The PNP pedal with negative ground trade off? Charge pump

Frequently asked questions regarding powering your pedal.
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mike_EME
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Post by mike_EME »

I recently came across some PCB designs of standard old school negative ground germanium TRansistor fuzz boxes wired up with an IC (i believe MAX chips -- can't recall the exact chip part #), but the part of the circuit that filters the power flips the power phase by making a standard positive ground fuzz box like (fuzz face, etc) into a negative ground. Anyone have any thoughts on circuits with this kind of circuit? Do you trade off some quality or any issues with buffering or tone loss? I'd love to see some circuit examples and hear thoughts on this type of circuit layouts. Thanks

I believe it was referred to as a charge pump?
Because PNP transistor fuzzes are positive-ground circuits, they must have a separate power supply from the rest of the effects in a chain. To overcome this limitation, a charge pump chip has been integrated to allow this board to be powered by the same source as all of your other effects. This is great for daisy-chained pedal boards, as well as integrating this into an enclosure with other effects circuits.
http://www.guitarpcb.com/apps/webstore/ ... ow/3246523

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soulsonic
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Post by soulsonic »

I've done this many times, and it works very well. I usually use a TC1044 for the charge pump chip because it's inexpensive (from Mouser) and seems more rugged than the MAX1044 you see most often. I've used it with Fuzz Faces, and Rangemasters, and custom fuzzes, and it has always worked well.

Alternatively, you can flip the circuit "upside-down" and wire it up with the usual negative ground. This works just fine with Rangemasters and other single-transistor circuits, though people frequently have problems when trying to do it with a Fuzz Face style circuit - it tends to start oscillating. But, even that can be worked around. I found that decoupling each stage of a Fuzz Face with a 100 ohm resistor in series and 100uF cap to ground at the point where each stage connects to the positive voltage rail, works perfectly every time at allowing you to run it negative ground without any oscillation problems.
"Analog electronics in music is dead. Analog effects pedal design is a dead art." - Fran

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