
Somewhere between 2.5 and 3 VDC.
Can you think of something why that is? I checked for shorts, solder bridges. Nothing. Could it be, that I did not completely populated the board?