Fuzz Face note decay issue?

FlyingWild · Post by **FlyingWild** » 03 Apr 2019, 22:06

I'm bread boarding the Silicon Fuzz Face trying to decide what I like with regards to transistors and any modifications, I've never played a fuzz face before so it's an interesting journey, but I'm hooked.

I have one issue that I don't know if it's something I've done wrong or if it's the nature of the fuzz face, it's the way the note decays, as the note dies away there comes a point where fuzziness just drops off and the clean note carries on, it's a noticeable step transition, and it seems to be the same with every transistor set I try, and with the straight Fuzz Face circuit, the AxisFace circuit and the Sunface circuit. I'm playing a normal strat, into the fuzz face into a Yamaha THR10C set clean.

Voltages:

Q1
C: 1.39v
B: 0.6v
E: 0v

Q2
C: 4.52v
B: 1.39v
E: 0.75v

I've had to change the 33k resistor from the battery to Q1 Collector to 100K to get the bias voltage to 1.4v, which I read somewhere was the right voltage... only wish I could remember where I read it.

Basically I've ripped up the bread board several times, tried various transistors and slight circuit mods, and this effect of the fuzz cutting off if I play a single sustained note is ever present... is this just the nature of the fuzz face and why I never hear anyone sustain a single note on any of the youtube demos? Well maybe they do into an already over driving amp

Any thoughts or advice would be great, thanks.

Electric Warrior · Post by **Electric Warrior** » 07 Apr 2019, 20:09

FlyingWild wrote:I'm bread boarding the Silicon Fuzz Face trying to decide what I like with regards to transistors and any modifications, I've never played a fuzz face before so it's an interesting journey, but I'm hooked.

I have one issue that I don't know if it's something I've done wrong or if it's the nature of the fuzz face, it's the way the note decays, as the note dies away there comes a point where fuzziness just drops off and the clean note carries on, it's a noticeable step transition, and it seems to be the same with every transistor set I try, and with the straight Fuzz Face circuit, the AxisFace circuit and the Sunface circuit. I'm playing a normal strat, into the fuzz face into a Yamaha THR10C set clean.

Voltages:

Q1
C: 1.39v
B: 0.6v
E: 0v

Q2
C: 4.52v
B: 1.39v
E: 0.75v

I've had to change the 33k resistor from the battery to Q1 Collector to 100K to get the bias voltage to 1.4v, which I read somewhere was the right voltage... only wish I could remember where I read it.

Basically I've ripped up the bread board several times, tried various transistors and slight circuit mods, and this effect of the fuzz cutting off if I play a single sustained note is ever present... is this just the nature of the fuzz face and why I never hear anyone sustain a single note on any of the youtube demos? Well maybe they do into an already over driving amp

Any thoughts or advice would be great, thanks.

Maybe you're experiencing the "clean up" everyone is talking about?

The voltages do look good.

1.4 on Q1C is within the range of usable voltages. Silicon Fuzz Faces with low gain transistors tend to bias in that ballpark. A hfe of approx. 200 should get you there with a stock circuit.

As you had to use a larger resistor on Q1C, I guess your transistors have very little gain? What types did you use and what are their hfes? Higher gain types may help..

Also, Q2C seems a little high. I'd expect a lower voltage with Q1C at 1.4 V, but it can vary a lot because of the fuzz pot's tolerance – or did you tweak its collector resistor as well? I don't think this would be a problem, though.

FlyingWild · Post by **FlyingWild** » 09 Apr 2019, 06:54

Hi Electric Warrior, thanks for responding.

I am using lowish gain silicon transistors, 82 for Q1 and 136 for Q2, regarding Q2's collector voltage, that was set to 4.5v using a 10K trimmer pot. The fuzz pot is a C1K that measures 1.028k

With regards to Q1 voltages, I know that the emitter should be at 0, and that the base needs to be at least 0.6v, but not sure what is setting that voltage, is it the 100k feedback resistor? I'm looking at a couple of circuit analysis but they are concentrating on the PNP germanium version of the fuzz face, so although still relevant for helping me understand the circuit a little better the guide voltages they suggest don't work for silicon, well that's my understanding, but happy to be wrong as long as I learn something.

