Sunday, 26 February 2012

Fuzz Face with NPN transistors (MPSA18 amplifiers)

After amending our FuzzFace design to use a positive power supply, we've had a couple of enquiries about the schematic. Mainly that a few readers weren't familiar with the PNP transistors used (nor seeing them drawn "upside-down" in the circuit) so we've found a design that uses NPN transistors and different resistor values (including a potentiometer/variable resistor to adjust the amount of "fuzz")

FuzzFace with NPN transistors

Here's the PCB layout. We've not had chance to try this, as we're still waiting for some 20uF capacitors.

That said, we've a few 22uF caps lying around here (large black barrel electrolytic types) and since 22uF is just within the range of a 20uF with +/- 10% (and 20uF is within the range of a 22uF with +/- 20%) then it may just be a suitable replacement. We hope so, since 22uF caps can be easily found all over Farnell and eBay for just a few pence whereas the cheapest 20uF rated capacitors are about £3 each.

FuzzFace NPN pedal PBC layout
(print the above at 100% no scaling to create your own press-n-peel image for toner transfer)

Since simplifying the design (using 22uF instead of 20uF capacitor for example) we've managed to source all the components needed to make this pedal, so it's off to the nerd cupboard now to crack open the Ferric Chloride and get etching!