Tube amp tone control question

[Electron Tornado]

Anyone ever try a tone control like either one of these?

C1 and C2 with potentiometer VR1:

Sorry for the tiny images. Click on each one and they will open in a larger size.

[GibsonGM]

The bottom one isn't uncommon, and can work well for partial-boosting.

The top one, I haven't seen but I bet it would be fun to play with!

[Electron Tornado]

The bottom one isn't uncommon, and can work well for partial-boosting.

Have you seen the bottom circuit used with a pot? It would be interesting to hear a demo that shows how that control sounds.

I have a feeling that the top circuit would have a slight scoop at the mid point of the pot.

[GibsonGM]

I think you're right about the 2 cap setup....you see that at the input of some fuzz pedals, as a 'warp' control, for lack of a better term.  It's used to allow you to move from a bass to more treble input cap.   So I'd expect similar here.

Yes, I've seen the bottom one used just that way.  C1 gives a fixed boost, and C2 allows an amount of 'extra boost' you can adjust.  Ex would be make C2 1u, and C1 100n (from Merlin's preamp book). You would then have a fixed high boost, with a control allowing you to sort of bring up some lower frequencies with the pot.

You could simulate that in Tina or LT Spice 

[swamphorn]

The second circuit is half of the Gibson GA-30 treble control according to "Guide to Single Knob Tone Controls"¹. The other side of the pot rolls off the treble when the wiper is on the other side, but could be put to other uses (fading between a treble boost and a mid scoop, for example).



¹ http://chasingtone.com/yourguitaramp/guide-to-single-knob-tone-controls/

[Electron Tornado]

Thanks for the link, swamphorn. That schematic is kind of similar, but it must really kill the gain as it rolls off the treble.

The second circuit is half of the Gibson GA-30 treble control according to "Guide to Single Knob Tone Controls"¹. The other side of the pot rolls off the treble when the wiper is on the other side, but could be put to other uses (fading between a treble boost and a mid scoop, for example).



¹ http://chasingtone.com/yourguitaramp/guide-to-single-knob-tone-controls/

[imJonWain]

Coincidentally I've been playing around with that same style tone control lately.  You're right about the gain.  Here is a quick simulation I did of a similar tone control in some Garnet amps (same layout but different values).




I've been experimenting with transistor versions of the same tone control.

[antonis]

Severe gain "killing" happens due to pot dual action..
When high resistance is set in parallel with cathode resistor (lowering gain) low resistance is also set in parallel with plate resistor (also lowering gain)..

[antonis]

as a 'warp' control, for lack of a better term.

I know you can come through terminology much better, Sir..