Monthly Archives: August 2012

Siel DK-600

A very interesting synth. It’s one of the first (or last) “original” analog synths with both MIDI and complete knobs-and-switches controls.

As received:

No backup battery installed
Missing most screws
One broken key & one key missing
Missing left end panel
Several broken plastic pieces
Adhesive goo all over panel
Bottom case full of mouse poo

It did power up, though, and made sounds when poked at.

Despite the odd end panels, it’s one of the easiest synths to work on I’ve run across. There are acres of open space, all the cables are nicely run, and everything is labeled. The one downside is the odd shape, which made fabricating replacement end panels a bit of a challenge.

When I removed the main board, under the keybed assembly, I got completely squicked out when I realized the case was full of mouse droppings. Although that was fairly gross, the other thing I found were bits and pieces of the foil wrapper from a chocolate coin. Which may have been rodent food, but since foil is (obviously) conductive it was also a disaster waiting to happen. I’ve gotten some pretty filthy hardware in the past, but this is the first one I’ve ever had to hit with Lysol.

At this point, locating replacement keys isn’t much of a problem. I have several sources, and apart from the fact that one is a slightly different color and is missing a bit of the front apron, they went in without a problem. The velocity-sensitive key triggering mechanism is unusual. In most of the other synths I’ve seen, each key has two contacts, one set slightly in front of the other. When a key is struck, the time difference between the two contacts is converted into velocity information. Here, instead of individual contacts a pair of buss bars is used, and the interval measured is the time between breaking contact with one and connecting to the other.

The missing backup battery was easy to identify – there was a screened sqare labeled “backup battery” on the main bord, with the terminals clearly indicated. After removing the old solder and broken terminals, I tried to find the most sutiable replacement. My first choice is always a standard CR2032 socket. The pin spacing was correct, but there were a couple of resistors and a disk capacitor in the way. Thought of just mounting it on the bottom of the board, but the plastic bottom case has a reinforcing rib running exactly where it would have ended up. With a little creative lead-bending, I was able to mount a 1/3 AA socket on the top.

Downloading the factory patches was a challenge. I was able to locate a WAV file, but spent more than an hour trying to match volume levels to get a clean restore, with no success. Finally, after much web searching, I found a SysEx dump that I was able to reload using MIDI-OX. Somewhere I also dug up the original patch list. The synth came with the patch list on a label stuck to the front panel – hence the paint chips – and I laid out the new list to match the original as closely as I could.

The patches loaded correctly, and everything sounded okay. The odd numbers on the keypad, however didn’t work. I was able to determine that one of the pins on the DIP-style connector on the ribbon cable was missing. These are readily available, but rather than wait until the next time I order from Mouser I rigged a small piece of metal in the socket so that it would contact the little stump of the missing pin. It works fine.

I’d iniitally intended to make very nice end panels, but because of the odd shape decided that a basic set would do, particullary if I was reselling the unit.So instead of oak, I used clear pine, and instead of mounting them on the outside of the case and filling in with more wood, I mounted them on the lip next to the edge instead. After filling in the original screw holes and painting the lip black, it looks fine.

One of the nifty things I didn’t realize until I’d actually finished working on it is that it has a set of fold-down legs to angle the unit upwards, making the control panel easier to access when standing. Kind of neat.

Determinng the value of something like this is always tricky. I’ve seen them sell for close to $800 on Ebay. However, I’d rather trim my nails in a Cuisinart than go through the hassle of trying to sell something this large and this vintage-y that way. I’ve done my time. Instead, I posted it on craigslist with a low yet still fair price. It sold within  a couple of days; the buyer was very happy, I got some hassle-free cash, and it went to a good home. Everybody wins!

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Breakfast Time

Another guitar-less noodling. I was going to say it’s much more current, but I just realized it came out in 1995. Yeah. Well, time flies when you’re having fun.

For some reason a lot of people seem to pick on this song, but I’ve always liked it. It’s not deep, isn’t complicated, and doesn’t make any grand statements. It’s just kinda fun. And actually, I cheated a little. There is actually some acoustic guitar in here,  pretty well buried in the mix.

Just Like Davy – Breakfast at Tiffany’s

Sequential Circuits Prophet 600

This was a recent repair job. When it was dropped off, the owner said it had a bunch of non-responsive keys and he wanted to see about getting the battery replaced. Testing it, however, showed an additional problem. The patches were all really, really wrong, and it would hang up randomly. I let the customer know; he just said “fix it’.

One of the things I absolutely love about older equipment is how easy a lot of it is to work on. Four screws, fold the control panel up, everything is there in front of you.  The date of manufacture – 10/19/83 – is clearly visible here. I was in high school when this rolled off the line.

I’ve got keyboard rebuilding down to a (tedious) science. As expected, it took about an hour. Also as expected, all keys worked.  I checked the battery; despite it being the original I was still getting the correct voltage. Since there’s no way to know how long that would continue, however, I went ahead and replaced it. Although it’s mounted from the top, I had a holder that was perfect for it.

Replacing the battery, of course, completely wiped out the memory. I was unable to get the factory preset WAV file to load, so I used MIDI-OX to push the SysEx files over. One bad thing about this unit is that there’s no indication that it’s receiving, so had to unplug it, schlepp it downstairs, and hook it back up to the amp to see if it worked. And it did! The memory must have been hosed from the start, because all the patches sounded fine and the locking up problem went away. But…

Two of the voices were really, really off; the oscillators were nowhere near each other in pitch. Since the unit tunes itself, that meant that the main voice board needed to be rescaled. Fortunately, SCI built in a relatively painless procedure for doing this. It took about twenty minutes, but after that it was all working perfectly.  I replaced a few missing screws, touched up the stain on the end panels, vacuumed the inside, cleaned the outside, and let the customer know it was done.

He got back a fully-functioning synth, and I got to mess around with a classic piece of vintage gear. And got paid for it,  too…everybody wins!