odd-ball PI circuit identification, and headroom question - diyAudio
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Old 28th June 2012, 08:47 PM   #1
diyAudio Member
Join Date: Jan 2011
Location: Columbia, MO
Default odd-ball PI circuit identification, and headroom question

Hey there! I also posted this in Tubes/Valves as the amp started out non-instrument:

Going in the guitar amp direction with this one -

This schematic is modified from an old Bell & Howell projector amp for model 302 - PP 6v6's with a 12AU7 PI. Can anyone identify the PI circuit? It appears closest to "floating paraphase" to me.

My only complaint with this circuit is that I'd like more clean headroom/volume. Driving it with a guitar, I'm getting clipping at about 1/3 of the way up on the volume.

The clipping/distortion itself is pretty musical to me - that keeps me from switching to LTP or some other type of PI. But I'm looking to get a more "drummer friendly" volume from the amp without being slaved to a ton of crunch - idealy I would have a workable "clean" volume and then hit a boost pedal to push it into saturation.

I don't have all the specs of actual voltages and such to provide, but I did send a sine wave at 1v rms through the amp and found that the PI is distorting well before any Preamp stages - I don't even know that the preamp reaches saturation/clipping.

Basically, I really love to tone of this amp, but want more range of use and volume.

What can I change in the PI circuit to get more or to reduce clipping?

Thanks for any input!
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