[Build] CAPI CA-0252, Vintage 2520 Type Opamp, Official Support Thread

[Rhdwave]

Have you had issues with him not implementing the shield?

 

[Walrus]

Never.

 

[Rhdwave]

Perfect)

 

[jsteiger]

The original 2520 had a small piece of thin single sided copper clad board covering the solder connections, which acted as a shield (of sorts) for hum and rf.
This was connected to the 0v pin.

Yes 100% accurate. Melcor did not have a shield in their 1731. Nobody has had it in the reproduction kits, except maybe a copper ground plane. We tested side by side with a vintage 2520 and notice no difference in noise or hum.

 

[Rhdwave]

Great! Thanks for all the quick replies

 

[Golgoth]

@jsteiger I'm sorry if it has been discussed already, I couldn't find an answer, but how do they compare to current production API 2520s when it comes to gain? I'm looking to replace the 2520 in my Pultec EQP-500X that is too hot for my liking.

 

[jsteiger]

@jsteiger I'm sorry if it has been discussed already, I couldn't find an answer, but how do they compare to current production API 2520s when it comes to gain? I'm looking to replace the 2520 in my Pultec EQP-500X that is too hot for my liking.

Unless there is a problem, pretty much any discrete opamp should be within a 0.1dB of any other. So, yeah they are the same. You'd probably have to modify the gain setting resistors. Have you talked to Steve Jackson about it? I'd ASSume those EQ's are unity gain?

 

[Golgoth]

Unless there is a problem, pretty much any discrete opamp should be within a 0.1dB of any other. So, yeah they are the same. You'd probably have to modify the gain setting resistors. Have you talked to Steve Jackson about it? I'd ASSume those EQ's are unity gain?

Well that makes sense! I don't have Steve's contact but will try to get in touch, my unit is around 2db louder when engaged with no boost or cut happening. Not the end of the world but if any I would have prefered a 2db loss!

 

[Golgoth]

Unless there is a problem, pretty much any discrete opamp should be within a 0.1dB of any other. So, yeah they are the same. You'd probably have to modify the gain setting resistors. Have you talked to Steve Jackson about it? I'd ASSume those EQ's are unity gain?

I have ordered a ten pack anyway as future replacements!

 

[jsteiger]

Well that makes sense! I don't have Steve's contact but will try to get in touch, my unit is around 2db louder when engaged with no boost or cut happening. Not the end of the world but if any I would have prefered a 2db loss!

I would contact Steve just to see. I'd wager to guess that they are setup to drive a 600ohm load at unity gain, just like most all older API EQs. That is usually around a 1.75dB increase in gain if driving a high impedance load.

 

[jsteiger]

I would contact Steve just to see. I'd wager to guess that they are setup to drive a 600ohm load at unity gain, just like most all older API EQs. That is usually around a 1.75dB increase in gain if driving a high impedance load.

You can also ask about adding a load R across the outputs. 604R maybe. That can be problematic if you also drive a 600ohm device with the EQ.

 

[T Burger]

I just built my 12th CA-0252 and this is the first one to not work for me. I noticed there is a scratch on the bottom of the pcb. Is this possibly the culprit? If not, where should I start troubleshooting? I already verified that the transistors are placed in the correct spots, and the diodes are oriented properly. Thanks!

 

[TheseGoToEleven]

It’s hard to tell from the photo but could this be a solder bridge? Might just be flux. You wouldn’t want to short Q7 and D3.

 

[T Burger]

It’s hard to tell from the photo but could this be a solder bridge? Might just be flux. You wouldn’t want to short Q7 and D3.

Thanks, I don't think so but I will triple check. I used the flux cleaner that CAPI recommends.

 

[TheseGoToEleven]

Thanks, I don't think so but I will triple check. I used the flux cleaner that CAPI recommends.

Yeah, the board looks nicely cleaned which is why I wondered if the shiny spot between those two pads might be a solder bridge. Hopefully it is, because that’ll be an easy fix.

 

[Golgoth]

You can also ask about adding a load R across the outputs. 604R maybe. That can be problematic if you also drive a 600ohm device with the EQ.

Thanks Jeff

 

[Jollister]

Hi everyone, I recently built 4 0252's for a pair of VP28's. 3 of them are working while 1 is causing a staticy popping noise which starts after about 15 seconds of being turned on. It is affected by the switches/knobs and it's much quieter when in the VP28's fader DOA slot, louder in the preamp DOA slot. The preamp does pass signal.

Any ideas what could be wrong? Does this indicate a bad transistor?

 

[mkerlin]

This may be a dumb question. Is the + pin connected in the board to the B leg of the Q2 transistor. If not it seems impossibly close on the top side of the board not to have a bridge. I wanted to make sure since my first DOA attempt was a bust. Thank you for your time.

 

[mkerlin]

This is my first attempt at a DOA. I learned a lot. I think this DOA is the reason that my preamp doesn't work, but I won't be sure until I receive a prebuilt this weekend. I check for continuity around the area were I carelessly scratched up the board and I have continuity between the three indicated locations. I know continuity is not necessarily a legit indication, but should I have it between these connections, and if not I assume I have no shot at fixing this and should chaulk this one up to experience? Thanks for your time.

 

[jsteiger]

This is my first attempt at a DOA. I learned a lot. I think this DOA is the reason that my preamp doesn't work, but I won't be sure until I receive a prebuilt this weekend. I check for continuity around the area were I carelessly scratched up the board and I have continuity between the three indicated locations. I know continuity is not necessarily a legit indication, but should I have it between these connections, and if not I assume I have no shot at fixing this and should chaulk this one up to experience? Thanks for your time.

The non-inverting input goes to the center lead (base) of Q2. The inverting input goes to the center lead (base) of Q3. These are close by design.