pnp fuzz with negatve ground

[POTL]

Almost all germanium fuzzes
Use pnp transistors and negative power
To make these effects with classical power and to enable the use of a fuel tank, power converters are used as in this schematic

At the same time, there are manufacturers who simply turn over the schematic

I also noticed that zvex fuzz factory is a modified tone bender mk ii with an inverted outline
Zvex

Tone Bender

tell us what are the drawbacks of this circuit in comparison with the scheme with a power converter?

[R.G.]

Old, old issue. It's been on this forum many times.

Let me preface this with a quotation from Yogi Berra. " In theory there is no difference between theory and practice; in practice there is."

In theory, you can simply swap the + power and - power and call either one ground, and everything works. The thing that makes this work is the + and - sides of power being ***perfectly*** linked  by a zero-ohms power supply impedance and the wiring of the pedal isolating power return wires and signal ground wires.

In practice, power supplies are never really zero impedance and power/ground distribution wiring are never perfect. The degree that this hurts you determined by how much current is pulled from the power supply by the parts and by the signal output loading, and how much gain the circuit has. The bigger the gain, the bigger the problem. Notice that the "stability" control on the zvex pedal is a variable resistor in series with the power supply. The bigger the resistance, the more likely it is to oscillate. What that doesn't show is that the internal resistance and inductance of the power supply bypass caps and wiring can also be a "resistance" at high frequencies. With modern semiconductors, the impedances of the parts at UHF and VHF can make it oscillate at frequencies that most general purpose 20MHZ oscilloscopes can't even see.

The good (or bad, depending on how you look at it) news is that this doesn't always happen. So the myth that since theory says you can swap ground from + to -, you can persists because people often get away with it. The practice is that some number of these people show up here with questions about why their swapped-ground pedal doesn't work or makes funny noisesl

[POTL]

Well: then why do many use power converters like max1044 icl7660s
In the next topic I was told that if you change the plus and minus, the power supply will burn.
The sound is not changed plus and minus, and the scheme is deployed upside down.

[R.G.]

Well: then why do many use power converters like max1044 icl7660s

That setup preserves the grounding. The power supply itself has a worse impedance, and some noise, but the signal ground to which signals are referenced is preserved. Many circuits have some tolerance of noise on their power supplies - for opamps, this is specified on the data sheet as the power supply rejection ratio - but noise on the ground reference is carried directly through to the outputs.

In the next topic I was told that if you change the plus and minus, the power supply will burn.

If you exchange the power supply and ground and change nothing else, most circuits will conduct through and burn out either the circuit or the power supply. Reversing the power supply DIRECTION, + for -, often damages things. Moving the power supply in a single direction - as in moving +9V down to be ground, and moving the (-) side of that 9V down to be -9V is not reversing the polarity of the power supply.

The sound is not changed plus and minus, and the scheme is deployed upside down.

This is a confusing topic for a beginner. There are a lot of things to be understood hiding behind the question.

[Plexi]

Ugh....ToneBender MKII...my living nightmare with positive ground form...

The Lovepedal Silicon FuzzMaster is the clearest example of upside down schematic

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