2nd LED in simple Marshall channel footswitch

[MrStab]

hi,

i've been meaning to resurrect a basic Marshall channel footswitch from the back of a cupboard for a while (my band's set doesn't have much room for clean tones...). it just has one SPDT, it's not the more common one with the reverb switch. it was designed to have just 1 LED stock. so i put a 1/4" jack in there so i could use it with any guitar lead, and stuck a white LED in before realising that was kinda dumb as my amp has red & green channels lol. i'd cannibalised the original parts, i didn't just needlessly change the colour. anyway, as you guys prolly know, the switching works by the voltage from the tip of the input going from ground to open.

so i was wondering: is there any way to put in a 2nd light for the other channel, instead of just having one light for one channel? presumably i'd need a DPDT. ordinarily i'd just try it, but my concern is making a connection between the tip and ground on the side of the switch where there should be none. would a JFET or MOSFET work, or would that be overkill and is there a simpler method? i noticed at first that putting the main LED in series after the tip before it reached the switch prevented switching, is that something i should exploit? (currently it's wired so the LED V+ splits off at the switch).

this isn't really an important one, just more of a "that'd be cool". i'm slightly colourblind and telling red & green LEDs apart often bugs me so i might go for white or yellow instead of green.

thanks!

[PRR]

Amp schematic?

[MrStab]

erm... i think this is at least most of it: http://elektrotanya.com/PREVIEWS/63463243/23432455/marshall/marshall_dsl100.pdf_1.png

probably goes without saying but i'm after an interchangeable solution, as Marshall footswitches seem to migrate a lot

[PRR]

Can't make sense of that; there must be something more in the off-board wiring.

Google "Marshall channel footswitch schematic" turned up many misses and some possibles.

http://www.amplifiedparts.com/products/P-H471-LED

But if I understand your request(?), it's now an on-off single LED, you want on/on dual LEDs?

[MrStab]

But if I understand your request(?), it's now an on-off single LED, you want on/on dual LEDs?

that's right. if it's any help, it's V+ from the amp fed (via. the tip) into an SPDT lug 3, and ground to lug 2. in my experience, it's compatible at least with the JCM900, JCM2000 and MG series'. i didn't think to measure the voltage when i was last in there - i may have read ~30V somewhere, but not sure if that sounds too extreme or not.

cheers!

[MrStab]

i've just realised - if a Millennium Bypass detects the difference between open circuits & resistance to ground, maybe that'd work, but i can only picture it working with a battery because the Mill. Bypass receiving power & sending it to ground would keep the switch in the On state. um... right? if that were an issue, is there any cheapskate, non-transformer way of isolating it maybe?

i always kinda figured all footswitches worked the same lol, not a technology i'd given much thought to before. screw it, i might try making an MBP and see what happens. i'll use a DPDT to isolate V+ if needs be. worst-case scenario, if all a battery is doing is powering a red LED, it could probably last for at least a few centuries surely. but then, i wonder if that will lock the state as well. now i know why you asked for the schematic, Paul!

[MrStab]

experiment results: using a Millennium (1) Bypass powered from the V+ from the amp, the voltage does indeed seep into the amp, resulting in the status LED on the amp itself glowing dimly when it should be in the Off state. also, the Millenium Bypass LED itself is extremely dim when on.

i'll try a 9V battery isolated to one side of the DPDT & report back.

this really is pointless but i'm taking a break from (other) frustrating failed experiments. lol

Update: seems to work with a 9V battery, the dimly-lit "off" light on my test amp (an MG100DFX) still exists, but there's no notable difference or interference in sound. my gigging amp, a DSL100, has separate lights on the amp itself for either channel, i'll see how that works out tomorrow. i figure i probably could've used the amp V+, but an isolated system is probably a safer bet

[MrStab]

(last unanswered post, i promise!)



one half of DPDT wired as normal for switching, the other with Millennium Bypass control connected to the middle lug, and (9V) battery negative going to the opposite side of V+. no notable issues with amp off standby but haven't tested it with a guitar plugged in as it's late. ive just realised you probably dont even need a MB, could just put LED ground right into it. ah well.