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Old 02-25-2013, 02:21 PM
Marshall Marshall is offline
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Question Allen R-100 midification

Hi. I'd like to add Midi to a 1972 vintage Allen Model R-100 - 2 keyboards + pedal, plus 1 expression pedal plus 3 "pistons". This is, I think, the first model Allen made of their "computer" organs. It has no midi at all at the moment.

I opened up the case and saw the keyboards have a 6 x 10 (+ 1) scan matrix layout, just exactly like in this post: http://forum.highlyliquid.com/showthread.php?t=327

And the pedal has a 6 x 5 ( + 2) scan matrix layout (the top and bottom notes are the "extra" ones - not sure if they're on the same select-wire or not).

I suspect I can use the same approach as in the above referenced post. But if anyone has specific experience with this particular model of Allen, I'd love to hear about it to avoid making newbie mistakes.

Since the organ currently works, I'd like to keep this as an "add-on". So - I'm not sure about piggy-backing on the existing key contacts - would adding wiring to connect the scan/data lines to the midi controller, in parallel with the existing wiring to the existing organ, mess up the existing organ?

Thanks for any advice on how to do this successfully.
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Old 02-25-2013, 05:34 PM
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John John is offline
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Hi Marshall, welcome to the forum.

Quote:
Originally Posted by Marshall View Post
Hi. I'd like to add Midi to a 1972 vintage Allen Model R-100 - 2 keyboards + pedal, plus 1 expression pedal plus 3 "pistons". This is, I think, the first model Allen made of their "computer" organs. It has no midi at all at the moment.

I opened up the case and saw the keyboards have a 6 x 10 (+ 1) scan matrix layout, just exactly like in this post: http://forum.highlyliquid.com/showthread.php?t=327

And the pedal has a 6 x 5 ( + 2) scan matrix layout (the top and bottom notes are the "extra" ones - not sure if they're on the same select-wire or not).

I suspect I can use the same approach as in the above referenced post. But if anyone has specific experience with this particular model of Allen, I'd love to hear about it to avoid making newbie mistakes.

Since the organ currently works, I'd like to keep this as an "add-on". So - I'm not sure about piggy-backing on the existing key contacts - would adding wiring to connect the scan/data lines to the midi controller, in parallel with the existing wiring to the existing organ, mess up the existing organ?
This last part will be tricky. If you were to connect a MIDI CPU to the switch matrix without disconnecting the organ's original drive circuitry, both the MIDI CPU and the organ's "brain" would be sending competing select signals to the switch matrix. This would cause a malfunction.

If the organ uses 5V signalling for the switch matrices, it is possible that the UMR2 could be used to generate MIDI output from the organ manuals. The UMR2 works in a way that does not interfere with existing control circuitry. Keep in mind that the UMR2 supports a maximum of 9 select lines, so two UMR2 units would be required for each manual.

There are other options, like:

- Adding duplicate switch contacts and matrixing them in parallel. That way, the MIDI CPU would work with a switch matrix completely isolated from the original. I realize that this would entail a great deal of labor.

- If the original sound-generating circuitry inside the organ can be retrofitted for MIDI input, the original key matrix drive circuit could be disconnected. Then, MIDI output from the MIDI CPU could be sent both to the organ MIDI input (to generate sound) and also to a MIDI Out for use with external sound modules or software.

I'd be glad to continue the discussion. Please share your thoughts.
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Old 02-25-2013, 06:22 PM
Marshall Marshall is offline
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Quote:
Originally Posted by John View Post
Hi Marshall, welcome to the forum.



This last part will be tricky. If you were to connect a MIDI CPU to the switch matrix without disconnecting the organ's original drive circuitry, both the MIDI CPU and the organ's "brain" would be sending competing select signals to the switch matrix. This would cause a malfunction. <snip>
I'm wondering - since the MIDI CPU is so configurable, could part of the configuration be a mode where the select lines are "monitored" instead of being "driven"? If so, what kind of voltages would be permitted? I'll have to dig out my little PC based oscilloscope and measure what the current voltages, etc., are on the current setup.

-Marshall
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Old 02-25-2013, 06:49 PM
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John John is offline
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I'm wondering - since the MIDI CPU is so configurable, could part of the configuration be a mode where the select lines are "monitored" instead of being "driven"?
Sorry, no. Actively controlling a switch matrix is "easier" than passively interfacing it. As it happens, the configurability of the MIDI CPU is what makes it ill-suited for the "passive" version of the task. All the other stuff that the MIDI CPU does would get in the way.

The difficulty of the task is why there is a dedicated product for the purpose: the UMR2. (And is also why the UMR2 doesn't have any extra functions.)

It is possible to do voltage level shifting, if necessary, to interface a non-5V matrix with the UMR2. We can discuss some strategies depending on what you find out with the scope.
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