Finally...

Up and running...

Wow, I can't believe how long it has been.  The last few years have been crazy (mostly in good ways), so nearly all of my studio & DIY stuff has been on hold.  Thankfully that has changed!  Towards the end of last year I set up my studio (wish I had more space!), finished a few stand-alone clones (ARP 2600, ARP 1601, and Buchla 208), and resurrected the Synthasystem.

The biggest problem was that while a bunch of modules were in the case, I'd only built a couple of power connectors.  So I made a bunch of those, built a second power supply, and finished the Input Amplifier module (which I'll post about later).  Here is the system in its current state:

There's clearly still work to be done, but it is a joy to work with.  I have a few PCBs that are mostly populated, and ordered the final ones today.  When all is completed, the rows will be arranged as follows, from top to bottom:

• VC Clock, Sequencer, Selective Inverter
• Triple EG, Frequency Divider, Triple EG
• 3x VCO (Type A)
• VCO (Type A), VCF, VCA, VCF, VCA
• Input Amp, Noise, Peak Selector, S&H, Voltage Follower, Voltage Processor, Noise, Ring Mod, Phaser, VCA

Originally I was going to build a Tuner/Monitor, and another Peak Selector.  But I realized that (for me) the Tuner/Monitor would be a bit of a waste of space.  And after using the system extensively for the past few weeks, I decided to skip them both and add a 3rd VCA.  (I'll still likely build the Tuner/Monitor, if only because I have the panel and it is about 95% complete.)

The bottom space in the rack will house a panel with some jack converters for input and output, a couple of V-Trig to S-Trig converters (maybe a couple going the other way, too), and possibly a PAiA Hot Springs reverb.

As the system nears completion, I'll post more photos, and hopefully some videos of it in use, too.

Sorry, I just couldn't resist! ;-)

(Variable) Noise Generator complete!

This morning I completed my second noise module.  The one I did previously had a switch to go between white and pink nose, this one uses a pot as a cross-fader between the two. The PCB and all components are the same, it is just a matter of connecting a pot to one header, or a switch to another.

It has been a while since I used my other noise module, so I can't do an A/B comparison quite yet.  But, yes, it does sound noisy. ;-)  I also just used one transistor, and didn't try a few and choose my favorite.  (I thought about it, but oh well!)  The sound is interesting with the cross-fader.  Turning it to the right is a bit like lowering the frequency on an LPF (with white noise input), but not quite.  It gives some interesting flavors of noise at middle settings.

My Input Amplifier and Tuner/Monitor are so close to being finished, but I'm cursed with missing about $0.80 worth of panel parts.  I also have boards to build some more of other modules, but those are competing with my 3-panel Best Of CGS build... most likely I'll jump back and forth.

Voltage Processor/Mixer complete!

Wow, has it seriously been 4 months since I last updated this blog?!  Things have been a bit of a roller-coaster here, but I'm finally getting back into this project.

Today I finished assembling the Voltage Processor/Mixer module.

It is a fairly straight-forward build, though with a number of jacks.  (Nothing nearly as complex as the Selective Inverter, however!)  I tested it and everything works great - the attenuated inputs amplify as well, which is a nice plus!  As with the S.I., the offset voltage is bipolar and doesn't center at zero (due to the +12V/-10V supply), so just bear that in mind with testing so that you don't confuse yourself like I initially did with the S.I.  (There's a reason why the switch is there!)  It should be interesting to play around with this one, with the various inversions and summings.

In the meantime, I'm finishing up a few other modules (Noise module with white/pink pot, Input Amplifier, and Tuner/Monitor - just waiting on a few parts), and should have PCBs in soon for some more VCOs, VCAs and VCFs.  In addition, I'm also getting everything together to (finally!) get everything together in a cabinet... the small rack I have has just been more of a pain than anything, and I really never got much set up in it!

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!

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.

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).