Buchla Tech

Harmonic Oscillators

2011-10-02T14:32:00.005-04:00

Buchla made the 148 Harmonic Generator in 1969. It is a sawtooth oscillator core, the same as the 158, with waveshapers creating 9 harmonics above the fundamental. The even harmonics are created with full wave rectifiers doubling lower frequency triangles. The odd harmonics are shaped using a series of diode clippers that mix the triangle with a clipped version to make a higher frequency triangle. The effect is a wavefolder, the precursor to the Timbre circuit in the 259.

I built a modified version of that design 10 years ago. The original has no -15volt rail, so it AC couples the signal in many places. I eliminated all these caps and powered the circuit from +/-15 volts. I never got the quality of the waveforms to where I wanted them. I have since worked on a Buchla 148 and found the waveshapes to be about the same as my clone. They sound a little wavetabley, especially the higher odd harmonics.

Legend tells that Buchla made a version of the Harmonic Generator for the 200 series. It was based on the design of the 148, but had a few extra parts added. It had reversing attenuators on the CV ins and an output mixer with sliders and even/odd outs. I have never seen this module and don't even know the model number.

In 2009 I started designing my take on this forgotten concept. I made up my own waveshapers using distorted CMOS opamps, like the 259 Timbre circuit, instead of diode clippers. This does not sound good. I have since thrown the design out.

Finally, I have my finalized design. The Harmonic Oscillator. The analog oscillator core puts out saw, square, triangle, and spike (208 style). The waveshaper puts out 10 decent quality sine waves. The voltage controlled mixer has sliders and CV ins for all channels as well as scanning circuitry (sort of freq. and bandwidth for the harmonics) and tilt (to favor the high harmonics or the low harmonics from voltage).

Prototype Music Easel!?

2011-03-18T17:54:00.004-04:00

The Music Easel is the street name for the combination of the Buchla 208 and 218 touchplate keyboard. I was recently called upon to repair the prototype unit, built in 1973. This unit was resurrected in 1987 and had since been in a basement, used from time to time without ever being moved. He built a very cool blue wood enclosure for it with a built in linear power supply.

When it changed hands, several problems appeared. The 208 module is built from a large motherboard with 12 perpendicular daughter cards, attached with .156" Molex connectors. The biggest problem was that the connectors had oxidized and the cards had to be jiggled around to get several of them to work. The 20 years that this thing sat in the same spot it was fine, but I guess shipping did a number on them. I replaced the female side on all 12 cards and things started to get better.

The Oscillator and some other parts were still not working properly, so I set out to find the problems. Being the prototype, there are several things that are not the same as other units. The panel has a sine wave in the modulation oscillator, when it actually puts out a triangle, the memory card edgecard connector is smaller, the Envelope and Pulser sliders are labeled backwards and the modulation oscillator's banana output jack covers some text. The boards are filled with cut traces and flying resistors. It was a lot of fun.

Finally, I got to the 218. It was only triggering notes while you touched one of the grounded frets. The original owner thought this was normal, but I have used these before so I had to figure out what was wrong. I found that the resistors controlling the keyboard signal's gain were different on the schematic, the parts overlay AND the picture that I had taken of a working unit when I serviced it. I tweaked these values until the keys triggered normally.

Good Ol' Filters

2011-03-18T16:45:00.005-04:00

The Lopass Gate is widely recognized as a sweet sounding filter with a Vactrol-induced slew to it. Set into the top switch position, it is a Sallen-Key filter very similar to the Korg MS-10/MS-20 filter. The LED/photocell elements, known as Vactrols, add something around 10ms of slew on the attack and 100ms of slew on the decay. This is more than an OTA filter for sure, but what if there was some REAL slew on the CV?

Then, there's the Buchla 192. A simple, nonresonant, 2 pole lopass filter, featuring an all discrete transistor signal path with the control elements made from photocells and incandescent lamps in a little bit of heat shrink tubing! The original run (it's quite rare, but I don't know how many are out there) of this module didn't even have a CV input. It has a slew of several seconds when the cutoff is changed.

