EHX TubeZipper modding

[DavidMP]

So... I have made a mod to my TubeZipper so I can use the Over Drive (OD) and the Envelope Filter (EF) separately and thought somebody out there might also want the do the same.

The pedal is true bypass but it is done in a slightly different way. The stomp switch controls the current through the coil of the relay and this switches the signal path.
You can manually turn the OD off by turning the "drive" knob completely counter clock-wise and the EF by turning both the "sensitivity" and "resonance" knobs the same way.

So the mod is very simple and uses two 3PDT stomp switches in the following manner:

OD: The "drive" knob is a ganged pot connected to the spots marked as "H", "I", "J" and "K", "L", "M" on the board. I de-soldered "I" and "L" (the wiper connections) and connected them to the common of a switch pole each. I then connected one end of each pole to the wiper (lets call this end "a") and the other ("b") to the pot ends connected to points "J" and "K" respectively.
The "power" red LED anode ("B" on the board) I connected in series with a 133k resistor and then to the common of the third pole; I connected end "a" to the ground point "A".

EF: The "sensitivity" knob is connected to "X" and "Y" (bridges wiper and one end of the pot); I de-soldered "Y" from the wiper and connected it to one switch pole common, returned it through "a" to the wiper and through "b" to the other end (the one connected to "X").
The "resonance" knob is connected to "T", "U" and "V"; I de-soldered "U" from the wiper and connected it to another switch pole common, returned it through "a" to the wiper and through "b" to the other end (the one connected to "V").
I changed the "status" LED for a blue LED, connected its cathode to the red LED cathode and the anode to the common of the third pole; I connected "a" to ground.

I also changed the "frequency" LED for a white one just for looks.

The 133k resistor compensates for the difference in internal resistance between the blue and the red LEDs so both will light up when both switches are on; it still allows enough current to pass through either one to activate the relay turning on the pedal.

[selfblessed]

I still wish I kept my Zipper. I think it would come in handy now.

[DavidMP]

I for got to include that EHX uses a fairly cheap LM342 quad op-amp chip for driving the filter. I replaced it for an MC33079 which is a drop-in replacement with much better (lower) noise characteristics and I do find it quieter at extreme settings but it is hard to quantify.