[Pics] Alesis Bitrman expression pedal mod, + mad noise reduction

[Processaurus]

my B.U.M. (blind urge to mod) came to fruition with this one.  Those that don't know already, the Alesis Bitrman is a (sadly discontinued) cheap plastic digital processor intended for DJs.  Its got the bitcrusher, sample rate aliaser, ring mod, frequency mod, and the frequency shifter (I initially got it for the frequency shifter).  The "bitr" knob controls the parameters for these effects.  To guitar-ize it, a while ago I made a stompable TB box with a volume control for the loop (because the Bitrman has no volume control, yet has huge amounts of gain  , plus I suspect it has the AD/DA going even in bypass), and recently got more motivated about the project and removed the remote footswitch jack to make an expression jack, to control the Bitrness with a gutted crybaby. 




The jack is a stereo jack with transfer switching for the tip, this allows it to funtion normally without something plugged in.  The way its wired, when the pedal is plugged in, the Bitr pot controls the maximum limit of how far the rocker pedal can sweep, and the minimum pot in the pedal does the minimum, so you can get just the section of the sweep you want. 



Plus, the programming makes it so when the 'bitr' knob is all the way down, you bypass the current effect.  So you can be playing normal, sweep the rocker pedal down and get the most sci-fi ring mod sweep, pull it back, and its back to normal.  Its really... neat.

I had trouble squeezing the switchcraft jack in there, they mash another PCB on top of the jacks, so to get it done and not have to order a special jack, I hacksawed a big square notch in the bottom PCB for it to sit down a little, and consequently re-route a SM resistor.  A bit of a pain in the ass, but not too bad.  If one had a Cliff stereo jack (all in there where mono, unfortunately), you could probably stick it on upside down dead bug style and have enough room.  Its definitely tight though...

Random note:  To take it apart, you need a deep socket set (metric if you have it) to get the nuts on the pots loosened, because they're way down in a hole.  That, and the screw on the bottom, and you lightly pry the plastic sides away from the metal bottom plate to pop the hood in these. 


When I put it together, I noticed the whine.  It had been there before I opened it up (I could reduce it if the input was from a low impedance source, ie a buffered pedal), but when it was apart it was quiet as a mouse.  As I put the top on (which has the PCB with the processor on it) the whine creeped in.  Hmmm.  All the analog stuff was on the bottom of the PCB, under a ground plane, but wait, the input jack is exposed, and stuck a fraction of an inch away from the main processor, and is probably going to a high impedance input stage.  A bit of a bad design, which is strange given the attention to all the ground planes in PCB design.  I remembered the boss tuner then, and how the input had a tin "hood" around the jack to shield it from the digital chirps of the tuner circuitry.  So the solution was to stick this rusty piece of tin (covered in tape on both sides) with a wire soldered to ground. 


Auugh, but it doesn't close...  so finally i punched little holes (after the picture was taken) for the plastic nubs on top of the jacks to fit through the metal, and finally it all goes together with a "click".  Test it, and its ohh soo quiet.  Sweet, but dang, what happened to my evening...

[Processaurus]

Oh yeah, with the zener diode to limit anything coming in, I think its safe to put an external 0-5v CV in.  I wonder if I should put a reversed biased diode to shunt any possible negative CV voltages to ground, on the jack?  Might be the safe thing to do.  A sequencer would pretty much have to sound great on this...

[ExpAnonColin]

You can also just use a BOSS EV-5 10k pot (or assumably higher values), and wire a switched stereo jack, after cutting the legs of the pots on the board.

-Colin

[Processaurus]

You can also just use a BOSS EV-5 10k pot (or assumably higher values), and wire a switched stereo jack, after cutting the legs of the pots on the board.

-Colin

Definitely, the value of the pot is unimportant as long as it isn't so low it loads stuff down.  The boss POS would be be better than the crybaby, because the  crybaby's pot is a weird taper, I imagine the boss to be more linear.  Why they gotta be $40?  Is there a decent plastic expression pedal out there for ~$25?