The one that landed on my workbench was living behind a Dual Reverb front panel with the labels scratched off. It was not functioning. Since I discovered at least one dead "optical element" and this device was such a hack anyway, the owner and I decided to mod it for actual VTL5C3/2 Vactrols. After all was said and done, it is a very interesting sounding lopass. Sort of like a 292 in lopass mode, but with an all discrete signal path.

Just because

2010-06-17T16:41:00.002-04:00

I didn't know Vactrols could do that!

2010-06-16T21:16:00.003-04:00

I recently repaired a 227. It has several problems: A dead channel, reverb wasn't working, I forget. It seemed like a quick turn around repair, until I sent it home and got the dreaded, "this thing's broken again!" phone call. Only now, it was completely shutting off the main output whenever it got hot. So, as long as I kept it on my bench, with air flowing around it, no problem showed up. After 5 minutes inside the boat, the main output went dead. This problem drove me nuts for a while, and in the end it was a Vactrol! Since the main output buss is quad, the panel volume control is actually a 4 channel Vactrol VCA. I guess diodes sometimes go open with heat if they're old enough. In this case the diode was a vintage Vactrol.

Good Times In Anaheim.

2010-02-01T14:10:00.001-05:00

It was great to meet everyone at NAMM. I'm glad I decided to go.

"I can't fit all these amazing modules in my system!"

2010-01-09T17:12:00.001-05:00

I'm going to NAMM

2010-01-08T19:34:00.001-05:00

BTW. If anyone is going to be at NAMM and would like to meet. Please email me in private.

MARF making

2010-01-08T19:23:00.002-05:00

I repaired a MArF a few years back, but nothing was like the undertaking of getting the 248-3206 from the Buchla garage sale working. I only know of a couple of these in existence and I don't know that any of them work. Someone bought the panels with only the motherboards attached. I have had them in my possession for more than 2 years. I had to design, assemble and troubleshoot the input board and 3 output boards for this beast. Each board is 14" x 6" or so, no small task. Today it worked for the first time.

Pictured is the working MArF as a reference. and the 2 panels from the double size expanded unit. A 3206 is a normal 1602 unit with an additional 4 space panel added to it. The expander adds another 16 stages of sliders and memory as well as 4 more output channels. The 6 total output channels can address the 32 steps in any way. This thing could be a 200 system's only source of modulation generators. LFOs, Envelopes, Sequencers, Quantizers, Voltage Processors are all possible. More infos to come.

Much more info to follow.

Finally

2009-09-22T16:02:00.001-04:00

I got the panels finished.

Some audio demos

2009-08-08T19:55:00.004-04:00

I have thrown together some quick examples of what the different functions of the Time Domain Processor sound like. There's no art here, it's just an ARP sequencer, 259, 281, 292 together with the delay unit. I think this thing takes simple stuff to the next level.

DELAYS

this is the simple sequence run through the module in delay mode. Since it has 8 delays happening at once, the sound can be very complex. I add a little feedback, just to make things interesting. Later in the clip I position the sliders so that the delays get louder as they go to the right, creating the reverse reverb type sound I mentioned in the last post.

PITCH

In this clip, the module is in pitch mode. The sense is set to turn on with each note. When the envelope follower opens, it hard syncs a sawtooth oscillator that is sweeping the delay time. This sounds like a pitch shift. With feedback it sounds like rising or falling echos.

SAMPLE FX

Here I send some sound in and then grab it in the loop mode. I retune the sample and sequence it. Basic loop stuff.

SAMPLE AS OSCILLATOR

In this clip, I am using a sample loop (sound sampled from the 259) as an oscillator. It's patched through the 292 and sequenced on the sequencer.

FM ON SAMPLE

Here I add some audio rate FM to the sample loop, to show how much it can be hurt.

Sometimes Experiments Work

2009-08-06T14:06:00.003-04:00

I have been talking about digging into the 288 schematics and redesigning the digital section to eliminate the obsolete shift registers. It's an 8 stage voltage controlled digital delay, BTW.

Well, upon building up the prototype, I came to find that several of my original ideas didn't work as I hoped they would. After some rethinking and experimenting, I solved those digital problems. I now have a working version of the design. It makes some very interesting sounds, that I haven't heard before. It's cool sounding to have the short delays very quiet and them get louder as they get longer, it sounds like reverse reverb. Also, the looping stuff is out of this world. Woah. Now I just need to get my silk screening done.

