Please help an idiot with his Fuzzface

[Greenwichpaul]

Yes, I'm an idiot. I tested a Fuzzface schematic on a breadboard, made sure it was all working. Back at Christmas. Then didn't transfer it to the PCB until the last couple of days, and in the meantime I've forgotten everything and definitely reverted to idiot level.

Circuit sounded fantastic on the breadboard. Now, on the PCB, it fires up - sound comes out, a kind of ripping sound with a tremolo. Horrible.

Maybe I fried the transistors? But I soldered each one pretty quickly, with a croc clip between board and transistor.

I checked the caps carefully. You can see the -ve sign clearly on the pics.

Have I wired the transistors the wrong way round? I am certain that the white tab on these CV7001 marks the emitter and that's how it was working. But I suddenly have doubts... if you look at the black CV7001 in the photo, with emitter on the left, and collector right, the base sits below them.

Have I simply wired the cables incorrectly? I checked twice against the schematic before soldering.

All connections seem to test OK. Can't see shorts on the underside.

Voltages differ from the electrosmash schematic, especially the voltage at the base of Q1.

Sorry for the entry-level query. Please be kind and help an idiot.

I;ve attached pic of the interior with wiring from pots etc. I followed the attached schematic from diyproaudio.

[Pedal love]

Yes, I'm an idiot. I tested a Fuzzface schematic on a breadboard, made sure it was all working. Back at Christmas. Then didn't transfer it to the PCB until the last couple of days, and in the meantime I've forgotten everything and definitely reverted to idiot level.

Circuit sounded fantastic on the breadboard. Now, on the PCB, it fires up - sound comes out, a kind of ripping sound with a tremolo. Horrible.

Maybe I fried the transistors? But I soldered each one pretty quickly, with a croc clip between board and transistor.

I checked the caps carefully. You can see the -ve sign clearly on the pics.

Have I wired the transistors the wrong way round? I am certain that the white tab on these CV7001 marks the emitter and that's how it was working. But I suddenly have doubts... if you look at the black CV7001 in the photo, with emitter on the left, and collector right, the base sits below them.

Have I simply wired the cables incorrectly? I checked twice against the schematic before soldering.

All connections seem to test OK. Can't see shorts on the underside.

Voltages differ from the electrosmash schematic, especially the voltage at the base of Q1.

Sorry for the entry-level query. Please be kind and help an idiot.

I;ve attached pic of the interior with wiring from pots etc. I followed the attached schematic from diyproaudio.

On the right as you hold it straight up on the artwork side, there is the area where the wires are soldered. The pads are very close together there. Check to make sure the solder on these pads, are not bridging to each other and check the connections elsewhere.

Sent from my SM-S327VL using Tapatalk

[Twhjelmgren28]

I don't have a ton of experience but one thing I've learned with DIY pedals is to be ready to troubleshoot. 

I had a similar issue when I wired up an axis face fuzz - kind of a farty noise that would cut in and out.  It ended up being multiple poor connections to ground (in my specific case).  In looking at your 1st photo, the black wire closest to the blue capacitors:  it looks like it may be fraying out a bit.  I personally would unsolder that, cut the wire so it's not fraying, and re-solder it to that pad.  Not saying that will fix anything but it at least eliminates that as an issue.

In my short experience, having frayed wires off pots, jacks, or perfboard are often buggers.  Also, audio probes are your friend:

http://www.diystompboxes.com/pedals/debug.html

[Greenwichpaul]

thanks folks, those are both very plausible suggestions.

I checked the pads to which the wires connect; although the photo shows some reflections in that area there's no solder bridging any pads. And you have sharp vision,  Twhjelmgren28, that wire was a little too thick for all the strands to reach thru, so a couple of strands are cut short.

Any thought on those strange voltages?

IS the consensus that the PNP CV7001 are orientated correctly?

[Govmnt_Lacky]

Any thought on those strange voltages?

What is so strange about them? The only one I see is the Q1 Collector voltage is about 0.5V low. Maybe something there. Maybe not.

