Effect pedal exp port with random voltage stuff as input

So, my girlfriend got this used Boss RE-20 Space Echo pedal for a good price, and after trying it out a bit I can say I like the sound, but it is a bit… boring (which I think was pointed out by someone on this forum a while back). I would definitely not have paid the full price for it.

However, I though I might try to use the expression pedal input for some fun stuff. I have never done this before, so I’m afraid I might overlook a few things, causing damage to the Boss pedal. First, I guess I might check out which voltages the RE-20 can bear. But that should be easy, right?, just measuring what output voltage you have from the exp port.

Second, I thought I would try to use my Minibrute to send CV to the pedal. However, I have also quite a few really simple, home-built curcuits which generates square waves from 0-9 V with frequencies in the audio range, controlling amplitude and pitch with a couple of photoresistors. Anything I should think of here? I’m not sure the pedal is built to be able to sample input from the exp port at audio frequencies, but might high frequencies damage the pedal?

So, I’m really a n00b when it comes to things like this and I’m not really sure what I’m doing. But that means I have lots of fun things to learn… hopefully without damaging too much in the process :slight_smile:

It might or might not work.

Expression pedal ports are not voltage inputs, but rather voltage dividers - the effect sends a voltage, the foot controller attenuates it, and the effect receives it back.

Depending on the part of the circuit in which this “loop” appears, substituting the pedal by a direct CV source might or might not work.

Sending an external powered Voltage into a Jack with unknown circuitry is generally a bad idea.

You can try this with a 9V battery, 2 Wires and the HDMI connector on your shiny new 62" Flatscreen, just poke the 2 wires somewhere and connect the battery, polarization doesn’t matter.

The Jack is clearly labeled Expression Pedal, so its not meant to receive Control Voltages from a standard Modular Plug, as the Pedal is powered from the Pedal and serves as a Voltage Divider:

Inserting a standard CV cable will short Ring and Shield this short +5V To GND. You might want to try an Insert Cable using only the one with Tip/Shield connected.

This only will work if the receiving Circuit inside sensors the Voltage, if it sensors Current you are doomed.

In any way i would not exceed the Supply Voltage of the Pedal, so you either need some clamping Diodes or (tadaaaa!) a Vactrol to make this idiot proof. And Modularitis™ is a mild form of imbecility, how else would you classify a behavior spending thousands of €s for ever more elaborate ways to produce bleeps’n’blurps?

I.e. the pedal might or might not die? :slight_smile:


@fcd72 Thanks, I found that schematic on the web when randomly surfing around for information. My preliminary plan was to measure what the output voltage on the ring was when connecting it to the exp port, confirming the CV I was planning to use did not exceed it. Then, connecting the CV to the ring, and the shield to ground and, well, see what happens. But I’m not sure if unexpected things might happen, like if my curcuits generate voltage spikes and stuff. I guess it is those kind of things a Vactrol might protect from…? Err, perhaps I’ll just play the piano instead.

Yeah, I feel every idea I get right now about how to make music gravitates towards the modular world. Modularitis starting to break out? :’(

I have some BusBoards left….

Yeah, i would look for the spikes, else use quick and dirty some clamping diodes.
A Vactrol is basically a Light Sensitive Resistor and some Light source, so the Minibrute would power the light source (LED) and you use the LSR + another Resistor as Voltage Divider.

@fcd72 BusBoards? Like BreadBoards? To me a Vactrol sounds quite similar to an optocoupler, or am I missing something? (Please, do tell if I’m asking you questions to which I could find answers just by googling, but sometimes I find it easier to get answers through discussions like these.)

Yes, an Optocoupler has a Phototransistor inside thats quick and has sharp edges (next to no hysteresis) and is tailored to reproduce as good as possible digital on/off signals.
A Vactrol is sloooooooooooooooow and has a light sensitive Resistor that has a more or less linear response thus perfect for Control Voltages.

Busboards like in BusBoard

@fcd72 Thanks! Hmm, so, it is a power distribution board for the modules in your modular synth setup? I guess this is a vital thing you should get right at the start (together with a case and a few modules…?), or what? At 16€ I’m tempted, even though I can’t afford anything else in the near future.

i did some googling for diy expression pedal … and this is what i got

Also some people mentioning that other none roland or boss pedals work with the re-20 … the behringer one seems to work too…

And i was the guy who said the re-20 is boring… I didn’t like the sound…Just sounded to digital to me. I want smudge!
Now i got the minifooger analog delay and i’m really happy with that one.

@shiftr Thanks for the link!

I think I don’t find the sound itself that boring, but the amount of possible variations in relation to the price tag. I admit that I am not that experienced in music making, but I can’t get so many interesting tones out of the pedal. Perhaps I just don’t like tape delays in general.