[the_unlord]

Hi,

I have a Marshall AVT150 amp that I'd like to be able to change channels with MIDI.
I think the TT MIDI switcher would be ideal for that, but I'd like a bit more information first.
So the amp has 4 channels that you control with a momentary switch of the footswitch.
The footswitch also has 2 latching switches to enable/disable the digital FX of the amp on channels 1/2 or 3/4 respectively.

So the TT MID switcher seems a good match: use A1-A4 for the channels and A5 and A6 for the DFX.
The problem is that the channel switching is done by momentary switches, while the TT MIDI switcher seems to have a permanent contact on the selected channel, right? Is there a way around that?
It also looks like I can't connect the outputs directly to my amp, but I'll need relays or optocouplers: maybe it can be fixed there?
Or would it not be a problem at all if you would 'keep pushing the channel button'? The amp switches directly as soon as you hit the button and nothing bad seems to happen if I keep it pressed...
The only problem I could see with it is that there are also buttons on the front panel of the amp I sometimes use for switching channels, and maybe they won't work anymore then? Unless they would also sent out via the footswitch cable... Maybe i should check that...

Another question is about power: judging from the schematic of my amp, there should be a 5V lead to the footswitch (didn't do any measurements yet): could I possibly use this to power the board? I know it expects 6.3V or up on the main power supply, but that is converted to 5V, so could I power it from the back-side of the power supply with 5V, or is that too risky? It would allow me to integrate the TT MIDI switcher into the footswitch itself with less hassle.

Any help or ideas appreciated!

[the_unlord]

No one seems to have an idea, so I decided to take the plunge.

So I can feed the unit from the 5V coming from the amp (as I suspected), so far so good...

I managed to switch a channel with a small test on a breadboard as well, so it looks promising, but I'll need some more tests to confirm.
But I fear the buttons on the front of the amp won't work anymore. We'll see!

[carlitz]

Hi,

the logic of the front panel switches and the foot switches is separated, so should not be a problem.

If I remember right, all foot switches are switches and not from a momentary style.

Check it out with a multimeter. Does the contact close on pressing the switch and open when releasing it?

The foot switch is tricky in a way, as the status of the channels, switch at the front panel, will also be indicated at the foot switch. There are separate wires to lid the LED's

[the_unlord]

The 4 channel switches are momentary, the 2 DFX selection switches are latching.
And that last part makes for a bit of a problem if I want to keep using the footswitch AND the TT Midi switcher (together or separately)...

Judging from the schematics, the front panel switches and the footswitch aren't really separated, I believe: they seem to pull the same lead to ground when pushed.
Haven't measured it with a meter, though...

Problem is, I don't really have much time to work on it... There always seems to be something else that breaks down in the house that needs more urgent fixing 

[carlitz]

If you do not have time, why should we spent time on the topic?