gar2520 build thread

Hi,

I assembled some of the 2520s for the CAPI VP28 kit, and I seem to have run into a snag.  I powered up the unit and fried the 10R resistors.  I don’t see any bridges and everything appears to have proper orientation.  Can poor pin connections cause this sort of reaction?

roartheband said:

Hi,

I assembled some of the 2520s for the CAPI VP28 kit, and I seem to have run into a snag.  I powered up the unit and fried the 10R resistors.  I don’t see any bridges and everything appears to have proper orientation.  Can poor pin connections cause this sort of reaction?

Click to expand...

Yeah if they weren't fully seated.
https://capi-gear.com/catalog/DOA_Install.php

Hello, Gary,

I'm building more of your 2520's and I was wondering how exact the value of R10 needed to be and I don't seem to have 806R resistors on hand. Would up to 2% be too much? Would it better to be to be higher or lower? I'd like to avoid making another order as I don't have a need for any other parts.

Thanks!

Paul

Hi Paul

As CLOSE  as you can come on the high side.

GARY

gar381 said:

Hi Paul

As CLOSE  as you can come on the high side.

GARY

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Gotcha.

Well, it turns out I also don't have any 1000pF caps and I'm short some 5R6 1/2W, so an order will need be made anyway. Oh well.

On a completely random note you should know that for the 550 553 style EQ I installed for the bus channels of my TAC Scorpion I wound up liking the 2520's over the 1731s. They were both close to each other, but when boosting the HF there was a slight euphoric sensation that I was physically feeling in my ears, which sounds corny, goofy, and a myriad of other subjective, unhelpful adjectives, but that is the best way I can describe it. I don't know if it was attributed to a distortion characteristic, but I A/B'ed in real time and that minor physical interaction was definitely happening. The 1731 also sounded real nice, but since I mostly use these EQs to boost HF and MF, the characteristics the 2520 for this particular band won the decision. Just thought you might be interested to know. I am pretty much using the original schematic for this particular equalizer and inductors are from Jeff, which are fantastic.

Thanks!

Paul

I assume you mean 553 since that’s the one with inductors. Did you make a new PCB for those?

Fuzz Face said:

I assume you mean 553 since that’s the one with inductors. Did you make a new PCB for those?

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Yes. Sorry. 553. Yes, I did. It is this:

https://groupdiy.com/index.php?topic=71753.msg911236#msg911236

Thanks!

Paul

That’s a really cool project, nice work! Sorry for the little sidetrack there

Potato Cakes said:

Yes. Sorry. 553. Yes, I did. It is this:

https://groupdiy.com/index.php?topic=71753.msg911236#msg911236

Thanks!

Paul

Click to expand...

Very nice work Paul 

Hi Everyone,
Finally I got approved by this blog and I can post a couple of questions.
After going trough all 17 pages about this build I got to solve my problem already.
Yes I inverted Q7 and Q8. and Yes R11 and R12 smoked, duh :-[! Is the first time that happen and I guess you know the feeling, is just horrible.
But I have just a couple of question since I couldn't find a solid answer here:

- First:  I run the "bad" 2520 on a Vp26 (that works great since a year ago when I build it). After the "fact" It smell burn like hell from the Opamp A1 section, up to the output transformer. Did I damaged something on the preamp? Can I put back the good Opamp and use it or should I check other stuff first? (I'm so scared right now)

- Second: if I replaced R11 and R12 with new one and switch the current Q7 and Q8 using the one I already have, am I good or probably other component will smoke again?

dose are my main concerned.
ps: I actually build a second one and found out I did the same mistake :'(, but I didn't plug it yet fortunately.
thanks

Hi Blondino

90% chance all will be well getting the outputs in the right place and replacing the Burnt Rs
Give it a shot.

Most likely your VP26 will be fine with a good op-amp.  I would ask Jeff to be sure but
I don't think there will be a problem.  I would double check the Voltages at the DOA socket
without the op-amp installed if you have an extender.

Best ..

GARY

gar381 said:

Hi Blondino

90% chance all will be well getting the outputs in the right place and replacing the Burnt Rs
Give it a shot.

Most likely your VP26 will be fine with a good op-amp.  I would ask Jeff to be sure but
I don't think there will be a problem.  I would double check the Voltages at the DOA socket
without the op-amp installed if you have an extender.

Best ..

GARY

Click to expand...

Thanks Gary,
That was actually my 6 build and after 4 went well I don't know how could have been that distracted :-[

So I actually don't have mine extension here with me, what I did I just put a good one and tried the pre crossing my finger. I know is not the smartest thing but apparently everything went well or at least nothing burned. Sounds seems fine, but I will compare it with my others one.

Thanks Alex

Blondino said:

Thanks Gary,
That was actually my 6 build and after 4 went well I don't know how could have been that distracted :-[

So I actually don't have mine extension here with me, what I did I just put a good one and tried the pre crossing my finger. I know is not the smartest thing but apparently everything went well or at least nothing burned. Sounds seems fine, but I will compare it with my others one.

Thanks Alex

Click to expand...

Funny story. On the 2 opamp  I missplace Q7 and Q8 (where one I actually burn  R11 and R12 and the other one did't even plug it).
For preserving the PCB I replace in both the 2 transistors Q7 and Q8, in the one I plugged in I also replaced R11 and R12, but in the second one I just replace the transistors.

I tested the one I burned, comparing it with another good one I already had, and it works like a clock.
When i plugged the "unplugged" one... pfffff... R11 and R12 burned  :-\. So I checked if i did the same mistake twice but I didn't. All the parts seems in the right place and there are not shorting on testing point, so what else can cause R11 and R12 to burn?
this is a big turn down :'(

Wrong facing diodes.

jsteiger said:

Wrong facing diodes.

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No all cathode are on the PCB white circle!

Look for solder bridges with R11 to either the V- or G pins.

GARY

gar381 said:

Look for solder bridges with R11 to either the V- or G pins.

GARY

Click to expand...

Ok, done. The opAmp works just like the others. Was not any bridges. For some reason I had the idea to check diodes values and I couldn't have any reading from D1A and D1B. I decided to replace them as well and now everything is just fine. For some reason I had 2 bad components or they failed in somehow the one time I plug it.

thanks for the support

Just had one give up the ghost after several years service, nothing obvious.

What's consensus on troubleshooting these?  Bother, or toss and replace?   

EmRR said:

Just had one give up the ghost after several years service, nothing obvious.

What's consensus on troubleshooting these?  Bother, or toss and replace? 

Click to expand...

Doug

Is the problem magic smoke or is it that  it just doesn't  pass signal ??
It depends on how much time you want to devote to trouble shooting. 
If nothing obvious,  then personally for the cost of time and materials,
I would just toss and replace. 

GARY

gar381 said:

Doug

Is the problem magic smoke or is it that  it just doesn't  pass signal ??
It depends on how much time you want to devote to trouble shooting. 
If nothing obvious,  then personally for the cost of time and materials,
I would just toss and replace. 

GARY

Click to expand...

No magic smoke, just didn't come up one day.  I think I agree with toss/replace, seems much more expedient.