Recently got a handbuilt Ge FuzzFace clone that is wired point-to-point, and though it sounded decent it would go into "oscillation" in two different ways:
1. When the volume pot on my guitar was turned all the way down.
2. When the fuzz pot on the pedal is max or near max, especially when using both pickups (center switch position) on both of my telecasters (tele thinline copy with single coils in neck and bridge, and a tele custom with a wide range fender humbucker in the neck and single coil in the bridge) i noticed that it would also oscillate if switched to just one of the two pickups seems to be related to the output strength of the pickup, the higher the output the stronger the oscillation.
I checked the battery (alkaline) that came with it and it measures 9.48V, also switched to a zinc chloride type that is even stronger (9.55V) and it also caused the pedal to oscillate with even a slight stronger "volume"/ "pitch".
I read and searched here thru several threads on various ways to resolve this type of oscillation, so before doing any of the recommendations (caps, resistors add-ons and etc...) I decided to do something very simple, a long recommended way to power any type of "vintage" fuzz by using lower power output 9V. I put in an alkaline that measures 8.67V and gave it a try, and wow! there is not ANY oscillation in either of the 2 ways i was getting it before as mentioned above, and it also seemed to improve the overall tone/sound of the pedal (though only tried it at less than normal volume on my tube amp) making it less "boomy" and ""muddy" sounding.
I'm just trying to understand abit more why this seems to be a solution (at least in my case) to what seems to be a common problem with fuzzface circuits... would love to wrap my head around an explanation, the closest that i've read is that on beavis audio on voltage sag. i'm now assuming that this pedal will sound optimal with a power supply between 8.5V - 9.0V?
i didn't even go as far as checking bias voltages or any other troubleshooting... anyways some more info on my pedal:
Negative ground circuit can be powered by standard Boss style 9V power adapter & battery powered.
Built with hand selected NOS 60s Germanium AC128 Transistors
1960s NOS Mullard Tropical Fish Capacitors
1960s Allen Bradley Carbon Resistors and High Quality Tantalum Electrolytic capacitors.
Thanks!
Quote from: scott_v on September 07, 2011, 09:57:34 PM
Recently got a handbuilt Ge FuzzFace clone ... would go into "oscillation" in two different ways:
1. When the volume pot on my guitar was turned all the way down.
2. When the fuzz pot on the pedal is max or near max,...
it would also oscillate if switched to just one of the two pickups seems to be related to the output strength of the pickup, the higher the output the stronger the oscillation.
I checked the battery (alkaline) that came with it and it measures 9.48V, also switched to a zinc chloride type that is even stronger (9.55V) and it also caused the pedal to oscillate with even a slight stronger "volume"/ "pitch".
...
I'm just trying to understand abit more why this seems to be a solution (at least in my case) to what seems to be a common problem with fuzzface circuits...
Negative ground circuit can be powered by standard Boss style 9V power adapter & battery powered.
Built with hand selected NOS 60s Germanium AC128 Transistors
Sigh.
I lost count of the number of times where I told people that using PNP germanium circuits and doing the quick and dirty negative ground conversion would give problems with noise and oscillation.
I rather suspect, based on experience with a lot of these, that if you un-did the negative ground and put it back to positive ground, the oscillation problems would vanish. It has for many people with similar problems.
People always think "Kewl, I'll just make it work with this neato negative reversed ground circuit. None of that oscillation stuff will happen to ME."
Until it does.
You might be able to get it patched in by using bypass caps and other bandaids on the power supply. Maybe. Works sometimes.
The fix is to put it back to positive ground.
Thanks R.G. for the recommendation, again I received this pedal wired as negative ground and this was NOT my build, then after re-reading your post and the previous recommendations (mostly yours now!) about switching to positive ground that I may now consider doing the same...
however since its now not oscillating i may not mess with it... however i'm assuming either of these methods is the way to go:
http://www.generalguitargadgets.com/diagrams/switch_lo_3pdt_tb_dcj_pnp.gif?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
http://www.generalguitargadgets.com/diagrams/switch_lo_3pdt_tb_dcj_pnp_gi.gif?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
> its now not oscillating
General thoughts:
1) Amplifiers like to oscillate.
2) Oscillators quit if you starve them.
So it seems you are right on the razor edge between #1 and #2.