Combined Volume And Expression Pedal

[Truth_David]

Hi all,

I am a complete newbie to electronics, and have been for some time involved in the Sustainer project thread. If possible, I need to be able to convert an expression pedal so that it functions both as a volume pedal and an expression pedal simultaneously.

The only pedal I have found that is commercially available that might achieve this is the Visual Sound Visual Volume. But when I wrote to them to enquire about this possibility they said that it might work, but that they would counsel against such a use of the pedal.

The reason I need access to the combination of both in one pedal is that I am trying to find a means of controlling the output from my guitar to my stomp boxes, which are solid state and transparent in terms of the effect they have on the amplifier's sound and tone, whilst simultaneously being able to introduce digital FX in a different point in the signal path, so as to avoid having them going into the front end of the amplifier. I like to be able to 'swell in' my digital reverb, delay and chorus separately from the front end solid state effects, but obviously it is not physically possible to manipulate two foot controllers simultaneously, hence my request.

I need to understand why one could not simply connect the I/O from the guitar to the same pot being used by the expression pedal - I tried it without success. The reason that the Visual Volume pedal might work is that it is a stereo volume pedal that employs a separate gain booster stage for either channel. It is also designed to function as either an expression pedal or a volume pedal. Visual Sound customer support said that it may be possible to use this configuration to have one channel control the expression pedal and the other the volume from the guitar, but that it could damage the circuitry, especially if one were to try using the booster circuitry at the same time on one or both channels.

Can anyone please help with this? As an experienced musician, I would say that such a device would make a great deal of sense, and offer a product that might well have considerable commercial merit, being something that no-one seems to be offering presently. I believe that it would be an indispensable tool for anyone seeking to simultaneously use an effects processor and volume pedal - that's to say anyone who does not rely entirely upon their digital multi-effects processor for all aspects of their sound, and thus only obtain control of the volume by continuous controllers (MIDI messages), which is rather limiting.

So, to re-iterate, the way I intend using the combined expression and volume pedal is to be able to control the input to the stomp boxes in order to gradually introduce gain just as one would with a normal volume pedal, but the idea is to simultaneously also control the selected parameters in the digital effects processor at a different point in the signal path.

Those parameters depend largely upon the device in question, mine is a Boss SE-70, which offers a reasonably wide choice of parameters, and several applicable simultaneously to the expression pedal controller.

At present, I combine compression, overdrive level and digital delay and chorus in order to have them either introduced or faded out according to the position of the pedal. That is fine and works very well, but now I want to experiment with solid state external pedals for the compression and overdrive, and I don't want to have to use the SE-70 as a preamp driving the front end of my amplifier, because it (the amp) is all valve, and I don't want to colour its sound with digital signals.

Thanks to anyone who offers help or advice,

Speak soon,

David

[curtisa]

Without knowing how the unit works I couldn't really say. The manual makes mention of using a standard insert lead when using the pedal for expression duties - do you have such a lead? Can you make the pedal work in expression mode with the SE70 anyway?

Sorry, I've got no idea how the pedal achieves the functions that it does. If you can't make it work the way you just described it, I would guess that it's going to be a hack-up job to do it, requiring a reasonable working knowledge of electronics, and voiding any warranty on the unit in the process.

I'd be doing all that kind of crazy multiple-paramater controlling through MIDI, but then I'm a bit of a control nut anyway

[GregP]

If your device accepts 1/4" expression pedal, it's controlled by a TRS connection coming off a 100K pot. That's all. But it's done by creating a circuit and measuring the resistance through the potentiometer. You can't just "send" expression pedal information-- the effects unit will send some current of its own to the pedal and then measure the amount returned on the other lead.

I don't see how you'd be able to do this successfully with just one pot. Your pedal would have to control 2 separate Pots. Now THAT is something that would be possible, but it'd take some design work.

Greg