Effects that require negative voltage

[Warrior_Bass]

What are the caveats of effect units that use a negative voltage to operate? How do they cooperate with effects that are positive voltage? Is it safer practice to give the effect a positive voltage and a common ground, and then flip the voltage internally using a voltage inverter IC? I did a search for these topics (even on google) and didn't find much of anything. My guess is there is no cause for concern, or, there are so few of these effects (germanium PNP fuzz anyone?) that the concerns aren't well documented. Any ideas?

[Taylor Livingston]

There are two things that could be called negative power - one refers to the wiring of the jack, and one refers to the voltage potential between "ground" and "power" (when talking about unique cases like this, the terms ground and power become less descriptive than usual - something of a philosophical discussion which I'll leave for later ). It sounds like you already know about all that, so I'll avoid talking about tip-negative vs. tip-positive power jacks.

For pedals that really do need negative voltage supplies (pretty much only PNP fuzzes as you mention), you can't daisy chain them with pedals using standard +9v. Most people building these PNP fuzzes don't put power jacks in them, because at some point it's likely that someone will daisy chain them, killing the fuzz, possibly other pedals, and possibly the power supply. When using a battery you don't have to think about it or worry.

You are right that a charge pump like the MAX1044 or (my preference these days) LT1054 can be used to derive a true negative voltage rail in reference to power ground, and if you had a pedal with this little subcircuit you could daisy chain it with any other pedals and you'd never need to worry about any power troubles - you treat it like any +9v pedal. I have a PNP germanium fuzz on my pedalboard doing just this and it works perfectly, but I'm not sure who's doing that commercially, if anybody. The charge pump circuit is quite simple, just the IC and a couple of caps, so if you have any experience soldering, you could make it easily - just consult the datasheet for your IC of choice for the application circuit.

[Warrior_Bass]

Originally Posted by Taylor Livingston

There are two things that could be called negative power - one refers to the wiring of the jack, and one refers to the voltage potential between "ground" and "power" (when talking about unique cases like this, the terms ground and power become less descriptive than usual - something of a philosophical discussion which I'll leave for later ). It sounds like you already know about all that, so I'll avoid talking about tip-negative vs. tip-positive power jacks.

For pedals that really do need negative voltage supplies (pretty much only PNP fuzzes as you mention), you can't daisy chain them with pedals using standard +9v. Most people building these PNP fuzzes don't put power jacks in them, because at some point it's likely that someone will daisy chain them, killing the fuzz, possibly other pedals, and possibly the power supply. When using a battery you don't have to think about it or worry.

You are right that a charge pump like the MAX1044 or (my preference these days) LT1054 can be used to derive a true negative voltage rail in reference to power ground, and if you had a pedal with this little subcircuit you could daisy chain it with any other pedals and you'd never need to worry about any power troubles - you treat it like any +9v pedal. I have a PNP germanium fuzz on my pedalboard doing just this and it works perfectly, but I'm not sure who's doing that commercially, if anybody. The charge pump circuit is quite simple, just the IC and a couple of caps, so if you have any experience soldering, you could make it easily - just consult the datasheet for your IC of choice for the application circuit.

Good stuff, thanks for the reply.

Since PNP Ge fuzzes are more and more rare, throwing in an IC would seem to take away the 'mojo' and perhaps why it's not a commercially available item. I'll probably throw something like this together so I can use a standard +9V supply...batteries are impractical in effects units.

[Taylor Livingston]

I agree completely about batteries! I am a little surprised that nobody seems to make a PNP fuzz with a built-in charge pump, since it's so simple. But you are probably right about people having an aversion to it for "mojo" reasons.

The MAX1044 was at one point the goto IC for this, but because its maximum input voltage is 10v (and most regulated "9v" supplies are actually more like 9.5v) and also because it can only handle 10ma current draw, I recommend the LT1054 for its higher max input voltage and 10 times greater current handling.

[Nightlyraider]

There isn't a "negative voltage", but a Moog pedal for instance has a positive center pin instead of the 9v pedal format.

The pedals power input is wired opposite "standard", but the voltage does the exact same job as every other effect you have.

[bongomania]

Well, except that mixing different ground planes can lead to noise, hum, and even some units just shutting down and acting "broken". That's why it matters, and using an adapter plug does not necessarily fix the problem.