si fuzz, hook emitter to power?

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Shiny_Beast
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Post by Shiny_Beast »

I just spent hours fighting with a new fuzzface buid only to get it to work when I swapped the pins.

I had to connect the emitter to the 470r on q2.

I notice on this diagram on this page for si the arrows are pointing down to the ground, does this mean the trannie are upid down?

http://fuzzcentral.ssguitar.com/fuzzface.php

Are my bc108s fake and just screwed up? They are the motorola ones available on ebay.

The red lead from the battery is going to the 33k and 470 and all my caps hav neg to ground.

puzzled...

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Post by Mr.Grumpy »

Are you paying attention to polarity? the BC 108s are NPN type, the power needs to be connected to the + on the battery, and the negative terminal to ground. Sounds like you need to put your transistors back in correctly and swap the + and - power leads. Compare the PNP and NPN schematics, and note that the battery polarity is different.

There are transistors that don't conform to the standard pin out, but I don't know if BC108s are one of those. Usually there's a dot or marking to indicate the emitter leg of the transistor.

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Post by RnFR »

108's are CBE, the little tab marks the E, and NPN. if you have all of the above sorted, it could just be a manufacturing error.
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Post by Shiny_Beast »

I'm prety sure it's connected right, I checked quite a few times.

With my probe get an open circuit can to emitter, but zero resistence collector to can. I assume the can is supposed to short to the emitter for grounding purposes?

These are supposed to be old motorola, did they do them different back then?

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Post by Shiny_Beast »

So I tried reversing oth trannies and it stoppdworking again. Did some reading and collector to case short looks like it may be typical for old to-18 devices.
So I setup Q2 as some kind of follower and the noise went away.

It's not just a noise issue, the sound itself is brittle.

How are you supposed to use these old bc108s?

<sigh>

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Post by Shiny_Beast »

So I threw a pf cap across the coll-base of Q2 (just holding i with my had), magic hiss erasor...wtf? The gains are around 220-300 each, not 700. How did they ever use these trans in the old days? I'm guessing these are NOS, but not the legendary NOS of legendary ff days and basically suck for pedals, at least in terms of noise.

So where do you get some rea vintage 108 :)

small bear?

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Post by mictester »

Shiny_Beast wrote:
So where do you get some real vintage 108 :)

small bear?
Don't bother. You will be wasting your money. A modern BC108 will be exactly the same as a 1970 BC108. That's why the part numbers are the same. In many cases they will be coming off the same production machinery today that they were forty years ago.

If a simple circuit like a Fuzz Face doesn't work, you have made a wiring error, or put the components in the wrong places, or put the transistors the wrong way 'round, or your soldering is bad, or you have a short somewhere, or your battery's dead....
"Why is it humming?" "Because it doesn't know the words!"

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Post by DrNomis »

I found that a good modern alternative to the BC108, and BC108C, is the BC548C NPN Silicon Transistor, these come in a black plastic case, you can also use a BC549C, a BC547B, and a BC547C too, these will all behave in the same way as the BC107, BC108, BC109 when used in a Fuzz Face circuit... :D


Check the voltages on the collectors of both the transistors with a multimeter set to read volts, when the circuit is working normally, you should see about 1.2 to 1.6V on Q1's collector, and about 4.5 to 5.4 V on Q2's collector.... :D
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Post by Shiny_Beast »

Those are the readings I get, there's just so much hiss, mind you I have the vol and fuzz hardwired to max, eventually there will be a volume pot.

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Post by DrNomis »

Shiny_Beast wrote:Those are the readings I get, there's just so much hiss, mind you I have the vol and fuzz hardwired to max, eventually there will be a volume pot.

You will get alot of hiss with Fuzz Face circuits, especially if you use carbon composition resistors, sometimes the hissing can actually be the circuit self-oscillating at very high frequencies, the way to improve it is to put a 100pF capacitor in parallel with the C-B junctions of each transistor.... :D
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Post by mictester »

Shiny_Beast wrote:Those are the readings I get, there's just so much hiss, mind you I have the vol and fuzz hardwired to max, eventually there will be a volume pot.
You've got the Volume wide open - that'll be LOUD!!! Bypass the HF noise with 100 or 220 pF base to collector of each transistor. My "preset" silicon fuzz face circuit uses two 560 ohm resistors in series from the emitter of the second transistor to ground. I then put a 10 uF electrolytic from the junction of the resistors to ground. This sets the "Fuzz" pot halfway up, which I find to be about right.
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Post by Shiny_Beast »

ya the cap trick does it, I bet 10pf would work on Q2.
So that's transistor oscillation then...cool

tx all

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Post by DrNomis »

Shiny_Beast wrote:ya the cap trick does it, I bet 10pf would work on Q2.
So that's transistor oscillation then...cool

tx all

10pF is too small a value, and won't work well enough, 100pF should work fine, and in fact it does, I made a Si Fuzz Face using two BC548C transistors with an average gain of about 600, and put two 100pF caps in parallel with the C-B junctions of both the transistors and that was enough to stop the self-oscillation.... :D
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Post by Shiny_Beast »

So how do these modern builders do it? cherry pick the bc108s? I doubt there's a lot of CB caps in the AM bc108.

I guess in the 60s many of these units you just couldn't turn the fuzz all the way up?

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Post by DrNomis »

Shiny_Beast wrote:So how do these modern builders do it? cherry pick the bc108s? I doubt there's a lot of CB caps in the AM bc108.

I guess in the 60s many of these units you just couldn't turn the fuzz all the way up?

