Gain Recovery in an amp

[Ripthorn]

So in my continuing mission to tweak my submini tube preamp, I am looking to do some gain recovery after the tonestack (a passive baxandall which is bypassable).  I figured I would do one of these http://www.muzique.com/lab/boost.htm, the opamp one with variable gain.  The problem is that it is clipping my signal.  So I have two questions:

1) Did I misunderstand Jack's article and use a clipping section as a level boost?

2) Could someone point me in the direction of a solution that will work, preferably using an opamp.  My current situation is a TL071 with +12V supply.  My DMM reads an input voltage of .5VAC, so I don't think I am slamming the input. 

If anyone has any suggestions, I would love to hear them.  I am simply looking for something to boost the volume to recover the level drop due to the tonestack or at least close to it.  Anyone please?

[waltk]

1) Did I misunderstand Jack's article and use a clipping section as a level boost?

Your input of .5VAC to your boost stage with a 12 volt supply should be fine unless your gain is set too high.  What is the output from your boost stage?  It shouldn't clip unless the input times the gain exceeds the headroom allowed by your supply.  Try setting the gain lower - just enough to compensate for the attenuation by the tonestack.

2) Could someone point me in the direction of a solution that will work, preferably using an opamp.  My current situation is a TL071 with +12V supply.  My DMM reads an input voltage of .5VAC, so I don't think I am slamming the input. 

Check out Jack's article on simple buffers, where he shows an example of an inverting opamp buffer.  You can easily convert this buffer to a booster by making the feedback resistor a pot - and it would both boost and attenuate as required.  (If your other gain stage(s) are before the tone stack, you might actually want to attenuate instead of boosting.)

[petemoore]

  I don't know if you can count on a 'DMM' to be accurate when measuring 'AC', in the form of complex input waveforms.
  If it's correctly wired [check the OA pins bias V's], and you attenuate the input or increase the supply voltage and it cleans up, well, there are two options that clean it up.