Tuesday, February 5, 2013

TR-707 Driving the Arpeggiator on my Polysix

Recently, I purchased an old Roland TR-707 drum machine.  In addition to the drums sounds (and the classic Roland x0x step programming interface), I was excited at the possibility of using the 707's trigger output to control my analog synths.  Specifically, I was hoping to use the trigger out to drive the synth's "gate in" to create interesting rhythms.  At the very least, I was hoping to drive the arpeggiator and keep it in sync with some drums.  For an example, check out the video below.  Electro party!

But that's getting ahead of myself.  When I got the TR-707 home and out of the box, I first wired it up to the "Gate In" on my Korg Mono/Poly.  I was hoping that it would trigger the notes on my Mono/Poly so that I could create some sweet syncopated robo-rhythms.  Sadly, it only kinda worked.  The problem was that note coming out the Mono/Poly was just a tiny little "blip".  Very unsatisfying.  Boo!  Why?

Trusty Roland TR-707
To trouble-shoot, I plugged the 707's "Trigger Out" into my oscilloscope and got the picture below.  I found that the trigger is a +5V pulse (which is fine) and that is only 20 milliseconds long (whoa, short!).  But of course!  The trigger is not intended to be a "gate on" signal (which would need to stay on for the entire duration of the intended tone) but it is merely a pulse that is supposed to mark the start of a discrete event...like of a drum sound.  When I tried to use this 20 msec pulse as a "Gate On" signal to my Mono/Poly, the resulting note would only be 20 msec long.  That's not much of a note.  Now it makes sense.

Trigger Pulse from TR-707
So, if it is just a clock pulse, then I thought that it would be perfect for stepping the Mono/Poly's arpeggiator.  It's easy to try because of those awesome patch points on the back of the Mono/Poly...just unplug from "Gate In" and plug into "Arp Trig In".  Unfortunately, it didn't work at all.  I'm not sure why.  Maybe the pulse is too short?  I don't know.  I'll investigate more in the future.

Failing with the Mono/Poly, I tried to drive the arpeggiator of my Korg Polysix.  For some reason this worked marvelously.  As a demo, see the video at the top of this post.  Or, for a somewhat different vibe from the synth, check out the video below.  The video below doesn't have a complicated patch on the synth, nor is it a complicated arpeggiation, but it is in sync with the drums and will stay that way.  Groovy.  Thank you 707 trigger out!


  1. But, if you once more have a look with your scope at the arpeggiated polysix, you should see that the notes are 20ms late.
    That is because while the 707 sends a +ve 5V trigger, Korg synths expect a trigger which is a 5V drop to 0V.
    it is probably also the cause of the Mono/Poly not reacting,

  2. Hey, thanks for the comment. You are very correct about the arpeggiator being late because its looking to trigger on a downward side of the pulse instead of the upward side. At high BPM (say, 130+), this 20 ms delay really messes with the groove. One of these days, I'll make a V-Trig to S-Trig converter and be able to lock in the groove nicely. Thanks again for stopping by!

  3. Hey there! I was just trying to research this issue myself. Check out these links to buy an adapter that converts Roland V-trigger to Korg S-trigger:

    or build the thing yourself!