Servo Fuzz Face

[szukalski]

Just two layers. I have a contiguous ground plane, but this may change once I redo the layout

 

[Chuck D. Bones]

Unless we're doing high-speed stuff (which we are definitely not), a power plane is a nice-to-have, not a gotta-have. Vcc just doesn't go that many places.

 

[szukalski]

Yeah, I had a couple of layouts recently where it really helped keep the layout clean so I take the option when it makes sense.

 

[szukalski]

Took another take at the layout. This feels a bit better now.

 

[Gordo]

Too damn clean for a fuzz face. Love it and love the color.

 

[PedalBuilder]

I noticed that this uses the "flipped PNP" approach to converting a positive ground circuit to negative ground. When I've tried that in the past with the Fuzz Face, I've had intermittent and unpredictable oscillation issues. Has anyone who built this circuit had that issue before? Or does the servo (or something else) prevent the oscillation problems that would otherwise occur?

 

[Smrtokvitek]

I have used Chuck's servo circuit in a "regular" fuzz face (without the tone) and it worked although it is still a work in progress as I did some modifications on the input. It will be a question of specific transistors, and maybe a layout in my opinion.

 

[cooder]

I noticed that this uses the "flipped PNP" approach to converting a positive ground circuit to negative ground. When I've tried that in the past with the Fuzz Face, I've had intermittent and unpredictable oscillation issues. Has anyone who built this circuit had that issue before? Or does the servo (or something else) prevent the oscillation problems that would otherwise occur?

Mine with pnp flipped version works great. No problems with oscillation as far as I can tell in my setup.

 

[Chuck D. Bones]

Mine with pnp flipped version works great. No problems with oscillation as far as I can tell in my setup.

Same here.

I noticed that this uses the "flipped PNP" approach to converting a positive ground circuit to negative ground. When I've tried that in the past with the Fuzz Face, I've had intermittent and unpredictable oscillation issues. Has anyone who built this circuit had that issue before? Or does the servo (or something else) prevent the oscillation problems that would otherwise occur?

It's all about power supply filtering and grounding. Get that right and oscillation will not be a problem. The other thing to look out for is the routing of the trace from Q1's base. It's very susceptible to noise pickup and if it's too long, it acts as an antenna.

The Fuzz Factory employs the "flipped PNP" topology and it only oscillates when the STAB pot is turned the wrong way.