GGG Boutique Early 70's Fuzz Face - Where Should Pots Be When Biasing?

[Rocket Roll]

Hi! I'm about to finish my GGG Boutique Early 70's Fuzz Face ( layout and wiring: http://www.generalguitargadgets.com/pdf/ggg_ff5_lo_b70.pdf , schematic: http://www.generalguitargadgets.com/pdf/ggg_ff5_sc_b70.pdf ). I've installed a 5k helipot trimmer at R5T (while using 1k resistor at R5, as stated in the schematic) and I planned on using BC109C transistors.

I've assumed that one biases one's fuzz while the fuzz is "in working condition" (ie. when everything is mounted - pots, footswitch, etc.) so I was wondering - where should the pots ("Volume", "Mids", "Fuzz") be when biasing (ie. turning the helipot so as to have approximately 4,5V on Q2)? Full up, all the way down, in the middle ("pots at noon")?

(As a footnote, Boutique Early 70's FF has three pots:)



As for transistors, I've got some BC109C with gains of 538, 588, 610, 630 hFE. Too strong? Which for Q1, which for Q2?

(I'm really sorry that I can't figure it out myself, and I would be really grateful for your help. Cheers!)

[GREEN FUZ]

As far as I know it`s not important whether or not the pots and switch are in circuit when biasing.

My recommendation is to just have at it and construct the circuit with what you have. Socketing the trannies is always a good idea. I`m sure you will get something interesting, if not pure and "authentic", upon which you can  base further judgement.

I think you`ll be pleased, as I was with my first completed pedal, just to get any sound out of the thing. You may find that the transistors you have nail the tone you`re looking for immediately without having to stress about the magical gain figures. Later on you can fine tune.
Build the pedal. Let your ears be the judge. If you`re not happy or need further advice come back and ask a million questions.

[Rocket Roll]

Socketing - yes, definitely!

Ok, tomorrow is the "paint day", and I hope I'll have it completed by tomorrow night.

[Rocket Roll]

Right. Finished, biased, found some BC109B transistors (gain around 380hFE), and it "sizzles". Also, some weird "gate" effect is going on. "Sizzle" is at its strongest when the "Fuzz" and "Mid" pots are on the max, but I can hear it in the background pretty much all the time...

...sounds like this: http://www.box.net/shared/rntjlvp4w4

What have I done wrong this time? 

The pedal looks like this:



Innards:

[GREEN FUZ]

What have I done wrong this time? 

Who says it`s wrong? What`s this thing meant to sound like anyway?

Have you tried fiddling with the bias trim whilst playing? Probably a bit tricky. Maybe get a friend to play while you adjust the trim. Point being; the "ideal" bias is not always what sounds best. Trust your ears. Sorry I can`t be more helpful.

[Rocket Roll]

Who says it`s wrong? What`s this thing meant to sound like anyway?

Sounds really great - just the sound I was looking for - now I know what a "classic fuzz sound" is all about, the legends were true! - but if it just weren't for this bloody "sizzle"...

Have you tried fiddling with the bias trim whilst playing? Probably a bit tricky. Maybe get a friend to play while you adjust the trim. Point being; the "ideal" bias is not always what sounds best. Trust your ears. Sorry I can`t be more helpful.

That's where the blues began, really.  I've start playing with the helipot and the pots (had everything at noon) and voila, it "sizzles". It was originally around 6V or so, sounded good... Then I've biased it and it sounds even better, maybe even more "bite", but this "sizzle" and "gating"...

I must debug this one, it has "the sound". I'll try finding some 2N2369A and / or some 2N2219A transistors, but it'll take a couple of weeks. In the meantime, what am I to do? Check transistor voltages?

[slacker]

To set the trim turn the mids all the way down, the other pots don't affect the bias so it doesn't matter where you set them.

