PI Design

[ninjadave7]

Hey all,
I'm in the process of building a little 17w amp with old ao-35 parts. I have a PI design based on my Goodsell Super 17, but noticed that the Dr. Z stuff had very different values for the resistors in the PI. A Matchless Spitfire and the Goodsell are virtually identical at this point, and much of the preamp etc. is the same as a Maz 18, so wondered what difference the Dr. Z values would make. It's the same tube, a 12ax7 for the PI.

Hope this question is clear...

Thanks!

[loudthud]

I've never hear of some of those amps and Dr.Z amp schematics are hard to find. Can you post links to schematics of some of those amps? Or post a partial schematic of one of the amps and describe the changes.

[ninjadave7]

I must have been taking crazy pills yesterday. Today I looked back at those schematics and didn't see what I thought i did yesterday. Maybe I'll find it somewhere...

[loudthud]

Have you looked at Aiken's site? He has a good tutorial on phase inverters.

The Long-Tail Pair

[ninjadave7]

I have read it, and just did again. It actually answered some questions and put me on track to find the answers to others. Thanks!

[imaradiostar]

The ao35 used a fixed bias phase inverter. Some claim this is part of what makes it a fabulous guitar amp.

here's a schematic:

http://www.captain-foldback.com/Hamm...atics/AO35.JPG

I've never built one but the Dr. Z Carmen Ghia enjoys a good tonal rep and it's this amp with a mid scooping tone control out front.

Personally- I'd build something with a pentode out front and a basic tone control.

I'm not advocating it (stealing) but if you look around on the web you can find various Dr. Z schematics. His designs are largely carefully tuned adaptations of classic designs. If you're anything like me you could never afford a Z amp anyway so you might as well build something of your own that you like!

jamie

[loudthud]

That type phase inverter is used in some HiFi amps. Sometimes offset (un-equal) plate resistors are used to equalize the gain much like Fender did.