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Building a 'clean' PI

5/31/2000 10:05 PM
Chris Harden
Building a 'clean' PI
On my amp I'm currently working on the PI, trying to get the most headroom I can. I've removed one of the gain stages so that the preamp is clean, but I only need to turn the master up slightly before I get distortion, almost certainly on the PI. I'm using a modified 12AT7 see-saw arrangement with 56k anode loads, a common 470R cathode resistor with a 220uF bypass, and a 300V B+. The stage seems to be running very cold at only 5mA for both triodes together, but I can't seem to get it to run any hotter, I think I need to have it at around 15-20mA combined anode current. Any ideas on increasing the headroom availiable, as I want to be able to play super-clean as well as OD.  

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