Midi-controlled analog volume pedal: how-to or available, anyone?

[bassdude]

In the interests of full disclosure, I'M NOT AN ORGAN PLAYER! However, it seems like there's right mix of expertise here to accomplish my goal, which is: To control volume of an analog (1/4" cable) signal via a midi expression pedal.

Now, before I get evicted as an imposter, I'd like to know if anyone here has already done this. Alternatively, I'm confident that someone could guide me through what needs to be done.

As per my handle, I play bass which I've recently midi-fied so I can play a Roland XV-2020 synth module. Midi/synth patch selection & continuous controller/expression comes via a Behringer FCB-1010. Since I have 2 expression pedals available, one of which already controls the volume of the midi chain, I'd like to be able to employ the 2nd expression where appropriate to also control the volume of the raw bass (analog) signal. The midi control via that pedal would need to be on a separate channel, and I envisage the required volume controller device would need:

- midi-in port
- 1/4" audio in
- 1/4"audio out
- (optional, nice to have) some switch/pushbutton/whatever to allow selection of midi channel to accept input on

Is there perhaps even some salvagable organ parts that could do something like this?

Peter Sharp
Ballarat Australia

[ggoodesa]

Hi Peter,

Rather an interesting idea... but wouldn't be easier to simply have a pedal that controls the Audio volume, rather than a MIDIfied pedal that uses MIDI signals that have to be decoded to perform the volume control? A simple LED -> Light Receiving Diode with a variable filter is the simplest solution (used by Hammond organs and many others).

Pop on over to the MIDIBox site/wiki/forum to get some DIY MIDI information (http://www.ucapps.de). A MIDI to CV solution might be the best approach if you want to stick with MIDI....

Kind regards,
GrahamG

[bassdude]

The attractive part of my idea is being able to use the 2 midi expression pedals together (if needed) to control volume of both signal paths in unison by operating both simultaneously with one foot. Also, it saves me having to run a send & return from the amp for live operation. The bass (with Roland GK-3B split pickup) plugs directly into an Axon AX100 (guitar to midi converter) - here's the setup:

Bass -> Roland GK-3B -> Axon AX100 -> Midi Solutions Quadra Merge -> Roland XV-2020 (half-rack synth module) -> Eden Nemesis ENX-260 bass amp (Aux input)
Also:
Behringer FCB-1010 -> Midi Solutions Quadra Merge -> etc
Plus:
The raw bass signal is fed directly from the Axon into the Eden's input line

A foot switch allows me to mute the bass input signal in the Eden, but the mute function has no effect on the Aux (synth input). However I'm able to effectively mute the synth with one of the FCB's midi expression pedals to control volume. Being able to control overall volume of both signal chains from the FCB would be much cleaner & more workable for me than to add another analog volume pedal into the clutter.

Thanks for the link - I'll explore that when I get the chance.

BTW, there is such a product available - see http://www.prostage.eu/en/shop/shop_1.html But at €198 I'd much rather explore a possible DIY solution if I can.

Peter

[bassdude]

Good news: I sent a query to Tom Scarff about Miduino kits, and his reply was that this kit (http://tomscarff.110mb.com/midi_light_dimmer/midi_light_dimmer.htm) can be easily adapted to control audio volume. And for about about 1/4 the cost of the above solution :-)

Peter

[ggoodesa]

Hi Peter,
I had forgotten about Tom's MIDI units... I used one of his earlier DIY boards with great success on one of my first Organ Console conversion to MIDI :)

Glad you found his site and got the information you needed,

GrahamG

[ggoodesa]

Hi,
I just had a look at Tom's site again, and see that he has a great range of MIDI bits that DIY people like myself can have a lot of fun with. Thanks again for posting the link.
GrahamG

[PeteKnobloch]

Good news: I sent a query to Tom Scarff about Miduino kits, and his reply was that this kit (http://tomscarff.110mb.com/midi_light_dimmer/midi_light_dimmer.htm) can be easily adapted to control audio volume. And for about about 1/4 the cost of the above solution :-)

Peter
I wonder if Tom thought you were connecting and analog pot to your swell shoe and feeding in a variable voltage into his board and the board would send out Midi volume commands.

The output from this board is normally “Pulse Width Modulated” output. Maybe you could take the PWM output, run it into a big capacitor-resister that would give you an analog voltage (0-5vdc) that would feed an analog FET circuit to give you control of the volume. There may be IC's that can control analog volume from a DC voltage but I don't know of any.

