Friday, April 13, 2012

Sequencer complete!

The sequencer is now ready!!  It is quite a dense and heavy beast...

Oops, there's a few bits of wire insulation that got stuck to the knobs. ;-)

As I mentioned, I didn't solder in the UJT initially, but just set it in there, in case there was any issue with it at high frequencies.  Tested it, and it worked fine on the first try!  (Well, I had two switches upside down, but it only took a couple minutes to fix those.)  So, I soldered in the UJT from the top, and just left the legs hanging down... no big deal.

I've mostly just played around with the clocking mechanism, but everything seems to work fine elsewhere too and it is really interesting.  The RYM (3rd row control of timing) is fun, as are the different modes. 

Now, if only the screws to mount these modules to the rails would finally arrive here(?!?!), I could get everything working together!

Friday, April 6, 2012

Sequencer Output PCB

And here's the second PCB in the Sequencer!  All of the stage pots, output attenuators, and LEDs are board-mounted, which will make wiring a whole lot simpler.

The pots & LEDs get installed on the other side (but soldered on this side).  The jacks & LED lenses had already been installed on the panel.  I've only added the standoffs at this point.  I also had to use diagonal cutters to clip the (plastic) pot shafts down to a reasonable length - a bit of a pain, as my large diagonal cutters are MIA.

Anyhow for the pots I plugged them in and soldered the wiper pins only, and make sure they were flush with the surface.  I then slipped the LED in, but didn't solder them, and then shoved it into the panel.  A little bit of juggling, but the pots all went in and I put the nuts on a few, and then pushed the LEDs into the lenses.  I then soldered everything in, and started putting the knobs on the front.

Thursday, April 5, 2012

Sequencer Logic PCB

The Sequencer is composed of two PCBs: the logic board, and the output board.  The logic board contains all of the clocking mechanism and other logic (number of steps, etc.).  The original boards only supported S-Triggers, but the current revision support both S-Triggers and V-Triggers.

It is a pretty full-featured sequencer, especially for the time, and has a fair amount in common with the Moog 960 - at least its features are more similar to that than the Buchla and Serge sequencers.

There's a lot of features to try and explain, and naming them off here in a couple of paragraphs here isn't going to be too useful.  But basically it is an 8x3 sequencer (i.e. 8 stages, 3 rows) with a built-in clock (w/voltage control). Other features include 16-step sequences (from rows 1 & 2), row output attenuators, stage trigger outputs, third row control of timing, and a bunch of other control options (stop/loop, reset, max stages, etc.)  David's Synthasystem website has a more detailed overview of the individual controls, and I'll hopefully make a demo that shows them too.

I've omitted all of the V-Trigger components - hopefully I got it all right!  I was tracing things based on the original schematic, etc.  I've used discrete transistors in place of the SSM2210.  I've also left off the UJT, which is the core of the oscillator.  Once I have it put together, I will test different UJTs and select one with the most appropriate range (there can be a variability in UJTs).  This PCB will be connected to the output board with a ribbon cable (note the 16-pin header).

Wednesday, April 4, 2012

Selective Inverter complete!

And now, the Selective Inverter is finished!

It is a really crowded build.   Getting the banana jacks on there was tough, as the nut drivers didn't cut it - I had to use pliers to get the nuts tightened.  (Of course, that's what I get for having all those multed jacks in a banana system!  But, I don't mind.) 

One thing that I didn't realize from the description, but suspected from the schematic, was that in the fixed mode the "B" output is always inverted (i.e. the trigger inputs do nothing).  Also, I was really confused at first while testing it, until I remembered that the offset voltage is bipolar (-10V to +12V).  Anyhow, I'm very much looking forward to trying this out with some "real-world" applications!

Tuesday, April 3, 2012

Input Amplifier PCB

A fairly obvious module, the Input Amplifier is used to bring external signals into the Synthasystem and pull them up to appropriate levels for the modular synth.  The module offers a few different input jacks (mine will probably be TS, banana, and RCA), although they are all multed into the same input (so, only apply one signal to the three inputs!).  There's a pot to adjust gain, a switch to set gain to high or low, and a switch to enable RIAA equalization.

(Sorry about the picture quality - I got a new phone and indoor close-ups are kinda blurry.)

It is a really simple build.  The current PCB revision has a couple additions that Nyle and David have made to the input.  Originally the input jacks were connected directly to the opamp, but now there's a capacitor to AC couple the input, and a pull-down resistor to hold the input to 0V when no signal is present.