Music Student in Need of Help

Why would you want to manually have to change the pots each time? Are you trying to get both analog and digital control of the pedal?

You could easily make an interface that converts the pedal to allow for digital control by using the digital potentiometers with a microcontroller and have an digital output interface(even make it midi compatiable if you wanted) to control the pots and switches digitally. The problem would mainly be that you would have to make an enclosure that will be able to whole the new circuitry if you want it to look professional.

The way to do it would be to use a pic and its built in ADC's to sample the pots on the pedal and use them to control the digital pots if it is in "analog" mode else to get the info from the computer. Conceptually its not that hard

1. Replace analog pots with digital pots.
2. Use a MC to interface the computer or the analog pots to the digital pots.
3. Write software.
4. Create new enclosure for circuitry.

You could even create your own little "midi" like control language so you could daisy chain pedals. Note that your power requirements would increase though.

What I'd suggest, if you want to get more into it, is simply design a new circuit that includes the circuit of the pedal with the new digital circuitry and implement it all on a new PCB. It would be much more fun and more professional. You might even be able to sale the pedals if you wanted.

You could also add a lot of "extra" features such as allows for additional controllable circuit elements. For example, in the clip circuitry of an distortion pedal you could use relays to add or subtract more diodes for addition clipping effects or even asymmetric clipping. You could do the same with digitally selecting different op amps, etc... You could get real crazy and have tons of controllable features(which means tons of new sounds) in a single pedal.

Jon

I will be removing the analog POTs so I wont be controlling the pedal manually - no anlog control in other words. I will be controlling the pedal via my computer and using a C program (interfacing to MAX/MSP via MIDI) to adjust the pedal settings in real-time in order to apply analog effects to my sound. I hope to use this pedal in a composition I'm writing for my thesis. Thanks for you suggestions! For now though, I wan't to keep things simple because I need to establish if my idea is going to work or not. If it doesn't, I'll need to look into alternatives.

Anyway, any suggestions regarding my question about TSOC sockets? How does my design sound? I'd like to build my own pedals, but I'll wait untial after my thesis deadline when I'll have more time to do so.

Thanks again for your help,

Barry.

If you just want to be able to control the effects electronically why not use a simple motor that hooks up to the analog pot(sorta like a gear). By using a microcontroller you can supply power to the motor(a servo would work best). This would be the quickest way IMO to do what you want and wouldn't require messing with the internals of the pedal. The hardest part about this would mechanically interfacing the analog pot with the motor. You could just "glue" and it might work or you could do it a little more advanced. Most of the software to do this can be downloaded and you only have to do a little tweaking and write the computer to controller interface(and midi would probably be the easiest because you won't have to worry about the software on the computer but just implementing a simple midi interface with the MC).

I'm not sure if they make sockets for the TSOC. The only ones I have seen are SOIC, PLCC,DIP, and there variants. Have you thought about "bending" the pins down to make it dip like or seeing if it could work in a dip socket(some have "shoulders" that might work if the ic is the correct size but it might not get a good connection). Or you could just by some extra's and try to soilder them. It is possible and shouldn't be that hard if you have a decent iron with the right tip.

Silicon Laboratories has a good tutorial on hand soldering SMT parts:

They have a tiny 28 lead part that has 0.5 mm (0.02") lead spacing. The TSOC is 0.05". I have hand soldered this type of part and it wasn't too difficult.

Also, check DigiKey or Mouser for "Surfboards", which have SMT pads and can be used as adapters to SIP or DIP.

The sockets I have found for fine pitch SMT parts are very expensive and usually used for testing and burn-in purposes.

Paul

Wouldn't the "steps" of the digital pot pose a problem for an audio application ? There will probably be an audible click at each move of the wiper.

vic

I've used the Microchip MCP41010 256 step digital pot that comes in a DIP-8 package. They come in 10k, 50k, and 100k versions and have the standard I2C interface.

Luhan

Yeah I've been thinking all along that this might be a problem. This is the circuit I'm hoping to modify -

You can see the 3 pots on it. I'm not really worried about the volume pot because I can control that on the PC. But couldn't I low-pass filter the stepped POT voltage? I don't have any real electronics background but I'm familiar with the concept of a RC lowpass filter. I'm not sure though how to do this for the circuit above because its simply too complex for my limited knowledge.

Anyway, I'd appreciate any advice you could give me.

Barry.

I'm not sure ... What is the spectrum of a single straight voltage increase or decrease ? Probably something centered around 0Hz so you may be able to filter most of it using a high pass filter with a low cut frequency (below what the human ear can detect). I really need someone to check this :)

The best thing to do would be to use a zero-cross detect circuit. I know some digital pots include one, but not the one you have in your possession it seems.

vic

A piece of rubber tubing over the shafts. RC servos are easier than a rat to control, but I don't know if you can get one with 270 degree rotation.

Good Luck! Rich

I've actually bought the digital POTs and a USB interfaxce to work with them so if any can offer my advice on using these POTs to control this circuit then I'd be very grateful -

Digital POT -

Thanks,

Barry.

The pots used in the pedal are log, whilst the Maxim part you indicate is linear, which will cramp all the adjustment at one end and also compromise adjustment resolution.

Have a look around the Maxim website - they do some log versions.

Not yet. Anyway, I'm not too worried about that issue. I can see how it works when I build the circuit. The stepping though is of concern to me. Any suggestions?