LFO Expression Pedal

[slammer88]

Def checkout the Madbean pedals Tappy project, it can output VCO, resistive, and optical control

Saw the tappy, uses the ic of electricdruid. Again it would be costly for me. Trust me, getting even a pencil from outside of Turkey costs shtload of taxes on customs. So i need to solve this with parts that i can find within the country borders..

 

[slammer88]

So.. What should I do?

Make a simple timer circuit from NE555, or go digital with digipots and such.

Assuming that I've made an LFO circuit, how should be the TRS connections then?

 

[lbrutti]

Hi everyone.

I want to make a simple layout that will act exactly like expression ramper; an automated expression pedal so to say.

I want to use this with any pedal that accepts expression pedal to tinker around with its settings externally & automatically.

Expression ramper seems based on Atmega and digipot, but this can be achieved in a more simple way by using a basic LFO circuit. First of all, I'd need a basic full on / full off -you can call pulse- type of expression, with a rate pot indeed.

Has anyone made something like this before?

Before I forget, I'll feed this circuit with 9V, along with other pedals, and the output voltages to EXP should be between 0 to 5V (or 0 to 3.3v, I need to measure the pedals input)

hello! i don't know if this thread is still alive, but I created something similar with an arduino and it's kind of working.
feel free to reuse the code (if you make some products out of it please credit me and, if you feel generous, send me one ).

https://github.com/lbrutti/arduinoModPedal

here a small demo of it

 

[slammer88]

hello! i don't know if this thread is still alive, but I created something similar with an arduino and it's kind of working.
feel free to reuse the code (if you make some products out of it please credit me and, if you feel generous, send me one ).

https://github.com/lbrutti/arduinoModPedal

here a small demo of it

Link seems Dead bro

 

[lbrutti]

Link seems Dead bro

sorry, i thought it was a public repo...just fixed visibility

 

[slammer88]

Can you provide some further info about it? What capabilities does it have? Any extra stuff to do? Which boards are compatible?

 

[lbrutti]

hello,
here's a short description (most insight are available in the code).
Note: the 555 timer in tinkercad is just a placeholder for actual digipot X9C103P.
The circuit is quite simple: an Arduino nano sets the value of a digital potentiometer resistance (specs in repository) according 6 different modes:
- sine
- triangle
- sawtooth
- reverse sawtooth
- square
- random walk

each wave is stored as an array of values at 10 bit resolution (i'm going on memory), rando walk is randomly generated.
Reading rate can be doubled and expression rate and depth (depth in terms of max resistance value) can be se using pots.

It should work on any TRS expression I/O but I tested deeply only on the DD7...well, i should test more with EHX Attack/decay and EXH Good Vibes...


Extra features would be a tap tempo like in the TWA one.

Please note, i created this project without knowing TWA exists, so don't see it as a steal/clone. i'm a nerd who plays guitar and loves tinkering with strange things

 

[pricklyrobot]

If I was trying to do this, I’d look at synth-style VCA circuits. Basically you feed the Send part of whatever pedal’s Expression I/O to the Input of your VCA, the Output of the VCA goes to the Return of the Expression I/O, and you use a Control Voltage (LFO or whatever) to modulate the VCA.

This way, the pedal never gets more voltage than it can handle on the Expression In, because you’re just using the VCA to dynamically attenuate the CV that the pedal itself is presenting at the Expression Out.

 

[giovanni]

If I was trying to do this, I’d look at synth-style VCA circuits. Basically you feed the Send part of whatever pedal’s Expression I/O to the Input of your VCA, the Output of the VCA goes to the Return of the Expression I/O, and you use a Control Voltage (LFO or whatever) to modulate the VCA.

This way, the pedal never gets more voltage than it can handle on the Expression In, because you’re just using the VCA to dynamically attenuate the CV that the pedal itself is presenting at the Expression Out.

IIUC not all pedals support CV as expression input. I know Moogerfooger and EHX do but I’m not sure about others?

 

[Feral Feline]

Even before I got the SideStep, I had dreamt of making something like it.

