Help with volume pedal electronics

[match]

Hi,

I'm busy with modifying a pedal.
I build a dual 100K b taper pot in it.

1 half will control my effect unit.
The other half of it I want to use as volume for a sampler.

The range reads between 30K and 90K because of the limited sweep of the pedal.

I have a few questions.

Since the sampler is stereo, how to make a circuit so that the 1 pot will control volume of both channels.
How to make it so that it can go from silent to max volume.

BTW. I want the volume sort of min/max (pedal up/pedal down), it's not necessary to have a perfect audio controlling.

Very basic drawing

A B
o o
o o*******
o o

A is controlling the effect pedal, B would be for volume.

[Mick Bailey]

What's the make/model of your sampler? Without this information it's difficult to tell if one pot can simultaneously control both channels.

If you want the pedal to go from zero to full volume you'd have to have the full range of pot rotation. Most regular volume pedals can't fully achieve this, but they will go to zero in the heel-down position. You need to adjust the pot so that the resistance reads close to zero in this position. Your figures show you're losing 40% of the mechanical rotation due to the limited sweep. If you rotate the pot so there's no volume heel-down, you'll only get 60% of the input signal coming out of the pedal at maximum volume.

[match]

actually it's a sample player: AKAI MPX8 compacte sampler machine kopen? | Goedkope | Promo | Sampler

I understand what you say about 60% and starting from zero.
So thats why I hoped maybe there's a little circuit which can handle the volume from min to max, triggered by the limited pot

[Mick Bailey]

Your sampler just has a straightforward stereo/mono output. To control both channels simultaneously you need a dual pot, otherwise you can only use the mono output.

There are circuits that can be controlled off a pot and give full range from the limited pot rotation, but they're usually not quite so simple. Over I've worked on a few that use a VCA (Voltage Controlled Amplifier) where the pot is used to provide a DC voltage that sets the gain of the internal amplifier. Last week I worked on a Vertex system, but the key part of the circuit was gooped with resin and I couldn't determine what components were being used, other than there was just a single IC and perhaps 7 other parts that made up the control side.

Using a VCA is another way round controlling stereo outputs from one pot. The control voltage could be used to simultaneously adjust both L&R channels.

[oc disorder]

Hi Match,

Best I can do is suggest some things to think about - food for thought.
I think you may have to get creatively busy with a hacksaw and build your own custom job!
I saw this picture of an early model Visual Sound volume pedal .. which got me thinking
that by using faders instead of a rotary pot in this manner means you can access the whole
travel of the pot..i.e. from no resistance (short circuit) to the full value of the pot.
The main obvious problem unless the faders/sliders are mounted sideways dirt and grit and drink spills
can fall in it !
You could use stereo faders which would leave you with a spare and as a bonus use it to control your quadraphonic Hi-Fi.


Mick has mentioned the use of a VCA. I'm not sure of your understanding of this but it entails active electronics .. basically it's like a remote control for volume. Some mixing consoles in the '70s and '80s with basic automation used them.

No audio passes through the fader on the desk with these .. the fader has a small dc voltage on it and as that is varied a corresponding
change of volume occurs in the electronic circuit it's connected to - a VCA. ( You don't really need shielded cable to connect to that fader.)

A computer can be connected to this and when synced remembers the voltages on the faders in real time.

Also you can control many channels with just one fader ( e.g. drum kit group of mics)

Here's a link to a VCA data sheet M5241L Datasheet(PDF) - Mitsubishi Electric Semiconductor

Here's another one slightly more sophisticated... http://datasheet.octopart.com/SSM216...sheet-3633.pdf

Another thought that crossed my mind was to use midi , specifically System Exclusive messages for the Akai.

I've been out of touch with the controllers available but there may be some sorta stand alone variable pedal that speaks the language ie
you can set it up to deal with the Akai machines Sys Ex which would turn the machines master volume up and down.

Of course this doesn't address simultaneously adjusting your Effects unit.

Another idea is to go down the Morley Volume pedal road !
I have never seen or tried one so this is an unknown to me (could be issues with min and max vol settings) but they use Light Dependent Resistors (LDR's) and vary the amount of light going to them with a mechanical arm for want of a better word !

