API active combining amplifier is it a 325 card with reverse polarity?

Coldsnow · Jul 22, 2012

Hi all is the API ACA or active combining amplifier used to combine channels on a mixer, just an API 325 card with the polarity reversed on the inputs of the opamp?

Coldsnow · Jul 23, 2012

http://www.waltzingbear.com/Schematics/API/API_325.htm
Here is the 325 schematic

Walrus · Jul 23, 2012

No. It is a 4 way board purpose designed as a summimg amp, sometimes with an FET switch to add in another signal, (cue, tone etc). I'll try and remember to upload a schematic to the group in the morning.

Walrus · Jul 24, 2012

Sorry slightly wrong with my answer. :-[
The 325 card *is* used as a combining amp, as you said, and is described on page 5 here http://www.classicapi.com/catalog/images/reference_docs/325-docs.pdf.

But generally an API *ACA* is as I said, 4 amps (2520's and AP2623-4 transformers) mounted on one card.
Just looked through all my schematics, and I don't have one for the ACA!!

gar381 · Jul 24, 2012

This maybe helpful..

http://classicapi.com/catalog/product_info.php?cPath=22_46&products_id=81

and

http://www.classicapi.com/catalog/images/reference_docs/325-docs.pdf

Gary

Coldsnow · Jul 25, 2012

Thank you very much. It looks like c3 c5. R1 and r2 on the 325 are not needed and can be left out, correct? Also, the manual states a 12000 ohm resister is used on each channel for summing? Is this correct? I'm only running 2 channels into it.

Walrus · Jul 25, 2012

If you are making your own 325 then you do not need to add those components.
The 12k summing resistor is correct with the values of Rf and Cf and voltage gains given in the table.

Coldsnow · Jul 25, 2012

Thank you for your help. One mor question, would you have the output of the card go to the negative side of the output transformer to reverse phase pack to normal or do it Fter the transformer?
Thanks again

Walrus · Jul 25, 2012

Either way is fine.

API active combining amplifier is it a 325 card with reverse polarity?

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