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Guitar Tube Amp

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Step 10: Controls

Picture of Controls
The Tone / Volume Control

This is one of the odd parts of the build. Instead of a more conventional tone circuit, I chose to modify the "Big Muff" filter schematic instead. Why? For one thing, there's very little insertion loss with this tone circuit.

OK--it's a little "experimental," but that's good, right?

I tried using the Duncanamps "Tone Stack Calc" designer, but it's useful as a starting point only. Simulations which yield nearly identical frequency responses sound VERY different when actually implemented. Lots of substituting caps, etc. was done before I was happy with it. And the "presence" pot was added after the simulation, since "Tone Stack Calc" doesn't let you change the circuit (just component values.)

Download the Tone Stack Calculator here...

Conventional design would have replaced the caps with smaller values. I didn't feel the tone had quite the body as with these values. To be honest, there really isn't much treble, even with the tone control at max... but it's big fat tone, and kinda fun...

The 1M volume control mirrors a 1M fixed resistor in the "Big Muff" filter. There's probably some interaction with the tone settings.

The "Presence" Control

The circuit is essentially a "notch" filter. I've set this up so that the notch is adjustable. The "presence" pot controls the depth of the notch, from maximum cut to almost a flat response.

Since a large notch attenuates the signal, the maximum volume and punch comes from the flat setting. That's what I'm calling "max presence." When the "presence" knob is turned down all the way, the volume is quite attenuated--because a large chunk of the sound was sliced from the middle! So there can be quite a bit of interaction with the volume control.

The 50K POT is a little large for this one. Substitute a 20K or 25K and it might be an improvement.

HMMmmmm

If there's one part of this build worth replacing, it's probably the tone control. Other (more conventional) types would probably make the build sound more like a typical Fender (and reduce some of the thick tones.)

There's far too much interaction between the controls, too. But they do work, and decent tones can be found, with a bit of messing about.
 
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reinovator3 years ago
Thank you for keeping PURE amplification Alive.This is a keeper!! Thank you.