swapping input transformers in vp25

[gevermil]

Ive been reading various threads about this and wonder if anyone has done the same and noticed sonic differences .
I moved my in/out transformers and op amps from 2 old fabio v3 312 preamp cards to capi vp25s .
My question is - will using the the components slated for the ca26622 ( zobel ect ) up to the op amp , hinder the performance of the cinemag cmmi 8-apc .
The Cinemag needs to see 100K followed by 9K76 & 22pF .
https://cinemag.biz/mic_input/PDF/CMMI-8-PCA.pdf
The ca2622 in the capi vp25 has different values .
https://capi-gear.com/catalog/images/build/VP25-26/VP25-Rev-C-Schematic.pdf
what components would you suggest I swap out for the best performance ?

is just dropping the 150k to 100k the major change or should other parts of the vp25 be changed as well /

there is a quote in another similarly titled thread
"if you're swapping in an API type pre like Fabio's boards, Reichenbach at Cinemag said just the 100k R, without the extra 9K76 & 22pF cap, should work fine...

If any one has any ideas please let me know
Thanks

 

[Flatpicker]

The resistor and capacitor in series on the transformer secondary (10K/220pf for ca2622 and ~10K/22pf for cmmi8) is called a zobel network (google it to learn more) and is there to prevent ringing/peaking that may occur with sharp transients. The manufacturer's recommendation is probably the best option, but it's not set in stone. If the preamp is a little too bright and ping-gy on the top end, you can make it flatter by increasing the cap value, and likewise if it lacks sparkle, then try decreasing the cap's value. So, given what I just said, using the cmmi8 zobel circuit with the ca2622 will make it slightly brighter and using the ca2622 zobel circuit with a cmmi8 will make it slightly more dull. Incidentally, the cmmi8's zobel of 10K & 22pF in series isn't going to do much, so I would agree with Reichenbach basically saying that the cmmi8's zobel can be omitted.

The 100K or 150K load resistor isn't going to matter as much (I've swapped these around in the past and can't tell much of a difference). As for R2, C1 and C3 (on the CAPI circuit), I don't know why those are there and would remove them if it were me. Same with R13 and C11. The rest looks ok.

 

[gevermil]

I appreciate it . Im aware of the zobel network . I also was trying to figure out the purpose of R2 C1 and
C3 . I was under the impression the load resistor was the big factor but i suppose ill start with your suggestions of
removing some things
thanks!

 

[Flatpicker]

The load resistor just reflects impedance back to the primary and sets it up to accept the mic's output impedance, which can vary depending on the mic. A fun experiment is to use a pot as the load resistor and "tune-in" the mic's sweet spot (some preamp mfgs add this feature), otherwise I'd just stick with the transformer mfg's recommended value. I'm guessing R13 and C11 are to prevent HF oscillations that can occur if running long cables, so maybe ok to leave them in.