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  #1  
Old 05-25-2011, 03:40 PM
Jon Jon is offline
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Default Amplifier switcher - 4 heads into one cab

I am looking to build a tube amp selector. Essentially, I would have 4 tube amplifiers sharing one speaker cabinet. The inputs to the amplifiers would be muted (via optos), and each amplifier would have its own load via an 8 ohm resistor (with an SPDT relay NC to the resistor NO to the speaker cab).

I have an existing midi controller that sends out CCs via instant access switches. The critical issue is that I have to ensure that only one relay/input mute pair is on at one time and the others are off.

It would be great to be able to control the amp switcher via either momentary footswitches with leds and via midi CCs (as outlined above)

I esentially need a logic circuit to control this and allow only one output at one time. (No matter how many CC's are sent - ie, if I selected all 4 on my midi footswitch controller)

Thanks!
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  #2  
Old 05-27-2011, 07:11 PM
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John John is offline
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Hi Jon, welcome.

Please check out some of the threads in the MSA support forum--some of the discussions over there are closely related (lots of guitar amp/effect stuff).

The MSA has 8 outputs. You can set it to respond with any 8-output on/off combination for each CC # 0-127. In other words, each CC command can be treated as a "preset select" or "patch select" command.

So for example, for each CC in use, you could configure the MSA to have only one output "on". Only the most recent CC received would determine the output state.

Let me know if this helps...
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Old 05-29-2011, 04:28 PM
Jon Jon is offline
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Quote:
Originally Posted by John View Post
Hi Jon, welcome.

Please check out some of the threads in the MSA support forum--some of the discussions over there are closely related (lots of guitar amp/effect stuff).

The MSA has 8 outputs. You can set it to respond with any 8-output on/off combination for each CC # 0-127. In other words, each CC command can be treated as a "preset select" or "patch select" command.

So for example, for each CC in use, you could configure the MSA to have only one output "on". Only the most recent CC received would determine the output state.

Let me know if this helps...
Thanks John.

What the main issue would be is this - at no time can more than one of the four relay opto pairs be ON.

I need to ensure that even if I select and send 4 CC's at the same time (by mistake, glitch, etc.) that the device will only enable one output and disable the other 3 - is this possible via programming?
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Old 06-02-2011, 02:25 PM
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John John is offline
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Hi Jon,

Quote:
Originally Posted by Jon View Post
What the main issue would be is this - at no time can more than one of the four relay opto pairs be ON.

I need to ensure that even if I select and send 4 CC's at the same time (by mistake, glitch, etc.) that the device will only enable one output and disable the other 3 - is this possible via programming?
Yes, you can do this. With MIDI messages, there really is no such thing as "at the same time"...each message is sent in series, one after the other (but sometimes very close together).

Anyway, when the MSA is configured for "preset operation", the 8-output state is determined only by the most recent CC message received. So if you set up the presets so that there is only 1 of 8 outputs "on" for each preset, you'll never have multiple outputs "on" at the same time. Same thing if you're using 2 of 8 outputs for each preset, etc.

Hope that makes sense...

By the way, Sqwerl will make configuring the MSA a snap:

http://forum.highlyliquid.com/showthread.php?t=453

Last edited by John; 06-02-2011 at 02:29 PM.
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Old 07-27-2013, 08:30 PM
ChrisR ChrisR is offline
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Jon, are you still around? Did you get anywhere with your idea? I have something similar only more extravagant in mind and wondered how it went.
Chris
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  #6  
Old 07-29-2013, 02:10 PM
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John John is offline
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One thing I failed to mention in my conversation with Jon is that the MSA also has a CC "match only" output mode for individual outputs. In a group of outputs each using this mode, but for different CC numbers, there can never be more than one output active at the same time.

In other words, there several ways to achieve the goals of the project using the MSA.
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