Help requested - Johnson J-Station footswitch

[Mark Hammer]

I dusted off my Johnson J-station the other day, to bring to a local blues jam.  The J-Station may be 25 years old, but it provides pretty much everything in a compact desktop package.  Probably a competitor with the early POD, Vamp and similar.  It has a TRS jack for a simple up-down 3-button footswitch to select which of 10 banks of stock presets and 10 user banks of programmable presets, and which of the 3 presets within each bank.  I had a little 3-button momentary footswitch box for something else, plugged it in and two of the footswitches worked fine: the one that scrolls through Banks...in the downward direction, and the one that scrolls through the 3 presets within each bank. 

Of course, the challenge is if you inadvertently scroll past a bank where your desired preset lives, you can't simply do up a bank.

I know there are multi-button footswitches for amplifiers that use a standard TRS plug/jack, but employ some dark magic with diodes to get the thirds and even 4th options.

Do any of you know of a posted schematic for the footswitch for this unit?  Or alternatively, any surefire tricks I could try to implement the 3rd switch?

[Rob Strand]

I know there are multi-button footswitches for amplifiers that use a standard TRS plug/jack, but employ some dark magic with diodes to get the thirds and even 4th options.

Do any of you know of a posted schematic for the footswitch for this unit?  Or alternatively, any surefire tricks I could try to implement the 3rd switch?

I know next to nothing about that unit specifically.

It seems the "J3" jack is only for the J3 controller.

What we know about the J3 controller is:
- it has a stereo 6.5mm jack (TRS connections)
- it has three switches  (channel A/B, bank up, bank down)

From what I can tell the other controller options don't use the 3-pin jack.

Beyond that it's all speculation.

Given the constraints there's still quite a few possibilities and yes you can used diodes and that brings up zillions of possibilities.

The simplest possibility is all the switches are momentary (ie. the channel A/B switch is also momentary).

Next is three combinations using basic switch connections.
- switch 1:   T to S
- switch 2:   R to S
- switch 3:   T to R

However we could have channel A/B going to say the tip as an on/off switch or momentary switch; switching from say T to S (or R to S).    Then the banks could be momentary say R to S (or T to S) with diodes pointing in each direction in series with each bank switch.

Sometimes you can measure the voltages between T and S, R and S, R and T and make a better judgement what is going on inside.

If all else fails you could use a midi controller.

EDIT:

I should mention you can use different value resistors in series with the switches to encode which switch!

[Mark Hammer]

Thanks, Rob.  I'm going to try connecting tip and ring, and see what that does (or doesn't do)

[Rob Strand]

Thanks, Rob.  I'm going to try connecting tip and ring, and see what that does (or doesn't do)

My natural inkling would be to try connections to the sleeve first.
(and with some paranoia using a 1k resistor to start with)

[Rob Strand]

I had an idea.  DigiTech is related to Johnson.  So what about a 3 switch DigiTech controller. 

Here's the schematic:



So one button on each line to ground and the third switch pulls both lines to ground via diodes.   (I did think of that method earlier but there's too many options to elaborate on.)

[RickL]

That's what I was going to post. You beat me to it while I was typing. I think you can get away without the third switch that is the equivalent of closing both of the other switches together.

It might even work with just two switches and no diodes.

[Rob Strand]

That's what I was going to post. You beat me to it while I was typing. I think you can get away without the third switch that is the equivalent of closing both of the other switches together.

It might even work with just two switches and no diodes.

It might work with two switches but a bit annoying to use.   A lot of momentary switches are only single contact I think that's why most set-ups use two diodes (1N914 is fine).

It's probably one of the easier versions to decode, at least digitally.  The Fender ones that use zeners seem complicated but they do suite analog decoding; and they get it to work on a two pin connector.   The cop-outs are the DIN 5 connectors.

These days I'm more worried about shorting the pins (hence the 1k resistor).   Modern controllers could be a powered device.  It's likely to have +5V or +3V and ground the some serial digital link (or resistor codes) going back over the  single line.   Virtually no compatibility between other brands or models!

[Rob Strand]

Hard to believe but there's a video:

Digitech FS 3 X Foot Controller On Johnson J Station
https://archive.org/details/digitech-fs-3-x-foot-controller-on-johnson-j-station

As far as I could work out from the digits on the display in the video
the buttons seem to be performing the correct function in terms of preset select
and bank dn/bank up.   ie. the button ordering is identical as well.

[Mark Hammer]

I had an idea.  DigiTech is related to Johnson.  So what about a 3 switch DigiTech controller. 

Here's the schematic:



So one button on each line to ground and the third switch pulls both lines to ground via diodes.   (I did think of that method earlier but there's too many options to elaborate on.)

Digitech owned Johnson, while they were still around. (Kinda makes me curious about what IP they may have taken from Johnson and applied to Digitech gear, but that's another matter.)

I did try connecting the tip and ring, but that did nothing.  I'll try the "diode magic" later today and see if that works.  Thanks!