ugly face always on

[peterg]

http://www.jiggawoo.eclipse.co.uk/guitarhq/Circuitsnippets/snippets.html
I've built the stock ugly face as per the attached schematic on page 26. The only change I made was installing the IN4001 diode from power to ground - not in series as per the scheme and installed an led and resistor. The oscillation is aleays present except when the sens, freq and thresh pots are turned fully CW. From the notes on the scheme it looks like the free running oscillation should not be on unless the threshold is set below a trigger point. Any advice on how to tame the oscillation?

[petey twofinger]

yeah i build one of these , hae you tired it with a buffered pedal in front / other pick ups / guitars ?

digit2t did some mods for this , i used them on my build  , i believe it was either the input cap or rather the cap for the oscillation maybe  . i used three caps on a switch , so i can get that osc to go a lot lower / pleasant freq  , also , my uf ( it doesnt have the lfo ) does not osc at most settings , you have tyo "make it" osc . i sam judt cruious as there may be something i did wrong or vice versa , no offence intended

forum search uf mods , maybe it will come up , if you cant find those mods pm me maybe i could find them as it was a few years back i just dont remember much .

[nocentelli]

http://www.jiggawoo.eclipse.co.uk/guitarhq/Circuitsnippets/snippets.html
The oscillation is aleays present except when the sens, freq and thresh pots are turned fully CW. From the notes on the scheme it looks like the free running oscillation should not be on unless the threshold is set below a trigger point. Any advice on how to tame the oscillation?

I replaced the 22k from +9v to the threshold ppt with a 56k which delays the onset of the oscillation to about halfway up the pot. However, the sens and frequency pots shouldn't have any bearing on when the oscillation occurs, so there may be another issue in your build.

[peterg]

Thanks guys. I'll replace the 22k resistor and see if that does the trick.

[peterg]

I replaced the 22k resistor with a 47k so the threshold pot provides oscillation or not. There only seems to be two settings - oscillation on or oscillation off. Is that correct?  I have another issue now. There is a lot of static at all settings. I toook voltage readings. I'm getiing negative voltage on lug 3 of the sens pot. Is thios to be expected?

[nocentelli]

Oscillation on or off sounds about right - the pitch of the oscillation should be controllable from the frequency pot. There is a huge amount of gain, and some white noise will be present but it should be gated to silence when you're not playing.

The voltage on the sens pot lug three should probably vary as you play (since it comes from the 386 output). Does playing dynamically alter the frequency of the effect? It should sound like the world's most extreme digital-sub-octave-fuzz-envelope filter.

[peterg]

Leo

It worked as I believe it should when I finished the board and tested it. Once I boxed it I got the white noise and it's consistant. It may be a pot and/or grounding problem. The voltages are in line with those I could find on line.

Could my first attempt at making an opticoupler be the problem?

[nocentelli]

Once I boxed it I got the white noise and it's consistant.

This bit is significant: take the back off and play with the wires, pots and board while connected to guitar and amp (roll the volume down a bit, perhaps) listening out for any changes to the noise level/character. Could be an intermittent connection that was broken when boxing, something touching something it shouldn't, cold joint on the ground connection made while boxing etc. If nothing changes, take it out of the box to verify the board does sound ok on it's own. I think roll-your-own vactrols are quite forgiving, there's no real art to it and it's a single optoisolator,so no matching required. I'd be looking for faults to do with the wiring, especially ground.

What did you power it with before and after the boxing? (i.e. has that changed?)

[peterg]

Good point about the power. I tested it with a battery before it was boxed up and used my Boss wall wart once it was boxed up. I'll check that out after work.

[peterg]

This one is giving me a workout! It works with battery or wall wart when I touch the positive lug of the power jack. I've checked the layout, connections, etc. and can't find any issues.

Another issue: At 9 volts I don't get any oscillation but get the fuzz effects. When I supply less than 9 volts either with a battery or my wall wart with selectable power supply I get oscillation when the threshold pot is at 3/4 cw or further cw.

Any ideas on what is causing these issues?

Edit:got it working! Changed the 22k resistor to 1k in order to get oscillation. Boxing it up took care of static.