Modulated Big Muff Tonestack using 2 LED/LDR combos and an LFO

[frequencycentral]

This is something I've wanted to try for ages, and just got around to it today.

I've got some homemade vactrols, LED/LDR combos encased in black electrical tape. Using two, I put one in parallel with lugs 1 and 2 of a BM tonestack, and another in parallel with lugs 2 and 3.

LFO's usually peak and trough a few volts either side of +ve and ground, therefore it's possible to fix up two rate LED's, one to show the peak of the waveform and one to show the trough of the waveform. They'll flash on and off alternately.

So I ran the output of an LFO via a 1K resistor into the anode of one LED, and connected the cathode to ground. I ran the output of the same LFO via a 1K resistor into the cathode of the other LED, and connected the anode to +ve. Therefore, as one LED fades in, the other fades out. So as the resistance of one side of the tonestack was decreasing, the other side was returning to its maximum. The position of the tone control pot itself defines exactly how much effect the sweep has at either end of the tonestack.

I don't have a schematic to share ATM, having just performed the experiment. The LFO I was using was perhaps not the ideal one for the job. I imagine an LFO with some funky waveform options would work really well.

I've also no soundclips to share ATM, but get a friend to wiggle your BM tonestack insanely - you'll get the idea!

The pedal I performed the experiment on was this one: http://www.diystompboxes.com/smfforum/index.php?topic=71050.0

Just wanted to share!



EDIT: Thinking about it, I guess you could use this same method to modulate any control of any pedal that's configured as a voltage divider.....................

[frequencycentral]

As the LDR's effectively half the value of the 100K tone pot, it would probably be a good idea to double the value of the tone pot. The pedal I used for the experiment has a quite extreme version of the tonestack, it would be interesting to calculate a really extreme tonestack using Duncan's. I'm going to play with this idea a little more. It strikes me that the sluggish response time of LDR's might lend itself to square waves (which teh LDR's would round off a little) rather than triangle or sine. S/H would also be an interesting possibility.

[frequencycentral]

Just thinking out loud. Using a similar LED/LDR arrangement to modulate the bias control of a Phase 90 (or Phase 180) would eliminate the need for the FET's (and FET matching). Or am I wrong?

[gigimarga]

Very interesting ideea...I'm waiting for some soundclips, anyway

[Morocotopo]

Wouldn´t it be faster and easier to just hire a guy to tweak your tone control knob? Human LFO! Infinitely variable waveform!



Good idea, I think most pedal circuits could have some sort of "modulated parameters", they would be much more interesting.

Sounds, please!

[frequencycentral]

Wouldn´t it be faster and easier to just hire a guy to tweak your tone control knob? Human LFO!

The guy I use to hire to do this was an ex-drummer, so no two sweeps were ever the same.  

On a more serious note, I'm going to do some more work on this idea soon, experiment with different LFO's and waveforms.

[petemoore]

As the LDR's effectively half the value of the 100K tone pot, it would probably be a good idea to double the value of the tone pot.
  That could be true, could be that the effect it makes is desirable...starting with the bigger value pot makes sense, it can be trimmed down, you can trim a pot 'up in value.

[petemoore]

  How's this coming along ?
  Is it chunky? Or do the LDR's slow the squared input off enough to make it smooth ? How do you like your peanut butter by the way ?
  When you say 'homemade', that'd be just some photocells layin' around or did you buy some 'spec' ones > did you measure the light/dark resistances ?
  Any other schematics of LFO's considered or used ?
  Did you need something to augment the LFO current drive to the LED's ?
  Seems like it could be a neat effect, a lot of possibilities and variability would require making experiments and choices I would guess.

[frequencycentral]

Hi Pete,

No new developments on this, I just did it as an experiment last weekend. It's 'filed' for future experimentation. Here's the schematic of what I did:



The fuzz part is based on the Colorsound One Knob Fuzz, then a BM tonestack and gain recovery stage. The LDR's are: typical dark resistance = 1M, typical light resistance = 2K - 4K. Each of the two LED/LDR combos is mounted on a tiny piece of perf (2x8), with the LED and LDR bent over to face each other. Then wrapped in black electrical tape to keep light out. The leads of the LED and LDR poke out of the bottom, so it's easy to plug into a breadboard.

As I said, I'm less than satisfied with the LFO for this application, as it kinda tails off at faster speeds, but the essence of what could be done was demonstrated.

[Taylor]

So I'm imagining this sounds sort of like a bass-treble panner rather than a usual filter sound, am I right?

[Ben N]

Wouldn´t it be faster and easier to just hire a guy to tweak your tone control knob? Human LFO!

The guy I use to hire to do this was an ex-drummer, so no two sweeps were ever the same.  .

Geeky DIY-er drummer jokes! I love it! (May be as important a development as the LFO-controlled Muff stack.  )

[petemoore]

  Boiled down nicely !
  Thanks for sharing the schematic !

[mac]

Wouldn´t it be faster and easier to just hire a guy to tweak your tone control knob? Human LFO! Infinitely variable waveform

DJ do this.

mac

[frequencycentral]

Bump!

(You saw it here first - before Slade is about to steal it and claim it as him own.  )

[Slade]

Bump!

(You saw it here first - before Slade is about to steal it and claim it as him own.  )

Too late, old man... You know what they say about great minds...

[frequencycentral]

Bump!

(You saw it here first - before Slade is about to steal it and claim it as him own.  )

Too late, old man... You know what they say about great minds...

Go @#$% a llama young'n.... 

[Earthscum]

I like how this was done... I tried something I thought was gonna be the same before I saw your schem.

What I had toyed with was varying the filtering resistors, which swept the notch back and forth (almost, but not quite "phaser-ish"), and then the knob acted like a blend... almost seemed worth throwing into a wah shell. Now I wonder how this would sound paralleled with what I had. 

When I pulled the LDR off the resistor for the LP side and set it, it made a kind of funky deep notch to bump tremolo that sounded pretty neat, as well.