However, before I managed to acquire the skills and knowledge to do so, along came the SideStep.

I've got the Tappy, too, but am interested in playing with those github files — thanks for sharing @lbrutti.

Headphones aren't working so I'll have to check out the vid later when everyone's awake.

 

[lbrutti]

I just tested it with Good Vibes and actually rocks

 

[pricklyrobot]

IIUC not all pedals support CV as expression input. I know Moogerfooger and EHX do but I’m not sure about others?

I may be wrong, but I think pretty much all Expression “Inputs” (they’re actually loops) work essentially the same way: they send a voltage (i.e. a CV) out (on either Tip or Ring of a TRS cable), it gets attenuated by the pot in the expression pedal, comes back (on Ring, or Tip, no standardization sadly) and adjusts something in your Effect.

The “problem” is that there’s no standard Expression CV range, that all Effects generate/expect back. So some things, like Moogers might be okay having an external modular voltage (roughly -10 through +10V) plugged straight into it, while other pedals (that might be using/expecting 0 to +5 or 0 to +3V) definitely will not be okay.

The beauty of the VCA approach is that you’re just feeding the the Effect its own CV (through a voltage-modulated gate) so you don’t have to worry about finding the safe range.

A couple caveats: you’ll want a VCA that is at unity when fully open and doesn’t add gain, and one that’s DC-coupled.
But if you poke around the synth DIY world there should be plenty stuff that fits that bill.

 

[lbrutti]

I may be wrong, but I think pretty much all Expression “Inputs” (they’re actually loops) work essentially the same way: they send a voltage (i.e. a CV) out (on either Tip or Ring of a TRS cable), it gets attenuated by the pot in the expression pedal, comes back (on Ring, or Tip, no standardization sadly) and adjusts something in your Effect.

The “problem” is that there’s no standard Expression CV range, that all Effects generate/expect back. So some things, like Moogers might be okay having an external modular voltage (roughly -10 through +10V) plugged straight into it, while other pedals (that might be using/expecting 0 to +5 or 0 to +3V) definitely will not be okay.

The beauty of the VCA approach is that you’re just feeding the the Effect its own CV (through a voltage-modulated gate) so you don’t have to worry about finding the safe range.

A couple caveats: you’ll want a VCA that is at unity when fully open and doesn’t add gain, and one that’s DC-coupled.
But if you poke around the synth DIY world there should be plenty stuff that fits that bill.

isn't it the same of applying a passive potetiomenter? that's what any expression/volume pedal essentially is...with a passive approach you're always sure to match the pedal max expected expression voltage.

 

[giovanni]

I may be wrong, but I think pretty much all Expression “Inputs” (they’re actually loops) work essentially the same way: they send a voltage (i.e. a CV) out (on either Tip or Ring of a TRS cable), it gets attenuated by the pot in the expression pedal, comes back (on Ring, or Tip, no standardization sadly) and adjusts something in your Effect.

The “problem” is that there’s no standard Expression CV range, that all Effects generate/expect back. So some things, like Moogers might be okay having an external modular voltage (roughly -10 through +10V) plugged straight into it, while other pedals (that might be using/expecting 0 to +5 or 0 to +3V) definitely will not be okay.

The beauty of the VCA approach is that you’re just feeding the the Effect its own CV (through a voltage-modulated gate) so you don’t have to worry about finding the safe range.

A couple caveats: you’ll want a VCA that is at unity when fully open and doesn’t add gain, and one that’s DC-coupled.
But if you poke around the synth DIY world there should be plenty stuff that fits that bill.

I am gonna need to look at a schematic for the expression input to really understand how this works. You are saying that using a VCA, i.e., a voltage, is equivalent to having a passive resistor (a potentiometer) and I am not sure I understand how that works

 

[pricklyrobot]

In this scenario, the VCA is the “Expression Pedal Pot”, and the LFO CV is “your foot”.

The VCA isn’t generating or adding any voltage to the ‘Expression Loop’, it’s just opening and closing (in response to the LFO) to allow more or less “FX V” to return to your Effect Pedal.