Pete

[PeteKnobloch]

You should be able to take the output of the PWM signal and send it to a light bulb (not a LED). As the Midi volume goes up, the lamp glows brighter. Use a cadmium sulphide (CdS) photo cell and place it in series with the audio input and output. This photo cell acts like a variable resistor, the more light that falls on it, the less the resistance is. Disadvantage is that you won't be able to turn the audio off completely. You may see some audio attenuation when fully turned ON do the input impedance of the power amp and your photo cell. Placing a resister in parallel with the output like a 470 ohm resistor can help with one issue but aggravate the other.

Pete

[bassdude]

Tom said he he could supply a readily modified version of that dimmer module that will output the required CV for operating a VCA circuit. If the unmodified module indeed generates PWM, then perhaps this (http://highlyliquid.com/midi-decoders/md24/) with 24 controls (logic or PWM) for about the same price sounds like a great deal! Someone posted that on another forum as a possible solution (or part thereof), but I've no clue about turning the PWM into a continuous CV.

Peter Sharp
Ballarat Australia

[PeteKnobloch]

What are the acronyms CV and VCA? I guess VCA is voltage controlled attenuator. And what does the VCA circuit look like that Tom is suggesting? It sounds like he can modify his board to feed the VCA but who supplies the VCA?

Pete

[bassdude]

Sorry if I sound like I know lots, 'cause I really don't :-) VCA = voltage controlled amplifier and CV = control voltage, ie. the CV is input to the VCA to control the overall output level of the analog input signal. The VCA Tom suggested is this one (http://www.musicfromouterspace.com/analogsynth/DLLVCA001/DLLVCA001.html), which is simply a PCB and parts list.

Peter

[DellAnderson]

Good news: I sent a query to Tom Scarff about Miduino kits, and his reply was that this kit (http://tomscarff.110mb.com/midi_light_dimmer/midi_light_dimmer.htm) can be easily adapted to control audio volume. And for about about 1/4 the cost of the above solution :-)
Peter

Thanks for posting that link. Did he give any specifics or even general clues how to 'easily adapt' to control audio volume? I'm especially interested in the analog -> Midi part, and I suspect that this link is more what would I'm interested in for converting an analog expression pedal to midi output:
http://tomscarff.110mb.com/midi_volume/midi_volume.htm

[Momboc]

This is overkill - but it looks like it will do what you want (responds to MIDI CC 7)

http://www.behringer.com/EN/Products/LX1B-PRO.aspx#featurelist

or build your own

http://midiboutique.com/midiboutique/products/productform.php?prod_id=70900

or this

http://www.doepfer.de/MTV16.htm

with the Control Voltage out of either of the above feeding one of these

http://www.doepfer.de/a130.htm

[PeteKnobloch]

Thanks Peter,

It sounds like Tom knows what he is doing. The LM13700 Transconductance amplifier function does exactly what you want in your project. To bad it needs 2 -12v power supplies (+ and -) to operate. And I am not sure about the range of the Control Voltage signal that is needed in this circuit to give you satisfactory results. Since I am not the expert here you will just have to trust Tom. From what I see, there will be some resistor changes need to get the CV voltages to operate from a 0 to 5v output from the micro processor. I think it is currently operating using a peak-peak voltage of about 8-10 volts due to the statement that says:

I have noticed that for control signals that are operating about ground (i.e. + and - 4 to 5 volts) the pot is usually toward the left when set to linear response and usually toward the right when set to exponential response.

The pot he is talking about is the front panel CV Offset Adjust knob.

Good luck with your poject.

Pete

[bassdude]

I think I'm settled on going with Tom's Miduino solution, to which I'll need to add a VCA kit. Tom said he's happy to supply the Arduino source code it ships with, meaning I can add some midi processing of my own to enhance the midi-out send. I also have a need to add some midi channel multiplexing logic to allow the FCB-1010 expression pedals to control synth volume (or other effects) over multiple channels simultaneously. That will allow me to make the most of the Axon AX100 string splitting capability (ie. separate channel for each bass string) coupled with driving an external synth (the Roland XV-2020). While I'm at it (tinkering with code), I may also add a reverse volume capability/option, so that instead of simultaneous fade & swell of synth & raw bass signals, I can instead also operate the 2 expression pedals in unison to fade out one signal while fading in the other. Sounds like it'll be fun :-)

Peter