Solid State Pultec question

[jrmintz]

Hi all,

I'm finishing up a Pultec with a Jensen input transformer and Sowter inductor. I want to try using an API 325 card for the amp. My question is this: I have a regular 325 card and a variant with a Jensen JE-11P-1 1:1 input transformer. Would there be any particular advantages or disadvantages with either version of the 325?

Here's the 325 schematic

Thanks

 

[MikoKensington]

Hey Seth.

I have to say that in the grand scheme of things I know very little. But I'll say that I'm working on a similar project with a Quad Eight line amp. The line amp doesn't have an input transformer. As far as I know the filter section's output is unbalanced. So why use an input transfomer you may be able to use someplace else.

Perhaps that Jensen may impart some sonic characteristic though?

I get my panels back from engraving for my Pultecs in a matter of days. I'm working a mount for my Triad inputs. Then it all gets thrown in a case. Perhaps we'll both have pics before the new year.

 

[rafafredd]

Pultec used interstage transformers between the EQ section and the gain makeup amp to macth impedances/noise, so a 1:! won´t be of much effect in here.

Use the 1:1 at the input, before the EQ section, then just shunt the input of the 325 card with a resistor of the desired filter impedance. (This resistor can change the way the EQ section works, so be carefull about this value).

 

[jrmintz]

Thanks guys. Rafa, could you explain a bit more about the resistor?

Thanks.