Crackle-OK solution, I think

[R.G.]

For about the thousandth time I got another question about how to remove the crackle from pedals that have "crackle OK" knobs. This time I think it slapped me in the face.

Use a dual 5K pot. One pot is wired as a variable resistor in series with a big cap. This is the AC impedance change. The other section is a voltage divider from a fixed voltage, maybe 5V or so, and it sets the current into a current source, perhaps even a current mirror, that sets the bias current. The two combined work the rest of the circuit the same way the old single pot did, but because there is no discontinuous conduction, there should be no crackle.

I'll mess with it some on the simulator and see if there are any undiscovered flys in the ointment.

[Papa_lazerous]

You do realise if this works somebody will have to re avertise that control as the "crackle NOT okay"

Just think for one minute about the trouble you have caused 

PS nice work

[R.G.]

I messed with it in the simulator a bit. It works mostly.

It takes some messing to get a tracking current source, but I got it within about 10% of the stock circuit currents fairly easily. The need to use a big cap to DC isolate the AC impedance still causes a step when you move the control fast, but I think it will come out more as a thump than a pop or a crackle, because the speed with which a person can move a control is finite, not almost instantaneous like a wiper crackling. More work to do, but I think it's a good starting place.

[ayayay!]

Someone school me here:  What's a Crackle OK control? 

[tommy.genes]

Someone school me here:  What's a Crackle OK control? 

Quite possibly the most controversial knob in the whole history of effects technology...

See: Zvex Super Hard On

[edit] Oops, I see that this could be read the wrong way. I was literally talking about the knob on the SHO. I was NOT calling Zachary Vex a knob!

-- T. G. --

[jpm83]

Someone school me here:  What's a Crackle OK control? 

Quite possibly the most controversial knob in the whole history of effects technology...

See: Zvex Super Hard On

[edit] Oops, I see that this could be read the wrong way. I was literally talking about the knob on the SHO. I was NOT calling Zachary Vex a knob!

-- T. G. --

That really gave me best laughs today (even when I don't know exactly the double meaning of knob, but I can guess what it is).

Janne

[Papa_lazerous]

Someone school me here:  What's a Crackle OK control? 

Quite possibly the most controversial knob in the whole history of effects technology...

See: Zvex Super Hard On

[edit] Oops, I see that this could be read the wrong way. I was literally talking about the knob on the SHO. I was NOT calling Zachary Vex a knob!

-- T. G. --

That really gave me best laughs today (even when I don't know exactly the double meaning of knob, but I can guess what it is).

Janne

Tickled pink by that remark, you gotta love an innuendo!

[rikkards]

Someone school me here:  What's a Crackle OK control? 

Quite possibly the most controversial knob in the whole history of effects technology...

See: Zvex Super Hard On

[edit] Oops, I see that this could be read the wrong way. I was literally talking about the knob on the SHO. I was NOT calling Zachary Vex a knob!

-- T. G. --

This could be a silly question, but reading up on the SHO it has a 5M impedance, and I recently built a buffer using an Opamp (2nd to last buffer from the top at http://www.muzique.com/lab/buffers.htm)  with two 1M resistors creating the voltage divider into the + input , would changing the 1M resistors to  5M (or even up to 20M) make it better?

I should have thought of trying it out before it was all soldered and I have no spare opamps on hand to see what would happen. Just curious.

[R.G.]

You'd have to know what "better" is to tell.

I'm only half-facetious. Better how? It will produce less treble cut than lower impedances IF you run the guitar right into it. Whether this is enough to be detectable by ear or not is subject to debate, as is whether it's "better".

There are other and probably better ways to get high input impedance than by increasing input bias resistors ever higher. The big resistors make for a lot of thermal noise and other issues.

[rikkards]

I think reducing treble cut was the word I was looking for. I have it early in the chain as the only thing in between is a Fuzzface which has TB and I built more or less as a project than out of necessity. Thanks for the input

You'd have to know what "better" is to tell.

I'm only half-facetious. Better how? It will produce less treble cut than lower impedances IF you run the guitar right into it. Whether this is enough to be detectable by ear or not is subject to debate, as is whether it's "better".

There are other and probably better ways to get high input impedance than by increasing input bias resistors ever higher. The big resistors make for a lot of thermal noise and other issues.

[soulsonic]

I think reducing treble cut was the word I was looking for. I have it early in the chain as the only thing in between is a Fuzzface which has TB and I built more or less as a project than out of necessity. Thanks for the input

You could try using a slightly smaller input cap, like around .047 or even .022. The 1M input impedance will still give you plenty of lows with those values, but it will lean out the bottom end a little bit and possibly make the treble more "present".

[rikkards]

Good idea. I think I may pick up a couple more opamps and proto it and see if it makes a noticable difference to get out the soldering iron.
Thanks for the input!

I think reducing treble cut was the word I was looking for. I have it early in the chain as the only thing in between is a Fuzzface which has TB and I built more or less as a project than out of necessity. Thanks for the input

You could try using a slightly smaller input cap, like around .047 or even .022. The 1M input impedance will still give you plenty of lows with those values, but it will lean out the bottom end a little bit and possibly make the treble more "present".