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4780 Sequencer Modification


Allows you to set and rapidly change the sequence length without patch cords.

I prefer to use as few patch cords as possible with my synthesizer and have therefore made extensive modifications to my 4700/S. One of the simpler and most useful modifications was the addition of a rotary switch to the 4780 sequencer which allows me to set and rapidly change the sequence length without the use of patchcords. Radio Shack sells a 12-position single-pole rotary switch (#275-1385) which is ideal. There are no electrical modifications to the 4780 and only a few physical modifications.

The switch fits in the lower right-hand corner of the sequencer (obliterating the word "out"). This hole can be drilled even after the module has been assembled, (my 4780 was already installed in the cabinet when I got this brainstorm), but you have to be careful. Drilling a small "pilot" hole is mandatory. Figure F shows the approximate location of the hole. Figure D shows the rotary switch. I recommend that you trim off the small tab on the front and cut the shaft down to about 1/4 inch. If the knobs you're using don't have set screws (such as PAIA knobs), you might try sawing a small slot in the shaft and squeezing the shaft together, then jamming the knob on (you could epoxy it, but then you'll never get it off). Figures A & B show the mounting configuration. In figure A the wiring layout is also shown - NOTE: the wiring layout in figure A is just to give an idea of what it looks like, the actual wiring order is in figure C. Basically, the switch takes the place of a patch cord coming from each stage's output jack.


You could wire all the switch wires directly to the jacks, but it's much easier to wire the lines that would go to Jacks J5 through J9, to the appropriate points on circuit board B (holes AA, CC, DD, FF, EE), besides, if your 4780 is already assembled, it will be impossible to get at jacks J4 thru J9. You may have noticed that one position of the switch is not connected to anything (if you want to connect it, you'd connect it to hole BB on circuit board B). The reason for this is that BB is connected to jack J4, the first stage output jack. Now, if you want a one event sequence, that's up to you, but leaving the first position in the switch unconnected allows you to switch to this position and have the sequencer operate just as it did before you added the switch. In particular, with the RUN/STOP switch set to conditional run, the sequence will end and the clock will stop after the last stage. If you don't provide an unconnected switch position on the rotary switch, you'll never be able to get a non-repeating sequence. Although there is no interference between the rotary switch and the 4780; unfortunately, there is interference between the rotary switch and the metal bar on which the modules mount (in the wing cabinet). Be sure to leave enough room between the 4780 front panel and the front disc of the rotary switch, the mounting bar will fit into this gap (or you could cut away that portion of the mounting bar that interferes). See figure E at the bottom of page 9.




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Polyphony - Copyright: Polyphony Publishing Company

 

Polyphony - Jul 1977

Donated & scanned by: Mike Gorman

Feature by Bob Yannes

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