Booster with mid boost and treble&bass boost lodes?

[roseblood11]

Hi,
I'm looking for a clean booster circuit with eq, to built it inside a guitar. It should work with two pots: a) Gain, unity gain when it's set fully ccw. b) a tone control that's completely neutral in middle position, going into a treble&bass boost on one side and a mid boost on the other. Does this already exist?
Maybe a variation of a baxandall or James tonestack, with a stereopot instead of separate treble and bass pots?

[antonis]

IMHO, you're looking for too many features in relation with control pots availiable..

A stereo pot can be wired to simultaneously cut/boost bass and treble for 2 band EQ but you'll need another pot for the 3rd band..

edit: On a second thought, by cutting bass AND treble you actually "boost" mids..

[ElectricDruid]

Hi,
I'm looking for a clean booster circuit with eq, to built it inside a guitar. It should work with two pots: a) Gain, unity gain when it's set fully ccw. b) a tone control that's completely neutral in middle position, going into a treble&bass boost on one side and a mid boost on the other. Does this already exist?
Maybe a variation of a baxandall or James tonestack, with a stereopot instead of separate treble and bass pots?

There are plenty of designs of mid-boost / mid-cut circuit that are totally flat in the centre position. Ok, mid-cut isn't *exactly* the same as treble&bass boost, but if you turn the volume up, it is!

A Baxandall mid circuit would be one option, or you could look at gyrator mid controls. THere's a ton of stuff (probably) more than you need) looking at different options on my page about the Hard Bargain pedal:

https://electricdruid.net/designing-the-hard-bargain-distortion-pedal/

In the end, I went with the Baxandall design, as you can see here - you could nab the "Mid Boost/Scoop control" section pretty much as-is:



The gain stage from unity gain to more gain is a simple non-inverting op-amp application. There's one of those on the front of the Hard Bargain too, acting as a buffer-with-gain.

HTH,
Tom

[roseblood11]

Cutting bass and treble is the same as boosting mids, that's how a baxandall works... The Boss FA-1 uses 50k linear pots for bass and treble, it would be quite easy to replace both with a dual ganged pot. But it might require some adjustments, and maybe a better circuit already exists?
The Blade VSC preamp is more complex, but with a similar approach: a mini switch for t&b / off / mid boost, with three internal trim pots for the gain of each band. But that way, you only get two presets, none of them being completely linear.

[roseblood11]

Thanx Tom, that's exactly what I was looking for.👍

[antonis]

Tom..

Hard Bargain implements 3 (three) pots where OP calls for a single one..

(OK.. IC3.1 may be wired as booster, but still we have a surplus pot..)

[ElectricDruid]

Tom..

Hard Bargain implements 3 (three) pots where OP calls for a single one..

(OK.. IC3.1 may be wired as booster, but still we have a surplus pot..)

What I meant was that:

The Mid Boost/Cut circuit does all the tone control elements the OP wanted - that's one pot. Then they need some gain too, so add a non-inverting op-amp with gain control - that's another pot.

There, that's just two pots, right?

[PRR]

Here is something, simpler, exactly one knob, morphing from boost at extremes to boost in the middle.



I fear it highlights the physical difficulty: blending from a / slope to a \ slope mean large phase shift, cancellation, unexpected curve.

But it would not cost a buck to try.

It will sure need a buffer/boost in front because a passive pickup can't drive the EQ impedances. Some of the makeup gain could be moved before the EQ. Some very clever Tee networks in NFB loops might drop the opamp count to two, but I can't bust my brain over a 9-cent part for a one-off. We have not discussed DC power and bias so that is left to the builder. Also the unity-to-boost goal which is trivial (might give an excuse for a fourth opamp).

[m4268588]

It's very difficult to fully satisfy the required specifications.


("Flat" position is 1 o'clock)

[Vivek]

The Baxandall Mid control has such a low Q at low boost/cut, it almost acts like a volume control in most of the middle of pot's travel,

Only developing some decent Q towards extreme of pot travel.

[Vivek]

It's very difficult to fully satisfy the required specifications.


("Flat" position is 1 o'clock)

Please tell me more about this kind of tone circuit. What is its name ?

What are the extra components trying to achieve ? Increase the Q ?

Where can I read more about it ?

Thanks

[ElectricDruid]

The Baxandall Mid control has such a low Q at low boost/cut, it almost acts like a volume control in most of the middle of pot's travel,

Only developing some decent Q towards extreme of pot travel.

My hard bargain page starts off with a Constant-Q Mid design, if that's important. For my purposes, I decided it wasn't and used the much simpler Baxandall Mid. But the OP might feel differently.

The trouble with the constant-Q design I used was that it uses three op-amps to do the cut/boost part, plus one more for the bandpass filter. That's not too bad if you're doing a whole EQ (just add one more filter per-band) but for a single band, it's a pretty big overhead. The design came from here:

https://sound-au.com/project75.htm

[Vivek]

Tom,

Are Gyrator mids any better than Baxandall Mids in terms of higher Q ?  Like the MT-2 Mid that you had analysed.

What is the best mid control with regards to high Q ?

Thanks

[ElectricDruid]

Tom,

Are Gyrator mids any better than Baxandall Mids in terms of higher Q ?  Like the MT-2 Mid that you had analysed.

What is the best mid control with regards to high Q ?

Thanks

Yes, you can get a much higher Q with a gyrator. The trouble with the gyrator mid control is that it doesn't really do anything until the extremes of the pot range. It was partly because of this that I went with the Baxandall in the end, plus I wasn't convinced that a high Q was what I needed. High Q's often give you that "peaky" cocked-wah sound, which is ok if that's what you're after, but it's pretty much just one sound.

[Rob Strand]

For higher Q's checkout the musicman circuit
https://www.diystompboxes.com/smfforum/index.php?topic=128906.msg1243513#msg1243513

In order to choose a particular Q and amount of boost-cut you will need to change the part values.
It's not a straight forward process unless you churn through the equations.

[antonis]

What Tom said:

BAX MIDs





GYRATOR MIDs Q pot (RES2)

[m4268588]

It's very difficult to fully satisfy the required specifications.


("Flat" position is 1 o'clock)

Please tell me more about this kind of tone circuit. What is its name ?

What are the extra components trying to achieve ? Increase the Q ?

Where can I read more about it ?

Thanks

I don't know the name. I came up with the analogy from "BAX." And "tilt" control.
Removing R25, 26 and C26 does not provide a flat position.

[Vivek]

Dear Antonis,

Could you please also post sweep of tone controls a noon, 25%, 50%, 75% and full, in both directions.

[antonis]

For Bax or Gyrator..??

[ElectricDruid]

Dear Antonis,

Could you please also post sweep of tone controls a noon, 25%, 50%, 75% and full, in both directions.

Here's the gyrator, every 1/10th of the control's travel:



As you can see, it only really does anything between 0-20% and 80-100%. The middle 60% is pretty subtle. The Bax gives a more even response around the knob travel.