Adding a tone pot to only part of a circuit?

[tuxedo3]

Hey guys, so I have a fairly simple boost circuit i've been working on that utilizes a spdt switch to engage some clipping diodes for some dirt as opposed to just boost. Here's my question, could I add a tone pot to specifically the clipping section? I basically don't want the tone knob to adjust anything when the switch is engaging just the boost circuit, but when you throw the switch to engage the diodes I want the tone to effect the signal, enabling you to shape the distortion. I have a schematic drawn up that I can post later but as of right now the diyguitarpedals 10 Minute Boost/Dirt schematic is pretty close. http://www.diyguitarpedals.com.au/shop/boms/10_Min_dirt_&_boost_Schematic.pdf

[Kipper4]

Hi and welcome.
Easiest way for my taste would be put a resistor to ground after C2.  So just put it in parallel with the diodes.
Then when you close the switch you will have dirt and tone shaping in one.

This will form a high pass filter. Google it.
Resistor of choice will shape the tone.

You will lose additional signal as a result of the high pass filter probably too.
Others may have better ideas.
Have fun
Rich

[PBE6]

Yes it's possible. I think the easiest way would be to make a guitar-style tone knob out of a capacitor in series with a pot, and then put that combination in parallel with the diodes. When the switch is disengaged, so is the tone stack.

47nF and 10k might be a good place to start experimenting.


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[tuxedo3]

Thank you guys for the responses, both are helping me think through what I'd like for this circuit.

I think the easiest way would be to make a guitar-style tone knob out of a capacitor in series with a pot, and then put that combination in parallel with the diodes. When the switch is disengaged, so is the tone stack.

Thanks for the response, I feel like I mainly understand this and it seems like this is what I want to go for. I definitely get where to put the cap and pot, but I guess I don't get the mechanics of the two together in a tone control enough to understand it totally. that cap will be connected to lug 3 and lug 1 will be grounded correct? That way as you turn the pot clockwise and the resistance between 2 and 3 becomes less, the cap is brought into play more, thus affecting the frequencies more? I'm unsure where lug 2 would be connected then.

[tuxedo3]

Would this be correct?

[Kipper4]

post edited
You beat me to it with your drawing.
to save a part simply make your C2 47nf and forget C3. Although it will alter the stock tone.

[samhay]

Convention says that you usually have tone controls arranged such that you increase the treble as you turn the knob cw.
If you want to stick with convention, connect lug 1 to ground and lug 2 to the switch (or vice versa). You can short lug 2 and 3 together for good practice if you like. You may find a log taper pot works better than linear. You will also want to audition the value of the capacitor.

[PBE6]

The drawing as shown is what I was talking about. I personally like "bright" on the right and "dull" on the left, so I would wire lug 2 to lug 3, but your configuration works as well.

My suggestion is a low-pass filter. Kipper4 has suggested a high-pass filter (resistor only, no cap). Try them both, see which one you like.


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[tuxedo3]

Convention says that you usually have tone controls arranged such that you increase the treble as you turn the knob cw.

This is what I would like, I guess I was thinking that the cap would be increasing the higher frequencies, and therefore the more that was let into the flow the "brighter" it'd be. But now I see that isn't the case.

... connect lug 1 to ground and lug 2 to the switch (or vice versa). You can short lug 2 and 3 together for good practice if you like.

I read about this being good practice at one point, but why would that be the case? Also, feel free to correct my thinking, but if I use the cap as a highpass filter and use the pot as the way to control what frequencies are being cut, would that just leave the original signal untouched by the cap when the pot is fully counterclockwise?

[samhay]

>but why would that be the case?

A common cause of failure in pots is the wiper (lug 2) losing contact with the track that connects lugs 1 and 3. If this happens and e.g. lug 3 is not connected to anything, then you get an open circuit. If the lugs are shorted, instead you get the behaviour of the pot at max setting, which shouldn't be too objectionable (in a fault).
In your case, the pot failing as an open circuit isn't going to cause any real problems, but if the variable resistor (which is what we are doing when we only use 2 lugs) is setting e.g. the gain, then this can get ugly.

>...would that just leave the original signal untouched by the cap when the pot is fully counterclockwise?

Not quite. The pot is forming one half of a frequency-dependent voltage divider (think volume pot). The other half is the impedance of the collector, which is about 3k in the schematic you posted. The voltage divider only lets high frequencies pass through the tone pot to ground (thus you don't hear then) and at min setting, you will still lose about 3/13 of your high-frequency signal. This may, or may not, be audible.

[anotherjim]

If you omit C3, you will get a high pass filter, but the tone control will also be a volume control as it can short the output to ground at minimum resistance. You would need a fixed resistance in series with the control to prevent this.

