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
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
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.
You will want to use larger resistances and smaller capacitances with valves though.
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.
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
1. Do these new values seem like they would do the job for a use with tubes?
An externally hosted image should be here but it was not working when we last tested it.
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
just want to know if those values would be considered alright.. also why do valves require higher resistances/lower capacitance? Some impedance issue?
Yes they look ok for tubes.. You might also be interested in a tilt+mid control I designed:
http://i81.photobucket.com/albums/j207/merlinblencowe/BoaneRayStack.jpg?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.
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.
Wha? Who says it's like a TubeScreamer?
sorry for bringing this old thread up, but...
i've picked up a Bottle Rocket pedal, made by Mesa;
it's cool, but lacks midrange and headroom.
i need help to fix the loss in tone stack and maybe reduce the clipping.
theres two places in the PCB with slots to install potentiometers: one for mid (20k), other for presence adjustment (1m)
i've tried these, there was a slight difference, but i've felt there was a faint loss in the output, tried with suggested values and diff. values too... no good
also tried diming to 0 bass + treble to achieve a mid tone, but this approach also resulted in loss of output rather than resolving my need
maybe we should start by lifting the tonestack to full bypass it with raw signal?
i've picked up a Bottle Rocket pedal, made by Mesa;
it's cool, but lacks midrange and headroom.
i need help to fix the loss in tone stack and maybe reduce the clipping.
theres two places in the PCB with slots to install potentiometers: one for mid (20k), other for presence adjustment (1m)
i've tried these, there was a slight difference, but i've felt there was a faint loss in the output, tried with suggested values and diff. values too... no good
also tried diming to 0 bass + treble to achieve a mid tone, but this approach also resulted in loss of output rather than resolving my need
maybe we should start by lifting the tonestack to full bypass it with raw signal?
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There will always be losses if you add passive components for tone controls.
You need to add some gain to adjust for it.
You need to add some gain to adjust for it.
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