Sony STR-6060 preamp NFB after recap

[eschenborn]

I have recapped-upgraded a Sony STR-6060 vintage receiver. It sounds very crisp and open, but is still a bit lean on bass. I am wondering if I should exchange the tranistors in the preamp (s. foto attached) to have a more bassy sound balance, as this has been suggested to me. I have discussed that with the folks at audiokarma, see here: Sony STR-6060F Restoration and Upgrade | Page 4 | Audiokarma Home Audio Stereo Discussion Forums

the amp sections are fully functional and it is a heritage piece of equipment, so I am not really inclined to change anything that does work. I have no experience regarding the choice of transistors influencing frequency range.

I pulled C632/R632 in the pre amp to interrupt NFB to see what that gives. there was a lot of hiss, but seemingly a much better low end (different impedance?). so a second thought is if I could put in low noise transisistors and get rid of the preamp NFB altogether. there is also not so much gain in the pre, I need to turn the volume to 12 o’clock for decent levels.

sound-wise it seems that there is some value deviating from factory settings. normally first generation solid state amps are quite bassy after a full recap. caps in the amp sections are all new. this job is not urgent but I am curious.

 

[JonSnell Electronic]

In the circuit you have shown, there is no NFB, what you are seeing is the DC level control.
Replacing the transistors will have little effect.
C632 is NFB for power amp.
The RIAA values look ideal considering the capacitor coupled output stage to the loudspeaker.

 

[eschenborn]

thanks, JonSnell Electronics, for your quick response. I was referring to R632/C633 and R732/C733 which are in the preamp circuit, as the image shows (they call it "flat amp"). sorry for the confusion in my earlier post. so to my eyes they cannot be about NFB in the power amp.

 

[DF96]

I have no experience regarding the choice of transistors influencing frequency range.

Nobody has experience of transistors influencing the audio frequency range, because they don't do this. Transistors work from DC up to RF. Audio frequency response is set by passive components, primarily the value of resistors and capacitors.

Two ways to get more bass:
1. add tone controls
2. add a resistor in series with the output, so the loudspeaker bass resonance is less well controlled