fulltone fuzz 69 conversion to negative ground

[balkanizeyou]

Hi,
Recently my friend who has no experience in electronics asked me to take a look at his pedal, diy clone of fulltone fuzz 69 made by some other guy. The pedal exhibited a "strange problem", meaning it worked fine as long as it was not powered by the same power supply as other pedals. The first thing that came to my mind was positive ground circuit, and looks like that was a good guess - fulltone fuzz 69 turned out to be modified fuzz face circuit with more knobs. Here's the schematic (the one that i'm working on doesn't have pulldown resistors):



My friend wanted to be able to power this pedal with the same supply as the others, so i decided to turn the circuit into a negative ground circuit using this simple schematic:


So here's what i did - i connected sleeves of input and output jacks to the negative side of power supply, the same with the volume pot, reversed the polarity of input capacitor and that's about it.

I've read, that this operation shouldn't change the sound of fuzz face too much (maybe increase the background noise), but to my surprise it completely ruined the sound of this pedal - the output level became REALLY low, there was almost no gain, it had no low-to-low-mid frequencies and there was noise all over the place.
So i suppose i did something wrong. I measured the voltages at transistors' pins and they were almost the same before and after (within the +-0,05V range, i may have turned the knobs a little during the conversion so that's probably it). I thought that it's maybe because the Fuzz 69 circuit is a little more complicated than the fuzz face, but it shouldn't be a factor from what i understand.

Oh, and when i soldered everything back to the positive ground setting everything went back to normal. Any ideas what i did wrong or maybe someone encountered a similar issue?

[Kipper4]

Did you double check the transistor pinout and have the collector to the +9v rail?
also note the higher hfe on Q2 top most schematic.
What transistors npn did you use?

[Groovenut]

You could use a voltage inverter such as this. The voltage coming in to the pedal is wired as normal, 9 vDC to positive, ground to negative. The fuzz circuit is wired V- to power, ground to ground. V+ is not connected to the fuzz circuit.

[balkanizeyou]

Did you double check the transistor pinout and have the collector to the +9v rail?

yup, i double checked

What transistors npn did you use?

i used the same PNP transistors that were used, i didn't change anything.

Groovenut - thanks! If nothing else works i will definitely use this voltage inverter. But first i would like to find out what I did wrong and if there is a possibility of fixing it, it really bugs me

[Cozybuilder]

I would trace the circuit that is actually in the box- it seems there must be another point (an R or something) connected to ground for your mods to have not worked. I've done PNP based fuzzes using negative ground, at worst you have to add some resistance on the input, which the Fulltone "69" does. I would also suggest looking at how the card itself is attached- maybe something contacts the enclosure.

[PRR]

> i used the same PNP transistors that were used, i didn't change anything.

Transistors have polarity.

When you "flip", you change transistors!

There are other ways. More complicated and trouble-prone. You "can" wire a circuit "upside down" and get signal through. Maybe. Sometimes it squeals like a pig. Or you can do an inverting power converter. This is sometimes fine, and sometimes squeals like a bat.

Also you must flip the emitter cap (on Fuzz pot).