Volume control... where?

[-frank-]

Hi all, this is my first post here....

I'd like to put a volume control after a tube preamp that has an op-amp buffer and a voltag divider... Which solution of these is better? 




Thank you! 

[jakenold]

I would pick the first one you have there. Try both and see what you like.

[Andre]

If you would move the Vb to the other side of the 22nF capacitor, you could use both.
The Vb has no function now since it's decoupled by the 22nF cap.
I would prefer the first one though, because I think volume control should be at the output of a circuit for noise reasons.

André

[d95err]

It is also good to keep the signal level high as long as possible for the best signal-to-noice-ratio, so the first approach is good since the volume is reduced at the very end of the circuit. You can use a small value for the volume pot (e.g. 10k) without tone loss. This is very good (the lower pot value, the less noice), and gives a decent output impedance.

With the second solution, you get a very low output impedance, but also a low signal level through the buffer. It is probably better if you wire the pot like a regular volume control instead of adjusting only the lower leg of the voltage divider. I.e. take the output to the opamp from the wiper of the 100k pot.

Another solution that combines the benefits of both these solutions would be to wire the opamp as an inverting gain stage with a maximum gain of 1 (well, -1 to be exact). Use a pot to adjust the feedback network to get a gain between 0 and unity gain. That would give you a very low output impedance and keep the signal level up as long as possible.

Good luck!

[-frank-]

Thank you guys 

I think I will use the second solution.... bye