It may be hard to build several independent circuits inside with only one light source.

Attaching early model Morley Schematic.

A final thought would be to build a stepped attenuator say 3 stomp switches with 6 preset type pots.

First switch turns everything silent. the second switch cancels the first and inserts the first 3 presets which you could set a half volume.
The 3rd sets it at full volume or whatever you set the other 3 presets at.

In the long run this sorta setup may prove to be more reliable.

I've run out of ideas now ..over to someone else...!

[match]

Thanks all for you interesting insights.
I have indeed build my own pedal from a Vox Tonelab SE. I love the design of that one with 2 pedals in one.
So the options of buying other pedals is a nogo.
As I understand the VCA option is not for starters. Now I am a experienced beginner (have build some little circuits in my life) but I think this is too high for me.

So that leaves me with 1 option. As I want only on(pedal down) and off (pedal up) there might be some simple circuits to switch a stereo signal on/off, controlled by the pot. Lets say above 60k is on, below 60K is off.

Thanks for thinking with me and maybe someone can help me out with the last option.
M

[oc disorder]

excuse rough knock up

oh dear another thought.... you could make 3 plug leads 3 of them to go from unit output to atten and amp/mixer in instead of 6 jack sockets and 6 leads !

[match]

excuse rough knock up

oh dear another thought.... you could make 3 plug leads 3 of them to go from unit output to atten and amp/mixer in instead of 6 jack sockets and 6 leads !

Thanks for your work, but I'm preferably looking for the pedal controlled on/off volume

[Mick Bailey]

Switching a stereo signal on/off from a single pot could be done. The problem you'll come across is that the idea is straightforward, but the circuit to do this is more complex.

When you switch a signal off, the signal source and signal destination expect to see different things. Your sampler would be OK running into an open-circuit, or load resistance, but may not be tolerant of a straight short across the outputs. At least, not for any length of time. Equally, your amp input would hum badly if you just had an open circuit. A shorted input is fine for the amp.

Signal switchers that mute usually take a dual approach - known as series/shunt. You have a switching element (FET, LDR, CMOS switch etc) in series with the input, and one across the output. So the input side goes open and the output goes short.

Using the pot as a switching threshold would require a comparator circuit and the output of this used to control the switching. Again, not entirely simple.

[oc disorder]

One more suggestion , What about using a motorized pot that are used in home theatre ?
That would give you 4 independent mono volume controls controlled by a motor.

The motor usually runs from a low voltage source so safe to make a pedal with momentary switches either end.

The pot could mount in a small box with patch points for audio and one 4 wire cable to the remote to be able to switch polarity
to the motor.

You may be able to find discarded ones , doubt if a quad one would turn up so may have to find 2 stereo ones and drive
both motors from the one supply.

Apart from that Boss make a stereo vol pedal.

[J M Fahey]

You can mount quite a few slider type pots side by side, glue a small metal/plastic/wood strip joining all sliders so they move in unison and move that "control bar" end to end with a piece of string or even better, a piece of semi elastic nylon fishing tackle.
Easily control up to, say, 6 pots; maybe even 8 of them.
The up/down rotating pedal plate has the piece of string attached to both ends, you'll need a small pulley/wheel or two so string moves horizontally front to back moving sliders in unison.
Use relatively short travel sliders (car / minicomponent equalizer type can be had as short as 1" travel, or less).
Hope my verbal description is enough, I won't draw it for you.

[Mick Bailey]

This thread has sparked an interest in exploring the VCA route.

I found a neat circuit here that's pretty straightforward and as soon as I get some personal time I want to breadboard it;

Theremin World - Topic: VCA Circuit

It's dual supply, so would need 2x9v batteries or an ICL7660 configured as a rail splitter.

[match]

This is the final pedal:


And the inside:


So the other options are not applicable. Thanks anyway for thinking with me!

I started this discussion also in a electronics forum and somebody came up with this, which seems to be the solution for my problem.
Help with volume pedal electronics | All About Circuits

[tedmich]

nice welds! If you could post the AAC image here we could all enjoy it without having to sign up!

[match]

nice welds! If you could post the AAC image here we could all enjoy it without having to sign up!

Thanks!

What is a AAC image?