adding a tone pot to an overdrive

[fuzzy645]

I'm sure there are numerous ways to do it. With my limited knowledge, I took a guess at one approach by simply wiring it the same way as a tone pot would be wired passively in a guitar such as a Tele. 

Questions:

1. would this work?
2.  pros / cons / recommendations / improvements?
3. does it matter if hooked up by the output vs. the input of the circuit?
4. what about pot value. Is the general rule the same as a guitar, namely 500K is brighter and 250K would be warmer?

Thanks

[nexekho]

Have a look at the EQ section of the schematics board.  There are many.  I haven't built any of them but this one interests me:
http://www.muzique.com/lab/tone3.htm
Just sticking any passive EQ after the output should do it though will cause volume drop.

[Mark Hammer]

What do you need the tone control to do for you?

For many overdrives, the principle function of a tone control is essentially to tame the treble so that the tone settings of the amp and the treble exaggeration produced by the clipping pedal don't conspire to singe the ears off of anyone within 50 paces.

On the other hand, some folks want tone controls that can "re-voice" the sound radically, such that the pedal can produce big scoops or thin reedy mosquito buzzes otr deep throaty grunts, and other variants.

Simple treble-taming is easy to do and doesn't "cost" much signal level.  Re-voicing controls DO cost signal level, which is precisely why, despite having oodles of gain, the Big Muff has an additional gain stage after the tone control, in order to compensate for that signal loss.

[fuzzy645]

What do you need the tone control to do for you?

Thanks.   I would like it to tame highs, with no significant loss of signal level. I assume then the pot and cap  i added by the output of the Davisson schematic above will do the trick. What about pot value though?  250K, 500K, 1M?   I suppose a "no-load" pot might be an interesting idea too.

That being said, my MAIN goal is to learn the various approaches and pluses/minuses of each.

[MikeH]

The pot value will depend on the cap value; the cap value will depend on how much you want to attenuate the highs.  Unfortunately, the only two ways to figure that out are experimentation or math.  And I don't know the math.

Also - with that arrangement of tone control I find it works better with the wiper tied to the unused leg- sometimes you get a 'funny' spot at the end of the control when that lug is floating free.

[Mark Hammer]

What do you need the tone control to do for you?

Thanks.   I would like it to tame highs, with no significant loss of signal level. I assume then the pot and cap  i added by the output of the Davisson schematic above will do the trick. What about pot value though?  250K, 500K, 1M?   I suppose a "no-load" pot might be an interesting idea too.

That being said, my MAIN goal is to learn the various approaches and pluses/minuses of each.

Then take a look at the SWTC and Jack Orman's excellent and creative labnote on variations thereof ( http://www.muzique.com/lab/swtc.htm )

[fuzzy645]

Then take a look at the SWTC and Jack Orman's excellent and creative labnote on variations thereof ( http://www.muzique.com/lab/swtc.htm )

Thanks for the link.  I appreciate it. I checked that out and it looks great. 

Now, since I often get confused in interpreting pot orientation from schematics (major NOOB), I attempted to incorporate the last Orman tone mod by using physical pot images.   Everything to the right side of the yellow border is his SWTC2 stuff (if that isn't obvious).

1. Does my drawing look as if the tone and volume are hooked in to the circuit correctly?

2. I don't really understand the purpose of R1 and R2? Any ideas on that?

Thanks.

[anchovie]

1. Does my drawing look as if the tone and volume are hooked in to the circuit correctly?

No. You've lost the 68k resistor from 9V to the transistor collector that's in the original Easy Drive schematic. Going straight from the 9V rail into the tone control won't work.

Just take the original schematic unaltered and tack your tone and volume control onto the output point.

[fuzzy645]

1. Does my drawing look as if the tone and volume are hooked in to the circuit correctly?

No. You've lost the 68k resistor from 9V to the transistor collector that's in the original Easy Drive schematic. Going straight from the 9V rail into the tone control won't work.

Just take the original schematic unaltered and tack your tone and volume control onto the output point.

Thank you.  Just confused as I have seen 2 versions of this schematic (Easy Drive), one with pots and one without. The one without pots uses a 68K resistor, and the one with pots does not. I did not alter the following 2 schematics (not sure if someone else did though....)

All I'm trying to do is add a 3rd pot to the version that has knobs to function as a tone control Are you saying  I should add this tone pot after that .1 uf cap to the output, or directly before it??

Easy Drive WITH pots



Easy Drive WITHOUT pots (includes that 68K resistor)

[anchovie]

Personally, I'd use the gain control from the "knobs" version but keep the 68k resistor. Then I'd put the tone control after the output cap on the "no knobs" version and the volume control last.

[Mark Hammer]

Then take a look at the SWTC and Jack Orman's excellent and creative labnote on variations thereof ( http://www.muzique.com/lab/swtc.htm )

Thanks for the link.  I appreciate it. I checked that out and it looks great. 

Now, since I often get confused in interpreting pot orientation from schematics (major NOOB), I attempted to incorporate the last Orman tone mod by using physical pot images.   Everything to the right side of the yellow border is his SWTC2 stuff (if that isn't obvious).

1. Does my drawing look as if the tone and volume are hooked in to the circuit correctly?

2. I don't really understand the purpose of R1 and R2? Any ideas on that?

Thanks.

I'd answer, but photobucket is blocked at work (even though the forum isn't).  So it'll have to wait unti later tonight after grocery shopping.

[nexekho]

I believe it forms an adjustable low pass filter.
http://en.wikipedia.org/wiki/File:RC_Divider.svg
"A low-pass filter is a filter that passes low-frequency signals but attenuates (reduces the amplitude of) signals with frequencies higher than the cutoff frequency"

[fuzzy645]

Personally, I'd use the gain control from the "knobs" version but keep the 68k resistor. Then I'd put the tone control after the output cap on the "no knobs" version and the volume control last.

OK, so I think I understand your recommendation. I drew up a new version (called version B) which operates as follows:

1.  leaves the 68K by the 9V+ as per the original Easy Drive schematic
2.  uses the gain pot as per the Easy Drive w/Knobs schematic
3.  Sticks a tone + volume pot AFTER the .1 output cap wired as if it would be in an on-board internal guitar (such as a Tele). Any reason the tone should come first?  Also, what about pot values?  In a guitar we normally use 250K or 500K.  Any reason we should use a lower value here such as 100K?

Note - this does not use any of the SWTC2 mods.  I'm just not sure where the extra resistors would go in that mod??

What is bugging me is how I'm grounding out the output signal in the same manner as you would on a guitar.   On a guitar we usually bend back the 3rd lug (grounding it out) as you lower your volume.   That is why I did that.  Boy, wiring up a guitar is like child's play compared to this stuff :-)

Thank you

[Mark Hammer]

Now that I can actually see it, your drawn circuit looks like it should work.  Whether that specific value of tone cap shaves off what you want to shave off is a matter for empirical testing, but it should work just fine.

[fuzzy645]

Now that I can actually see it, your drawn circuit looks like it should work.  Whether that specific value of tone cap shaves off what you want to shave off is a matter for empirical testing, but it should work just fine.

OK, thanks Mark!  I assume you are talking about the last drawn diagram (the one I labeled version B).   I will play around with values .022 uf vs. .047 uf for the tone cap to see how it works.

Either way I'll report back once I have it up and running (fingers crossed).

[arawn]

if it bothers you you could tie the wiper and unused lug together, it won't hurt anything.