bass fuzz modification

[yousufferbutwhy]

I've been messing with Anderton's Bass Fuzz circuit and have considered a fairly crazy idea.

For the sake of simplicity, I did not include on this drawing my added rotary switch - diode selection addition. I've already pretty much worked out the kinks and got the concept working decently on breadboard, with germaniums, silicons, and LEDs. I'd like to also include one of a higher forward voltage than the others in order to provide a "clean" stage while still halving the AC to be resummed. This way, one could dial up clipping isolated completely to one side of the waveform while the other is just boosted and colored by the op-amp.

I got to thinking about the possibilities here and it occured to me that before the diode selection would be a perfect place to patch in other passive components like tone control and ring mod. So, the idea is to have stereo, normalled switching jacks that operate like the send-return insert jacks on a mixing board. That way, I could do things like have a waveform clipped with an LED for the top half, and parallel an insert with an external filter, then back in have the top half cut off, and summed with the top of the clipped signal. If this at all possible, I'm sure this could get ugly really fast, and I'm kind of after that. The patching possibilities could go pretty far.

I didn't want to be too detailed since this still closely resembles the original.
SO:THIS IS PART OF CRAIG ANDERTON'S DESIGN NOT MINE. BUY THE BOOK.


It occured to me, that this idea may not work with the tone control circuit used. I realize that this shows I don't fully understand what's happening, but it isn't quite like the passive filters (eg Muff tone control) I've read about. So there's my question - if I want to accomplish this, should I just scrap the original capacitor placement and insert a tone control somewhere else? Perhaps place individual tone controls before or after each send/return?

I should note that I've started piecing together a sort of a mini modular synth setup (note: nothing yet that will operate with +/-10V typical modular synth levels) and I'd like to think this would serve me as a sort of crude waveshaper for VCOs as much as it would for simple processing.

So if this noob post isn't too obnoxious, any input would mean a lot to me. Thanks for making it this far.

[Meanderthal]

 The pot you have in there would be another gain control, assuming the 1m stock value of the fixed resistor. I'd remove the 1m in that case because it was there to set the gain, and now it's redundant. As far as filtering goes, switching between caps(like the origional version) as well as diodes will work. Keep in mind that any filtering will work backwards in the feedback loop, as well as more resistance allowing more gain.
Check out the Distortion+ schematic, and the way the gain and filter is set up in there- the more gain, the less bottom end. That's just an example, there's more that can be done in there...

I don't think it's would hurt to throw in an insert like you mentioned if you're building a modular synth... could be kinda interesting.

[yousufferbutwhy]

Thanks very much for your reply.

You've cleared up what I still hadn't wrapped my head around, though I could punch myself for it now. I hadn't deduced that the caps would only create a damn high-pass and that this is the feedback loop that will cancel things out, rather than be summed with the clip signal. I was concerned that this was some kind of bypass filtering. So, it looks like my concern about using it with the send-return isn't needed, because the filtering actually occurs post-clip/sum.

Yes, that's a 1M. I thought to replace the switch with a pot because I thought this would only add the capacitance and give variable rolloff control. I see now that the pot itself isn't just setting the time constant (duh). So, I take it that if I took out the 1M resistor and set the pot at 0 ohm, most of the clipped signal would be cancelled out?

It's the use of feedback in this circuit that I didn't quite grasp before, and I hate to post questions without having done my homework, but I'm getting there. Thanks again.

[Meanderthal]

So, I take it that if I took out the 1M resistor and set the pot at 0 ohm, most of the clipped signal would be cancelled out?

Yep. Also, you could eliminate the intensity pot...

But, before you abandon your idea for an insert in the feedback loop in the context of a modular synth... I wonder what would happen if you patched in a VCF with ADSR envelope generator right there, or maybe an envelope filter?... If you are building a modular, the more options the better, right?

[Meanderthal]

 Hey, wait a minute...

nothing yet that will operate with +/-10V typical modular synth levels

Uhhh... this one is +/- 9v to +/- 15v. Is that why the interest in this particular circuit? The reason I ask is because someone recently posted a simple waveshaping circuit called I think "The Blade" that did many more things than the basic square wave that a distortion usually gives ya...

[yousufferbutwhy]

Yep. Also, you could eliminate the intensity pot...

Well, I'd like seperate drive/intensity and tone controls. The intensity pot is preceded by an electrolytic cap and and couples into the 10k resistor at the start of the drawing. I suppose that more gain = more feedback and thus more filtering in this case. But I might still want to leave it all in for "clean" boosting option.

