Cascading Splitter/Blend

[ElPedro1970]

A buddy of mine is looking for a particular pedal.  I'm pretty sure I could physically build it if I had a layout, but I have no idea how to design the circuitry for what he's looking for.  Hoping y'all can help.

As I understand it, here's what he's looking for:
A box that would take four inputs, and have a single output. The four inputs would be blendable via an expression pedal. So, as you move the pedal, you would progress from input 1 only, to 1+2, to 2 only, to 2+3, to 3 only, to 3+4, and to 4 only.

If it makes any difference, all four of the pedals are overdrive types.

Thank you in advance for any assistance!

[R.G.]

That's one variation of the pedal-morpher I've been tinkering with for ... um, nearly 20 years now. The actual volume and mixing stuff is simple. Getting the correct controls to those volume/mixers is very hard.

It can be done in an analog way, but the complexity of the analog controls explodes as you add conditions and channels.

The simplest way is to use a microcontroller and have the microcontroller interpret what it's getting from the expression pedal and turn that into output signals that control the volume and mixing in some way.

Here's how what you described would work. The expression pedal gives a voltage signal that ranges from zero to five volts (for example). At zero volts, channel 1 is at max volume. As the output of the expression pedal rises from zero to 0.625V, the volume of channel 1 drops to -6db and the level of channel 2 rises to -6db, giving an equal volume as it goes. Then from 0.625V to 1.25V, channel 1 fades smoothly to zero while channel 2 rises the remaining 6db to full on. While these fades are going on, channels 3 and 4 stay at zero volume.

From 1.25V to 2.5V, this fade out/in works for channels 2 and 3, leaving channels 1 and 4 at zero level. Channels 3 and 4 fade out/in from 2.5 to 3.125V, while 1 and 4 stay at zero, and so on up to full channel 4 at 5V.

Forcing the two non-active channels to stay at zero is about as complicated as doing the cross fades.

None of this is magic, it just takes fiddling with the circuits to make the control signals happen the right way.

My effect morpher idea skipped the expression pedal control, I just used foot switches. I designed up a set of voltage controlled amplifiers to do the fading in and out, one per channel. Each channel got a control voltage circuit that ramped up and down at a rate controlled by a user knob - the ramp speed. The section ramped up when fed a logic "1" voltage, 5V in my implementation, and ramped down when fed 0V.

Then I used a CMOS "radio button" circuit to let me set which channel I wanted to be on. Punch the footswitch button for channel 3, and 3 ramps up at the speed set by the ramp speed knob, while all the others either stay down or ramp down if they were on. Punch the button for "1" and channel 1 fades in while 3 fades down, and so on.

This sidestepped the ugly question of how to make channels stay at specific voltages at certain control settngs.

Today, I would probably use a microcontroller to read the switches and buttons, and put the desired output voltages in a lookup table. 

[PRR]

What he said.

> move the pedal, you would progress from input 1 only, to 1+2, to 2 only, to 2+3, to 3 only, to 3+4, and to 4 only.

To get juices flowing, I transposed it to a parallel application-- select/blend four drinks.



You can deliver beer, or tea, etc. You can serve beer+tea, or tea+booze, but you can not serve beer+Moxie. Proportioned as shown, the "blend" overlap would be impossibly small.

An analogous machine for audio levels could be LDRs behind a sliding (or rotating) mostly-opaque mask.



The fade-overs can be adjusted by shaving the mask windows.

But LDRs are going out of style. And having built a similar such thing I think you may spend a LOT of time fighting attenuation/gain/impedance and matching issues; also mechanical issues.

Ah... the windows might be eliminated and the mechanics simplified with a small spot-light (directional LED).



This could obviously be built inside the pedal. Still LDR based.

[PRR]

There is a simple direct electrical approach.....

If you take the carbon-rod out of a battery, and tap/wrap four wires to it, and run a slider along the length, you get the desired action.



The nearly-ready-made solution is to open a wah-pot and use defogger paint to add taps (and bridge any idle-zones at the end).

The mechanicals are simple. But mixing two signals which happen to be out of phase will result in cancellation. Two different fuzzes won't cancel totally. But there's only a handful of basic Fuzzes. And two "similar but different" fuzzes, out of phase, the "similar" will drop-out while the "different" comes through. Which is an effect, but surely not what he hears in his head.

Also the impedances of various fuzzes, and the impedance going out, strongly suggest buffering.

And all four fuzzes presumably get the same input. But 4 fuzzes is a heavy load for some sources.

So that is four fuzz buffers, each with a phase switch. A fuzz-split buffer. An output buffer. At least six opamps if the phase-swap can be done in a single opamp. (R.G. has a plan, but the impedance must be considered.)