I'm building a fuzz for a friend who plays bass in a grindcore band. He already used some effects before, but he wasn't happy with them. Basically muddy lows or something like that.

So I decided to go with a Buzz Box (two Bazz Fuss in series) with leds as diodes to distort the highs, and a LPB1 in parallel to get clean lows, each one with their own volume pot. And a simple buffer after them.

Will this work, or I'll have some problems like phase cancellation or something else? Or any other suggestions? I know I should breadboard it first, but I don't have skills with breadboard .

Hello

Your problem is the two ways (Fuzz in one hand, and flat preamp on the other are in opposite phase : The two fuzz stages invert two times the signal, so they are globaly non inverting, but the flat preamp is one stage, and for that reason inverting...
So when you mix the txo signals with the pots, one is substracted to the other.

If you want to keep the two Fuzz stages, you need a non inverting flat way... It can be an OpAmp, using the non inverting input. If you want to use vintage discreet technology, your flat preamp must use two transistors.

I have not schematics ready to use, but can easily design one, and test it on computer simulation if you need it. Just ask.

Happy to give a hand
Guitar Poppa

Might I humbly suggest this one 



I designed this a few years back using the Bazz Fuss as the fuzz engine (but you could use any overdrive/distortion/fuzz circuit you would like). The biggest issue with any bass overdrive affect is keeping the bass frequencies clean while distorting the mids and highs. The MegaDEN design achieves this by allowing the clean signal to be mixed with the fuzz signal.

I think the only adjustment I have made to this over the years was using a 500k for the Fuzz pot.

Guitar Poppa, got it. So I need to use only one fuzz stage, or two clean preamps in series (or maybe a non inverting single stage preamp?).

Lawrence, I think this should be close to what I'm looking for, but I was thinking in something a little bit simpler (no input buffer and only one output buffer or maybe no buffer if it's possible ). Also I don't know if one Bazz Fuss will have enough gain to play grindcore, but looks like something I should build one for myself, even I'm not a bass player . Do you happen to have a soundclip of if?

Quote from: Marcos - Munky on December 02, 2015, 11:39:10 AM
Do you happen to have a soundclip of if?

How about a vid demo?   

just curious: do the output caps or something else about this circuit make it okay to join opamp outputs like that, Lawrence? i was under the impression it's bad, from a few "opamp stacking" threads, but if you've been using it for ages without issue then maybe it's fine.

https://e2e.ti.com/blogs_/archives/b/thesignal/archive/2013/03/26/paralleling-op-amps-is-it-possible

QuoteDirectly paralleling inputs and output of two op amps is sure to start a serious argument between the two. Differing offset voltages will cause them to fight over the correct output voltage. They may burn all their output current capability in the battle with one output current (sourcing) flowing into the other (sinking current).

@MrStab: Capacitive reactance is a load for IC output..

1μF (Lawrence values) has a resistance of 16 Ohm at 10kHz, 160 Ohm at 1kHz, 1k6 at 100Hz e.t.c. which are more than enough for current sharing purposes..

ah right! cheers, might come in handy for part-count-reduction someday.

Lawrence, it sounds great! I surely will add it to my personal build list. But I think it needs more gain to play grindcore, which should be achieved with two bazz fuss in series, but it'll probably result in phase cancellation too...

a third bazz in series (ever been done before?) would again invert, and solve that cancellation problem. and there should be a mixing resistor (10k, everyone's favourite) at each 50k vol pot, before the buffer.

and the 2 input caps are backwards, especially once you add the pull-down resistor. and the output pull-down.

3 bazz fuss in series? That would give loads of gain! Gonna try it . But I think I should search for a non-inverting clean preamp too, to use with 2 bazz fuss.

For the input caps, I tried them separately in a breadboard and they worked as drawn. But I didn't used any pulldown resistors, so I'll invert them.

And for the 10K resistors, they go between wiper and buffer output cap, right?

yes.

three in a row might be called "big bazz pie". or some similar combination of words.

You can use the MegaDEN circuit with three series Bazz Fuss as is. For two in series, rearrange the inverting opamp stage at the end of the fuzz signal line to be the same as the one at the end of the clean signal line and it will work fine (adds two components).

So, here's what I have until now:


3 bazz fusses in series. Loads of gain here. Also, loads of oscillations and noise too, but I think this is due to breadboard and wirings. I added a gain pot at the first stage. When I breadboarded it, I didn't added those 1K resistors between stages, but I think they'll help to tame the noise and oscillation.

Also, I tried it with a LPB-like in parallel (but with guitar, not bass), sounds like what I'm looking for. I'm not sure, because of the high noise level. I'll try to etch a pcb and see if the noise will be lower. I'm more comfortably etching test pcbs than breadboarding

You could also try running small caps across D1, D2 and D3-D4 to tame the oscillations. I would start with 10p and work up until they are gone. The larger the cap the more you'll hear it affect the tone though.

In parallel with the diodes?

Quote from: Marcos - Munky on December 05, 2015, 12:53:56 AM
In parallel with the diodes?

yes

So, after almost 2 months being busy with some stuff I'm finally building this:


I've built it on breadboard and tested it with my guitar, and I think this will make my friend happy. I forgot to add the values for the caps in parallel with the diodes, I've used 100pF. The "clean" part isn't actually pretty clean, it distorts a little bit, but it doesn't really matter.  I just don't know if I'll get clean lows and distorted highs with those caps values on bass.

your R11 shows 470R - is it really this low, compared to the collector resistor? the combo shown will have a whack load of gain, I think. any decay sputter from the top half?

Yeah, it's 470R. The "clean" part is just a LPB, which uses a 390R, but I happen to be out of 390Rs. It have a whack load of gain, and there's some decay sputter from he top half. I think this is maybe because of the lack of emitter resistor in Q2 and Q3. I also remember there's 2 Bazz Fuss versions, one with 100K resistors and one with 10K resistors, and one have better decay than the other. Just forgot which one have better decay, I just used 10K because I have lots of them XD.