The day the music died!

Yesterday while developing my C++ program for the Kurzweil 1200 synth, it stopped responding – in a really bad way, no display, no lights on, nothing. I’d heard it click the relay a few times before and sort of hoped it was nothing and it would just go away if I ignored it.

If I left it for a while it would power backup for a few seconds and then die again. So I took the unit out of my rack, opened it up and had a good poke around. I eventually managed to simulate the problem by wiggling the power cable between the transformer and the power supply circuit. I took the board out to have a closer look and found a really bad set of dry joints on the power header. I resoldered them all back up, and a couple more I found on some capacitors. Thankfully this seems to have done the trick and it is now running really well, with no intermittent clicks or anything.

Kurzweil 1200 – Ongoing efforts

I’m making great progress on my application to control my 1200 Pro 1 unit. I can now send and receive a full list of all items available in the unit – LFO parameters, Sounds, Programs etc.

It took me a whole day just to figure out the chksum formula, once I’d got it working, and reread the explanation it was pretty simple:

for(count = 0; count < len; count++)
chksum = ((chksum << 1) | (chksum >> 15)) + msg[count];

It was the rotation part that I had misunderstood.

Another thing I learned today was “strict weak ordering” this is required for the sort algorithm in the C++ STL template libraries. C++ is very fussy about how you write a compare routine for the sort function. I had taken a shortcut in my code by using a flag for the sort direction (ascending or descending). After I had resolved if A was less than B, I used the direction flag to invert the logic at the end. The problem with this arises when you have comparisons where A < B is not an exact inversion of B < A. This occurs when A and B are the same, in this situation A < B is false, and B < A is also false. By doing the comparison in one way only, and inverting the logic at the end I don’t return the same answer. This has a major effect on the sort routine, causing it to start submitting random memory locations to the compare routine causing a seg fault.

Kurzweil 1200 Pro 1

I just recently acquired an old Kurzweil 1200 Pro 1 synthesizer. I’ve had to replace the LCD screen as the electro-luminescent backlighting on the old one was pretty faded. I put in a new LED backlit one, and had to cut down the screw posts to fit the deeper profile in, and added a small pot inline to set the contrast. It’s now very clear, and the unit sounds pretty sweet – (in a sort of 90’s synth way).

I’m now starting to get to grips with all it’s many features, and am developing a MIDI application to control the unit as I go along, so far I’ve got full front panel control and display working. Next step is to get full control of all the many synth parameters and layer settings.

The application is being developed in Linux using the excellent Juce class library – see for an overview. The beauty of the Juce libraries is that they can be easily recompiled to target Windows and Mac (and iOS/Android too but I’m not familiar with those areas yet). It’s main strength is it’s good support for music devices, both MIDI and audio. This extends to developing VST applications too.