One knob tone control

[BobBeaston]

Hi I am new here..

I am in the middle of designing a tube overdrive preamp (for guitar) with 2 12ax7s . I am looking for the right tone control. I have not decided on how many clipping stages but I think there will be 2 (so that uses up 3 of the 4 triodes). I may compromise for 1 clipping stage because the tone control is most important to me. I want a simple one knob control. I actually like the extreme mid sounding tubescreamer frequency response. I have been using simulating software and can't exactly get what I want out of various filters. For those of you that are not familiar with the tubescreamer it cuts the high frequencies after clipping with a simple RC low pass filter at about 720Hz. After that it goes to an active op amp which is a treble boost/cut of +/- 6 db an octave at 3.2KHz. Here is a link.. www.geofex.com/Article_Folders/TStech/tsxtech.htm.

I am open to use any filter. I had been messing around with an inverting anode follower design. If anyone could push me in the right direction or let me know if it is even possible to use 1-2 triode stages to accomplish this. Thanks

[BobBeaston]

any ideas at all??

[Zibi]

AMZ Stupidly Wonderful Tone Control 2

[Merlinb]

Probably the best is the Big-Muff Pi type control. It can be adjusted to provide mid scoop or mid boost, or a flat response: AMZ Presence Control

You will want to use larger resistances and smaller capacitances with valves though.

[m6tt]

I have tried a few of the one knob tone controls for guitar. I generally end up just setting the optimal low point with a coupling cap value or two, and using the "one knob" for a simple high cut (pot and cap). The tone will fatten as you decrease the value of the pot.

[BobBeaston]

Thanks for the info guys..definately helped. Here is the control I have inserted into a spice program. It seems to do the job in terms of a close matching frequency response to the TS and in terms of what I want.

1. Do these new values seem like they would do the job for a use with tubes?

2. Also I don't want to use 3 clipping stages for this overdrive preamp so I don't think I want to use this as a passive control. What would be the best way to incorporate this so that the 4th tube being used doesn't clip or put out additional gain (cathode follower, negative feedback anode follower?)?

3. It seems this control works by feeding a high pass and low pass filter into a pot. With the tubescreamer a 220 ohm resistor and .22uF cap give a rolloff or boost at 3.2K. Wouldn't a resistor of 390K and a cap of .0012uF give a rolloff at around 300-400hz? why is the response so similar to the tubescreamer?

Thanks

[BobBeaston]

just want to know if those values would be considered alright.. also why do valves require higher resistances/lower capacitance? Some impedance issue?

[Merlinb]

Originally Posted by BobBeaston

Thanks for the info guys..definately helped. Here is the control I have inserted into a spice program. It seems to do the job in terms of a close matching frequency response to the TS and in terms of what I want.

1. Do these new values seem like they would do the job for a use with tubes?

Yes they look ok for tubes.. You might also be interested in a tilt+mid control I designed:
http://i81.photobucket.com/albums/j2...g?t=1269469948
Tubes need high resistances because the tubes themselves have high output resistance. If you tried to connect the output of a tube to a low resistance you will lose most of your signal level.

2. Also I don't want to use 3 clipping stages for this overdrive preamp so I don't think I want to use this as a passive control. What would be the best way to incorporate this so that the 4th tube being used doesn't clip or put out additional gain (cathode follower, negative feedback anode follower?)?

Not sure what you mean. You could just attenuate the signal level before it reaches the 4th stage, or make the 4th stage a cathode follower.

why is the response so similar to the tubescreamer?

Wha? Who says it's like a TubeScreamer?