People have asked for bass-oriented fuzzes, so I figured I 'd take a shot at one. The tentative result can be seen here:
http://img.photobucket.com/albums/v474/mhammer/Gruntbox.gifI say "tentative" because it is essentially an untested theory-based design on paper. I'm perfing it tonight once the football game is over. If it sounds okay, I'll try and whip up some sound samples and post a schem+sounds package at my website.
The premise is that a bass fuzz wants a clean bottom and some lower-order harmonics. Too much sizzle and the bass loses its role and place in the ensemble. Bass is allowed to sound "angry", but it still has to generally keep its cool if playing behind others. So, what I've done is split the signal into a clean and fuzz channel, with the fuzz channel strategically filtered and mixed back in with the clean. The schem provides a great deal of technical info, a sort of circuit walkthrough in a schem.
The clean channel has a gain of 10 applied and can be full bandwidth or be rolled off. I used the SWTC (Stupidly wonderful tone control) as a variable lowpass filter for the clean channel. The output volume control allows this to be attenuated for effect/bypass level-matching.
The ultra-low stuff from the bass is filtered out before fuzzing, as well as filtered out between stages. Essentially 80% of the fundamental you hear will come from the clean channel. The corner frequencies are sheer guesses. Once I perf and test with my bass I'll know if they're suitable or not. The basic design may hold but component value changes may be needed.
The quad op-amp (LM324/TL074 pinout shown) is used entirely in inverting mode. In order to assure the harmonics are in phase with the fundamentals, the fuzz chennel inverts then re-inverts. Just for the hell of it I figured I'd split the clipping over two stages, as a kind of "affordable experiment" (i.e., tried out something different where it couldn't hurt). One half-cycle is clipped in one stage and the other half cycle is clipped in the subsequent stage. The diode is oriented the same way because the signal is inverted.
The cascaded gains of 10 and 22 give a total gain of 220 at the first clipping stage. This is multiplied again by 10. Because the one half-cycle is clipped by the first diode, I wouldn't consider the total gain applied to be exactly equivalent to 2200. That being said, by the time the other half cycle hits the second diode, it's hot enough. Normally, that much gain would get you over-the-top fuzz. However, with the bottom significantly cut, I'm betting that the resulting signal is just hot enough
The two clipping stages restrict the high end significantly such that mostly lower order harmonics are generated. The highpass filtering after the Harmonics Level control should result in that control introducing mostly a gurgly edge to the bass tone.....or at least that's the hope.
There are only three controls, but quite a bit of flexibility in those three controls. The Clean Tone and Harmonics level controls allow you to dial where the mids and highs come from. Because there is greater sensitivity to the fuzz signal than the clean signal at the mixing stage, rolling off the clean tone and goosing the harmonics should get you a nice bark. Alternatively, you can shut off the harmonics, roll the tone control up to full treble and use the unit as a clean booster if you feel like it. The rolloffs at both the input and output stages shuld help to keep hiss at a minimum.
Once again, this is a
hypothetical circuit, to be verified by a build. It should "work", but whether it sounds as intended using the component values shown is another thing. Even if it sounds as intended, this will not sound all that hot for guitar. But that's fine, guitarists have enough fuzzes of their own I should think. Bass players need a little TLC too.
I kind of like the way the schem is done, and encourage others to include similar sorts of information in the future. It wil be very helpful for newbies, and those trying to jog their thinking.
