Help W/ Adding a Tone Control

[jermarcar]

I am trying to add a tone control based on the schematic from Beavis Audio.  The pedal is an Arlo Art Vintage Fuzz with volume, gain, and bias controls.  I am going to use the Jack Orman version.  I would like to wire it from the volume pot.  I am obviously completely new to this and need a little advice on the best way to connect this into the existing circuit.  Thanks in advance.

[electrosonic]

I think you are trying to add a BMP tone control to a circuit, right?

It might be a bit easier to add Mark Hammer's "Simply Wonderful Tone Control" or SWTC.

http://hammer.ampage.org/files/SWTC.gif

Andrew.

[jermarcar]

I guess I should have stated this.  The problem I am having is the pedal is dark sounding.  I am wanting to add treble.

[Mark Hammer]

In general, anything that adds harmonic content, be it an overdrive, distortion, or fuzz, will up the treble and require something to remove it, in order to achieve some sort of balance when the effect is bypassed and it's back to guitar-into-amp, or when the effect is engaged.  The idea is that either the pedal should be designed, or should have some sort of control included, such that bypassing it or engaging it, doesn't make you want to run frantically to the amp and start adjusting things.

It is easy to imagine a design that has included some sort of compensation to yield a more balanced tone, but which does not achieve what you want, as a result.  The question is what to adjust.

Tonal balance can be a matter of adding something, taking something away, or both.  If the pedal is capable of being loud, then taking away something to arrive at that balance won't be a bad strategy, because you can always turn the volume up if what you took away also lowered perceived output.  If the pedal has only modest output, relative to bypass, then you'd lkely want to add something instead of taking it away.  Either way, what you are aiming for is for some portion of the spectrum to notdominate what you hear.

Without giving away secrets, is this a discrete (transistor only) or an op-amp-based circuit?

[jermarcar]

Discrete transistor only.  I don't think there are any secrets to worry about.  The pcb board is labeled in detail.  The volume is at about 2:00 to reach the same volume level when the pedal is bypassed.  I can turn the volume up on the pedal and turn my guitar volume down to roll off the bass; however, at that point there is not enough saturation to get a pleasing tone.  That is why I was thinking of trying to jump in on a pot and add some treble. 

[mistahead]

Find the first input cap and replace it with a switch that lets you flick between stock and half-stock values.

Those input caps are basically highpass filters - the bigger the value the more of the total frequency band counts as "high" to pass (I hope I didn't reverse those with the morning dose lol).

[jermarcar]

I am trying to avoid messing with the PCB board.  Input goes direct to ac128 and volume pot 1 and then to C1, etc.  After looking this over a little better it looks like a low pass filter would work better.  I could add a switch, but getting the right amount would be tedious.  Could I possibly cut into the input (between the PCB and Vol 1) and wire a bass cut pot?  I think I will have enough gain left to compensate for volume loss.

[mistahead]

Sorry - am I missing something.... you are using a LOW-PASS filter to improve the trebble response?

I am on too strong a 'script methinks.

[smallbearelec]

Based on the description at Arlo Art, I'm pretty sure that this is a straight germanium Fuzz Face with a bias control. I'd strongly suggest that you Not try to mod this thing as a first project. I'm not saying that it can't be done. I'm saying that you don't want to mess up a $300 pedal while you are first on the learning curve.

I suspect that part of your problem is that germanium devices in an FF are going to be by definition a little "smooth" or "dark" sounding; that's what they do. I would want to use either silicon or silicon/germanium and re-bias accordingly. Yes, a tone stack would help, and you Really Don't want to try to mod that into a manufactured board as a first build. Breadboard A Basic FF First!:

https://www.smallbearelec.com/HowTos/BreadboardSiFF/BreadboardSiFF.htm

That article will walk you through setting up the circuit on breadboard, and the parts are not expensive. The pedal that you can build based on those ideas is the Fur Face:

https://www.smallbearelec.com/Projects/FurFace/FurFace.htm

and it will give you the sharper, more edgy distortion that I think you want.

Regards
SD

[LucifersTrip]

Discrete transistor only.  I don't think there are any secrets to worry about.  The pcb board is labeled in detail.  The volume is at about 2:00 to reach the same volume level when the pedal is bypassed.  I can turn the volume up on the pedal and turn my guitar volume down to roll off the bass; however, at that point there is not enough saturation to get a pleasing tone.  That is why I was thinking of trying to jump in on a pot and add some treble. 

Is the problem that you don't have enough treble when you turn the volume down and it's good at full?  ...or for the full range?

[drolo]

Probably just sounding a bit muddy and bassy like FF's tend to be, especially if you use humbuckers and the original circuit has a biggish input cap. You could just insert a smaller cap in series with the input. that will get rid of some of the bass.

[jermarcar]

I am using single coil G&L tele with stock mfd pickups.  Those pickups are very bright.  I also have a CS strat with vintage modern which are fairly bright in the bidge position.  You are correct this is a fuzz face type circuit.  The treble on this pedal is great.  The only reason I was going to add treble was because I though I might suffer volume loss adding a stack.  However, after some consideration I think there is enough gain/volume to compensate any tone loss.  The biggest issue is the pedal is so dark it is completely unusable at higher gain settings except for the G, B, and E string and even those are very dark.  It I roll back the volume it does clear up the bass frequencies, but it also lowers the gain to unusable levels.  I have had a lot of fuzz faces and this is the darkest by far.

[Mark Hammer]

In which case it is starting to sound like you'll want to reduce the value of one or more series capacitors to de-emphasize the bass.  If there is an electrolytic capacitor connected to the emitter of Q2 (and I am guessing about the circuit, based solely on the FF topology), you may want to reduce that too.

Like I say, it's all about balance.  If you are satisfied with the treble response, and your pickups are acceptably bright, then the imbalance would appear to be in keeping too much of the bass through the circuit.....at least from your description.

[jermarcar]

Exactly right Mr. Hammer.  That I can do.  The Q2 cap is easily accessible.  Thanks for the help I will let you know how it goes.

[deadastronaut]

from what i recall when breadboarding the fuzz face for a time..

and if i remember lucifer Correctly...

the vol pot 500k, can be changed to a 100k to be brighter too..

just my 2p...

was that right lucifer?.

[Mark Hammer]

Exactly right Mr. Hammer.  That I can do.  The Q2 cap is easily accessible.  Thanks for the help I will let you know how it goes.

That particular cap, will typically be in the 15uf to 47uf range.  Lower/smaller values will confine the boost/gain to parts of the spectrum starting a bit higher up.  We're not talking THAT high up, but certainly enough to reduce any woofiness.  If you have 22uf in there presently, try 10uf, instead and see if it does what you want.