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Old 12-31-2012, 11:59 PM
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John John is offline
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Default Carvin Quad X-Amp MIDI Retrofit

C. writes:

I have a older model Quad X with no footpedal. It has a midi [input] section, but they are all 1/4" female jacks. I want to make a foot pedal to change channels. (1-4).


All I want to be able to do is change channels.
can I connect a 1/4" ts plug to a spst momentary switch, and plug into each midi control
Based on the Quad X-Amp manual, it appears that a simple SPST switch on a TS plug will trigger each of the "MIDI" inputs. (Which actually has nothing to do with MIDI, really.)

So, you can use a basic mechanical footswitch plugged into each of the inputs to get result you want.

If you have an existing MIDI-output foot controller, then you can use an MSA-P or MSA-R to accept the MIDI signal from your controller and "flip the switches" in response to MIDI.

to put it another way:

Each output of the MSA-P or MSA-R is an SPST switch (a photo relay or reed relay).

So, you can wire each of the seven switch inputs on the back of the preamp to one of the MSA outputs. (The MSA has 8 independent switch outputs.)

So then, whatever MIDI messages are sent by your MIDI foot controller, the MSA can be set up to respond and select the channel and/or effect that you like.

In other words:

Commercial MIDI foot controller -> MSA-P/R -> Preamp

Thanks, that worked.

One more question please. How can I put LED's on each switch so that I will know which channel is on?
The MSA also has indicator LEDs that reflect the status of each relay output. You can mount these on the MSA or itself, or remotely on a control panel if you prefer.

If you are going for manually controlled switches:

You can set up an LED for each input so that the cathode is connected to ground when the amp's control input is grounded. Connect the LED anode to 5V through a series resistor (1kohm is usually a good place to start).


(5v)----[1k resistor]----|>|"-----{control input}

...this way, when the control switch is "open", the LED cathode will be left floating and the LED will be dark. When the control switch is closed, the LED cathode will be grounded and current will flow, causing the LED to light.

Last edited by John; 01-01-2013 at 12:02 AM.
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