Hi, I’m using the Salas Low MC Pre-Pre in my 0.25mV cartridge to reach MM signal level before entering the Phono PreAmp, this works really well and had no problems with it.
A few days ago I was reading the info about the new Pass Labs XP-27 Phono Preamp (https://www.passlabs.com/preamplifier/xp-27) and something call my attention:
Just immediately remembered that I had saw YouTube video of a Wayne Colburn interview at CES where he shows internal views of some power amplifiers, XS Pre and XS Phono Pre (YouTube), here you can clearly see 3 vertical signal input daughter-boards per channel (the XS Phono support 3 different turntable/tonearm inputs) and in the main board a set of 8 relays for capacitive and resistive loading, and another set of 3 relays for input select (I guess).
Now the question, referring to Salas’s circuit, it’s possible and reasonable to move the loading resistor R2 in-between Q2 & C3?, this means after the MC 0.25mv signal was amplified and left the Q1 & Q2 without input load.
A few days ago I was reading the info about the new Pass Labs XP-27 Phono Preamp (https://www.passlabs.com/preamplifier/xp-27) and something call my attention:
“The XP-27 input and gain circuitry are similar to that found in the Xs Phono. This means switching and loading is done at higher signal levels, minimizing noise and improving low level performance.”
Just immediately remembered that I had saw YouTube video of a Wayne Colburn interview at CES where he shows internal views of some power amplifiers, XS Pre and XS Phono Pre (YouTube), here you can clearly see 3 vertical signal input daughter-boards per channel (the XS Phono support 3 different turntable/tonearm inputs) and in the main board a set of 8 relays for capacitive and resistive loading, and another set of 3 relays for input select (I guess).
Now the question, referring to Salas’s circuit, it’s possible and reasonable to move the loading resistor R2 in-between Q2 & C3?, this means after the MC 0.25mv signal was amplified and left the Q1 & Q2 without input load.
No. It won't give the cartridge the right loading.
And why?
IF the cartridge needs loading, right where it is is the most logical place.
There IS an alternate with some promise of hiss reduction. Use NFB and Miller effect to emulate a small resistor with a larger resistor. However for the usual values of MC cart and load the hiss improvement is very small. And you need to know your gain pretty exactly or the emulated load won't be right. And in vinyl playback the amp hiss is a small part of the total playback noise.
This does not look like something I could do at home. "...the most intensive and difficult design effort made at Pass Laboratories." "...internally this makes for a very complex piece of hardware...
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