Roland TR analogue trigger strangeness - Korg KPR77

[Circuitbenders]

Does anybody know if theres anything different about the analogue trigger outputs as seen on the Roland TR707, TR727 and TR626, and the triggers on just about every bit of kit that uses a standard +5v pulse?

I ask because i've just spent ages trying to trigger the individual voices from a Korg KPR77 drum machine using the trig out's from a TR626 and a TR707 and it refuses to work. I measured all the standard internal korg triggers with a scope and they are all more or less identical to the 707 and 626 triggers. Having just spent an hour or two poking around inside the Korg and staring at the schematics completely baffled as to why it didn't work i decided to try the trigger out on my Kawai R100, which it turns out triggers the korg perfectly. The arpeggiator output of two Midi-CV converters also works fine, as does the trig out from my mates TR909.

I've taken a look at all these triggers signal on the scope and they are identical to the TR626 or the TR707, yet neither of those two machines will trigger the korg. is there some fundamental trigger knowledge i'm missing thats so commonly known that nobody has even written it down anywhere?

I know some korg gear uses negative triggers but in this case the sequencer part of the KPR77 seems to generate positive triggers which are then inverted to trigger the synth section. Injecting a trigger from something like an R100  just after the KPR77 sequencer works perfectly.

[nochtanseenspecht]

on the vintage synth' 626 page i read something that might be helpfull;

quote:
you have to modify the tr626 board to do the trick. but it's not difficult. first get a 7404 chip in an electronic store, then verify on the datasheet the pinout. the NOT logic port has only one in and one out. then connect the trig out of the tr626 to the input of the NOT logic gate, and the output to the trig in of the KORG stuff you want to synchronize.
don't forget to power the 7404!
i also added a switch to operate both positive/negative trig.
better results are in connecting it to a KORG SQ10, since a lonely trig signal is too simple for a decent control.

but maybe it is not relevant to your problem
in my opinion old gear sometimes just behaves strange, part of the character i guess

i have a problem syncing my cr8000, i think i might open a topic about it

[Gordonjcp]

You could probably use a transistor and a couple of resistors to invert the pulse, too.

[Circuitbenders]

The internal triggering of the KPR77 seems to work by sending very short +5v pulses (v-trig) from the sequencer section, to what appears to be a dedicated conversion board which takes these pulses and converts them into negative (s-trig) going triggers of different lengths depending on what sound it is.  I've got a little V-trig (Roland) to S-trig (korg) converter circuit i built and it is possible to trigger the sounds at the output on the converter board using this and a TR626/TR707, but due to the different pulse lengths it needs and the fact that the clap wants three tightly spaced triggers, injecting triggers at that point means the sounds don't sound quite right. Also, the kick and the snare seem to trigger on both the negative and the positive going edge of the trigger pulse which gives an annoying flam effect.

Injecting +5v pulses at the input to the converter board like the KPR77 sequencer does, appears to work fine using anything but a Roland and i really can't work out why this is the case. Having checked it out again i've found that the pulses from the KPR77 sequencer are a lot shorter than any normal +5v trigger but that doesn't explain why a longer trigger from a Kawai R100 works fine and the exact same trigger from a TR707 doesn't