need stupid simple suggestions for putting a pot under lfo control

[pinkjimiphoton]

dicking around with yet ANOTHER fuzz, (of course)
and i wanna put the tone pot under lfo control...it just sounds cool when its swept over the first half of its range, so i wanna make it so i can hit a second footswitch and have it just sweep up n down in a basic sine wave. i figure the tone control already would control the range of the sweep, so i'd need to have the speed of the lfo and a depth control for it added...
first thing that comes to mind to me is putting an ldr across the bottom of the tone pot, and using the lfo to light an led or small incandescent bulb  flashing to control it.
but there's like, a gazillion ways to do this, and we all know i'm about as bright as your average blown led, sooo.... figured i'd put it to you guys to hopefully guide me to some good circuits to look at.
the fuzz is just a bone-stock fox tone machine circuit pretty much with a couple tweaks <1n270, matched, for the octave part, and 1n60, again matched for the clipper, and low gain si q's, 2n7904 with the b n c connections twisted to fit the board>

first thought is tim escobedo's circuit snippets... but i wanna do this
cheap
eloquently
small parts count

sooooo figure screw it, i'll ask if there's any better ways to do this. it sounds ridiculously good, but i can't afford a roadie to sit there and spin the knob all the time for me.

so... suggestions?

thanks fam

[ElectricDruid]

If you're going for "stupid simple", I'd go with the LDR/LED like you suggested originally. And I'd drive it with a StompLFO to save mucking about with any kind of LED driver. That'll do a sine wave no problem. Other wave shapes are then a bonus.

You'll probably have to experiment with where you put the LDR. You could do like you suggest and stick it across the bottom of the pot, or you could parallel it up across the whole pot. If the pot only uses two legs (e.g. used as a variable resistor not potentiometer) then you could replace it with the LDR entirely (or LDR with parallel fixed resistor to get the range right), and then use the Offset CV on the StompLFO to control it when the LFO depth is turned down to zero.

HTH

[iainpunk]

that bridged-T tonestack is a real picle to graft an LFO on to, since its not a resistance to ground.
i think that a LDR and a uni-vibe style LFO are your best option. unless you like endlessly dicking around with a Jfet to get it to work and bias just right.
cheers, Iain

[pinkjimiphoton]

If you're going for "stupid simple", I'd go with the LDR/LED like you suggested originally. And I'd drive it with a StompLFO to save mucking about with any kind of LED driver. That'll do a sine wave no problem. Other wave shapes are then a bonus.

You'll probably have to experiment with where you put the LDR. You could do like you suggest and stick it across the bottom of the pot, or you could parallel it up across the whole pot. If the pot only uses two legs (e.g. used as a variable resistor not potentiometer) then you could replace it with the LDR entirely (or LDR with parallel fixed resistor to get the range right), and then use the Offset CV on the StompLFO to control it when the LFO depth is turned down to zero.

HTH

i like the way you think, bro... it would certainly seem to simplify it. i only really need to modulate the bottom half of the tone control to get that pseudo vibe effect, so it may well be worth looking into. for a one off, definitely...
that's why i was thinking just paralleling the "bottom" side of the pot with an ldr... figured i could use the rest of it to set the "range" where it happens. gonna need to read the data sheet on the tapflo, looks like all i'd need to do is add a regulator, the chip and an led to get something functional... my only concern is cost, but even at 4 euro its not prohibitive... i'm just cheap as hell tho

[pinkjimiphoton]

that bridged-T tonestack is a real picle to graft an LFO on to, since its not a resistance to ground.
i think that a LDR and a uni-vibe style LFO are your best option. unless you like endlessly dicking around with a Jfet to get it to work and bias just right.
cheers, Iain

thanks iain!
i'm not REALLY looking at it as a resistance to ground, just as a variable resistance. i figured a variable resistance in parallel to the bottom half of the pot should do the trick, or am i wrong?
to go thru the hassle of doing a univibe style circuit seems like overkill. i'm looking for cheap, easy, low part count stuff my dumb hippy brain can work with.
i make a mean fuzzbox, but.... no idea what any actual theory is or anything. monkey with a breadboard here lol.

all i need to do is make the bottom half of the tone pot wiggle. seems to me adding a parallel resistance to it should do the trick, especially with it NOT going to ground.

am i getting this thru my thick skull a little? please be gentle, i am but an egg... a very old, very smelly egg, but an egg, just the same

[iainpunk]

that bridged-T tonestack is a real picle to graft an LFO on to, since its not a resistance to ground.
i think that a LDR and a uni-vibe style LFO are your best option. unless you like endlessly dicking around with a Jfet to get it to work and bias just right.
cheers, Iain

thanks iain!
i'm not REALLY looking at it as a resistance to ground, just as a variable resistance. i figured a variable resistance in parallel to the bottom half of the pot should do the trick, or am i wrong?
to go thru the hassle of doing a univibe style circuit seems like overkill. i'm looking for cheap, easy, low part count stuff my dumb hippy brain can work with.
i make a mean fuzzbox, but.... no idea what any actual theory is or anything. monkey with a breadboard here lol.