There are quite a few choices, although as clipping adds some very high harmonics, low pass filtering with the guitar style control shown could be more useful.

Another tactic is to put the pot between C2 and the switch and connect C3 between wiper and ground. When the wiper is close to C2, it gives a lowpass filter working before the clipping diodes which would give a smoother "cello" tone from the clipping. When the wiper is close to the switch, it is a lowpass on the clipped sound giving a warmer fuzz. This arrangement of the control would be effective whether or not the diodes are switched in.

[robthequiet]

Just trying to understand here,

I basically don't want the tone knob to adjust anything when the switch is engaging just the boost circuit, but when you throw the switch to engage the diodes I want the tone to effect the signal, enabling you to shape the distortion.

So far I'm counting an on/off switch, a clipper switch, tone and volume controls. But we don't want to lose the clean boost, right? If we were to get a relatively neutral setting at the mid-point of anotherjim's in-line pot, is there enough juice in the circuit to make the clip switch into a knob and vary the clipping level? So you would have one effect on/off switch, a tone pot, and a dirt pot?

Or do we just want to use the tone pot to shape the clipping side alone?

[tuxedo3]

The voltage divider only lets high frequencies pass through the tone pot to ground (thus you don't hear then) and at min setting, you will still lose about 3/13 of your high-frequency signal. This may, or may not, be audible.

This is really good and insightful, thank you.

Another tactic is to put the pot between C2 and the switch and connect C3 between wiper and ground. When the wiper is close to C2, it gives a lowpass filter working before the clipping diodes which would give a smoother "cello" tone from the clipping. When the wiper is close to the switch, it is a lowpass on the clipped sound giving a warmer fuzz. This arrangement of the control would be effective whether or not the diodes are switched in.

Okay, I think this makes sense, thanks a ton.

So far I'm counting an on/off switch, a clipper switch, tone and volume controls. But we don't want to lose the clean boost, right? If we were to get a relatively neutral setting at the mid-point of anotherjim's in-line pot, is there enough juice in the circuit to make the clip switch into a knob and vary the clipping level? So you would have one effect on/off switch, a tone pot, and a dirt pot?

Huh, that's a pretty cool idea, I honestly didn't think about something like that because I've been so focused on just "clean boost with dirt switch" in my head. Using the tone knob to shape the clipping section seemed to be the most simple approach but I say that only because I have very little experience with anything past simple buffers. I'm not super set on making a clean boost for the utility, but mainly because it would be some really good practice. So if this could be more useful (which it sounds like it may?) and still a good way to learn, I'm all about it.

The current clean boost circuit has a pretty decent amount of juice to it. (Im assuming the effect on/off switch be the footswitch, not the spdt?) Would that "dirt" knob be a knob in regards to the actual amount of clipping, or to the volume of the clipping?

[GGBB]

I would personally go a different route. Get a double pole switch and do it this way:



I think the tone control will work better this way. Optionally (as mentioned already), put the clippers after the tone pot.

[robthequiet]

Would that "dirt" knob be a knob in regards to the actual amount of clipping, or to the volume of the clipping?

I was just going back to Jack Orman's More Saturation Controls where Jack has provided several examples of diode clipping methods and one in particular might be worth a try:

_{Credit: Jack Orman, muzique.com}

In order to stay true to your original idea you end up with a two-channel box that does 1) clean boost, and 2) a clippy channel with tone preset. You could do it with two footswitches, with power being switched at the battery/power jack. Two pots: Overall volume and clippy tone. I was thinking out loud a bit with the variable clip level, but half the fun imo is tinkering with it to see how the parts interact. Maybe add one feature at a time and see how you like it.

[Brisance]

^^ this is genius!

[tuxedo3]

You guys are all awesome, thanks for all the great info. I'm definitely gunna try a  few of these suggestions.

I think the tone control will work better this way. Optionally (as mentioned already), put the clippers after the tone pot.

This is a cool idea, I'll definitely be trying it out.

In order to stay true to your original idea you end up with a two-channel box that does 1) clean boost, and 2) a clippy channel with tone preset. You could do it with two footswitches, with power being switched at the battery/power jack. Two pots: Overall volume and clippy tone. I was thinking out loud a bit with the variable clip level, but half the fun imo is tinkering with it to see how the parts interact. Maybe add one feature at a time and see how you like it.

I'll totally be trying out that idea. I'll be messing around with parts and order as well cause as you said, that's half the fun.

[tuxedo3]

I would personally go a different route. Get a double pole switch and do it this way:

Maybe i'm confused, couldn't this be done to a SPDT switch?

[GGBB]

I would personally go a different route. Get a double pole switch and do it this way:

Maybe i'm confused, couldn't this be done to a SPDT switch?

Not that I can figure out.