Yesterday I received some BC182 and BC183 so will have a play with some higher gain transistors, but I'm already suspecting I'll end up building two pedals with different transistor sets, the low gain ones clean up really nicely, and I love the middle area where the fuzz creeps in with a slightly heavier picking technique.

Thanks again for your help.

Electric Warrior · Post by **Electric Warrior** » 09 Apr 2019, 12:27

Oh yeah, the trimmer explains it. If you set it to 8k2 you'll probably end up with a lower voltage on Q2C.

The trimmer on Q1 sets the voltages for both, Q1 and Q2 as Q2's collector voltage mostly depend on Q1 and how it is set up.

What's the problem with Q1's base voltage? It mostly depends on the transistor's specs and will always be around 0.6V with silicons in a stock circuit. I wouldn't worry if it were a little lower. With germaniums it's around 0.1V.
As Q1E connects with ground it can only be 0, as we're measuring the voltage between the leads and ground.

The BC183s I have measure between 160 and 200 iirc. In this range it still cleans up perfectly. Maybe yours will be in the same range.
Transistors with higher gain should have a lower voltage on Q1C and a higher voltage on Q2C.

You can also experiment with the hfes. Try matching the transistors instead of using a higher gain one for Q2 to see if you like that better.

FlyingWild · Post by **FlyingWild** » 10 Apr 2019, 08:08

Thanks again Electric Warrior,

Interestingly last night I build a 'Transistor Tester' GM328 for £10 I thought I was worth a go as although my multi meter will read the hfe it seems a bit hit or miss getting good contact with the pins in the socket.

So I retested the two transistors I had in my bread board and got quite different readings:

Q1: 61 (82 - Original measurement)
Q2: 68 (136 - Original measurement)

With a BC183 my new tester is reading 181 and my multi meter 262

Nothing like having significantly differing readings to make you wonder which is correct. My feeling is that the new tester is more consistent, but no idea if it's accurate!

I think there is a simple bread board circuit I can hook up and take measurements and do that maths, which hopefully will shed some light on which is giving me the more accurate reading. I guess at the end of the day for my purposes as long as it's consistent and I can therefore know the relative gain differences between Q1 and Q2 the rest comes down to how it sounds.

I'll be sure to play around with transistors in the same gain range too, thanks for the tip.

Manfred · Post by **Manfred** » 10 Apr 2019, 16:41

Nothing like having significantly differing readings to make you wonder which is correct. My feeling is that the new tester is more consistent, but no idea if it's accurate!

The DC-gain is depending on the collector current the gain decreased to 60% form the maximum in direction to small currents.
Have a look at the datasheet of the BC183.
Therefore, the read gain value is depending on from measuring current.

Manfred · Post by **Manfred** » 10 Apr 2019, 17:55

Here the datasheet:

bc182_bc183_bc184.pdf: (74.53 KiB) Downloaded 111 times

DrNomis · Post by **DrNomis** » 17 Apr 2019, 09:31

I recently converted my red Jim Dunlop JD-F2 Fuzz Face pedal over to two BC108C silicon transistors after the stock circuit board with it's two NTE 158 germanium transistors stopped working, I used a circuit board that I had ordered from Pigeon FX, anyway, from what I remember the two BC108C transistors I used had a very high gain factor of about 800 each and actually sounded really good and smooth, I'll post a list of voltages for you shortly, if you're interested in hearing what my JD-F2 Fuzz Face sounds like, here's a link to a demo I recorded and uploaded to my soundcloud account:

Okay here's a list of voltages that I'm currently measuring in my JD-F2 Fuzz Face pedal, all fixed resistors are 5% carbon composition types with the following values, 470 Ohms, 8.2k, 33k, and 100k, the pots are the 1k Linear and 500k Log CTS types that were fitted as stock standard at the Jim Dunlop factory where it was manufactured.

Q1:

E= 0V.

B= 0.562V.

C= 1.193V.

Q2:

E= 0.608V.

B= 1.193V.

C= 4.00V.

Battery Voltage = 9.29V.

Voltages are positive with respect to ground.

Here's what it currently looks like on the inside of the JD-F2 Fuzz Face pedal: