I like using my Korg ER1, I have an EA1 too but
never use it. I have always wanted to have the ER1 sync
with my diy synths, which don't have midi.
I worked out a simple circuit to get a BPM trigger out
but did the operation on my EA1 as I didn't mind if it
blew up or worse. The boards in the ER1 are the same so
this mod would work there too, but there is less free space
so you would have to be imaginative about
where to put the jack.
Also the BPM led on the EA1 no longer flashes after doing this,
but you do get a nice 8V trigger signal instead. If that is an issue
put a switch in the line from the led to
the 4N25 to turn it off when not needed.
I ran the power leads from the EA1, near the main capacitor.
Maybe not the best place but easily accessible, be sure the cap
is drained before going near it with a
From Led 22 on the EA1 connect two wires to pins 1&2 of 4N25.
The plastic case seemed a bit brittle, so I was a bit wary of drilling it
and made a hole using an old soldering iron,
kept especially for melting holes in plastic.
It goes thru like a hot knife thru butter.
If you try this mod, it is at your own risk.