Tinnermanned

2009-06-17T14:16:00.003-04:00

Buchla 100 cabinets have wood strips that the modules screw into. It's a functional system, except that wood is not grounded or protective from RF interference. Early 200 cabinets had each module in it's own chassis box, then these boxes were held down from the front with metal strips between the rows. The strips cover the module name and the bottom credits, probably why modules form that era don't even have "Buchla & Associates" or "CBS Musical Instruments" even "San Francisco Tape Music Center Incorporated" at the bottom. ;)

The later 200 series cabinets, the model 203 series, use the "boat" system, that is still in use by B&A today. The cabinets fold in half, and the boats are relatively shallow, not wasting huge amounts of space like a Moog type cabinet. Sometimes this shallowness bites you in the ass, (like when trying to mount a 208 module in your cabinet for instance) but usually it is great. The only time I lose my temper is when I get "Tinnermanned."

The Tinnerman nut is named after noted mechanical engineer.... I don't know who Tinnerman was, but I bet Carroll Smith's Nuts, Bolts, Fasteners, and Plumbing Handbook has that information in it. Tinnerman Nuts, or Speed Nuts, are used instead of threading the rear piece, when attaching a piece of sheet metal to another. The Buchla 200 and 300 series boats have larger holes milled into them and then a Tinnerman nut that the panel screw threads into. To be "Tinnermanned" (a term Reed Hays and I coined after being victimized by it repeatedly) is to start threading in the screw and realize that the threads on the back half of the Tinnerman Nut have not grabbed on the screw and you are in fact screwed and have to take the panel off again and reposition it.

New 200e cabinets have threads built into the boats' rails. Although this means that some of the modules I have built have mounting holes that are slightly out of allignment with these boats, users of these cabinets will never be Tinnermanned. All that said, I have been asked where to get some Tinnerman Nuts.

I've gotten them from here

http://www.mcmaster.com/#94808A158

They look slightly different than the ones that came on Buchla cabinets, but they work the same. In fact, they are a little tighter fitting, so I have had better luck with these than vintage ones.

Happy screwing!

Knobs

2009-04-21T14:12:00.006-04:00

The modules pictured in the last post were a special request.

I in no way intended to indicate that I am no longer using black or blue knobs.

Don't Worry About Me...

2009-04-20T22:32:00.002-04:00

I have had lots of problems including back ordered parts and my own health, leaving me behind schedule. I apologize.

All custom modules were either shipped last week or are going out this week, with very few exceptions (pulsers...).

The picture above is of a 254 and a 258v dressed in Selco knobs. Most have been made with blue Rogan knobs and black Davies respectively, but they do dress up ok this way too.

Thanks for everyone's understanding and I promise to post more now. I will be diving in to this 248 and hopefully getting it going very soon. Details will follow.

1.2 volt per octave input

2009-02-18T23:47:00.003-05:00

Pictured is the 258v with the addition of a trimmed 1.2 volt/octave CV input (the grey banana jack on the left). I have decided to go with this system because it gives the trimmed CV in I want, but doesn't take away any other inputs or outputs. The fine tune control for the left most CV in, I believe only was useful when scaling that input for a keyboard.

I'm working on them, and still waiting on the Selco knobs...

Gentlemen, I give you the 258v

2009-02-06T19:51:00.004-05:00

This is a clone of the Buchla 258 oscillator. Despite what some people might tell you, it is totally true to the original in sound and response. I made all the electronics fit between the panel controls on a single PCB, as opposed to wiring to it like the original. I replaced the obsolete heated transistor pair with a modern matched pair and a tempco. The CV inputs respond exactly the same as a 258c. This one has the CV input fine tune control on the left, but I will be doing them with a grey banana jack in place of that. It will be trimmed to 1.2v/octave, but the other CV inputs are unaltered. Now I just have to build the rest of these....

Verbos' little workshop

2009-01-18T20:23:00.003-05:00

I have a full on production line going here. I <3 my new Swiss Assembly Jig!

"Hey Mark, why is the timbre always on?"

