API 514L Preamp Module Help

Hello,

I've been trying to dissect my API 514L to figure out exactly how they work. This module is similar to the 312, the biggest difference being that it has a different (ap2157) output transformer.

Upon closer inspection, I learned there are a lot of different values thoughout the circuit. Most notably to me right now are the three "extra" resistors between the mic input and the (ap2622) input transformer. I've never seen resistors on the front end of a mic pre before like this, so I have no idea what they do. I am inclined to jumper them out of the circuit. But, since I dont know what they do, I figured I would get some insight from you fine folks first.

The values are;

1200 ohm
1200 ohm
160 ohm

There are, of course, phantom power resistors connected to the XLR connector in addition to these.


What do these do? Is this for some kind of input impedance thing?

I created this beautiful drawing for ya'll smart schematic reading people. It's aesthetic expresses my knowledge of electrical engineering. I figure this will help all of you creative types better understand where Im at.

"schematic"

Also, can anyone tell me where the 23ohms is coming from?


Thanks!

Jon

Looks like a pad , perhaps the xfmr overloads too easily

if those are anything close to the 212S the API modules for the sony console those mic pres would distort pretty quickly

I decided to download some "proper" schematic drawing software and draw up the entire 514L schematic.

I think this is correct, but this is the first time I've ever attempted to draw anything up.

I know the trannies aren't drawn correctly. I couldn't find a quick enough way to alter the transformer type. They are wired the same as the 312.

Can anyone explain to me what's going on with the + input to the 2520? What's C8 doing here?

Also, do C1 and C2 seem like they are too high of values? What is the purpose of this? Are there any adverse effects here?

Hopefully I haven't screwed anything up and this all makes sense to you.

Thanks!

Jon

API 514L Microphone Preamplifier Schematic