I was putting together a panel with 9V outputs aiming to power guitar, etc, effects for use with (modular) synthesizers and I thought, I could add a little circuit to have an -9V output as well to power PNP transistor pedals and such. Normally, I use MAX1044 or ICL7660 inside the pedal to get that -9V, but I have been eyeing this little circuit that uses a 555 and a few extra components that promises to do just that. I have loads of those cheap non-CMOS 555s so I thought of giving it a try.
I looked around, and this must be the source schematic of the stripboard layout. Apparently, if you throw 1k, 33k, and 1nF in the equation for the astable configuration you get 555 to oscillate just above 20kHz, but I was not able to get -9V output. It seems that the output capacitors need some time (and turning the power on and off) to charge and discharge and the voltage stays way less, or goes way more, than -9V.
So I added a load in the form of an indicator LED (with a hefty current limiting resistor) and I got a stable voltage of -7.2V which is conveniently what you get from a dying 9V battery connected backwards. So, in a “why not” moment, I put it together on an stripboard off-cut, rearranging things a little to fit the extra parts on the available dimensions.
To test it, I put a fuzz face on a breadboard, and powered it from that -7.2V. It did not sound too bad, even though it would have been better if I could bias the transistors properly. If you have any idea of how I can make this more efficient, or what I possibly did wrong, let me know!