2009-01-16T16:14:00.002-05:00

Sometimes analog switch chips will not respond to the front panel controls if the control pin is missing!!!! How did that happen? I don't know.

Holding Pattern

2009-01-15T17:02:00.001-05:00

As I wait for my silkscreen guy to come back into town and the rest of the back-ordered parts to arrive, I give you a picture of a 258 clone with no front panel legend.

funny waveshapes

2009-01-04T00:25:00.005-05:00

Some people think that a good waveshape is one that looks like what is printed in a textbook. A clean SAW wave is not always the best sounding one. Buchla 259s do not address the waves at the main output by the way they look, but rather by their harmonic content. Sure, there's a square and sine output, but the main output is a blend between even and odd harmonics, between hi and low order harmonics and between lo and high timbre. This always seemed, to me, like the better way for a musician to deal with oscillator output. The 258 claims to have a saw and square wave, but I feel that the spirit has always been about even or odd harmonics. They crossfade from sine to saw on the top oscillator and square on the bottom. The waves never look perfect, but they sound so good that the oscillator has a cult following. People clone it left and right. The above 'scope pics are from the prototype of my clone.

Here you will find some scope shots from an actual vintage Buchla 258C:

http://www.synthtech.com/pix/buchla/b258/b258_w1.jpg
http://www.synthtech.com/pix/buchla/b258/b258_w3.jpg
http://www.synthtech.com/pix/buchla/b258/b258_w4.jpg

Looking good. Sounding good. Feeling good.

Big Bag of Bananas

2008-12-16T22:21:00.004-05:00

Have you ever wondered what a bag of 500 Johnson banana jacks would look like? Here it is. I have included my old (and useless) cell phone in the shot to give some reference for the scale.

Reed, your friends have arrived

2008-12-16T22:15:00.005-05:00

I have been looking for a suitable replacement for the buttons on the 246. Reed has several sequencers that need to have them replaced and the original part is long gone. In a perfect world they would be available in blue and red and have LEDs inside them, instead of incandescent light bulbs that will burn out again. I found a solution, but it was back ordered for 6 weeks. The part showed up, I can't wait to try them out!

What's this?

2008-12-10T22:28:00.003-05:00

I have done a lot of PCB design and part ordering lately and I am waiting for packages to come every day.

I got some PCBs in the mail today. They're a crazy color, almost white. I stuffed all the parts I had around into the prototype boards. Now I have to wait for the pots and last few other parts to get here. This is going to be a lot of work, but I'm looking forward to it.

Where Buchla Keyboards Go to Die And Be Reborn

2008-12-10T07:45:00.002-05:00

I have had these 3 keyboards since I was sick. When I got them the farthest away worked fine and the closest just needed to be tuned up and the middle one didn't work at all. I went through various stages including one point where all three stopped working! @#$%$U&^*

Anyway, they are all ready to go home now. For a minute there, I thought I might actually be the charlatan I'm afraid of being...

Quickly of interest there are two 221s and one 219.

The 219 is serial number 5, evidently the last one ever made. It's actually a great keyboard, 48 keys laid out like a piano, 8 keys with individual tuning, 2 pairs of awesome benders and 3 kays with pressure and trigger outs. It's 4 voice polyphonic! I don't know if one could get analog oscillators to track close enough to actually play chords, but maybe with 259Es. The Joysticks light up. They're made from a plexiglass stick glued to a Davies Molding knob that uses a tiny incandescent light bulb as the ball in a "ball and socket joint." Four photo resistors get exposed the light from that bulb to change the resistance and give CV output. Wild.

The 221s are exceptional in that they are the only Buchla touchplate keyboards that DO NOT have trim pots on all the keys. Its a slick design, sadly it uses a few rare parts, so it's not really clone fodder. I don't know that I like the idea of having all those buttons that are useless, since they were intended to control a 300 computer. The joystick is normal on this one, but these two have different length sticks. If you leave space on the sides put a light in the boat, you can move the whole keyboard left and right to get additional bending. That Buchla thought of everything....

I'll put up some pictures of the guts in the next couple days. What a load off. Now I can clear up some space for the next wave...

