ch switch

[Valvehead]

Ok, im trying to find a schematic on how to do this...Ive searched for hours....nothing.

Want to add a switching circuit to a 2 input jcm 800 that also has a volume (in the Lo jack hole) for the "clean" level.

Ive seen these online but cant find ANY info....ive heard the names SDM and Colossal Amps brought up ...but neither seems to exist.

any scems out there? or does anyone sell a kit ??

[nickb]

If I guess that you want to be able to use a single jack input and then switch it between high and low functions and also that you can control the gain of each then you can do it like this. The diagram is a bit clunky as it was done for a different purpose. V2 represents the input hi jack and the component references don't match the 4010 but you should get the idea by comparing it with the 4010.



Better colors :



4010:

[J M Fahey]

Agree and add: I guess you´ll want fries with that ... sorry, I meant footswitching

You can replace that finger pushed switch with a relay and add a dedicated relay coil jack so you can switch channels remotely.

IF you will do that, ask again and we might suggest a schematic to do so.

[Enzo]

Juan, I believe he has the one where the high gain input jack feeds through an extra gain stage, the low gain jack is after that stage. No switch.

[Valvehead]

yes , i want to foot switch with the low jack , or a new jack , regular mono 1/4" ...so it would switch it as if you were switching the stock lo/hi jacks and adding a volume to even them out. its a 1985 2 input jcm 800 .

if i need to add a relay thats fine, but ive never done that

[J M Fahey]

Juan, I believe he has the one where the high gain input jack feeds through an extra gain stage, the low gain jack is after that stage. No switch.

The original one has no switch, as you say, you must manually unplug and re plug your cable, buy I was referring to Nick B´s suggestion.
Click on the jet black rectangle in his post and you´ll find a hard to see schematic where he shows how to add a switch and an extra volume pot.
I just suggested replacing that *new* switch by a relay.

[nickb]

The original one has no switch, as you say, you must manually unplug and re plug your cable, buy I was referring to Nick B´s suggestion.
Click on the jet black rectangle in his post and you´ll find a hard to see schematic where he shows how to add a switch and an extra volume pot.
I just suggested replacing that *new* switch by a relay.

Sorry about colors Juan- that's another story - I just edited the post with an easier to read version.

This was done as true two-channel JCM800 4010 for someone. The switch was actually a relay (several actually). There was a footswitch and a front panel switch. It looked like this when it was all done.

[J M Fahey]

Oh, I wasn´t dissing your post, quite the contrary
It´s just that I missed it the first time and I guess Enzo also did, so I pointed at the possible cause

As of the relay, wiring it is easy, small problem is where to get power for it.

One possibility is rectifying 6.3VAC filament , getting some 6VDC and using that to feed a 5V relay (plus a LED to indicate channel switching) .
Only problem is that footswitch jack *must* be plastic/isolated from ground, because those +6V will actually be +3V/-3V symmetrical from ground, no big deal, just needs to be considered.

I know some amps (or amp mods) do that; if somebody is aware of one such circuit, please post it for our friend Valvehead; if none appears I´ll draw one, but on my spare time, no promises so as to speed.

FWIW Soldano does a similar thing to feed channel switching Vactrols.

[Valvehead]

thanks JM !! if i can get a scem im sure i can do it

[dstrat]

look up Marshall 2550.
should be all ya need.

[Enzo]

Valvehead, please always use model numbers. JCM800 is a series of amps. Nickb for example uses the 4010 as an example.

Nick circuit is the basic approach, though it still neds anti-pop resistors, and I would use a DPDT relay so I had extra contacts to ground off the high gain signal when it is NOT selected.

[nickb]

thanks JM !! if i can get a scem im sure i can do it

What Juan described is pretty much exactly how I did it. I used a plastic jack for the footswitch connector to isolate it from the chassis. I still have the schematic (below). The two coils marked LU20 are the two relays, you will need only one. One set of contacts is used for the channel switch, the other for the LEDS. There is no need for bleed resistors Enzo mentioned as there is no DC on the contacts - proven and tested in real life. I did get some noise on the rectifier supply and the purpose of the 100nF ceramic capacitor is to remove that.

[Valvehead]

this is a 2204

[nickb]

this is a 2204

It's similar enough to the 4010:

[Valvehead]

what kind of relay will work? i dont need any of the Led stuff.

where it says Htr winding..where exactly does that connect in that circuit ?

same with DC supply