Odd-ball PI circuit identification request and headroom question


Posted on Feb 5, 2014

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


Odd-ball PI circuit identification request and headroom question
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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. Hey Soundguruman - thanks for the attempt - it could be diyAudio, as I can see the schematic from here (a different computer than the original post) and diyAudio is going super-slow for me right now. That is the dropping resistor that can be decreased, causing the PI supply to go higher in constant voltage. causing the available headroom to be realized. Checking each stage with the o scope, you "could"see that the clipping of the stage is equal in both positive and negative voltage swing of the sine wave. "could" Rebias each cathode to accommodate a higher plate voltage, when you get it up there high enough. Thanks for the suggestions. I thought of lessening the 10k, and of compensating to keep the voltage "downstream" the same by raising the next resistor by the same amount so that I don`t have to rebias other stages. I guess I just...




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