October 7, 2008

The Good Thing About Standards: So Many To Choose From

I love Buchla as much as the next guy (probably more), but his evolution can teach a designer a thing or two. On the subject of standards we can definitely learn to commit.

The 100 series has a few conventions. The power supply used +24 volts, +15 volts and a single Ground. The audio level are at 0 dBV or roughly 1 volt RMS. The CVs swing from 0 to +15 volts. All pulses are on RED banana jacks and all CVs are on BLACK banana jacks. Pulses are 15 volts. All indicators are large 24 volt lamps. Most modules in the system were a single PCB so depths weren't too big, some had two PCBs, but that doesn't matter because the cabinets stand upright and have an open back. Modules are labelled "San Francisco Tape Music Center" or "CBS Musical Intruments."

The early '70s modules of the 200 series or so called "black knob" modules had their own set of slightly modified standards. The power supplies had +/-24 volts, +/-15 volts, +/-5 volts and two Ground lines. Audio levels are +4 dBu professional line level (1.228 V RMS). CVs swing from 0-15 volts. All pulses are on RED banana jacks and all CVs are on BLACK banana jacks. Pulses have a short 15 volt spike followed by a 7.5 volt sustaining gate. Indicators are 24 volt lamps, or small LEDs. Panel components are all mounted to the panel and wired to the PCBs, which in some cases are as many as 3 deep behind the panel wiring, but parallel to the panel. Each module came in it's own chassis with a Cinch connector hanging out. These boxes were assembled into cabinets and secured down with a bar accross the front. Not that it matters because the cabinet covers up whatever is outside the lines at the top and bottom of the modules, but many modules had no brand name on them at all!

The later 200 series or "blue knob" modules also had a unique set of standards. The power supplies now had +/-15 volts, +5 volts, +12 volts and 2 ground lines. Audio levels remain +4 dBu line level. CVs now swing from 0-10 volts. Pulse outputs are RED banana jacks, but pulse inputs are Orange (sometimes at this stage and always by the end of the 70s). CV ins are still BLACK bananas, but CV outs are now BLUE or sometimes PURPLE bananas. Pulses have a short 10 volt spike followed by a 5 volt sustaining gate. All indicators are red LEDs. Behind the scenes now all controls are mounted on a "mother board" and multipin connectors run to the other PCBs, making assembly easier. Cabinets now have large "boats" where a whole horizontal row of modules shares one chassis, which is a part of the cabinet. Power is still the Cinch connectors, but evolves to 10 pin edge connectors by the end of the 70s. Modules now mount into the cabinet using screws through the panel into the boat using tinnerman nuts. The boats are only 3" deep without the power system, so consideration must be made for if a module can even fit into a cabinet. Some modules (208, 227, 296) have daughter cards mounted perpendicular to the motherboard and can only fit in a boat with no power connector and in the middle where the bottom doesn't slope. The modules are now labelled "Buchla & Associates."

The 200e has it's own unique set of standards. The power supply is a 12 volt DC wallwart that connects to 3 DC-DC converters inside the center boat. These converters put out +/-15 volts and +5 volts, the unregulated +12 volts is available from the wallwart. Audio levels are back to 0 dBV. CVs are 0-10 volts. All pulse inputs are Orange, all pulse outputs are RED, CV ins are BLACK or GREY, CV outs are BLUE, PURPLE or GREEN. Pulses have a short 10 volt spike followed by a 5 volt sustaining gate. Knobs are blue capped if their position will be stored memory or white capped if they won't. Indicators are all different colors of 3mm LEDs. Power is all 10 pin edge connectors (but now with data lines on some pins). All panel components are board mounted, but now most modules are just a single board with the panel components and the whole circuit on it. Being micro based makes them lower parts count in many cases and surface mount stuff is small. Boats in the cainets are even shallower, not allowing some modules to fit. All modules labelled "Buchla & Associates."

What's the point? The point is that on a basic level all Buchla modules can be used together in one system, but these little things make headaches. Later 281 modules don't open up a black knobbed 292 all the way. 208 modules physically don't fit in a 200e cabinet. 249e pulse outputs won't step a 246. Should older modules be updated? Should 200e modules have their outputs boosted? I don't know. How do you put a 284 into a 203 cabinet that has no 24 volt supplies? Good question. I made a daughtercard that boosts a 12 volt rail to +/-24. Or you could just tap a line off of the big cap in the 15 volt supply. It's probably only about 18 volts, but it will work. I have seen a 246 modded with LEDs instead of lamps and with it's oscillator adjusted to not need a 24 volt line. That works, of course that same one had blue knobs on it but that's another story.... Hey at least the panel size has stayed the same.


Christian said...

i've been using a black knob 292 with a blue knob 281. i've noticed there are two different types of blue knobs; the kind with four indentations and the kind with, i guess you would call it tapering, all the way around. is age in anyway predicated on this distinction? this particular module has the four indentations. do the later 292s (the ones that where intended for use with the 300s i guess) operate with less input to open fully or something like that?

mark verbos said...

Yes. The blue knobs with 4 indentations are on the older 281s. If the PCBs inside are blue, the 281 puts out more voltage then the later yellow boarded ones. the later ones stick to the 10 volt standard. If you have a later 281, I would suggest modding the 292B to open all the way from 10 volts.

cbm said...

I recognize that I'm responding to an old post, but I figure that this is a good place to ask this question.

Is there a proper way to wire the edge connector for power as far as the pin numbers go? The reason I ask is that I have them both ways on different modules. I guess it really doesn't matter, as long as the proper pin is keyed for polarity, but if there is a "right" way I'd like to do that. The two ways are:
1 black quiet ground
2 white -15
3 red +15
4 nc
5 0range +5
6 brown noisy ground
7 polarizing key
8 yellow i2c clock
9 green i2c data
10 nc

1 nc
2 green i2c data
3 yellow i2c clock
4 polarizing key
5 brown noisy ground
6 0range +5
7 nc
8 red +15
9 white -15
10 black quiet ground

Synovatron said...

Hi Mark - A really useful post for someone like me who gets asked to design and build custom Euro to Buchla interfaces! Do you have anything on Buchla input and output impedances for CV, audio and pulses?