How to build and attach a "Stupidly Wonderful Tone Control"?

[steveyraff]

Hey all,

So, I want to make a little simple build for fun. Namely a one knob-eroo fuzz pedal. I'm thinking of going for this, specifically the Black Arts Ritual version:
http://tagboardeffects.blogspot.co.uk/2013/04/1-knob-fuzz-bonanza.html

In the comments, someone inquired about adding a tone control. It's something I haven't done before, so I thought it might be good to practice on a simple build like that.

So this is the schem for the tone control - Mark Hammer's is the first one:
http://www.muzique.com/lab/swtc.htm

I'm really not great with reading schematics, so its hard for me to understand how this tone control is built, and moreso, how it is attached/incorporated into the fuzz circuit?

Is there any other guides that show it in reality in a more visual way I can understand? Any help is appreciated really.

Many thanks,
Steve.

[Kipper4]

C1 to fuzz output ?

[steveyraff]

I just can't really work out schematics DOH. 

What are the values of R1-R3 and C1? 

What kind of tone pot is recommended and how is said tone pot connected?

Still unclear as to how the whole thing is then connected to the fuzz circuit.

I know this has to be basic stuff, but its quite new for me so I am trying to learn as I go along with this one.

[Granny Gremlin]

Depends on what you want it to sound like.  You're going to have to breadboard it and try out a few things.  The link you provided does suggest a starting point, so start there and tweak.  There is math you can do to figure it out but that is, itself, only an estimate/starting point and you have to know the F3 points that sound the way you like, which most people don't.

[Mark Hammer]

The SWTC is essentially an extension of the volume control.  In other words, it always goes just before the volume pot, and although there are no hard and fast rules, it should generally be a value less than the volume pot.  For example, one would not likely use a 500k pot for the SWTC in conjunction with a 100k volume pot.  Depending on how much volume you can afford to forfeit, the added tone pot can approximate the volume pot value.  So if the pedal doesn't put out GOBS of signal, I wouldn't go above 10k with a 50k-100k volume pot.  If it does put out far more level than you ever really use then you might go up to 25k or even 50k with a 100k volume pot, or 5k on a 10k pot.

[dbp512]

...If it does put out far more level than you ever really use then you might go up to 25k or even 50k with a 100k volume pot, or 5k on a 10k pot.

For a circuit with enough output, how would a 50k/100k compare to a 5k/10k arrangement? Would there be any difference, or did you just list 50k/100k because you were talking about a 100k volume pot anyway?

[Groovenut]

...If it does put out far more level than you ever really use then you might go up to 25k or even 50k with a 100k volume pot, or 5k on a 10k pot.

For a circuit with enough output, how would a 50k/100k compare to a 5k/10k arrangement? Would there be any difference, or did you just list 50k/100k because you were talking about a 100k volume pot anyway?

The output of the circuit doesn't matter quite as much as the output impedance driving the SWTC and the volume pot. Far a given output, the lower the output impedance of the stage driving the less signal loss due to loading. For an opamp stage the difference between the two sets you listed would be negligible, but if the driving stage was a Jfet amplifier you would get more signal loss due to loading.

[dbp512]

The output of the circuit doesn't matter quite as much as the output impedance driving the SWTC and the volume pot. Far a given output, the lower the output impedance of the stage driving the less signal loss due to loading. For an opamp stage the difference between the two sets you listed would be negligible, but if the driving stage was a Jfet amplifier you would get more signal loss due to loading.

So unless you know what you'll be driving next, its generally best to use a low value? How would you determine how much resistance is necessary?

[Groovenut]

The output of the circuit doesn't matter quite as much as the output impedance driving the SWTC and the volume pot. Far a given output, the lower the output impedance of the stage driving the less signal loss due to loading. For an opamp stage the difference between the two sets you listed would be negligible, but if the driving stage was a Jfet amplifier you would get more signal loss due to loading.

So unless you know what you'll be driving next, its generally best to use a low value? How would you determine how much resistance is necessary?

The driving stage being the one upstream from the SWTC and volume pot.

I believe Mark was just using the most common examples of Volume pot values. A majority of circuits use 100k or 10k Volume pots, so it makes sense to use those two as a basis for his tone pot value recommendations.

[Kipper4]

Maybe this will help Stevie

http://www.joedocmusic.com/wp-content/uploads/2014/09/Axis-Face-Si-Fuzz-Layout.png

[Mark Hammer]

Output impedance matters, but my recommendation was really focussed on having treble cut without sacrificing level.  As noted, one has to think about the added tone pot as an extension of the volume pot, and the tone cap is essentially inserted at a tap-point on that pot.  So, if you have a 25k tone pot in series with a 100k volume pot, it behaves as a 125k pot that can never be turned up beyond 80%.  If that tone pot were 50k, the whole thing would behave like a 150k pot that can never be turned up beyong 2/3.

If the circuit is tolerant of a combined pot value such as you have in mind, you still need to ponder the question "If I divide the maximum output down by this much, will I have still enough output for my needs?".  For instance, folks who have, or have built, an MXR Distortion+, or DOD250, will tell you that, at gains much less than max, there isn't a lot of output.  Certainly enough to get a modest volume boost, but if that gets cut back by 33%, you may never be able to use the pedal at medium gain settings.

So...
- First you determine the largest combined pot values the circuit will still behave well with.
- Then you determine what the impact could be on maximum output level.
- Then you pick the closest common pot value that suits those needs.
- Then you figure out what sort of cap value would give you the rolloff you want at max treble-cut (using pot and cap value and the standard formula).
- Then you figure out a suitable range for the control and the corresponding minimum resistance value for a series resistor just ahead of that tone pot.  Roughly 10:1 is usually pretty good (e.g., 5k6 for a 50k pot, 1k for a 10k pot, etc.)