Origin of 2520 Schematic?

rp3703 · Mar 4, 2016

Does anyone know the story behind the API 2520 schematic that is floating around on the internet? As far as I can tell, it is only two components off from the GAR2520, which people say sounds very close to the real thing. Does anyone know where that schematic originated from? I have read posts where people say it is bogus but that does not seem to be the case.

My3gger · Mar 5, 2016

This is old topic we wrote about extensively, i'm sure you will find those posts. API 2520 went through many revisions, IIRC two most known are Melville and Huntington, later being prefered by many years ago. Melcor 1731 is the one to check too, could be predecessor of 2520 or not. I remember people using RCA discrete op amps for the same application too, also seen IC op amps with discrete output transistors to properly drive difficult loads, Jensen/Hardy 990, etc. Even simple NE553x was used in place of 2520, not sure if it can properly drive API output transformer.
There are many new revisions, from diy CAPI thing to Scott Liebers copies of early Melville and Huntington. I might be wrong about things written here, so check it to confirm how 2520 changed over time and why. Two links that could help you:
http://groupdiy.com/index.php?topic=4499.0
http://eli-audio.com/styled-22/index.html

I've seen your project, don't worry about 2520 revisions at this stage because differences due to slight bias or transistor changes aren't that big. You could try different schematics on veroboard, later play with nice pcbs and things like Mill-max pins, etc.

Good luck!

Sredna · Mar 8, 2016

Which one do you mean? There are several similar ones out there.

Whoops · Apr 15, 2016

Was checking my docs and I only have two 2520 schematics,
there only a slightly diference between the two, it's in the way D2 connects to Q9

here is the first one: