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Music Student in Need of Help

Discussion in 'Electronic Design' started by [email protected], Jul 3, 2006.

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  1. Guest

    Hi everyone,

    I wish to replace the analog Pots in my distortion pedal with digital
    equivalents so as to control it in real-time from a computer. To
    achieve this, I have purchased 1-wire Maxim Digital POTs -

    The package I have purchased is a 6-pin TSOC.

    The pedal I'm modifying is called a Turbo RAT -

    I have built a few amplifier circuits before, designing and
    constructing PCBs for them in the Electronics department in my college.
    If I remember correctly, the package type of the amplifiers I used was
    called DIP. When building these circuits, I used a socket for my
    amplifiers so that I didn't have to solder on the opamps directly. This
    way handy if the opamp was damaged later on.

    I'd like to do the same again with the TSOC chip but I cant find any
    sockets on Farnell for this package. What would you suggest? Also, do
    people actually solder these devices onto pcb boards by hand? The 6
    pins are so small...

    Also, my plan for the digital POTs is to build a little PCB for each of
    them. I can then suspend each little PCB above the pedal PCB in place
    of the analog POTs. This will give me flexibilty so that I can easily
    remove a POT and attack it to a different pedal - or whatever. The
    1-wire master communicates with the POTs via a RJ-11connection, so I
    will also place RJ-11sockets on each POT PCB. In addition, I will need
    2 terminals on my POT PCB for power and I will also need to include
    drilled holes so that I can wire the 3 POT pins to Pedal PCB. In other
    words, the POT chip will sit in the center of its little PCB board and
    the tracks will run out to the edges as required. How does that sound?
    Is it a good approach?

    Thanks for your help,

  2. 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
    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

    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.

  3. Guest

    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

    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,

  4. 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.
  5. Silicon Laboratories has a good tutorial on hand soldering SMT parts:
    You might need to set up a free account to access this.

    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.

  6. vic

    vic Guest

    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.

  7. Luhan

    Luhan Guest

    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.

  8. Guest

    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.

  9. vic

    vic Guest

    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.

  10. Rich Grise

    Rich Grise Guest

    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

    Good Luck!
  11. Guest

    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 -


  12. TuT

    TuT Guest

    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.
  13. Guest

    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?
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