Splitting after pultec filter section

[Coldsnow]

Hi all,
I'm trying to make a pultec with two outputs and then summed together at the mixer.  One output using Gyrafs make up gain tube section and the other an API opamp makeup gain.  Can I just y a split after the filter and run a line to each?
Thanks

 

[Coldsnow]

Anyone know if there would be phase or impedence issues?

 

[okgb]

Phase sounds like a possibility , impedance possibly
At the least you could make it switchable , either or
and if the two don't behave together in any blend, then you still have the option
of Tube or Discrete individually

 

[bruce0]

Not the tube guy... but here is what I think:

Gyraf's section has no interstage transformer, and a very high impedance input to the buffer (472K grid resistor).
If it is also high impedance then it should be present no problem.

(Post a schematic of the API section you want to use as the other output buffer, or link to one of the many schematics in the Technical Documents section).

It is important thought that some transistor buffers, and the buffer on the Gyraf have offsets.  The transistor buffers because they can't get rid of them have small offsets that probably won't effect the filter. The Tube buffers, because they are necessary, have very large offsets (bias) that would effect your transistor buffer.  So you should make the so called "split" before the coupling cap and at least leave the cap on the Tube Buffer leg (and maybe have one on your transistor buffer depending).

Are you going to combine these outputs, or is this supposed to be switchable?


This is really hard without schematics or sketches, my Gyraf schematics have no part names and I don't know what circuit you are going to make using the transistor opamps.

 

[Coldsnow]

I'm actually using an API 325
http://www.waltzingbear.com/Schematics/API/API_325.htm
I'd split the signal after the filter section and before the 220n cap on the gyraf schematic
http://gyraf.dk/gy_pd/pultec/gy_pd_sch.gif
I'd use a 220 n cap running to the API and another running to the gyraf tube section with a 470 k resister running to ground on each as well.

 

[bruce0]

Glancing at API Line amp looks like 12K input impedance. This is probably high enough and from memory similar to the input impedance of the original interstage transformer used.  Switched or continuous.  If it is switched the API will attenuate the circuit more than the tube, and so you will need different gain to get the same output, if you want the same output.

Need a description of what you are attempting, and then smarter guys than me could comment.

 

[okgb]

I think you should just go for it, and you'll be able to make it work one way or the other .
the gyraf is a proven circuit, so start there [ or with your " proven circuit of choice ]
and add the api with switching or blend circuit .
see if you can find other examples  [ the U.A. twin finity ] there is a dual path summit eq, but
don't see many summit schematics around . Switching sounds " easier , blending may require
some buffering for mixing the two, I agree having the best of both worlds is appealing , take note
there a few phase alignment tools for mixing/ blending different signal paths on one source, you know
you throw up two mics on a speaker and some combinations work and others not so well .