Fender expression pedal questions

[daz]

I have a fender mustang modeling amp. The amp comes with a footswitch but has an optional 4 button switch which i bought that does much more and has a lot of circuitry in it including a LED readout. There is a expression pedal thats optional too, and it plugs into the 4 button switch and i don't think it can be used without the 4 button unit. That tells me that it's probably a simple pedal with a pot and maybe a few components that uses the 4 button switche's circuitry to do it's thing.

Heres why i ask. I want it's volume function to control each patch's volume. But i do NOT want a pedal. I want a simple switch to switch between 2 slightly different volume levels. So if all the expression pedal does is control the volume function via a pot and maybe a few component using the 4 button switch's circuitry, then i think i could build a box to do the same. So the question is, are expression pedal all pretty much the same thing regardless of brand/model of the device it's controlling, and if so are they just simple with a pot and a few components with the control circuitry in the device (or in this instance in the 4 button footswitch) or do they contain a lot of circuitry of thier own?

[Jazz P Bass]

I have not had any of these come through.
That said, I highly doubt that the EXP pedal is 'mearly a pot'.
What the pedal does is it changes 'parameters'. (volume with one click, wah & delay parameters with another click)
If anything, there will most probably be an encoder inside with possibly a small microcontroller so the pedal can communicate with the floor board.
After all, this little beasty of an amp is basically a computer with a speaker.

[daz]

I have not had any of these come through.
That said, I highly doubt that the EXP pedal is 'mearly a pot'.
What the pedal does is it changes 'parameters'. (volume with one click, wah & delay parameters with another click)
If anything, there will most probably be an encoder inside with possibly a small microcontroller so the pedal can communicate with the floor board.
After all, this little beasty of an amp is basically a computer with a speaker.

for the record, if it's telling at all, it is programmable in the amp to assign it to different parameter functions. So it may be that the amp does the work and all the pedal does is change a voltage that signal the end of the parameter and another that signals the beginning such as no volume to 100% or wherever you decide to set it. so it could be that the 4 button switch's circuitry is where at happens and the pedal does nothing more than change a resistance or voltage. i wish i knew someone with one so i could pulling the guts and see whats there. I'm not suggesting it's only a pat by the way, but it could be minimal components and it's only a extension of the 4 buttons circuitry. Look at it from this perspective....what if it and the 4 button were a single combined unit. Then you too the pot the pedal controls and physically removed it from the 4 button and reconnected it via 2 wires. The IS likely just being used as a variable resistor. So they could do it that way and not have to have separate circuitry in both, and this would also speak to why the pedal can't be used w/o the 4 button switch.

I know Enzo is a fender warranty tech...Enzo, any idea?

[Jazz P Bass]

Note: just saying.
A variable resistor is not going to be a very good input to a digital anything.
They are too noisy.
Encoder, phototransistor, hall effect switch, optocoupler.
These are digital inputs.

But, as you said, until someone guts one......Or Enzo gets DSL service at his new digs.

Maybe a call to Fender would shed some light on this quandry.

[Jazz P Bass]

Here you go.
Technology at it's finest.
An Ernie Ball pedal that uses a string.

[g1]

It is my understanding that even with the EXP1 pedal, the volume is a global parameter. A different volume setting can not be assigned to each patch. If you want to change the volume at any time, for any patch, you must do it in real time with the pedal set to volume function.
If this is true, then it can not do what you want to do, having different volume settings for each patch.

[daz]

It is my understanding that even with the EXP1 pedal, the volume is a global parameter. A different volume setting can not be assigned to each patch. If you want to change the volume at any time, for any patch, you must do it in real time with the pedal set to volume function.
If this is true, then it can not do what you want to do, having different volume settings for each patch.

Actually it CAN. All it's functions are per preset and it won't control the global master. Thats fine with me tho.

[teemuk]

That said, I highly doubt that the EXP pedal is 'mearly a pot'.

Well, generally they are pretty much just that.

The manufacturers have few select "standards" of how to wire the pot (and usually one or few series resistors) but overall the insides of the pedal are plain simple, because they can be.

You have a basic analog resistive divider. The controlled unit usually sends it some DC voltage and the varying voltage at wiper is converted to a digital signal, which then effectively doubles as numerical value for the controlled parameter. This is then further on converted to, say, MIDI commands, driving signals for VCAs, etc. But generally what goes and comes out of an expression pedal is just plain DC. All analog and simple. The complexity usually resides in the "receiving end".

But an "expression pedal" implemented to an effects unit or footpedal doesn't neccessarily have to follow any "standards" because it just plugs to specific application. You don't have to worry if an expression pedal in footswitch of a specific amp works with a random selection of keyboards or outboard effect units from various manufacturers because in the end you don't have a separate expression pedal, you have a footswitch for a specific amp.

The "expresssion pedal" in my Zoom 606 multieffect, for example, works with the aid of a magnetic sensor IC that senses the distance of a small metal plate mounted to the rocker pedal. Obviously it suffices as parameter readout configuration, but works entirely differently than resistive division of DC voltage converted to a digital signal. These two interfaces would not be interchangeable with each other, and same applies to all other different interfaces one could imagine. Needless to say, expression pedal in the said Zoom 606 is implemented only to control the Zoom 606, you can't use it as an external control. I would imagine this is also the case with the footswitch of a Fender Mustang.

That said, when it's not a separate expression pedal the designer may have configured it to work in any way he saw fit.

[daz]

If it helps, it connects to the "brain" (i assume the 4 button switch which has a lot of circuitry in it) or 4 button switch via a simple 2 conductor cable. When i say 2 conductor i'm talking tip/sleeve as in guitar cable. So it's gotta be pretty simple. The 4 button switch also uses that cable. You plug the 4 button into the amp normally, but if you have the Ex pedal, you plug the Ex pedal into the amp and the 4 button into the 2nd jack on the ex pedal. The 4 button has just one jack. I wonder if i just put a pot as a voltage divider between the 4 button and amp and select the function i want a Ex pedal to control in the amp's utility if that might either work or give me a clue as to how it might work. On the other hand i imagine that can't work or else any volume pedal would.

[Jazz P Bass]

I found this info over at the Fender Forum.

The Two Button Footswitch:
"Quote:

Has anyone analysed the signal on the wire for this switch?

I decided to do this myself and answer my own question.

The 2-button footswitch is normally open-circuit. Pressing either button closes the circuit with a resistance, for the duration the button is pressed down (ie it's a "non-latching" action rather than "momentary"). The only difference between the two buttons seems to be the resistance value. For the left-hand button, it's about 5 Kohm; the right button is about 15 Kohm (I say "about" as my ohmmeter is old and not completely accurate!).

So I guess the amp detects which button is pressed by measuring the current flow through the switch (or equivalently a voltage drop across the switch):
- no button pressed, no current flow, full voltage drop
- right button pressed, small current flow, medium voltage drop
- left button pressed, big current flow, small voltage drop."

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