Baxandall tone control circuit in a guitar?

GuyBoden

I'm thinking about putting a Baxandall tone control circuit inside a guitar with a single pickup, so I'll have a Vol, Bass and Treble controls. I've read that the circuit looses a lot of the signal, but I don't think that's a problem because the signal can easily be boosted with a preamp or boost pedal.

Any experience with the Baxandall tone control circuit?






Baxandall tone control circuit

frankus

why not boost the signal before the tone circuit?

GuyBoden

frankus said:

why not boost the signal before the tone circuit?

Thanks,  but I don't really want a preamp and battery inside the guitar to boost the signal. I'm thinking about putting the Baxandall tone control circuit inside one of the guitar's cavities.

samzadgan

this is really interesting...bookmarked!

ICBM

The Baxandall is strictly an active circuit. [/pedant ] (I know that diagram says Baxandall on the page!)

I'm not sure how it will react to being driven by a very high-impedance, inductive source. It might well work, or not...
although I think you may want higher resistance and lower capacitance values, probably by about a factor of 5 or 10 all round, including 250K or 500K pots. As it is there, the DC resistance from input to ground is only 111K, which is pretty low and will dull the tone quite a lot even before the EQ gets applied.

But I could be wrong since I've never tried it in a guitar.

I do like the much simpler passive treble-cut/bass-cut tone system you get with just a standard tone control and a series bass-cut control. I also like the 'amp type' interactive volume and tone control that you get if you connect a treble-pass cap to the top terminal of the tone control, like a Fender 5F2-A Princeton.

I share your dislike of putting actives in the guitar too .

citizen68

Is that the tone circuit that's in Xotic pedals? Maybe just get a BB or an AC if so...

GuyBoden

ICBM said:

The Baxandall is strictly an active circuit. [/pedant ] (I know that diagram says Baxandall on the page!)

I'm not sure how it will react to being driven by a very high-impedance, inductive source. It might well work, or not...
although I think you may want higher resistance and lower capacitance values, probably by about a factor of 5 or 10 all round, including 250K or 500K pots. As it is there, the DC resistance from input to ground is only 111K, which is pretty low and will dull the tone quite a lot even before the EQ gets applied.

But I could be wrong since I've never tried it in a guitar.

I do like the much simpler passive treble-cut/bass-cut tone system you get with just a standard tone control and a series bass-cut control. I also like the 'amp type' interactive volume and tone control that you get if you connect a treble-pass cap to the top terminal of the tone control, like a Fender 5F2-A Princeton.

I share your dislike of putting actives in the guitar too .

Many thanks for excellent info, because it's not a very difficult circuit, I'll give the passive circuit a try and listen to the results.

Many thanks again.

Here's what I'll be using:

randomhandclaps

I wouldn't do it.  Certainly not as above. 

For a start, as would be expected @ICBM is completely correct that a Baxandall EQ circuit is actually an active circuit.  The diagram above is merely the actual filtering section of it.  It's designed to be driven from a low impedance source with a make-up stage following after.  The circuit above floats around as a possible insert into other circuits that already have this.

Despite the response curve shown the EQ section in merely subtractive and applies no boost.  Any boost in signal comes from the op-amp prior to filtering.

Used in the version above (or as a passive EQ) you are not only going to have huge signal loss even when set flat but any adjustment will rob even more. 

If you want to be able to filter out bass and treble frequency passively at the guitar there are far better ways of doing it.  However all versions will reduce you original signal.  If you want to boost any frequencies on board then you will need an active circuit.

GuyBoden

randomhandclaps said:

I wouldn't do it.  Certainly not as above. 

For a start, as would be expected @ICBM is completely correct that a Baxandall EQ circuit is actually an active circuit.  The diagram above is merely the actual filtering section of it.  It's designed to be driven from a low impedance source with a make-up stage following after.  The circuit above floats around as a possible insert into other circuits that already have this.

Despite the response curve shown the EQ section in merely subtractive and applies no boost.  Any boost in signal comes from the op-amp prior to filtering.

Used in the version above (or as a passive EQ) you are not only going to have huge signal loss even when set flat but any adjustment will rob even more. 

If you want to be able to filter out bass and treble frequency passively at the guitar there are far better ways of doing it.  However all versions will reduce you original signal.  If you want to boost any frequencies on board then you will need an active circuit.

Thanks for the input, yes, I agree, because it's a passive circuit, the signal loss will be huge, but I can boost the outgoing signal with a preamp or boost pedal. I'll give the circuit a try, I build many circuits, so this isn't going to take more than an hour. No harm trying. 

ecc83

I don't think you are being in the least pedantic IC!