I suggest the following:

1) Verify proper values and orientation of EVERY component. This includes resistor values, capacitor values and orientation, transistor orientation. Download the datasheets to verify legs on the transistors
2) Verify proper wiring and connections. This is a PnP Fuzz. Make sure your voltage and Ground is going where it is supposed to.

Any reason you went with the B100K instead of the A500K for the Volume on the schematic?

Good Luck! 

[Electric Warrior]

Any thought on those strange voltages?

What is so strange about them? The only one I see is the Q1 Collector voltage is about 0.5V low. Maybe something there. Maybe not.

Any reason you went with the B100K instead of the A500K for the Volume on the schematic?

Good Luck! 

The voltages are all way off. The ones in the schematic as well as the measured ones.

The schematic seems to show measurements for a misbiased silicon fuzz face. 0.6V between Q1B and ground gives it away. Germaniums should measure a lot lower. Around 0.1V is realistic.

Q1's collector voltage is quite high (which is bringing down Q2C). Vintage units measure between 0.3 and 0.7V here. Either the transistor doesn't leak enough or it's a pinout issue. As it was working alright when you breadboarded it I guess it's the latter.

A 100k volume pot will tighten the low end. MK1.5 Tone Benders (on which the fuzz face is based on) often used 100k volume pots.

[Govmnt_Lacky]

The voltages are all way off. The ones in the schematic as well as the measured ones.

The schematic seems to show measurements for a misbiased silicon fuzz face. 0.6V between Q1B and ground gives it away. Germaniums should measure a lot lower. Around 0.1V is realistic.

Q1's collector voltage is quite high (which is bringing down Q2C). Vintage units measure between 0.3 and 0.7V here. Either the transistor doesn't leak enough or it's a pinout issue. As it was working alright when you breadboarded it I guess it's the latter.

A 100k volume pot will tighten the low end. MK1.5 Tone Benders (on which the fuzz face is based on) often used 100k volume pots.

My work is done here! 

[PRR]

> Voltages differ from the electrosmash schematic

The ES voltages are doubtful. If they truly had a Germanium AC128, there is NO way the base voltage would be 0.6V. That would be typical for Silicon, true. For Ge, I like your 0.06V better. (Maybe there's a lost zero on ES's floor.)

Your basic symptom is that Q2 C-E is hard-ON. Near equal voltages. Dozens of mV drop suggests a short (or measurement slop) rather than a solder blob. The most likely cause is R4 not really conducting.... if it was, Q1 B would pull up, pull-down Q1 C, which would turn-off Q2.

Solder joints at R4 and related points.

[Greenwichpaul]

Thanks PRR and everyone. I checked the joints and they seem good. One possible problem has to be that I've fried a transistor.

I've gone back to the breadboard. I had tested a large number of STC germanium but then threw them back in the box once I wired the circuit (argh) so rather than measuring gains all over (my multimeter hfe function has stopped working for some reason) I bought two OC75 so I could rebuilt with something I know worked. Got that breadboarded and working again. Sounds great .

Then swapped a couple of other STC , one of them marked IR, the other a TK 1002 . They all work... and sound great, surprisingly similar to the OC75, although I'm limited by working in a shed where I can't try the amp loud. On these I assumed the collector was marked, not the emitter. THat's another source of error perhaps. My next step will be to add sockets for the transistors to the PCB and try again...

[Greenwichpaul]

FInally sorted.

I removed the transistors, added sockets, retested them on the breadboard. All fine. Tested them with sockets, then when they worked wired them in permanently.

I'm not certain what the problem was, but one peculiarity I found is that the circuit actually works without battery power, but simply sounds awful. So maybe - duh - my battery was simply flat?

The other possibility is I got the collector the wrong way around - I rested to confirm that it was the collector makred on the CV7001.

Anyways, it sounds awesome. Much thicker and creamer than the silicon board, but gnarlier too. Mine seems to have loads and loads of gain; I really have to back the pots down to have anything other than an insane rise in volume.

Thanks everyone for the support. I've owned thie Fuzz Face since it was new, but this is the first time it's sounded really good.