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Zapper Exp Mod?

gregonbass

New member
Has anyone done a mod of the Zapper using a trs jack to an expression pedal for the pot controlling the sweep?
 

Chuck D. Bones

Well-known member
It's a great idea, but very risky. The FREQ pot connects directly to the inverting input of an opamp. That connection needs to be short, a few cm or less. Otherwise, you'll end up with an oscillator or a radio receiver. If you are serious about remoting the FREQ control, then install an LDR in place of the FREQ pot and use an Exp pedal to modulate the brightness of an LED. Or build this board into a wah pedal shell. Another way to do it, and it would be a major redesign, is to use a variable-gain amp like an LM13700 in place of IC2.4.
 
Just finished up my Zapper recently. I paired up the Zapper with my Phase II - very nice, very nice.

If modding the pedal itself is treacherous, you could always keep the Zapper intact but pair it with another type of modulation pedal or build two-in-one with an order switch. That could be your express ticket to Tone Town...
 

zgrav

Well-known member
The Zapper comes from the Systech Harmonic Energizer. I've seen some stories on the internet that, on some tracks, the sound engineer would manually rotate the frequency knob on the box while Frank Zappa was playing to get that changing wah sound from the effect. That is why it would be cool to drive that control with a pedal, picking dynamics, or maybe an LFO. As Chuck notes, it is an adjustment to the inverting input on an op-amp so it would be better to drive it through an LDR to separate the electrical connection from the variable resistance.
 

gregonbass

New member
It's a great idea, but very risky. The FREQ pot connects directly to the inverting input of an opamp. That connection needs to be short, a few cm or less. Otherwise, you'll end up with an oscillator or a radio receiver. If you are serious about remoting the FREQ control, then install an LDR in place of the FREQ pot and use an Exp pedal to modulate the brightness of an LED. Or build this board into a wah pedal shell. Another way to do it, and it would be a major redesign, is to use a variable-gain amp like an LM13700 in place of IC2.4.
Thank you for your advice
 
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