When it comes to BC108 transistors, you don't have to be as picky when selecting them as you do with Germanium transistors, the BC108 is a Silicon NPN transistor, and is therefore more stable than a Germanium transistor, if you get together a few BC108 transistors, you'll find that they will measure very close to each other in an HFE test, this is because Silicon transistors have leakages about 1000 times less than Germanium Transistors, we're talking Nano-Amps here as compared to Micro-Amps in the case of Germanium Transistors, so, you should be able to use any pair of BC108 transistors in a Fuzz Face circuit and they should work fine..... :D

Incidentally, the inherent stability of BC108 Silicon NPN transistors is why Dallas Arbiter switched over to them in the first place, back in the 40's when the transistor was first invented by Brattain,Bardeen, and Shockley, they used Germanium as the semiconductor, they experienced alot of trouble getting any gain out of the first transistor they invented which was a point-contact type, that is, thin wires with sharp points were made to touch the sliver of Germanium, as transistor technology developed and matured, they gradually managed to increase both the gain and also the frequency range that the transistor could operate on, granted the early transistors weren't actually that good at all, eventually Germanium was phased-out in favor of Silicon... :D
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Post by Shiny_Beast »

So I got it working, I can see this as a fuzz used by players that use clean amps. I put an input resistor to keep from overloading the input, but on this one I'm sort of wishing I left it out, it's kind of bright.

I like by ge ones in front of my marshall, ths guy has too much gain for that IMO right now, no surprise there. Its hard wired fo max gain, geuss I'll have to muck around with that.

Thanks all

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Post by Shiny_Beast »

DrNomis wrote:
Shiny_Beast wrote:So how do these modern builders do it? cherry pick the bc108s? I doubt there's a lot of CB caps in the AM bc108.

I guess in the 60s many of these units you just couldn't turn the fuzz all the way up?

When it comes to BC108 transistors, you don't have to be as picky when selecting them as you do with Germanium transistors, the BC108 is a Silicon NPN transistor, and is therefore more stable than a Germanium transistor, if you get together a few BC108 transistors, you'll find that they will measure very close to each other in an HFE test, this is because Silicon transistors have leakages about 1000 times less than Germanium Transistors, we're talking Nano-Amps here as compared to Micro-Amps in the case of Germanium Transistors, so, you should be able to use any pair of BC108 transistors in a Fuzz Face circuit and they should work fine..... :D

Incidentally, the inherent stability of BC108 Silicon NPN transistors is why Dallas Arbiter switched over to them in the first place, back in the 40's when the transistor was first invented by Brattain,Bardeen, and Shockley, they used Germanium as the semiconductor, they experienced alot of trouble getting any gain out of the first transistor they invented which was a point-contact type, that is, thin wires with sharp points were made to touch the sliver of Germanium, as transistor technology developed and matured, they gradually managed to increase both the gain and also the frequency range that the transistor could operate on, granted the early transistors weren't actually that good at all, eventually Germanium was phased-out in favor of Silicon... :D
So why do I have to put a cap across the junction of Q2, or not turn the fuzz all the way up? Every gut shot I've seen of modern or old bc108 fuzzes has none of tis, or any extra emitter resisters etc...

I just have crappy bc108s I guess.

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Post by Shiny_Beast »

Sop I cleaned up the lead dress a bit and that seemed to help some what. Also I think I'd scorched the test trannies I had in there pretty good s I grabbed some fresh ones. Still some white noise, but it's starting to make sense. Strill oesn't sound as clean as the demos on youtube though. Maybe those guys just throw 10 or 20 nto the jig untill they find a nice quiet pair that sounds right? Especially for Q2...

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Post by DrNomis »

Shiny_Beast wrote:
DrNomis wrote:
Shiny_Beast wrote:So how do these modern builders do it? cherry pick the bc108s? I doubt there's a lot of CB caps in the AM bc108.

I guess in the 60s many of these units you just couldn't turn the fuzz all the way up?

When it comes to BC108 transistors, you don't have to be as picky when selecting them as you do with Germanium transistors, the BC108 is a Silicon NPN transistor, and is therefore more stable than a Germanium transistor, if you get together a few BC108 transistors, you'll find that they will measure very close to each other in an HFE test, this is because Silicon transistors have leakages about 1000 times less than Germanium Transistors, we're talking Nano-Amps here as compared to Micro-Amps in the case of Germanium Transistors, so, you should be able to use any pair of BC108 transistors in a Fuzz Face circuit and they should work fine..... :D

Incidentally, the inherent stability of BC108 Silicon NPN transistors is why Dallas Arbiter switched over to them in the first place, back in the 40's when the transistor was first invented by Brattain,Bardeen, and Shockley, they used Germanium as the semiconductor, they experienced alot of trouble getting any gain out of the first transistor they invented which was a point-contact type, that is, thin wires with sharp points were made to touch the sliver of Germanium, as transistor technology developed and matured, they gradually managed to increase both the gain and also the frequency range that the transistor could operate on, granted the early transistors weren't actually that good at all, eventually Germanium was phased-out in favor of Silicon... :D
So why do I have to put a cap across the junction of Q2, or not turn the fuzz all the way up? Every gut shot I've seen of modern or old bc108 fuzzes has none of tis, or any extra emitter resisters etc...

I just have crappy bc108s I guess.

The capacitor acts as a negative-feedback path from each transistors collector, to it's base, reducing the gain of each transistor at high frequencies.... :D
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Post by RnFR »

sometimes noise at max gain is the nature of the beast with these old fuzzes. that is why people have come up with these modifications. if you still don't have a volume control, and the gain is maxxed out as well, of course it is going to be noisy. you are probably slamming the input of your amp, which is compressing the shit out of the signal and bringing up the noise floor. put the volume control and gain control on the circuit. also, boxing up the effect will have an effect on the noise as well.
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