Big Muff Q1 voltages way off, other trans OK, tried everything...

[Cortex]

Yes. It's unbelievable how many Big Muff debug topics exist out there, and I am really sorry to contribute to the repository but I have to
I made a couple of Muffs [Black Arts Pharaoh version] before and everything was fine.

I made a third one, did it for me personally, and with this one I have problems hehe. I just can't manage to bias the Q1 properly. The voltages on Q2, Q3, Q4, are spot on [looking at the GGG voltage guidelines], but the Q1 is way off. I'm getting like, 5.5V, 0.91V and 0.32V! I can't find the problem at all. Looked for bad solder joints, wrong resistors, even unsoldered them to check em, nope, no errors. Quite frustrating. Any ideas?

I did swap the Q1=MPSA18 [hfe=1000] for the BC550C [hfe=450] just to try it out, and other than the sound becoming a little less aggressive no changes.

Should I fiddle with the resistors until I get the voltages right?

[skrunk]

how does it sound?
those voltages seem ok to me, maybe 0.32v is a little high for Q1E, but even of you got it down to 0.03v or whatever, you probably won't hear a difference, as there's so much clipping going on with the diodes anyway.

[Kesh]

If you're using this vero



then Q1's emitter resistor is way bigger than normal muffs (if there is such a thing) and Q1's collector resistor a little low too, and this would explain your voltages.

[Cortex]

Yep, that's the one.
I made two of these before, for other people, here's a clip of the first one made with carbon film resistors and italian Arcutronik caps

http://soundcloud.com/earthless/faraon-heavy    [just some mindless noodling, heavy riffage between me and my drummer on a rehearsal waiting for the bass player to appear, played on a SG through a Fender Bassman]

This is the other one, metal film resistors, same caps => http://www.youtube.com/watch?v=ScDtrw94L1c   [strat, pop band context, solo starts around 0:50 minute mark]

I made those quite a while back, so I can't remember the voltages, maybe those have the same voltages like I got with mine. I used carbon comp resistors on mine, Evox Rifa sulfide caps [expensive] , Styroflex caps, all the beauties...and I don't like mine I LOVE theirs hahaha. What a bummer.

So, this is R5 that we are talking about right? I should reduce that in order to get those voltages to be close to the GGG guidelines? Will do. Might as wel put a trimpot in there and fine tune this beast.

[Kesh]

Yeah R5, down to 100 or so. But it might not make much difference.

It's a bit weird to have R3/R5 and R2/R1 so close (10 and 12 respectively). I think your going to get about x6 voltage gain out of Q1 instead of the usual x12. Maybe good for taming humbuckers.

Probably won't make too much difference with all the clipping stages yet to come though.

Can't say I believe in cap brand making that much difference in something like a muff. Unless tolerances change C6, C7 and C10, C11. And not resistor type either.

[skrunk]

Yep, that's the one.
I made two of these before, for other people, here's a clip of the first one made with carbon film resistors and italian Arcutronik caps

http://soundcloud.com/earthless/faraon-heavy    [just some mindless noodling, heavy riffage between me and my drummer on a rehearsal waiting for the bass player to appear, played on a SG through a Fender Bassman]

This is the other one, metal film resistors, same caps => http://www.youtube.com/watch?v=ScDtrw94L1c   [strat, pop band context, solo starts around 0:50 minute mark]

I made those quite a while back, so I can't remember the voltages, maybe those have the same voltages like I got with mine. I used carbon comp resistors on mine, Evox Rifa sulfide caps [expensive] , Styroflex caps, all the beauties...and I don't like mine I LOVE theirs hahaha. What a bummer.

So, this is R5 that we are talking about right? I should reduce that in order to get those voltages to be close to the GGG guidelines? Will do. Might as wel put a trimpot in there and fine tune this beast.

sounds like the correct solution would be to take back the one you built for your friend, and give them yours then 
I wouldn't waste time with trimpots.
like Kesh says, it could be just down to the tolerance of the coupling caps.
in what way do they sound different?

[Cortex]

I'm gonna check the voltages on the first one I made tomorrow night, I asked a friend to lend me that one for a minute or two hehe and I will post the voltages here. If it so happens that they are the same, than that's just the way it is, these components that I've put into mine are just not that nice sounding to my ear and that's it.

Well, I used the Evox Rifa caps because I LOVED the sound of them in my Zendrive build [also for a friend haha] and the sound of my Pharaoh muff is very middy [I was going for this so that's okay] and very smooth, there's very little aggression going although there's monstrous gain. I liked the metal film version the most in the end, it gives the already mushy distorted tone an edge, a crisp character, it just sounds way tighter, whereas my carbon comp build sounds way looser. I'm not trippin this, it's true heh.

Here's another clip of the metal film version, but this time I used my Line 6 UX1 and Pod Farm to record this, great tone, at least in my opinion

http://soundcloud.com/earthless/faraon

My sounds way mushier, it has a closed sound, too smooth, I don't know, I'm gonna rebuild it with shitty components and be happy. [Ok, those that I used on builds for friends are not shitty, but worse, or let's say cheaper than very expensive that I used on mine]