ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

previous: dale never quite understood the theory t... -- 4/27/2000 4:25 PM

Re: Post-PI master any good?

4/27/2000 4:53 PM
andyfuchs	Re: Post-PI master any good? I've found that the way you configure the actual circuit, can change the sound alot. There are a few methods of doing post PI masters. I've seen the potentiometer used as a plate load (dual-100K). It doesn't sound bad. The "dennis" method (The Sundown Governor), which is just putting a pot from plate to plate , which I don't care for the sound of. THis can also be done on the output end of the coupling caps too. This would mess with the grid bias feed resistor value the tube actually "sees" though. There can also be an extra set of coupling caps that feeds a dual 500K pot and then the second (wiper) output) set that actually feeds the tubes. Each version has it's own tonality, and end result. The value of the cap going into the driver can change the sound alot, when using a Post-PI too. If theres too much bass, the distortion can be overly "brown". The values of the coupling caps (when adding the extra set) also needs to be addressed too, since the caps are in series when the pot is fully up. I don't presently use this technique in anything I own or make, as It always struck me as a last resort for producing overdrive without adding gain stages. I've seen it added to many amps I serviced in the past.

4/27/2000 4:53 PM

andyfuchs

Re: Post-PI master any good?

I've found that the way you configure the actual circuit, can change the sound alot. There are a few methods of doing post PI masters. I've seen the potentiometer used as a plate load (dual-100K). It doesn't sound bad. The "dennis" method (The Sundown Governor), which is just putting a pot from plate to plate , which I don't care for the sound of. THis can also be done on the output end of the coupling caps too. This would mess with the grid bias feed resistor value the tube actually "sees" though. There can also be an extra set of coupling caps that feeds a dual 500K pot and then the second (wiper) output) set that actually feeds the tubes. Each version has it's own tonality, and end result. The value of the cap going into the driver can change the sound alot, when using a Post-PI too. If theres too much bass, the distortion can be overly "brown". The values of the coupling caps (when adding the extra set) also needs to be addressed too, since the caps are in series when the pot is fully up.

I don't presently use this technique in anything I own or make, as It always struck me as a last resort for producing overdrive without adding gain stages. I've seen it added to many amps I serviced in the past.