I built the sili face at Runoffgroove. I breadboarded it first and it sounded awesome! http://www.runoffgroove.com/sili-face.html
Move it over to perf, added trimmers for the two 100 k (one 33k in series with a 100k trimmer, and the other 47k in series with a 47k) and now it aint workin. I'm bummed, but I checked the resistors and they all seem ok. I get signal when I hit the stomp switch when the effect is bypassed, so its not the jacks or switch. Here are my tranny voltages:
(batter at 8.35v)
Q1 - C 5.2, B 4.34, E 4.01
Q2 - C 4.7, B 5.19, E 4.54
The trannies I've tried are2n4401, 2n3904, and 2n2222, all of which worked fine on the breadboard.
According to RG:
QuoteFor linear amplifying, the collector must be more positive than the base; the base must be more positive than the emitter by about 0.4 to 0.7V for silicon, and 0.0 to 0.3 for germanium; the emitter should be the most negative pin. The voltage difference between the collector and emitter is the biggest voltage that the transistor can swing linearly. If the collector is not a volt or more above the emitter, or the base is not a base emitter drop above the emitter as noted above, the transistor cannot be acting as an amplifier. This is a very good pointer to what can be wrong. See the debugging example below. If the collector is at the same voltage as the base, or even closer to the emitter than the base is, the transistor is saturated and simply can't be amplifying. Likewise, if the base-emitter is below the cutoff voltage for the transistor, no current can be flowing.
On Q2, my base is higher than my collector, which must be the problem, but what causes this problem? I'm thinking of ripping out all of the trim pots (except Q2's bias, which is correct) and replacing them with static resistors.
I would check for wiring errors with both trimpots, which would account for the excessive voltages. Carefully triple-check your soldering.
On the other hand, if it sounded good to you with the stock values, you may just want to put in the schematic-specified values...
I'm happy to hear that you liked it (when it worked on the breadboard!)
Yeah, it is an excellent variation. Very easy to get it to sound good.
By the way, its amazing what connecting Q1's emitter to ground will do for a fuzz face! Well, not really. :D
Works now and sounds awesome!
My idea was to add an extra socket for each tranny (to put two trannies in parallel, minus the collector, to halve the gain), and to have trimmers in place of most resistors. I could then mount the perfboard on top of the pedal, under a clear plexi flip top. That way, I could change stuff around without ever opening up the innards.
I took the pots off, but I may solder them back on and I haven't tried RG's idea about putting two trannies in parallel yet.
By the way, I used metal film resistors in this, and there is no noise whatsoever, so I was able to leave out the ceramic cap in the schem and also the filtering cap (I'm using a 9volt).