API 312 Transformer ratio issue. Inter group connection?

[mmadu]

Hey guys, I'm building an API 312 microphone amplifier for my console project, but I'm having trouble connecting the output transformer 2622 to the output transformer 2503.

In the 312 schematic, connecting 14 and 13 can result in a low impedance/low gain input, but aren't they two windings? Aren't they disconnected between them? How can the signal be transmitted? The same problem also occurs between 11/12, 6/8, and 5/7.

My guess is that in the API drawing, HI/LO actually refers to the HOT/CLOD inputs used for balanced differential, is this correct?

I am eager for any suggestions, thank you!

 

[a soBer Newt]

Hopefully this clarifies the input a bit for you. There are two windings that can be setup to be in series or parallel giving you an option of 150R or 600R

 

[mmadu]

Hopefully this clarifies the input a bit for you. There are two windings that can be setup to be in series or parallel giving you an option of 150R or 600R

Oh! Thank you for your help. I think I understand the wiring of the 2622 input transformer. In the API schematic, HI/LOW refers to the differential pair input - HOT/CLOD. By switching the switch, the input impedance can be switched between 150/600.

However, I am still confused about the output transformer 2503. If this wiring method is followed, the output ratio seems to be 1:2 or 1:1. However, on the API official build 312, there is a 1:3 button. Various indications suggest that it seems to be the ratio of the output transformer. How can it be achieved?

 

[a soBer Newt]

 

[CJ]

Usually run 1:2 with an extra wind for a vu meter.

Simply use 1 wind for the PRI and two winds in series for the sec. Observe polarity to avoid cancellation.