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How does "Power Scaling" work?

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10/18/2000 8:04 PM
BrianH	How does "Power Scaling" work? Does anyone know how Kevin O'Conner does the power scaling thing in his amps? www.londonpower.com schematics?

10/19/2000 11:16 AM

There was a lot of talk about power scaling on here earlier this year. Basically it uses an 'AC linear regulator' which is just an electronic variac controlled by the power scaling knob. That feeds the PT primary, so allows you to adjust the B+. The bias supply varies in proportion too, which is just what you want.

A separate transformer is used for the heaters (and maybe the preamp B+ too)

You might get schematics in one of O'Connor's The Ultimate Tone books.

There are other ways of doing power scaling though. You just need to drop the B+, and the bias supply proportionately. I designed an amp with a high-voltage B+ regulator a while back. Although I never did, it could easily be modded for power scaling. I'll try it out in my next amp.

http://homepages.strath.ac.uk/~cnbp111/toaster.html

Steve C.

10/24/2000 1:46 AM

Re: How does "Power Scaling" work?

Steve

What you are saying could be one way to do Power Scaling, but it isn't the one that Kevin O'Connor advocates in his books.

Instead of using a separate heater transformer, he advocates varying the B+ & Bias voltage AFTER the PT secondary. These voltages are varied in proportion to maintain their ratio (ie. 10 to 1). The heater voltage does not change.

By only putting AC on the pot to generate a reference voltage, you can get away from "earthquake" noises when rotating it.

Check out "The Ultimate Tone Vol.2". Its all in there.

BTW - I have one of Kevins' amps, and they are every bit as good as advertised. I have checked out the circuit and you could make one yourself, if you have some smarts. Buy ze book, & read ze book!!

Craig

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