My 207 #2

2008-12-10T07:35:00.005-05:00

Through a series of trades, I ended up with a front panel from a 207 module. I had to clone the PCB in order to make it into a finished module. The module is mostly finished now, it simply awaits the microphone transformer. I have one lined up, I'm just waiting to get my filthy hands on it. Anyway, someone asked how the PCB I made looks, so here it is blank.

Here it is with some parts stuffed. Notice I went with film caps in the audio path instead of the 1uF electrolytics. I just felt like it was a good idea. I don't know if I'm making the world a batter place, but I'm trying, one capacitor at a time.

I did that messy kludge just like the original ones have too, but I didn't take a picture. it's in the cabinet now, so that will have to be shown off some other time. I don't know how much crosstalk would have been added by placing the resistors on the PCB, but I figured it wasn't worth tempting fate.

Ruff Club

2008-11-29T20:18:00.002-05:00

This is just a rough mock up of what I have been thinking about for a single space mixer. It's 6 channels, each with voltage controlled and manual level and panning. There is a stereo, unity gain expansion input and a mono output. A mute switch on each channel. The 3 channels to the left pan right with higher voltage and the 3 channels to the right do the reverse. Panning is equal powered, so there is no dead zone in the middle. I think it fits the bill.

Mixers Mixers Mixers

2008-11-26T03:57:00.004-05:00

With the release of the Buchla 206e, there's been some chatter about mixers. Evidently some people wanted to have the patch storage, but not the MIDI control for their 200e. But people more like me said they would like a 1 space all analog mixer for their system. This got me thinking, "what have the mixers been so far?"

206 "elegant" 2 x 3 channel mixers that are also summed to operate as a mono 6 channel one. It has mute and monitor switches on all channels.

205 2 x 5 in 4 out matrix mixers that also sum to make a simple 10 in 4 out one. Monitor switches on each input channel. Not exactly small at 3 panel spaces.

207 jam packed 6 input stereo mixer with manual pan on 4 channels and CV pan on 2. Pre amp. Monitor and mute switches on all channels. Monitor output on the front.

The 226 and 227 are quad interfaces that for the purpose of this discussion are irrelevant.

I think it would be nice to have a 6 channel, stereo mixer with CV controlled level and pan on each channel. I love sliders too. I don't know if anyone besides Grant uses the monitor system, so that might be eliminated.

The 207 uses a pair of Vactrols to do the panning, but because of the way the equal power curve is implimented, I don't think I could just send the level CV into the bottom of the differential pair. I could put basically a lopass gate in gate mode on each channel before the panner. The parts count could add up REALLY fast. That's 18 Vactrols! That's a lot of board space.

I'm thinking about solutions that are more elegant, like how the Serge Universal Audio Processor works. It's just 2 VCAs per channel that are controlled for the gain and panning. It would be nice to get a fast moving VCA in the equation, for the times when you want a snappy percussion sound. Three SSM2164s could do it.

I'm studying up on equal power voltage controlled panning circuits now.

getting my modules together

2008-11-21T20:47:00.005-05:00

After a month of downtime, I am back in the saddle. I got tonsillitis and had to go to the hospital, then my grandmother died. It's been a bummer, but I've done a little bit of work on a couple modules that I'm ready to show. These pictures are just the panel designs on paper with knobs laying on top, but they give a suggestion of what the finished modules will look like.

The first is a clone of an oldie. I don't care too much for the idea of cloning old modules (I'd rather do something new), but people keep asking me about 258 oscillators. It makes sense that some 200e users would crave the raw analog sound of the classic 200 sound source. There are a couple things that make this a funny one to re-do in modern times.

The first is that it used a µA726 matched transistor pair. That transistor is heated to maintain a constant operating temperature, so the scale doesn't drift as it heats up. This part is long obsolete. Although I could buy NOS ones on ebay, I have decided that this is not the best idea. Since the 259 uses a regular matched pair and a tempco resistor and the 208 switched from a µA726 to a regular matched pair and tempco in one of it's design revisions, I figured it would be ok to do this one with an LM394 and a tempco resistor. I also have redone the PCB so that all the panel controls mount on it. It makes the module much cleaner looking and less prone to failures. If the pots fail 20 years from now and nobody is making the same ones I have used, one could always panel mount some and wire to the PCB like the original design. It could be built up using the original knobs, blue knobs (if I can get the big blue ones!) or the ones Don is using now on the 200e modules.

