EHX - Deluxe Octave Multiplexer Schematic Redraw

[Scruffie]

Not as far as I know, not many people have 2 x CA3094s spare, bit of a waste of them to build something new really.

I was eventually gunna try and replace them with a LM13600... never got round to it though, not sure how worth it the build is, might just stick to the Pearl OC-7

[liquids]

The tracking section is most of the thing here, and it's, probably the most thorough design going, though to me it's a little clunky because the filtering is a lot of circuitry for not that much better (at least for me) than subbing you're standard set-frequency op-amp based 3-pole LPF found in boss/microsynth and many others.  Converting the OTAs into a 13x00 chip has been discussed around here notable by Harry Bissell, and it's pretty much your standard affair if you're used to OTA-based VCFs.

The compressor that preceedes it, however, is intense and helps a lot.

The rest - well, utilizing bipolar supplies and true comparators isn't for the uninitiated, but I imagine the results are great. Can't say I've built it in full. Most people are content with the 'simplified' boss OC-2/Microsynth and consider that 'good enough' tracking response, for better or worse...if not, then this design is the one to turn to IMO.

[liquids]

Would anyone be willing and able to explain what is going on in the network of components surrounding the 311 comparator driving the 4013?   

[merlinb]

Would anyone be willing and able to explain what is going on in the network of components surrounding the 311 comparator driving the 4013?  

The compressed, filtered audio signal is presented to the 311 comparator. By now it's basically a sine wave. The 311 turns this into a square wave and feeds it into the clock input of a D-flip flop (4013). This flip flop is arranged as a frequency divider, so produces an output that is one octave below the original audio. This is fed into a second D flip flop, giving yet another square wave, two octaves below the audio.
These sub-octave square waves are used to switch the FETs around U5B/U6A, which chop up the audio signal in a clever way, resulting in octave and sub-octave audio outputs.
The OC2 (and pretty much all analog sub-octave effects) work exactly the same way.

Most people are content with the 'simplified' boss OC-2/Microsynth and consider that 'good enough' tracking response,

Oh, and don't forget my U-boat, which is simpler than both...
http://www.diystompboxes.com/smfforum/index.php?topic=93387.0

[liquids]

U-boat is cool merlin, that's my first sight of that, thanks! 

I guess I was looking more for the inner workings of that 311 arrangement in particular.   How does the mute section work?  Why all the feedback r-c networks, what do they do?  I guess, in comparison, I've been using a LM311 in more simple fashion to do the same thing - signal to + input, - input to center rail, output with a ~5k pullup resistor to V+, drive a CMOS chip...

Further down the circuit, I'm looking more for the fuzzed out square wave PLL/sub-octave stuff rather than cleanish sub octave, not that it matters entirely.  Your U-boat does seem aimed to simplify which is quite useful in many cases, but I'm working on a 'spare few expenses if it improves tracking' kind of toy, within a certain limitation (mono, standard guitar-pickup signal for example).

Any further details?  Here's what I see - signal post compression and tracking filter sees the center rail (of the comparator's rails, that is) via a voltage divider, then the - side sees a passive r-c filter (why more audio filtering would be needed, I dunno), the + side sees the same signal but an different r-c network that feeds back/foward(?) to the comparator output, comparator output is pulled up via the 5.6k resistor for current and squaring to feed a logic device (or something), output of comparator includes a small pf value cap for some reason...etc.

[merlinb]

I guess I was looking more for the inner workings of that 311 arrangement in particular.   How does the mute section work? 

As the note decays the DC voltage in the side chain of the compressor drops, and when it gets tooo low it disables the 311, which should avoid spluttering as the note decays. i.e, the sub octave shuts off cleanly, jumping straight back to the original audio.

Why all the feedback r-c networks, what do they do?

Just a bit of slew-limiting and hysterisis (positive feedback).  It creates a dead zone around the zero crossing of the sine wave to stop the 311 triggering multiple times by accident (due to noise etc).