But, before you abandon your idea for an insert in the feedback loop in the context of a modular synth... I wonder what would happen if you patched in a VCF with ADSR envelope generator right there, or maybe an envelope filter?... If you are building a modular, the more options the better, right?

Oh, I've not abandoned it. With your help I'm seeing that it's almost certainly possible. And yes, there's all sorts of things to try when I get there - ring mod one half of the wave form with a split final output as the carrier and other insanity. And of course, there's tremolo, phasing, VCF with various modulation sources, etc.  Glad you like the idea I was halfass able to test it out using VAZ modular synth software, by messing with the waveshape module and scope until it seemed to roughly emulate a diode. With two "opposing" waveshapers, I was able to blend differently effected halves of the waveform back together with pleasing results.

Uhhh... this one is +/- 9v to +/- 15v. Is that why the interest in this particular circuit? The reason I ask is because someone recently posted a simple waveshaping circuit called I think "The Blade" that did many more things than the basic square wave that a distortion usually gives ya...

Actually, I should have specified that I was talking about the audio signals. Modular synth audio AC is generally a great deal higher than line or guitar level, and requires padding down to cooperate with line level effects and pedals. Cynthia and CMS have modules for the purpose of stepping them down and back up this way. I mentioned it because I didn't want anyone to think I was blasting those kinds of levels through a circuit designed for guitar/bass/keys. The supply voltage doesn't really matter as it's not really designed to work as a VCA.

Yeah, I'm really pleased about the possibilities here. If I had the same CV driving a sawtooth oscillator and a LF filter set just above the fundamental, I could run the clean saw in, patch out one side to the VCF, clip that side to square and leave the other clean. Instant (but probably imperfect = character-filled) hybrid cycle wave. I'll be redrawing this soon. Again, I really appreciate your help.

[Meanderthal]

 Cool. I've always wanted to get started building a modular(sounds like you're well on your way), but I already have my hands full with an Avatar, Mg-1, Pro-1, Polysix, and Juno 106 that I never really use... the forbidden planet is right downstairs...

[yousufferbutwhy]

Well, aside from effects, the start of my "modular" system will be a modified SH-101 arriving in a month. Luckily (for now) my understanding is that it has more or less line levels. A lot of the synths you mentioned can be patched out much the same way, but of course, to the detriment of historical value if they're in good shape.

Okay, so, I've been messing around in LTspice and have almost reached the conclusion that I misunderstood the implementation of using a cap and pot (in series) parallel to the "initial" cap in order to have variable capacitance. Basically, I think I'm going to scratch those the tone circuitry in here, mess with some existing tone circuits, and find one that sounds good "backwards." I'll post a drawing soon, if you or anyone else doesn't mind following up. Thanks again for all your help.

[Meanderthal]

 Check out the filter in the morley wah I was discussing in the other thread. You were pretty close, you just have to tie the pot to ground.

http://www.morleypedals.com/clwes.pdf

[yousufferbutwhy]

Okay - I've hit another (imagined?) stumbling block. I've been reworking the layout and I realized that, with the insert jacks in the type of configuration shown above, any external processing would apply to the negative feedback loop only. Will this just flip the polarity of the resulting waveform, or will it come out as a sort of "reversed" version of the effect? This is where my understanding of phase is reaching its practical limits.

[Meanderthal]

 Yeah, it's reversed- a lowpass will act as a highpass, etc, and attenuation raises gain. That's what makes it an interesting insert point...

[yousufferbutwhy]

Yeah, I can fathom now how the filtering works.. but what about other effects? I suppose I won't really know until I'm able to try, but what would, say, patching in a chorus, delay, or another distortion pedal do? I'm wondering that if the time and/or frequencies got offset/mangled enough, it would cease to cancel out the original waveform and just pass a lot of it?

[Meanderthal]

 Hmmm... see, that's where it gets interesting... I can imagine a delay possibly becoming reversed for instance, but I guess a chorus would still be a chorus.? I also imagine there might be distortion too, but that might be useful. I suppose if the external effect had an inverting output it would only reinforce the signal, not cancel it out, so you'd wind up with a rather nasty sounding opamp distortion. DC offset shouldn't be a problem with coupling caps.
I'm afraid I really have nothing more than imagination to go by at this point though, I've never actually done this, but it's sure something to keep in mind!