Naim NAC 32.5 Gain board lower gain

[maouna]

Hello. i was wondering whether i could lower the gain of this preamp by changing the resistor values of one of feedback resistors.With the original values of R14=12K and R9=1K ,the gain is 22dB. By changing R9 to 4.7K the gain is about 10dB.

But is there going to be any stability problem?

 

[Mooly]

Probably OK

Is that really a 330k in the emitter of TR1 ?

 

[maouna]

yes. the original schematic and the modded one are here.

Modifying Naim Audio preamps

Here is LTspice file if you want to play

 

[Mooly]

Thanks for the file. It's fine, no stability issues and good if a little "soft" on square wave testing.

Reminds me a little of the old Radford ZD22 stages.

 

[maouna]

i made a stereo layout... transistors are not soldered yet. i have to choose between BC549C, BC550C, BC560C, BC546B, BC556B

 

[Mooly]

BC549C is a classic low noise device (for TR1) although its not that critical in something like this tbh.