Can't get Fuzz Factory to oscillate/scream

[lauwe]

I've built a Fuzz Factory using the schematic I found here:
http://tagboardeffects.blogspot.nl/2012/10/zvex-fuzz-factory-compact-layout.html, using AC128's I got from here: https://www.banzaimusic.com/Fuzz-Face-high-gain-transistor-set.html

I added in an 3pdt foot switch and LED and put it in a box:



My problem is that although it does seem to work, I'm not getting as much reaction from the controls/knobs as I was expecting (It's behaving too nice  ). I checked the wiring a couple of times but the only thing 'wrong' is that my potentiometers are 'reversed' (I swapped pin1 and 3) which I think shouldn't make a difference?

Here's a video (knobs from left-to-right,top-to-bottom: Gate, Comp, Volume  Stab, Drive) 

Could this be a problem in the wiring, or could this be the wrong transistors?

[Cozybuilder]

Check that all cuts were made on the perf, and are the volume and gate pots grounded? The vero layout you referenced differs from the 2008 Chittum schematic only in the 1M anti-pop resistor at the input.

[lauwe]

Volume 1 and Gate 1&2 are grounded. Checked the cuts and they seem to be fine (I also measured this before I started soldering).
I tried removing the 1M between input and ground as well as the 100R between the 9v and stab 2&3 which should make it more like the Chittum schematic and  it seems like I can get a little more variation with the knobs now, but still not able to get it to scream .

[Cozybuilder]

It looks like there is a 4K7 where there should be a 47K. I can't read the bands for the 5K1 resistor, you should check it again. The 1M input cap bleed won't affect the circuit like you described.

[lauwe]

You are right about the 5k1; I didn't check it carefully and it actually appears to be a 4k99 (yellow;white;white;brown;brown). Would this make a big difference? (I can try to add the 100R which I removed ).
The 47K appears to be ok (difference between orange and red for the third band is hard to tell so I measured it again just to be sure )

[Cozybuilder]

The 100R just assures you don't go to full 9v at max pot travel on that bias pot (stab). 4K99 is close enough to 5K1, that won't account for it. At his point it looks most like either a solder joint or bad transistor.

[chuckd666]

Your hands... are immaculate.

[vigilante397]

I've built a handful of these on the same layout and can confirm it's legit, though I have had varying experiences depending on the transistors. I bought a huge batch of NOS AC128's (from Bulgaria I think) and even from the same batch I had some that were much nastier than others.

So frankly your best bet is getting a big batch of them and trying them out (it helps to measure hfe and get them in matched pairs first) to see which set gives you the tone you want. Buying them from international sellers takes longer for shipping, but you can usually get a pretty big batch WAY cheaper than buying from a US seller.

[chuckd666]

Agreed, germs can be a real jerk to get affordably and with decent specs. I'd try minifux on eBay (in Germany I think) who sells bulk transistors for good prices.

[One-Eyed Shaman]

Perhaps the HFE values of your transistors are not high enough. I made one with trasistors with HFE values at like 65 and 70 or something like that, and another one with like 90 and 100. The first one sounded fine, just no oscillation - like you're describing. The second one had plenty of oscillation. If you read the comments on the tagboard post your referencing, someone suggests HFE values that should work well.

[Elijah-Baley]

I'm building, almost done, the same circuit.
I messed up around the pots wiring, because reading some schematic I found some differences. The meaning difference was the Stab pot, clearly reversed. Then I adjusted the connecting of Comp and Drive, but I noticed no changing with those. I replaced the 100 Ohm resistor with a jumper, because it there's no in the "original" schematic.

I don't recognize in your pedal the right sound, the pots seems to me not have a real effect.
Do you find this circuit loud? I mean extremely loud?

If you have a pair of silicon BC558 you could try to replace for a moment your AC128. But I dare to say could be something wrong in the circuit.

[duck_arse]

I count six bands on the yellow/white/white resistor. if the last one is red, for 2% tolerance, there are far too many bands. do you have many of those resistors, and are you meter sure of it's value?

