Stripboard Fuzz Face not working.

James89 · September 01, 2019, 04:50:56 PM

Hi all,
I have moved on to building a fuzz face circuit on stripboard, having (after a 5 or 6 attempts) finally got it working on a breadboard.
I'm on the second build on the stripboard as the first did not work at all, but seems I'm having similar issues again and wondered if someone could help out.

I'm just getting hissing upon rotating the knobs, I've checked everything and can't see an issue in the circuit. But I'm getting some funny readings and thought maybe someone could figure out what's wrong if I give you those. (I'm following the silicon schematic here, http://fuzzcentral.ssguitar.com/fuzzface.php )

The readings I'm getting are, 9.4v in, 9.4v after the 330 resistor and 9.4v after the 8.2k resistor. Yet, with a clean connection to Q2 I am weirdly getting a reading of 0.28v on the collector (given right before it is 9.4 why would the collector read so low?).
I have checked both the resistors and they still read their correct resistance values, but don't seem to be doing their job as you can see.

Just in case it helps, Q2 base is reading 1.4v and emitter is 0.28v.

Anyone any ideas?

Thanks!

Electric Warrior · September 01, 2019, 05:16:07 PM

Maybe you shorted the collector with the emitter?

The base and emitter voltages look good for a low gain silicon Fuzz Face. You should be getting around 3V on Q2's collector with everything hooked up correctly.

James89 · September 01, 2019, 05:34:04 PM

Can't see any shorting there. If they were shorted wouldn't the collector and emitter both read 9.4v though? Given that the 8.2k prior to the collector is feeding in 9.4?

Electric Warrior · September 01, 2019, 05:45:55 PM

The voltage should be lower after a resistor - btw... funny you're getting the same reading before and after the 330Ω. Are you sure you haven't forgotten any trace cuts?

James89 · September 01, 2019, 05:55:11 PM

Yeah I'm getting the same reading over the 330 and all the way through to the end of the 8.2k. 9.4v over 2 resistors and in between.

I've checked all the cuts, definitely all good and there doesn't seem to be any solder overlapping onto other tracks.

PRR · September 01, 2019, 08:59:53 PM

> 9.4v after the 8.2k ... 0.28v on the collector

They supposed to be directly connected together. Clearly they aren't. Bad solder joint?

James89 · September 02, 2019, 05:40:16 AM

Checked for continuity and right enough, it was intermittent. Reflowed on the 8.2k resistor and that connection seems to be working now. Thanks very much PRR.

Unfortunately, the circuit still isn't working though. *sigh*
I'll continuity check every single joint and see if anything else is a little iffy. Hopefully a reflow on something else is all it takes.

Thanks again!

James89 · September 02, 2019, 08:21:02 AM

So I am now getting it working. But with WAY too much gain!
I'm assuming that is due to the high voltage hitting Q2.

I've checked for shorts across the 330 and 8.2k resistor and cannot find any. They are both giving their correct resistance readings when checked with the DMM too. Is there any other reason they would fail to drop the resistance?

MaxPower · September 02, 2019, 12:51:51 PM

What are the voltages at the collector, base, and emtter?

pinkjimiphoton · September 02, 2019, 02:50:39 PM

Quote from: James89 on September 02, 2019, 08:21:02 AM
So I am now getting it working. But with WAY too much gain!
I'm assuming that is due to the high voltage hitting Q2.

I've checked for shorts across the 330 and 8.2k resistor and cannot find any. They are both giving their correct resistance readings when checked with the DMM too. Is there any other reason they would fail to drop the resistance?

its probably right then. a GOOD fuzzface SHOULD have over the top gain. if your guitar sounds muddy and buzzy as hell full blast, but cleans up as you turn the gtr volume knob down, it's probably ok.

what kinda gain are the q's you used? ya wanna keep them under about 250hfe generally, but the standard of 70-90 and 120-ish hfe on q2 seems to work well as always reported.

if it's too hot, try adding emitter resistances to ground. start around 100r and 47r for q1 and q2, and adjust up or downwards as necessary til it responds the way you like. this will affect the GAIN of the transistors, not the biasing.

fuzzfaces are a total pain in the ass. but nothing sounds as good to my tin old jaded ear

James89 · September 02, 2019, 05:46:29 PM

I'll need to check the voltage across the transistors tomorrow. But I know the collector of Q2 is now getting 9.4v.

The gain is definitely too much. I had built this on a breadboard before and maxed out was still usable. Cleaned up nice too. Now though it's a spluttering mess from about 60% upwards.

I think the issue is the lack of voltage drop over these 2 resistors but can't work out why I'm getting this issue.

MaxPower · September 02, 2019, 10:14:49 PM

If the collector is at 9.4v, that implies a short from the collector to the power supply. Disconnect the 8.2k resistor from the collector and take a resistance measurement across the 330 and 8.2k resistors. If it's about 8.5k, then take a resistance measurement from the collector to the power supply.

MaxPower · September 02, 2019, 10:21:28 PM

Take a resistance measurement from the collector to the power supply before disconnecting the resistor to see if you have a short.

James89 · September 04, 2019, 08:00:35 AM

So I've checked the resistors and I'm getting 8.53k.

My voltages over the transistors are:
Q1: C=1.08 B=0.59 E=0
Q2: C=9.3 B=1.39 E=0.65

I only seem to be getting a 0.1v drop. Checked multiple times for any shorts and cannot seem to find any.

PRR · September 04, 2019, 11:44:24 PM

Is the *Emitter* resistor ("Fuzz" pot) right-value and properly soldered?

Electric Warrior · September 05, 2019, 02:28:07 AM

Quote from: James89 on September 04, 2019, 08:00:35 AM
So I've checked the resistors and I'm getting 8.53k.

My voltages over the transistors are:
Q1: C=1.08 B=0.59 E=0
Q2: C=9.3 B=1.39 E=0.65

I only seem to be getting a 0.1v drop. Checked multiple times for any shorts and cannot seem to find any.

There's something wrong here. Q1c connects with Q2b. They should read the same voltage

James89 · September 05, 2019, 05:28:37 AM

Yeah there is definitely something very wrong. Cannot see where though. No solder joints overlap on to other tracks, no legs of components are touching and nothing seems to be wired in the wrong place. Obviously there is something I'm not seeing though.

I rebuilt one on a breadboard and got vastly different measurements. Also, obviously, a much better sound.

Reckon I'll just start over on the stripboard and maybe re-plan the layout to give some extra space to components.

Does anyone know where copies of the old style PCBs can be purchased in the UK or EU? It's not cheap to get a small amount made. And I don't fancy buying 100 to get the cost down.

MaxPower · September 05, 2019, 08:39:31 PM

Try perfboard with point to point soldering. For a circuit this small you can use a piece of cardboard. Poke some holes in it for the components and solder it up. Be careful not to set it on fire.

Electric Warrior · September 06, 2019, 01:46:20 PM

Quote from: James89 on September 05, 2019, 05:28:37 AM
Does anyone know where copies of the old style PCBs can be purchased in the UK or EU? It's not cheap to get a small amount made. And I don't fancy buying 100 to get the cost down.

Try ebay.

Quote from: MaxPower on September 05, 2019, 08:39:31 PM
Try perfboard with point to point soldering. For a circuit this small you can use a piece of cardboard. Poke some holes in it for the components and solder it up. Be careful not to set it on fire.

In my experience perfboard is a lot messier and harder to get right that stripboard...

MaxPower · September 06, 2019, 09:26:58 PM

We've two different experiences. With perfboard it's very easy to see what is soldered to what. No trace cuts to worry about. Much simpler to debug imo.

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Stripboard Fuzz Face not working.