Modifying an analog stomp box with programmable digital potentiometers.

[grjeff]

    I would like to know if this is possible. To start I want to take an old vintage effects pedal and severely modify it. I will take a Pro Co Rat distortion for my example.
    Here you have a distortion unit, very distinctive in its tone and color and some purist don't want to part with it. Very understandable. So how can we get more capability out of it? In the digital world of preset performance both live and in the studio, by the way I'm always thinking in terms of a live performance. To me it makes since to call up any Madrid of sounds in ones library in real time.
    I used to envision a matrix of multiple FX loops to insert a collection of stomp boxes to be controlled by turning on and introducing each ones sound into the signal path. Many companies have done this in the past and allot still are. So let's say you really like the Rat's sound and you can get many different sounds that reflect different moods for different parts of a song
    One sound at the start of a song might start out with the RAT a little warm, mellow with a slight dirty growl. Then in the next verse, you might want the RAT for a high gain crunchy rhythm. Next, the lead solo comes up so now you need some where in between the first and second sounds but with the volume boosted for the solo. Then finally, to end the song with the first or second sound or even a fourth sound altogether.
    If you look at what I was saying earlier, you would need first a programmable multichannel FX loop or a series of ABY boxes under programmable control. Second, I talked about one song with possibly four different sounds from a Rat. All you would do is purchase four Rat units and put each on in its own loop channel. Then adjust each Rat for its own different sound.
    Once that's done you now can call up any one of four different Rat sounds at any time. Pretty cool huh.
    Well I'm rethinking of a more efficient way of doing this from just one Rat. What if it was possible to remove the potentiometers from the Rat, you have one. Volume 2. Tone 3. Distortion amount or gain and four. A foot switch for on/off. Four different variable parameters. Now remove them and replace them with a programmable digital equivalent.
    The volume, tone and gain are now replaced by programmable pots and each of the pots can be adjusted but the turning of the pot makes a voltage value that is interpreted by a micro controller. Once you get the desired sound you can store it in a nonvolatile EEprom so it can be saved and called up for later use.
    Sure, you may need to take the guts out and mount them in something bigger but from this point you now have programmability limited only by how many bytes of memory you have in the EEprom and how many sounds a Rat can make. From there it should be fairly simple to incorporate it under MIDI control.
    The only other thing I want to account for is the possibility or fear that this modification may not be as transparent in tonal characteristic as it was in its original state. However, the beauty of engineering is to find crazy ways to make things work. Therefore, if a mod like this somehow causes a loss in its vintage character then maybe it's possible to compensate the loss by adding capacitance or inductance in certain areas of the circuit. To maintain that old tonal quality. But to get that small and in-depth in the subatomic world of RF you'd need a decent network and/or spectrum analyzer$$$