Marshall - JMP-1: footswitch schematic?

[Solidhex]

Does anyone know where I might be able to find a schematic for the Marshall JMP-1 preamp's footswitch? My friend wanted me to build one for him since they are sort of hard to find/super expensive. He thinks it uses a midi cable. Not sure its something I want to tangle with but was hoping to take a look and make sure...

--Brad

[JiM]

As a start you can look at the JMP-1 schematic here : http://www.drtube.com/marshall.htm#JMP-1
On page 5 you can see it has MIDI in/out/thru sockets, and a Footswitch connector too. It looks like a DIN connector, but with 6 points, not 5 as MIDI.

According to the pull-up resistors R2, R3, R4 and R38, I would try to switch the pins 1, 3, 4 and 5 of the FS connector to ground (available on pin 2) in various combinations, and see what it does.

For field testing, an unfolded paperclip will do

[Solidhex]

Yo

Awesome thanks JIM. Looks like 6 pin DIN cables are plentiful. Seems a lot simpler (hopefully) than I thought. If its just a matter of routing 1,3,4, and 5 to pin 2 (ground) with footswitches that would be a cinch. I'm guessing pin 6 is providing some positive current for routing through leds on the fooswitches...

--Brad

[JiM]

You're right, it's really simple.
In the meantime i've found a thread on a french forum explaining the build (unfortunately the pictures are gone) : http://www.guitariste.com/forums/le-coi ... 88564.html

quick&dirty translation of the relevant part of the original post :

testing with 2 paperclips, i've found that you just need to connect pin 1 to ground to activate memory 1,
pin 3 to ground activate memory 2
pin 4 to ground activate memory 3
pin 5 to ground activate memory 4

bottom line :
4 momenty switches, 1 din male solder connector, 5 meters of 6-wire câble : 15 euros
1 box : 30 euros

If you don't want the LEDs, you just need 4 SPST MOMENTARY footswitches :

Code: Select all

1  3  4  5
|  |  |  |
 /A /B /C /D
|__|__|__|
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2

But if you want the LEDs, you'll need DPDT momentary and some kind of latching ... maybe that's a reason of the high price of the original Marshall part.

[Solidhex]

Yeah

Not having much luck finding a latching momentary dpdt footswitch so my friend will have to do without the leds... Think I'll order up some of these from Small Bear... Http://www.smallbearelec.com/Detail.bok?no=26

Thanks, Brad

[JiM]

This one is half the price : http://www.smallbearelec.com/Detail.bok?no=672

When i said "some latching", i meant flip-flops (discrete or IC like two CD4013). I don't think an hybrid switch (DPDT with one pole momentary and one pole latching) exists, let alone in footswitch version.

For example, the NC contact of each SPDT switch is connected to the SET of its own flip-flop, and to the RESET of the other three flip-flops. All SET and RESET pins must have pull-up resistors. The output of each flip-flop drives a LED (maybe thru a transistor for more current).

When you hit a footswitch, you connect its center pin (GND) to the NO contact, ie the JMP-1 input pin. At the same time, you disconnect the center pin from the NC contact, allowing the pull-up resistor to Set the flip-flop and to light the led. It also activates the Reset pin of all the others flip-flops, shutting off all the other leds. When you release the momentary footswitch, the Set pin gets connected to GND again, and the flip-flops keep their previous state : one led is still lit, and the others stay dark..

So if you want indicators you'll need : 4 leds and their protection resistors, 2 CD4013, 8 pull-up (100k ?) resistors, 4 transistors (any NPN will do), and 4 SPDT momentary footwitches (instead of SPST).
Or you can tell your friend that it's too complicated

[Solidhex]

Ah!

I see. I got a little confused with the term latching. I wouldn't mind taking on a little challenge (for me and my limited knowledge of things like that). I'll go online and educate myself a bit about Flip Flops...
I really appreciate all your help. Hopefully I can get a schem/layout for it together to share.

--Brad

[Circo Maldito]

This one is half the price : http://www.smallbearelec.com/Detail.bok?no=672

When i said "some latching", i meant flip-flops (discrete or IC like two CD4013). I don't think an hybrid switch (DPDT with one pole momentary and one pole latching) exists, let alone in footswitch version.

For example, the NC contact of each SPDT switch is connected to the SET of its own flip-flop, and to the RESET of the other three flip-flops. All SET and RESET pins must have pull-up resistors. The output of each flip-flop drives a LED (maybe thru a transistor for more current).

When you hit a footswitch, you connect its center pin (GND) to the NO contact, ie the JMP-1 input pin. At the same time, you disconnect the center pin from the NC contact, allowing the pull-up resistor to Set the flip-flop and to light the led. It also activates the Reset pin of all the others flip-flops, shutting off all the other leds. When you release the momentary footswitch, the Set pin gets connected to GND again, and the flip-flops keep their previous state : one led is still lit, and the others stay dark..

So if you want indicators you'll need : 4 leds and their protection resistors, 2 CD4013, 8 pull-up (100k ?) resistors, 4 transistors (any NPN will do), and 4 SPDT momentary footwitches (instead of SPST).
Or you can tell your friend that it's too complicated

Hi, thanks for all that, gonna get home and try it, on the other hand I must do this, visit my web site http://www.circomaldito.cl and you can download my entire new CD from http://www.circomaldito.cl/Circo_Maldit ... _circo.zip ... and if you have a couple of minutes give a feedback or spread the music .... greetings from Chile. Tito.

[patafix]

Caution necro bumb !

I Just bought a JMP1, and plan to build a 4 button pedalboard for it.

One seller en Reverb builds one, which contains a small PCB, with 2 IC's, a few resistors and capacitors. Il found a schematic for a 6100 pedalboard (3 button).

http://home.myfairpoint.net/vze1u14s/si ... switch.gif

This makes such a schematic quite appropriate, connecting pin 5 of the HC86 to the 4th switch instead of V+ !

[karul]

One seller en Reverb builds one, which contains a small PCB, with 2 IC's, a few resistors and capacitors. Il found a schematic for a 6100 pedalboard (3 button).

patafix, keep in mind for the next time, links for the schematic like the one you've posted can be lost. In order to be preserved it's better to upload the image directly on the forum. I hope xD.

[patafix]

Thanks very muck Karul, I didn't even know such an upload was possible.

One seller en Reverb builds one, which contains a small PCB, with 2 IC's, a few resistors and capacitors. Il found a schematic for a 6100 pedalboard (3 button).

patafix, keep in mind for the next time, links for the schematic like the one you've posted can be lost. In order to be preserved it's better to upload the image directly on the forum. I hope xD.