5v Fuzz Factory

[stoopkid]

I made a fuzz factory, then just for fun I decided to try a digitally controlled fuzz factory with presets and whatnot. I got a 10k six channel digital pot to control the 5 pots on the schematic(stab and volume being half the resolution as they only go to 5kohm). I got it all wired up to test and it freaked out my micro controller. Turned out that the digital pot was only meant to use up to 5v, even for the lines it was controlling. I can't find a lot of info on the digital pots that do control >9v so while thats an option I want to be sure what im going to do before I start. I remember once seeing a schematic for a fuzz factory that used less than 9v. I know that the stab controls voltage so simply reducing the voltage of the circuit wont do, but i think that this schematic was calibrated for lower voltage or something. I cant find it now though. But anyway, is there any way to have a 5v fuzz factory that acts the same? Or is anyone aware of this schematic?

[Taylor]

This is not something I'd ever do, specifically, but I'm subscribing because it's an interesting topic. I can't think of a way to properly simulate something as erratic as the FF.

Out of curiosity, what 6 channel digipot do you use?

[WhenBoredomPeaks]

I have done things like this with an Arduino and an AD5206 digi-pot (there were an SPI library released "recently" for Arduino, but when i started you had to code SPI commands in moonspeak)

The biggest limitation is the 5v thing and noise, you are not supposed to send audio through a digital pot. It is probably good for substitute the voltage sag and bias pots but for volume control and things it is not good. So use microcontrollers and LEDs with LDRs instead of digipots when you want to control audio signals..

[Jaicen_solo]

That's what i'd do, add five optocouplers to replace the five pots.
If you get it working, I can see Zach being interested in it. Imagine a programmable FF, with a second stomp switch to scroll through presets. Very useful, particularly if you want repeatable results.

[WhenBoredomPeaks]

That's what i'd do, add five optocouplers to replace the five pots.
If you get it working, I can see Zach being interested in it. Imagine a programmable FF, with a second stomp switch to scroll through presets. Very useful, particularly if you want repeatable results.

That is what i wanted to do but with an EQ but i abandoned the project at that part where i had to make voltage dividers acting similar to a real pot with only one changeable element. (the LDR.) With a pot, both resistor's value changes as you turn the knob but with one LDR yo can change only one side. It is not a real big problem but balancing an LDR/ fixed resistor combo to act at least semi linear and stuff looked like too much of a hassle.

On the other hand in the FF 4 of 5 pots are variable resistors so that circuit is more suited for this idea.

[stoopkid]

aha, I thought that LDR thing was crazy first time I heard it, now I get it. Is there a "right" way to do it? Like any tutorials or anything? Can I just use PWM on the LED's and wrap them together so they don't interfere?

Sorry for the delay, you guys are being really helpful. I was getting kinda pessimistic with this whole project until now.

[stoopkid]

Ok wait, I do have one question. How do I replace a pot with an LDR in a circuit where for instance one end of the pot is going to the signal, the other to ground and the wiper to my output(volume). It seems to me like I would need two LDRs working opposite if eachother. Or is there another way?

[earthtonesaudio]

None of the pots really has to be a pot.  All of them can be approximated with 2-terminal variable resistors.  The Drive control is wired as a pot but you could replace that pot with a 10k fixed resistor and then add a variable resistance in series with the 10uF cap.  The volume is the more problematic, but you can get close enough with one series resistor and one shunt (to ground) resistor, and vary one of them to get volume control.  Probably would be best to vary the shunt to ground resistor and have a fixed series resistor.

You can make a potentiometer with two LEDs and two LDRs, but why bother if you can get by without it?

I am speculating but it seems possible to control 5 LEDs with one PWM output.  The edge of each pulse would advance a counter which in turn cycles a multiplexer.  That multiplexer passes the pulse to an LED, and then the pulse width determines LED brightness.  Of course the max brightness you can get is now 20% of what you could get if you were driving only one LED per PWM, but that may be good enough for this purpose.

[edit]
The serial PWM to 5-optocoupler idea works in simulation.  Each LED's maximum current is limited by the 100 ohm resistor, and can be on from zero to 25% of the time, resulting in 0-25% brightness.  It might make more sense to invert this so the LEDs are on 75-100% of the time, since in the fuzz factory we typically want the resistance values to be near zero rather than many hundreds of kilohms.
link

Of course, if you have 5 PWM outputs available from your uC, you can PWM each LED directly, no need for the multiplexer craziness.

[stoopkid]

Ok I have more questions now about this now.

Basically, how do I get 0-10kohm or 0-5kohm out of a LDR? I know how to use a voltage divider to adjust voltage from 0 to max and how to calculate that resistor, but I have no idea how to use it as a more precise variable resistor.

[earthtonesaudio]

CdS photocells can be varied (depending on the particular component) from a couple hundred ohms up to several hundred k.  Put the LDR in parallel with a 10k resistor: 300 ohms in parallel with 10k is about 290 ohms, and several hundred k in parallel with 10k is very close to 10k.  So your new range is ~300 to ~10k.  Real-world pots get weird near "zero" resistance anyway so this approximation may not be too far off what you get in a FF built with actual pots.

[stoopkid]

Ok, cool i got it going from aprrox 0-10k ohms BUT it's ridiculously non-linear... Do I just have to try to fix that with programming?

[earthtonesaudio]

Hm... some more details about your setup would be useful.  Are you sending the LED a voltage or a current?  Brightness should be somewhat proportional to current, but exponential with voltage over a very small range.  Or is the LED getting a PWM signal?