300:2.7K Xformer and input switch for API 536 (line level) input?

[JW]

Can someone look at this schematic and tell me if it will work properly? It is the combination of (PM2000) multiwafer input pad switch, a 300:2.7K input transformer, and then the API 536 line input circuit. Unmarked resistor from secondary + to 470pF cap is 27K (Yamaha value) Also, I'm not sure about that 6.8K resistor. Lose or keep?

 

[Rogy]

Hi,

You seem to have obmitted a lot of the original PM2000 preamp schematics...
It uses a 5-wafer gain switch. You have thrown out the wafer that sets IC1's gain...

What is your goal? Use a 2-wafer gain switch because that's what you have at hand?

For reference, Yamaha PM2000 mic pre schem:

PS Here is an old thread of someone using PM2000 parts to build an API-style pre (although with a pot as gain control element): API Mic pre (with Yamaha parts) ***COMPLETED***

BR,
Rogy

 

[JW]

I'm not using IC1 as Yamaha has it, where after a certain level, this DOA kicks in. Actually the high positions on the switch wouldn't be used. Just +4dB, and the next few steps. So, in other words, not a mic pre, but strictly a line receiver. So, my schematic would be the equivalent (I'm hoping) of bypassing IC one and going into IC2, but instead of the Hitachi opamp, I've drawn the input to API's DOA, but with the negative input grounded like IC 2 in the PM2K circuit.

 

[JW]

Bump. I can't find answers anywhere. What should the 2520 look like with a (line) transformer in front of it? I understand most of the line inputs they built were unbalanced by the DOA itself. Wasn't there an earlier API though that used the 2261 or 2164 input transformer? Schematic? Card number?

 

[Vyvyan]

https://flyingeyepro.wordpress.com/2015/10/07/imitation-is-the-sincerest-form-of-flattery/

 

[Vyvyan]

much more info thru the link