[vigilante397]

I posted without watching the video, and now after having watched I'm leaning toward something being wrong with the circuit. Make sure the orientation of your AC128's is right. The second one I built I had them in backwards and it sounded very similar to this.

[Elijah-Baley]

Make sure the orientation of your AC128's is right.

Easy wrong the orientation, but easy check it. You need the fuzz factory schrmatic, of course, and the pinout of ac128. Search the images of it on google.
I always check the right orientation so.

[Cozybuilder]

AC128 pinout:

You can verify easily enough- this is PNP, so place the neg lead from your DMM (on Diode setting) on the base, and measure from base to emitter, then from base to collector. The higher reading is the Base-Emitter junction.

Your photos indicate the transistor is in the correct orientation.

[GGBB]

I don't know how the ff is supposed to work, but have you tried any other power supplies or batteries? That GP 170 rechargeable "9V" is only rated for 8.4V. Maybe the transistors are always starved for power?

[Cozybuilder]

Look again at the input and output jacks and the circuit card input and output. These might be reversed.

[lauwe]

Your hands... are immaculate.

White-balance of the webcam was a bit off (and my hands haven't seen enough guitar-practice-hours) 

I'm building, almost done, the same circuit.
I messed up around the pots wiring, because reading some schematic I found some differences. The meaning difference was the Stab pot, clearly reversed. Then I adjusted the connecting of Comp and Drive, but I noticed no changing with those. I replaced the 100 Ohm resistor with a jumper, because it there's no in the "original" schematic.

I don't recognize in your pedal the right sound, the pots seems to me not have a real effect.
Do you find this circuit loud? I mean extremely loud?

If you have a pair of silicon BC558 you could try to replace for a moment your AC128. But I dare to say could be something wrong in the circuit.

With the 'additional resistors' removed I get more effect from the pots.
It's not loud to me; the volume-control works pretty well actually. I got a pair of BC558's today but I can't get any sound out of the circuit at all with those 

I posted without watching the video, and now after having watched I'm leaning toward something being wrong with the circuit. Make sure the orientation of your AC128's is right. The second one I built I had them in backwards and it sounded very similar to this.

I checked the orientation (and tried putting them in backwards, which made it worse); there's a little flange at the emitter side.

I count six bands on the yellow/white/white resistor. if the last one is red, for 2% tolerance, there are far too many bands. do you have many of those resistors, and are you meter sure of it's value?

the last band is the temperature coefficient. So that resistor works out as being 4.99k ohms; ± 1%; 50 ppm/°C

Perhaps the HFE values of your transistors are not high enough. I made one with trasistors with HFE values at like 65 and 70 or something like that, and another one with like 90 and 100. The first one sounded fine, just no oscillation - like you're describing. The second one had plenty of oscillation. If you read the comments on the tagboard post your referencing, someone suggests HFE values that should work well.

Just did the measurement as described here: http://www.geofex.com/Article_Folders/ffselect.htm . The leakage-currents I measured were 0,16mA and 0,25mA which, according to the description, should be OK. The HFE numbers work out to be approximately 60 and 70 which would make it comparable to your example.

So I did what a couple of you also recommended; ordered a couple more AC128s

Thanks!

[Elijah-Baley]

With a pair of BC558 it should work.
Anyway, the orientation of the AC128 seems ok. Mine are placed like yours.

My circuit with high gain and "stable" setting is very loud, I can't set the volume pot over 3/10 about, but it is a well-known issue of this pedal.
Your knob have a very subtle effect. So:
1. "wrong volume";
2. subtle effect of the pot;
3. "wrong sound".
I say: these are signs of something wrong.

I'm seeing the images, and my wiring pots is different enough from yours (thought I can't see how you had exactly connect them).
Try to follow the layout about the wiring pot and their value like I did.

[Cozybuilder]

Easy enough to try out if the input and output leads are reversed- plug your guitar into the pedal output, and the amp into the pedal input. I'm assuming you have normal orientation of input on right and output on left when the pedal is stompswitch on top.