Channel Switching Mod-on a JCM 800?

[Icarus]

Maybe I can help

I have a JCM 800 combo version of the 2203

I have had it modded to have
Two Masters and Two Gain knobs

So I can footswitch between one clean and one dirty ( sound/channel )
or any other combination

I still have the low and high inputs

Also I have had a tube buffered FX loop

Both are modded to be foot switchable ..ie Channel switch and FX loop on/off

I doubt the tech that did the mod will give me any Schematics
But I can take some Pic's if anyone is interested

[neikeel]

Maybe I can help
I have a JCM 800 combo version of the 2203
I have had it modded to have
Two Masters and Two Gain knobs
So I can footswitch between one clean and one dirty ( sound/channel )
or any other combination
I still have the low and high inputs
Also I have had a tube buffered FX loop
Both are modded to be foot switchable ..ie Channel switch and FX loop on/off
I doubt the tech that did the mod will give me any Schematics
But I can take some Pic's if anyone is interested

Would be great to see

[Icarus]

Yeah will do

Im just out of town for a few weeks ,
I will get the pics up when I return home

[sixpakldp]

I'd be interested in this as well. I have my amp set up as a Neil Special from SDM's layouts, when in 2203 mode I can use an A B switch to jump channels easily. The issue is the difference in volume between 2203 high and low makes it too hard to be usable in a live situation. The independent volume control would be good to see as that's the key to remedy the issue. Interested in seeing this.

[herbvis]

Its easy to add an independent volume to balance the channels. Just need to have a relay and add a switchable ground to ground out the added volume pot when you are in the other channel. Switchable grounds are a neat little trick I discovered. You can also use them to prevent the channels bleeding into each other. Im using a collosal amps relay kit and I have 3 channels. The clean has its own gain and additional volume pot in series With the master. It gets grounded out when I switch to the higher gain channnels. Works like a charm.

[garbeaj]

This sounds awesome. I'd love to be able from my regular high input channel on my Rockstah Mod 5 2x12 Marshall combo to a clean channel with no volume drop. It would be awesome to have one guitar (say a strat with an out of phase "Mark Knopfler" tone that isn't achievable on any humbucker equipped guitar) plugged in the clean channel and jump to another guitar (say a Les Paul or Explorer bridge pickup engaged) and use the regular high input channel.

This seems too easy...why don't more amps have this ability?! Maybe I'm just a rube...but I haven't seen an amp with channel switching work that well with no volume drop before.

[sixpakldp]

So I've been talking to Dave at Colossal amps and have ordered one of his relay boards and one of his power supply boards. We exchanged emails a few times and for starts I am going to set my 2 in 1 Plexi/2203 to be foot switchable between Plexi and 2203 mode. He told me that the relay is essentially a dpdt device so I can replace my 1 meg push pull dpdt with a regular 1 meg pot and the relay board. I already have an extra hole in the back of my amp so this is pretty non evasive.

Going to try this first, my end game would be to footswitch between Plexi, 2203 dirty and 2203 clean all with balanced volumes.

That would pretty much be the end all amp solution for me. I don't think there's anything more you could want other than a boost switch so you could switch to a lead sound instantly.

Anyway, well will see how this turns out.

[Tone_Chaser]

Has anyone made any progress putting together a schematic or getting some pics of this mod? I'm still interested in doing it on my amp.

[wdelaney72]

Unfortunately, I’m not able to access the mod in question here. I can, however, share a mod I’ve done with good results.
1. The 2555 layout from SDM has the easiest, simplest switching power supply I’ve seen. It works great.
2. I’ve concluded that to get a usable clean and dirty 2-channel amp out of a jcm800, shared tone controls do not work. Any type of shared volume pot also doesn’t work. At a minimum, an additional volume pot is needed to separate the volume on the 2 channels. Otherwise, I couldn’t get a good volume match between the 2-channels.
Based on this, I resorted to taking the 2203 amp and adding a switchable 1959 channel. For 1959, the tone stack for me always sounds best with Treble and Mid dimed and Bass somewhere around 3-4. I used fixed resistors and created a board for the 1959 tone stack…plenty of open chassis space. I also utilized the 4th preamp tube socket for the 1959 Cathode Follower. I split the signal after the .022 cap from v1 and then bring it back at the PI input.

You will get popping on the footswitch by just splitting the signals as listed above. This can be eliminated by placing a diode across the voltage pins of the relay and also running the 4.7M resistor to ground from each of the relay common pins.

There may be a more simple way, but I use this amp to play out in a cover band and it was the only way to keep the tone pure and match the volume levels from each channel.

If you look at the small board on the far left, you can see the tone stack. There’s also a switchable #39 mod on the 2203 channel, but that’s irrelevant here. Just trying to outline how I did my channel switch. You need a 5th pre-amp tube for the #39 mod.
https://www.facebook.com/DelaneyAmpsGui ... =3&theater

[Tone_Chaser]

That's a pretty cool idea. I was thinking about adding a fourth tube for a switchable extra gain stage anyway so I might just do that and use the other half for a clean channel like the BE-100. I could put a volume in one of the low input jacks and the bass and treble on the back side of the amp.

Thanks for the reply.

[herbvis]

I really need to make a clip of my amp switching between the 3 channels.

[motherdrive]

Hey Folks,

I'm building my first 2204 and I want to add a footswitchable lead mode that has it's own gain and master volume, I don't mind sharing the tone stack. Does anyone have any experience with something like this? I've built a bunch of fender tweed clones over the years but haven't used a relay before.

Any input or direction would be appreciated.

Thanks!
Max