From the sound clip it sounds like it might be oscillating or on the edge of oscillating this is probably because your transistors have too much gain.  To stop it try increasing the value of C4 and C5 say 100 - 470pf should do it, or try some lower gain transistors like 2N3904.

You could also post your transistor voltages in case there's a bigger problem.

[Gus]

Do you have C6 installed?  Do you have a different brand battery you can try? 

[jimma]

I've had a few silicon fuzzes do that at max gain, even the GGG 70's fuzz I built, and even my Lovepedal 200 lb does it. I wonder if it's just the nature of the beast. Lower gain transistors helped in my case, but ultimately I run my fuzzes at a little less than max gain into an overdrive set for low gain. Sorry if this doesn't help...

[Rocket Roll]

I'm grateful for the advices, and I've tried them:

To set the trim turn the mids all the way down, the other pots don't affect the bias so it doesn't matter where you set them.

Right, "Mids" do have an effect on bias! When I've turned the "Mids" down, I've noticed that the voltage at Q2 collector had jumped from 4,5V to 6V. I've rebiased.

You could also post your transistor voltages in case there's a bigger problem.

I've measured them (battery reads at about 8,6V), but I can't read them. How do they look like to you, please?

Q1 
Collector: 1.29      (GGG Fuzz General Instructions Guideline: 1,4V)
Base: 0.59            (GGG Fuzz General Instructions Guideline: 0,6V)
Emitter: 0.00        (GGG Fuzz General Instructions Guideline: 0,0V)

Q2
Collector: 4.52       (GGG Fuzz General Instructions Guideline: 4,5V)
Base: 1.29             (GGG Fuzz General Instructions Guideline: 1,4V)
Emitter: 0.66         (GGG Fuzz General Instructions Guideline: 0,8V)

Do you have C6 installed?

I didn't install C6, as I wanted for this fuzz to be battery only - but maybe I should?

Do you have a different brand battery you can try?

I've put a Varta battery in, and get the same "sizzle". Maybe a bit different in character... Here's how it sounds with Varta: http://www.box.net/shared/1795lmy8s0

I've had a few silicon fuzzes do that at max gain, even the GGG 70's fuzz I built, and even my Lovepedal 200 lb does it. I wonder if it's just the nature of the beast.

I'll get some lower-gain transistor ASAP - but, judging by the transistor voltages (again, I can't read them), is there a possibility that anything else is wrong?

Thanks very much for the help!!!

[GREEN FUZ]

+1 on trying lower gain transistors.

Meanwhile, there`s a tip HERE on reducing high end "buzz and hash" which might be pertinent to your problem. Scroll down near to the end ("Refine" your pedal and smooth the tone out ).

There`s some other nuggets of information on the same page which might interest you also.

[Gus]

I would install a C6 start at maybe 100uf 16V at the board.  If the sizzle sound changed with the battery this might help the sizzle part.

Look at the node of R2, R9, R8, R4 the mid? control decouples the battery from the circuit as resistance is added and allows the two gain stages to interact(current in each leg) via the battery internal resistance as a possible cause of what sounds like oscillation(sizzle) .  As you posted the sizzle is min at mid control at 0 ohms?  As a test connect  C6 to this node (R2, R9, R8, R4)and/or keep the mid control at 0 ohms with C6 at the stock spot.
 
The gating is part of the sound of some Si ff types some like it one can design it out
http://www.diystompboxes.com/pedals/gusFuzzFace.gif
This has a bias adjustment, gated to smoother and can use a lot of different Si transistor numbers, high hfe etc.
If you look close it is kind of like the Vox two transistor fuzz.  I added the 100 ohm and 10K to control the first stage gain and the gain/bias pot can be a fixed 2K gain and no 5K or a 1Kgain pot  and a 1K resistor(for the 5K pot)  I like to make the 5K pot external to use it as part of the control of the sound.

