Fuzzbutt = BassThru + Silli-Face II + Miss Piggy

[Bent Penguin]

Hi, I'm a newbie to pedals who's been reading a lot. I've got an interest in a fuzz tweaked just how I want it. It's for an active bass and I'm shooting for consistent, smooth controllable fuzz. Much subtler than the usual fuzz since I don't play rock.

What I've done so far is nabbed the schematic for the Sili-Face II, chosen for silicon stability and the rolled off tone.

http://www.runoffgroove.com/sili-face2.html

Plopped it in between BassThru (of Moosapotamus "paralooper" fame). Chosen because it was the only blend I could find that I could make sense out of, and they used the magic word, bass.

http://www8.plala.or.jp/KandR/cir_bassthru.html
http://www.moosapotamus.com/paraloop/paraloop.htm

And added piggybacked trannies (socketed so I never have to decide) from Miss Piggy v.4

http://www.members.optusnet.com.au/~jethro.dog/index.html

And am trying to stuff that all into one box like this

http://www.damprabbit.com/stomp/Fuzzbutt-1.pdf

I'm breadboarding it first and then going to perfboard but I still have a bunch of questions. Here goes...

Is the 470pf on Q3 there just as a low pass and can I roll off more highs by simply swapping in a bigger cap? Could I even take a trim pot and another 470pf in parallel, wire that in series with the first cap and blend between 470 and 940pf? Any guesses on a value for the trim pot?

Input and output caps. Should C1 be changed from .047 for an active 5 string bass? C10? This is supposed to be a circuit for bass already so I assume they're fine.

Can I remove the resistors and caps between U1 and Q1 (C4, R5, R17, C13) and between Q3 and U3 (C11, C6, R7) as leftover I/O buffer garbage? R7 looks like a keeper maybe.

Is C13 backwards? It seems tying the out of the BassThru to the in of the Sili-Face gives me 2 caps in series going different ways. That can't be good. But who cares really if I delete it in the step above.

VR4 as the volume of the Sili-Face part seems redundant since the box will have a wet/dry blend. Delete it? Or is it more than just a volume?

Apparently input levels to a fuzz are critical, any obvious problems here? Any other thoughts, wishes or warnings? I have some peripheral skills so I feel I know what I'm doing but I really don't. I'm greatful for all snippets of wisdom.

Thanks a bunch and yes, I will be trying the Batman LED.

[brett]

Hi.
I haven't gone over the schematic in great detail, so I might be missing a thing or two.  But here's a couple of ideas.  I think you probably should get rid of R5, R17 and especially C13 (it's way too small, anyway).  C4 will isolate the bias on U1 from the input bias of the Miss Piggy.  

But keep C11, C6 and R7, because you've got a grounded component (VR4) between the output of the Miss Piggy and the input of U2.

Concerning the 0.047 caps.  The input impedance of the op-amps is effectively 1M (R4 and R7), so the cutoff frequency is about 1/(2.pi.1Mohms.47nF) or about 4 Hz (I think).  Anyway, it's ultra, ultra low, so they're aok.

That 470pF cap seems big compared to what I use on a regular guitar signal (100 to 220pF), but given that you're talking bass, you might as well try it out.  If you think it's cutting overtones, reduce it.

Anyway, have fun with it and let us know how it goes.  Cool name, too. :wink:

[Bent Penguin]

Hey Brett, thanks for the tips. I'm having all kinds of trouble getting this to work on the breadboard so I think I'm just going to trim it down to just a fuzz and come back to the blend controls when I understand a bit more.

Thanks again.