Friday, April 6, 2012

Poly-61 MIDIfied!

Finally, after two years, I installed the CHD Elektroservis Poly-61 MIDI retrofit kit!
So why did it take so long? First and foremost, I'm lazy, OK? Takes me forever to get my thumbs out and actually do something that I really want to do.
Second, and this is a practical reason, I didn't have any good way of making a 16mm diameter hole for the MIDI connector, and I sure wasn't going to have a dangling MIDI-connector next to the synth.
Most people don't have drilling machines that can handle drills with 16mm diameter.

One way could be using a conical drill, preferably stepped. That seemed like a good way to screw everything up since I don't have anything to keep everything in place with. No vise, no pillar drill...
So, after winning a 5/8 inch (15.875mm) hole punch on an online auction, I got to work the same day it arrived in my mailbox. If you don't know what a hole punch is or how it works, look it up.
It's really great!

Drilling and punching

First I drilled a hole using a 3mm drill (tried 6mm but it kept walking away from the mark I made).
Then I made a bigger hole using the 6mm drill. I also had to use a file to make the hole a bit bigger so the bolt of the hole punch could pass through, as it was about 6.5mm in diameter.
Then it was time to test the hole punch. Here it is in action :)

So then I just had to tighten that bolt until the punch pushed its way through the metal.
I'm not sure why they're called "punches" actually as there's no punching involved...
Anyway, it was really easy to get through the metal case using it! After that I drilled two 3mm holes on each side for the screws, which gave me this:
Ok, not entirely symmetrical, but what the hell :)


I then attached the MIDI connector using the screws provided in the kit and then, following the instructions provided, I soldered the +5V and GND wires to the CPU board and put the interface board in its place.

The red (+5V) and blue (GND) wires coming from the small board were supposed to be soldered directly to the pins of the 74LS04 chip on the CPU board, but I just didn't feel like cooking the chip by soldering directly on the pins. I found some vias on the PCB where the traces were exposed and soldered the wires there instead. Not that it's a nightmare to find a replacement for a 74LS04, but it's tedious to remove the board and replace the chip. My option seemed like a safer way.

Here's what it looks like from the rear :)

Two things:
1. The screws provided were of two different kinds. The rightmost one in the picture has a conical head and, I assume, was put in as a replacement. Annoying, but still works. Maybe I'll replace it.
2. I mounted the jack upside down :) It looked right, but when I compared to other synthesizers I have I realized it was upside down. Minor detail as well, but a bit annoying when you're fumbling with the MIDI connector on the rear wondering why it doesn't fit.


I powered it up and checked that I hadn't broken anything and that it still worked "locally".
Seemed to work ok. Everything was just like before.

Then I connected a MIDI cable to it and played a bit on my MIDI keyboard next to my computer.
It worked! However, it was only receiving on MIDI channel 1. While I guess I could change the MIDI channels of the other synthesizers in the same MIDI chain I want to be able to set the channel.
The way you do this is by sending sysex. Luckily there's a good way of creating your own sysex messages in Cubase Studio 4, which I am using. After making a sysex-message which changes the MIDI channel to 3 I tried sending MIDI on channel 3 to it, and it worked :)

Next up I guess should be the Polysix. It'll get the same treatment as I also have a Polysix CHD kit which I bought at the same time as this...
We'll see when I get around to do that, but I have 4 days off from work now (Easter) and not a lot of excuses NOT to get it done. But... Yeah.. :P

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