Mark I Channel Switching

[zebpedersen]

I have a 1977 Mark I and I want to use it as a channel switching amplifier. I used to have an A/B/Y box that did the trick, but I've since upgraded my switching system with an RJM Mini Effect Gizmo. I've set up the effect gizmo to use my BFDR as a clean channel and the Mark I for lead by hooking sends 4 & 5 to the input of the respective amps, but I don't want to have to take two amps everywhere (the Mark I is bulky enough on its own). I thought perhaps about having the output of the Gizmo sent to an A/B box in front of the Mark I, but I'd like to have the flexibility to switch using just the MIDI controller.

Anyone got any ideas? I seem to recall there being something special about the A/B switching required by the Mark I amps.

 

[KiwiJoe]

I have a 1977 Mark I and I want to use it as a channel switching amplifier. I used to have an A/B/Y box that did the trick, but I've since upgraded my switching system with an RJM Mini Effect Gizmo. I've set up the effect gizmo to use my BFDR as a clean channel and the Mark I for lead by hooking sends 4 & 5 to the input of the respective amps, but I don't want to have to take two amps everywhere (the Mark I is bulky enough on its own). I thought perhaps about having the output of the Gizmo sent to an A/B box in front of the Mark I, but I'd like to have the flexibility to switch using just the MIDI controller.

Anyone got any ideas? I seem to recall there being something special about the A/B switching required by the Mark I amps.

First, if you ever think of selling your Mk I, let me know. 8)
I'm not familiar with your MIDI switcher, but maybe you could simply use it as an A/B/Y. If not, a proper A/B/Y shouldn't be too expensive. Plus, that way, your Mark I has its own dedicated switch and is "self-contained".

As for "something special about A/B switching" on the Mk I, it seems that the only issue is a potential volume difference when switching between Inputs 1 and 2; owning one, I'm sure you're familiar with that. This from the MESA User's Manual:

Though the MARK I is not a “footswitching” amp in the true sense of the word, it is a two channel amp and therefore it is possible to switch between INPUT 1 and INPUT 2 externally. This is accomplished by using the accessory Mesa A/B Footswitch, and two very low capacitance shielded cables of the shortest possible length ( 6 feet or less ). Connect your instrument to the Common Jack of the A/B box. Then connect cables from the box’s “A” and “B” outputs to the two inputs of the MARK I and you can now footswitch between the two inputs. You will notice a compromise in volume levels is inevitable and necessary. Most probably when you set the INPUT 2 volume control to the right spot, INPUT 1 will be too loud. This is unavoidable because the channels are in series. With some time and guitar volume control changes you should be able to come up with a compromise setting that will “footswitch”.

http://www.mesaboogie.com/manuals/Mark1%20Reissue.pdf