[The French connection]

Maybe it could help but i've built exactly the same project with all the component C4 (100pF), C6 (100µF), C5 (10pF) and diode D3, my transistors are 2n3904 since i did'nt received the bc108 i ordered. Everything works fine except that the 5k bias trimpot don't permit me to go to 4.5 V (maxed at 2.7 V) but there's no sizzeling or nothing similar at all, really no noticeable noise...2n3904 are not really expensive, maybe you should give it a try...but it's not the old fashion tones!

[Rocket Roll]

I would install a C6 start at maybe 100uf 16V at the board.  If the sizzle sound changed with the battery this might help the sizzle part.

Unfortunately, it didn't.  Found a 16V tantalum, placed it at C6, nothing has changed.

The gating is part of the sound of some Si ff types some like it one can design it out
http://www.diystompboxes.com/pedals/gusFuzzFace.gif
This has a bias adjustment, gated to smoother and can use a lot of different Si transistor numbers, high hfe etc.
If you look close it is kind of like the Vox two transistor fuzz.  I added the 100 ohm and 10K to control the first stage gain and the gain/bias pot can be a fixed 2K gain and no 5K or a 1Kgain pot  and a 1K resistor(for the 5K pot)  I like to make the 5K pot external to use it as part of the control of the sound.

That one looks very interesting! I hope I'll build it soon.

2n3904 are not really expensive, maybe you should give it a try...but it's not the old fashion tones!

At this point, really, I'll go with any transistor that doesn't "sizzle"... It'll be a couple of weeks before I get some lower-gain transistors. As a sidenote - I have two more BC109B's, I've socketed them (380 hFE at Q1, 390 hFE at Q2) and nothing. The bias was slightly off, but the sound stayed the same.

[Rocket Roll]

Just a quick question regarding biasing! When I bias, do I:

a) keep the black multimeter probe on battery "minus" pole and red multimeter probe on Q2 collector, or do I

b) keep the black multimeter probe on Q2's collector and red multimeter probe on battery "plus" pole?

Because with method a) I get 4,5V and with method b) I get cca 4V. Sorry about doublepost, but I'd like to check everything!

[slacker]

You do it like in method a, black lead on ground/battery negaitive red lead on Q2 collector.

[Rocket Roll]

You do it like in method a, black lead on ground/battery negaitive red lead on Q2 collector.

Right. Got it.

As a comparison, here's how it sounds with "Mid" all the way down, "Volume" and "Fuzz" all the way up, bridge pickup (Stratocaster):

http://www.box.net/shared/alxg57yg4k

Sounds really great, as far as I can tell... Definitely the sound I'm after, definitely has "it". Everything I need, nothing I don't. If it just weren't for that "ssSSS" in the attack and that "szzzZZZZZt!" during the decay!

[Dragonfly]

btw...when biasing, don't shoot for 4.5V ... shoot for 1/2 the battery / power supply voltage. If its exactly 9V, great, shoot for 4.5V...bUT in your case, the battery reads 8.6v, so 1/2 = 4.3V ..something to keep in mind. When GGG or anyone else types "4.5V" that assumes a straight 9V supply. Most of the batteries I get are closer to 9.6-10V, so I set the bias accordingly.

Another tip : insert a small (47-100 ohm) resistor between the fuzz pot lug-1 and ground.

[afrogoose]

"Another tip : insert a small (47-100 ohm) resistor between the fuzz pot lug-1 and ground."

Dragonfly, I haven't heard of this one.  Does this bleed some of the high end off the signal?

[Rocket Roll]

...try increasing the value of C4 and C5 say 100 - 470pf should do it...

I will try this advice, too. I haven't installed a C4 ("GGG General Fuzz Face Instructions" says that C4 "may eliminate or reduce RF interference"), and "GGG parts list" says it can be 10pF or 100pF.

Which one should I use for minimal "loss" in sound? Also, should I use one or two capacitors? Parts layout actually show two optional 10pF capacitors (I've outlined them green):



So, should I use one or two capacitors? And would 10pF or 100pF be better?

(Thanks so much for your help!)