No actual progress on the drum synth itself, but instead I’ve been toying around with a sketch for a sequencer. As TR9090 is a plain sound module, adding a sequencer would make it more faithful to the original 909. More importantly, much more self-contained and ‘hands on’. Modifying something out of the MBHP platform would provide a relatively straightforward solution and maybe even I, the less programming oriented, could manage this. Heavy emphasis on the word ‘maybe’ ;) .. Here’s what I’ve been planning feature-wise:
After completing the QuadSID, I had one leftover encoder. The most obvious use for it besides spare parts? Yep, upgrade my Midibox SID incorporate the simple Control Unit A. After a bit of modeling, I decided to use a single perfboard copper tracks facing up (aka the same approach as with the QuadSID). Difference being, as there is no keyboard frame or such underneath, I can mount the electronics directly to the lower side of the board and use the LCD as mounting support. So, first step.. fashion a piece of perfboard approximately to right size, matching the display element:
Not much to it really after this. Just drop in the parts, cut the copper stripes in appropriate spots and solder in parts & bridges..
..and here are the close ups from the upper and lower sides of the plain control unit board..:
After the board was complete, I drilled holes for the buttons and encoder to the casing, removed the old stickers, lightly sanded the casing (light enough to leave some of the old scratches intact ;) and gave it a fresh layer of red and new set of stickers. The encoder knob wasn’t an exact match color-wise, but maybe I’ll come across a better one some time later.
As for pictures of the completed unit, head over to the gallery page :)
Time for lé complétion féstivál, as the unit now sits on my desk happily playing Für Elise over MIDI! Not really the prime choice for this synth, but that’s the first .mid I came across ;) .. nonetheless, yay it finally works 100%!
Editing the software didn’t go as smoothly as planned, needed a few sessions to get it right. Whilst fiddling with the software, it also turned out that the filter/envelope buttons and encoders had problem functioning smoothly (messages vanished after the 10th chip in the DIN-chain) so I ended up re-doing parts of the cabling for these. As with the banksticks, all the other schematics/layouts were also lacking the 100nF bypass capacitors next to all digital IC power supply pins, so I added some SMD ones. Placing this capacitor next to each digital chip is a common practise to smooth out / suppress digital noise leaking to the common ground.
The Bourns samples finally arrived yesterday, so I was able to complete the control surface. And here it is then:
Needless to say, there was much rejoicing! Now then, on to software and final testing. At least the default DIN/DOUT mappings need a bit of editing, reckon it’s not a bad idea to test the system fully before I hand it over.
To date, no luck locating a suitable encoder from any of the local shops. Then again, there was this one in the mail from a Bourns representative..:
Subject: [PEC16-4225F-S24 or PEC16-4225F-S12: Sample Request]
Hello Mr Arto
We sent you four samples of partnumber PEC16-4220F-S0012 on 11.02.2005 as we don’t have any samples of the requested partnumbers.
Customer Service Center Europe
Looks like the project is back on track! Yay \:D/ Thank you thank you thank you Bourns for saving my week!
Whilst looking at the datasheets for the encoders Petri had ordered from voti.nl, it came apparent that the pinout mentioned in the schematics is wrong for this type of encoder. Not a biggie to fix, just reverse cables for pins B and C and it’s sorted out. Nonetheless, good that I spotted this one early on.