Only a circuit built around a gain stage can be a true Baxandall tone control. Just one of several problems? The output point should really be the summing point of a shunt feedback amplifier. That point is at effectively ground and this is what gives the proper circuit its good isolation between treble and bass controls.

Then, to get low noise operation the circuit resistances can be kept low, especially if a good op amp is used such as the NE5532. I really don't get the objection to putting an active circuit in the instrument? If you are going to experiment, do it right!

In Small Signal Amplifiers, Duggy Self gives a nice TMB variant....Just the job for geetar I would have thought?

Dave.

ICBM

ecc83 said:

I really don't get the objection to putting an active circuit in the instrument? If you are going to experiment, do it right!

I just don't like putting actives in a guitar, from a long-term reliability and upgrade point of view - not just "guitars", I don't understand the obsession with it for basses or electro-acoustics either, really. I always think it's better to keep the batteries and the bits you might want to upgrade, replace or bypass in an emergency in a separate box. To me that's more "doing it right" .

Danny1969

I think a better way of doing it would be to build the circuit into the negative feedback of a good opamp. The normal Baxandall circuit is more designed for a wide-ish cut \ boost at frequencies that aren't that useful for a guitar .... being a guitar is more a mid instrument. A higher value of Q sweep-able like a parametric would be better

In the nineties I sold loads of my active boost black boxs designed for internal fit on guitars. The circuit was made free form and potted with 2 pack epoxy. Never had a failure 

GuyBoden

The circuit functions ok, but the signal loss is very extreme, especially when you cut the bass and treble. Also, the freq cut range is not really the range I'm after, so I'm going to do some more tweaking today with different resistor and cap values.

Thanks for the advice.

english_bob

For interest, comparison etc, here's G&L's passive treble and bass EQ circuit as implemented on their S-type guitars. 

ICBM

english_bob said:

For interest, comparison etc, here's G&L's passive treble and bass EQ circuit as implemented on their S-type guitars.

Exactly, that's the kind I like too. Simple and doesn't have any insertion loss when both tone controls are up full.

The only thing I would change is to change the treble control - connect the signal to the rotor not the '0' end and the .022uF cap to the '0' end, and move the 200pF treble-pass cap on the volume control so the right-hand (in the diagram) end of it connects to the '10' end of the treble control instead of to the '10' end of the volume control - that way you can control the operation of the treble-pass with the treble control.

You can do a lot with very simple passive controls if you want.

(And connect the '0' end of the bass control to its own rotor, which reduces pot movement noise.)

juansolo

You really want to make it active (Baxandall=active vs James=passive /pedant mode). The signal drop with a 'passive' Bax is huge. You'll either need about +20db of gain recovery or to make it properly active.

GuyBoden

juansolo said:

You really want to make it active (Baxandall=active vs James=passive /pedant mode). The signal drop with a 'passive' Bax is huge. You'll either need about +20db of gain recovery or to make it properly active.

Thanks for the advice, yes, the James circuit seems to be used more often as a passive circuit. I've used Duncan's tone stack calc in the past, when building amp tone tacks.

http://www.duncanamps.com/tsc/

GuyBoden

Any ideas for a more frequency controllable Tone Stack comparded to the usual one knob are very welcome indeed.

randomhandclaps

Well provided you are not looking to boost (which isn't going to be achievable without the addition of power) then if I was asked to do it I would simply add a high pass control to go with your tone (which is a low pass control) and the adjust the values of both until you were happy with the roll-off ranges.

The solution really lays in knowing what it is you are looking to fix about your current control.

GuyBoden

frankus said:

why not boost the signal before the tone circuit?

I should have listened earlier, yes, I'm putting a dual opamp active/preamp with the Baxandall circuit.

I'm just using fairly standard Capacitors values for Guitar Freq with standard pots values.

Treble, 5000Hz, 4n7, 100K pot
Mid, 600Hz, 6n8n, 100K pot
Bass, 100Hz, 56n, 500K pot

I'll post the schematic, when I've built and tested it in a few weeks.

ecc83

GuyBoden said:

frankus said:

why not boost the signal before the tone circuit?

I should have listened earlier, yes, I'm putting a dual opamp active/preamp with the Baxandall circuit.

I'm just using fairly standard Capacitors values for Guitar Freq with standard pots values.

Treble, 5000Hz, 4n7, 100K pot
Mid, 600Hz, 6n8n, 100K pot
Bass, 100Hz, 56n, 500K pot

I'll post the schematic, when I've built and tested it in a few weeks.

Why not come down about an order on those pot values and improve the noise performance?

And don't think you HAVE to use the ancient TL0XX series with their noise, poor drive and latchup issues. There are far better FET opamps  about now or you could use the NE5532.

Dave.