all i need to do is make the bottom half of the tone pot wiggle. seems to me adding a parallel resistance to it should do the trick, especially with it NOT going to ground.

am i getting this thru my thick skull a little? please be gentle, i am but an egg... a very old, very smelly egg, but an egg, just the same

yeah, an LDR from the middle to the lower leg of the pot should do the job, the only criticism i have it that the center frequency is going to change as well if you change the resistance of the pot, but i don't think is makes that huge of a difference.

you could build a wah treadle. or a system like that fluid tremolo from this thread

Back to topic, as far as I know two very first "effect boxes" ever were a volume pedal, simply titled "Volume Pedal", and an electro mechanic tremolo effect, titled "Tremolo Control", from DeArmond. Both manufactured by Rowe Industries in the early 1930's. The latter, initially a carry-on effect, was refined to foot-operated form in circa 1948.

I think I need one now!

cheers, Iain

[pinkjimiphoton]

thanks iain!
i'm not REALLY looking at it as a resistance to ground, just as a variable resistance. i figured a variable resistance in parallel to the bottom half of the pot should do the trick, or am i wrong?
to go thru the hassle of doing a univibe style circuit seems like overkill. i'm looking for cheap, easy, low part count stuff my dumb hippy brain can work with.
i make a mean fuzzbox, but.... no idea what any actual theory is or anything. monkey with a breadboard here lol.

all i need to do is make the bottom half of the tone pot wiggle. seems to me adding a parallel resistance to it should do the trick, especially with it NOT going to ground.

am i getting this thru my thick skull a little? please be gentle, i am but an egg... a very old, very smelly egg, but an egg, just the same

yeah, an LDR from the middle to the lower leg of the pot should do the job, the only criticism i have it that the center frequency is going to change as well if you change the resistance of the pot, but i don't think is makes that huge of a difference.

I think I need one now!

[/quote]cheers, Iain
[/quote]

man i'm SURE i @#$%ed up the quotation thing.... lol....

but changing the center frequency of the filter if ya turn the knob is actually what i'd consider a FEATURE, cuz it would let ya set the "range" over where the sweep happens, no?

this is looking more n more like it could happen. the tapflo would be easiest i think.

but what about using the wobbletron circuit? would that work, or....

[iainpunk]

but what about using the wobbletron circuit? would that work, or....

yes, it would work but then i quote myself:

unless you like endlessly dicking around with a Jfet to get it to work and bias right

[PRR]

Varying tone is just tremolo working on half the audio band. Look at various tremolos and wonder how you can get treble-only action. Or bleed bass around it.

[pinkjimiphoton]

hi paul!

yeah, not really necessary with this one... like iain said, its a weird kinda tone control. the main thing is, all it needs to do is vary the resistance of the tone circuit. i've looked at a lot of trems and oscillators and led-make-blinky things over the years, not that i UNDERSTAND an iota of it

that's why i'm looking for bonehead simple, preferably with crud i should already have on hand. pretty sure once i get the blinky blinky happening and can control the brightness and rate, the ldr should be able to do the rest. that's about the simplest i can think of.

i DID do a two transistor trem years ago that would likely work. but i need a low parts count, so i can stuff a daughter board in and mod the circuit. i expect it to give me endless trouble cuz, well, its me, so anything with modulation is gonna break my bawls. lol

[11-90-an]

Here's my idea...

Wobbletron lfo, instead of depth lug 2 going to and LED+, LED- to ground... (maybe would need a buffer but i'm not sure). you can even use the original 'status' led.. no depth control though...

Tack an ldr in parallel with yer tone pot lugs 2 and 3... or 1 and 2, dunno...

Shine light from led to ldr...hopefully should work

[pinkjimiphoton]

even easier. not the wobbletron, but the bearfoot fx magnavibe. should work perfect, i think...
low parts count, all crap i should have on hand... based on the wobbletron, but it works (unlike the wobbletron)




i gotta build a run of pedals today, will try n get to this over the next day or three to see how it works out. with a little luck.... i'll have kewl nuuz.

stay tooned....

[mdcmdcmdc]

even easier. not the wobbletron, but the bearfoot fx magnavibe. should work perfect, i think...
low parts count, all crap i should have on hand... based on the wobbletron, but it works (unlike the wobbletron)




i gotta build a run of pedals today, will try n get to this over the next day or three to see how it works out. with a little luck.... i'll have kewl nuuz.

stay tooned....

Necrobump but I'm curious if this worked out? I'm interested in trying something similar—adding auto-sweep to a pot that's being used as a variable resistor.