Running guitar effects at 5 volts

[Transmogrifox]

I think you have to take each of your FX one at a time as you work through this.  It's too complex to give a general answer.

The most general I can give you is that, yes, you can do this.  You can probably re-design most circuits to work with a digital pots in some capacity.

As for whether you are concerned about pushing the button on ordering digital pots -- this is going to be a trial-and-error R&D exercise.  It's going to take time and cost money.  If you are worried about the cost of your first order of digital pots being too much, then don't even start.  It will cost you a lot more than that by the time you have succeeded.

If you can afford to fail on the risk that the digital pots won't work out the way you expected, then order the damn things and get to work figuring out how to make this happen.

As for digital control of analog circuits, you will probably find there are a lot of different ways to skin this cat.  You may find that you will need to employ different strategies in different places to get the desired result.  One circuit at a time, one pot at a time...

[JustinFun]

Use 1N4001 (or other silicon) diodes in the charge pump rather than 1N5818 and you'll get more voltage drop, bringing you closer to 9V.

Be aware that the charge pump is limited in output current - maybe 100 mA ? - so even if you have a higher amperage USB charger, the output of the 9V pump will be limited.

Thanks, that's really helpful. Looks like max current is 160mA from the data sheet, so i'd probably need to run 2 or three to form a pedalboard supply (i'm thinking one unit per 2 outputs, running all of them in parallel with the input voltage).

[joakinrox]

I think you have to take each of your FX one at a time as you work through this.  It's too complex to give a general answer.

The most general I can give you is that, yes, you can do this.  You can probably re-design most circuits to work with a digital pots in some capacity.

As for whether you are concerned about pushing the button on ordering digital pots -- this is going to be a trial-and-error R&D exercise.  It's going to take time and cost money.  If you are worried about the cost of your first order of digital pots being too much, then don't even start.  It will cost you a lot more than that by the time you have succeeded.

If you can afford to fail on the risk that the digital pots won't work out the way you expected, then order the damn things and get to work figuring out how to make this happen.

As for digital control of analog circuits, you will probably find there are a lot of different ways to skin this cat.  You may find that you will need to employ different strategies in different places to get the desired result.  One circuit at a time, one pot at a time...

Yeah, I think that's the approach I'm gonna have to take. So far I think I'm going to try the following:

a)-Multiplying DACs for Volume Output Pots or Gain pots that are wired as a voltage divider before the first stage (As their output is buffered)
b) -Digital potentiometers for voltage dividers stuck on places like tonestacks.
c) -1 LDR + Led combo controlled by PWM for variable resistors (like for example a feeedback resistor of a opamp)
d) -2 LDRs  controled by 2 different LEDS in PWM mode to "make" voltage dividers with resistances higher than 100k (as pots larger than 100k can't be found for 9 volt operation or are too expensive)

The hardest part of this will probably be calibrating the LDRS to ensure consistency. I'm thinking of two aproaches:

-Try mapping various curves of their resistance at different duty cycles at several temperature conditions  and switch to a determinate curve based on temperature. This would mean using a temperature sensor (LM75?)

-Measuring the resistance of each LDR with the analog pins of the uController, and adjusting the duty cycle of the leds dynamically. this would probably involve some kind of algorithm to take the slow response time of the LDRs into account (that I'm frankly not sure I'd be capable of implementing)

[ElectricDruid]

I agree completely with Transmogrifox - all extremely good advice.

I'd just like to add one thing; I expect you've got a microprocessor of some sort in this system, since you're talking about adding memories and DACs and PWM and so on.
So given that there's a processor in the circuit, don't underestimate what you can move into the digital domain directly. For example, rather than use a uP to control two digital pots to control rate and depth of an LFO, why not generate the LFO signal in the uP directly and output it from there to the rest of the analog audio circuitry? You don't have to mess with your analog signal path, but you can save yourself considerable circuit complexity by rolling some of it up into code inside the processor. If one of the circuits is a PWM phaser, why not generate the LFO-modulated PWM signals directly in the processor? If it's a flanger, generate the LFO-modulated biphase clock in the processor. Or the do the same/similar for chorus.
Obviously if all the circuits are Fuzzface variants this approach won't be so useful...
HTH,
Tom

[joakinrox]

Guys, I found some Intersil pots (quite cheap, around 1 buck a piece);

https://www.intersil.com/content/dam/Intersil/documents/x9c1/x9c102-103-104-503.pdf

I read on the datasheet that these pots can handle +/- 5 volts with respect to the VSS pin, so could i power the pot at this to handle a 0-9 volts signal?:  by powering VSS at 4.5Volts and VCC at 9 volts? this would make 0 volts = -4.5   and 9 volts +4.5 right?

but now, if i do this i would have to shift my control signals as well right? I think 0-5 volt control signals would not work if my chip is powered from   4.5 to 9 volts right?

[ElectricDruid]

Guys, I found some Intersil pots (quite cheap, around 1 buck a piece);

https://www.intersil.com/content/dam/Intersil/documents/x9c1/x9c102-103-104-503.pdf

I read on the datasheet that these pots can handle +/- 5 volts with respect to the VSS pin, so could i power the pot at this to handle a 0-9 volts signal?:  by powering VSS at 4.5Volts and VCC at 9 volts? this would make 0 volts = -4.5   and 9 volts +4.5 right?

but now, if i do this i would have to shift my control signals as well right? I think 0-5 volt control signals would not work if my chip is powered from   4.5 to 9 volts right?

You'd have to power the rest of the logic from your 4.5V to 9V power supply too, yes. If you're shifting your ground, you need to be consistent. Otherwise it won't work, and would probably fry something.

What you've effectively done is create a +/-4.5V bipolar supply (as we often finish up doing in pedals, actually). You're then running the logic on the "upper half" - 0V to 4.5V.

HTH,
Tom