Thursday, March 21, 2013

Polysix - Boosting the New Keybed

As discussed in this post, my new Fatar keybed had too many feet and, overall, its height was a bit too short.  So, in the previous post, I showed how I cut the feet off so that it wouldn't interfere with the circuit boards in the Polysix.  In this post, took care of the height problem so that it stood tall enough to extend over the circuit boards.

Hack-Sawing a Long Plastic Bar into Pieces for my Keybed Booster
After cutting a few of the feet off the keybed, I sat it inside m Korg Polysix and saw that it was still resting on the circuit boards.  Obviously, that's a bad thing.  So, I removed the new keybed and set it next to the old keybed.  It was clearly shorter.  How did I not notice this before?  Luckily, boosting it up seemed pretty straight forward.

I measured that the new keybed needed to be boosted by about 3/8" to match the old one.  So, I bought a four-foot-long piece of plastic from McMaster-Carr (part # 9123K76, Delrin, 4 feet x 1 inch x 3/8").  Then, I measured out the approximate length of the pieces that I'd need -- one long piece for the front feet and two short ones for the back feet (to leave a big space in the back for the Polysix's circuit boards to fit between the legs.  After hack-sawing the plastic bar (see pic above), I placed the keybed on the plastic pieces just to make sure everything looked OK.  As you can see in the pic below, so far everything looks fine.

Placing the Keybed on the New Plastic Pieces to Check the Fit
At this point, the story gets a bit more complicated because these plastic booster pieces also have to address a second problem that I have: the Polysix doesn't really have enough space for all the extra electronics that I want to put inside.  To get everything in there, I'll have to utilize the space under the keybed.  One piece that can go under there is the controller board that'll do the keybed scanning.  I got the controller board from the folks at Keyparts UK when I bought the keybed itself.  It looks like a great board.  My idea is to mount it under the keybed by screwing it to my white plastic pieces.  Below shows a test fit, including with the aftertouch sensor strip plugged in.  It's a tight fit, but it looks like it'll work!

Test Fit with the Keybed Scanning Electronics In-Place.
Since it looked like it was going to work, I started drilling holes and screwing things together.  First, I started with attaching the controller board.

Securing the Keybed Controller Using Screws.  (Notice that I set everything onto a piece of wood 2x4 to catch the drill bit once it passes through the plastic.  Don't let the drill dig into your actual work surface!)
Once that was secured, I started drilling holes and attaching the plastic pieces to the feet of the keybed.  To get it right, this took a lot of measuring and re-measuring.

Screwing the Plastic Booster Pieces to the Feet of the Keybed
All along the way, it was critical to keep doing test-fits into the Polysix.  Through my repeated test-fits, I learned that the internal corners of the Polysix have little wooden braces, which shorten the available space for my white plastic pieces.  Because of these braces, I'd put in the keybed and then I'd try to put in the Polysix's end-piece (with the bend wheel and mod wheel) and it wouldn't fit!  The braces and my plastic feet would interfere.  I had to repeatedly trim my plastic pieces (with the hack-saw) to accommodate the brace pieces to get it to fit.  Luckily, because I used screws and not epoxy, it is really easy to remove my plastic pieces from my keybed so that I could rework the pieces.

Once I got all the pieces to the correct length, I could do my final assembly -- keybed with the new booster pieces plus the controller plus all of the cabling between the controller and the keybed.  The picture below shows it fully assembled (though still upside-down, of course).  I'm not proud of what I did with the cabling.  You can see it there in the middle all covered with duct tape.  The problem is that I needed something to hold the cabling up against the keybed so that it wouldn't dangle down onto the synth's circuit boards.  When I did a test run of the synth while the cabling was dangling freely, the digital signals on the cabling radiated into the near-by audio circuits and introduced buzzing sounds.  It was  bad.  I had to get the cabling up off the circuit boards.  So, I used some duct tape.  The tape is clearly not a long-term solution, but it's the best that I could come up with on the spot.

Fully-Assembled Keybed with Booster Feet, Controller, and Duct-Taped Cabling
Another important detail with this assembly is that, when you flip over the assembly to insert it into the Polysix, the screw heads will now be on the bottom surface of the plastic and, therefore, will be between the plastic and the inside of the Polysix.  Won't it wobble?

After talking (again) with the friendly chap who helped me with the hand-held saw that I used to cut off the keybed feet, he showed me how to use his counter-sink drill bit.  With this funny-looking drill bit, you cut a space for the screw head to sink down and be flush with the rest of the surface.  That's exactly what I needed!  So, I pre-drilled the screw-hole like normal, then I used the counter-sink drill to make space for the screw head, and then I inserted and screwed in the screws until they were flush.  Now the bottom of the plastic piece is flat and smooth and sits nicely within the synth.  What fun!

My New Keybed with Booster Feet and Electronics Installed
So now the keybed is fully prepared.  I dropped it into the Polysix and she seems to fit pretty well (though there might be one or two really tall capacitors that are still giving me some interference).  The next steps are to plug it all together with the other electronics and to make her sing.  For right now, though, I'm satisfied that this mechanical assembly challenge is complete.  The mechanical stuff is a lot harder for me than the electrical stuff.

Thanks for reading!

Update: Tipping over a few capacitors so that the keybed sits properly

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