Multi-fx: distortion / fuzz / PWM: signal splitter needed?

[Dogue]

I'm building a relatively simple multi-stage distortion/fuzz/PWM/octaver/etc.

Everything past the distortion stage uses the output from the distortion stage.

I'd like to be able to mix the outputs from the various parts (distortion, fuzz, PWM, octaver, etc.). So, I'm planning on having a simple opamp summing mixer at the end. Would it behoove me to put some sort of signal splitter after the distortion, before the rest of the stages? For instance, something like this?

http://www.muzique.com/lab/splitter.htm

[earthtonesaudio]

Yep. It would behoove you hard.

[Dogue]

Cool. Thanks. That's what I thought.

[Dogue]

One more question:

In the mixer stage I'd like to have a pot controlling the amount of Clean signal. (That is, not a "blend" pot but a pot only controlling the amount of clean signal.)

What is a simple way of doing this? Should I have another signal splitter at the very front of the chain, before the distortion, and then have one output go to the distortion and the second output go to the mixer?

I've seen a few of the blend circuits, but I'm wondering if there's a simple solution for this specific application. Thanks again.

[HydrozeenElectronics]

You might want to ad a phase switch to each channel, I was doing something similar and phasing became a real problem.

[Dogue]

You might want to ad a phase switch to each channel, I was doing something similar and phasing became a real problem.

Good idea. I'll try them out together and see if I need to switch the phase on any of the channels.

[RnFR]

it sounds interesting. let us know how it turns out!

[earthtonesaudio]

Should I have another signal splitter at the very front of the chain, before the distortion, and then have one output go to the distortion and the second output go to the mixer?

Yep.

You might want to ad a phase switch to each channel, I was doing something similar and phasing became a real problem.

That's a good idea, but you'll get the most benefit with "similar" signals. Two identical signals out-of-phase will cancel perfectly, but two different signals will not cancel so much. In distortions, the phase is totally mangled so the benefit is generally not as great.

[Dogue]

I'm now approaching the mixer stage.

It is looking like I will have 8 inputs: (Distortion, Fuzz/PWM, Chopper, Sub-octave 1, Sub-octave 2, Sub-octave 3, Weird thing, Clean).

I'm using this as a basis:

http://www.muzique.com/schem/mixer.gif

Is it possible to expand that to 8 inputs using the same TL071?

Also, I had been planning on powering the entire box with one 9V DC input, but the mixer requires 18V. How should I handle this (I'd prefer not to use batteries)?

Thanks again.

Edit: I'd also like to have individual level controls for each input. Assuming I keep the other values the same, should I then insert 100k Audio Pots in series with R1?

Furthermore, the output signals, including the clean, will all be inverted, correct? So if other effects are used in parallel there is risk of phase cancellation?

[JiM]

Is it possible to expand that to 8 inputs using the same TL071?

Yes. Beware of overloading the opamp though (hence the 18V power supply for higher headroom).

Edit: I'd also like to have individual level controls for each input. Assuming I keep the other values the same, should I then insert 100k Audio Pots in series with R1?

You're right, except not as variable resistors in series, but as voltage dividers. Just like volume controls.

Furthermore, the output signals, including the clean, will all be inverted, correct? So if other effects are used in parallel there is risk of phase cancellation?

This mixer inverts, but maybe your fuzz, octaves and "Weird thing" also do. So there's no single answer. You can tweak the splitter to provide an inverted signal if needed : take the output from the collector, like a cathodyne phase splitter in old tube amps.

[Dogue]

Cool, thanks for the advice.

What would be the best way to handle the voltage requirements? The individual stages need 9V, whereas the mixer should have 18V. Should I have an 18V in, and then use a voltage regulator to bring it down to 9V for the effects stages? Or is there a better way?

[earthtonesaudio]

Audio taper volume controls going into the mixer should let you attenuate enough so you don't need 18V. Just run the whole lot off 9V.

[Dogue]

Audio taper volume controls going into the mixer should let you attenuate enough so you don't need 18V. Just run the whole lot off 9V.

In which case do I still use the part of the circuit as is between the DC in and the TL071?

[earthtonesaudio]

Yes.

[Dogue]

Good. I had already wired it up.

One more question: I had originally intended on having quasi "true bypass" for each stage; that is, sending stage's input (from the splitter) and output (to the mixer) to ground when the stage was turned off. Is this worth doing, or should I merely switch the stage's mixer input to ground when switched off?

[Dogue]

So it now seems that when I have one of the unique fuzzes hooked up to the splitter, the other splitter outputs are also affected -- that is, you can hear a good deal of the output from the one fuzz in the splitter outputs, when you should only be hearing the output from the initial distortion stage. Any suggestions? Do I need to insert a diode somewhere? Do I need to use shielded cable for everything?

While this would be very cool if it all worked, I'm beginning to wonder if it wouldn't be much easier to have separate boxes with just a buff n blend on each.

[earthtonesaudio]

At this point a schematic would help considerably. You shouldn't be hearing any crosstalk in the splitter, so it seems likely that one of your circuits is coupling back to the splitter inputs. Also with so little info it's unclear what sort of bypassing scheme would be best.

[Dogue]

OK, here's a rough schematic:

MultiDistorionSchematic.png

[Dogue]

Well, in the process of starting to rewire things using shielded cable, I realized that on the 4093 I had inadvertently wired an output pin to the input, which explains the problem!

If you have other suggestions, though, based on the schematic, I'd be very interested to hear them.

[RnFR]

i wanna hear that thing!