The second thing is that the 258 has no keyboard input. Don decided to put a fine tune on the left-most CV in instead. I have never cared much for this and have entertained several other options. The first idea was to put a push/pull pot in the left-most position and when it is pulled engage a trimmed CV in rather than the scalable one that is normally there. Grant Richter told me he had done this on an actual Buchla 258. The problem I have with that is the depth of those pots would require really long stand-offs and panel mounted pots. The second idea I had was to put a gray banana jack in the hole where Don put the fine tune control on the left. This would work, but I don't know that I like having a banana jack in the area where the knobs are, call me weird. The final idea I had was to put a toggle switch where the fine tune was. If it's up, the input is trimmed 1.2volts/octave or whatever and if it's down, the CV goes through the control. I have set up my PCB so that the original fine tune control, the banana jack or the switch are all possible. I plan to try them all out and decide which suits best.

Although I did a couple 258 clones a few years back using a CA3080 instead of the discrete transistors in the core, I found the triangle symmetry to be imperfect and the whole exponential converter had to be changed to use a PNP pair, hence this module will be true to the original design using discrete transistors.

The second module I have ready to order parts for is the Quad Voltage Processor I wrote about last month. I thought I could get all the parts between the controls on a single PCB, using SMT, but I found that it was more parts than I anticipated. It is a motherboard with all the panel controls and a second board with the actual circuit. Since this is essentially 2 whole 257 modules, each with an extra CV input, I think that is respectable enough. I'm really looking forward to getting this one built up. This will be a boon to small 200 systems, where it will solve many control voltage situations.

Anybody interested?

292C secrets

2008-11-03T20:16:00.007-05:00

I cracked open my first 292c repair last night. I found some interesting things during this repair. First, there are some parts in the actual 292c that are not on the schematic. I probably found the most confusing way to draw this, but I just added it on top of the schematic in red. the cap around IC7 is going from inverting input to output, even though my artwork may look misleading. I'm not sure what the point of that resistor/cap kludge in the middle is. My guess is to roll off the highs (around 24k) a little bit in gate mode only. This makes me wonder why nobody has complained about oscillations in all this cloning that has been going on. Check out the hacked solution to solve the lower gain on the second channel. I don't think that's factory.

Second, the channels don't match! Well, the first one on the left has an error, so that doesn't count, but the second one doesn't have a 100p around IC7 at all!?

I love Buchla repairs, they are like an archeological dig.

Just for fun

2008-11-03T19:05:00.004-05:00

I have been way sick for the last week. My tonsils got infected and I haven't been doing any work. I took this shot just for fun. These modules will never live together, but it's a fun hypothetical 12 spacer. Now I just need to make them all work...

Unearthing Greatness

2008-11-01T18:20:00.001-04:00

In the last trade I did, I ended up with 2 modules that seem to be very early examples. The first is a 292B labeled "Prototype" on tha back of the panel. It's written in pencil, funny enough. This one worked well and matches the 292B I already had here.

The front panel was dirty, I had to take all the parts off to clean it up.

The other, a beat up old 207, has "Model" on an orange sticker, stuck to the back of the panel. I believe this means that Don built this up for the assemblers to use a reference while they were hammering them out. This thing had a few broken sliders, so I decided to replace all of them, since I was ordering a set for the 207 I was building from scratch. Synth Restore in the UK has re-manufactured sliders for ARP synths, and these were CTS too, so they work for Buchla stuff. To my horror, the inside of this thing was filthy! Balls of hair at the top and bottom of each slider and crumbs were everywhere.

I took out the sliders and blew out the crap to get started.

The sliders went in really nice and even though the shafts are shorter than Buchla used, they look great. Now, I just have to finish his buddy...

ADSR and the Buchla

2008-10-26T01:35:00.010-04:00

The Buchla is not usually associated with keyboard type ADSR envelopes.

I patched up a 281, plugged into the 107 voltage controlled mixer to make some percussion sounds. The good thing about a 100 series gate like this or the 110 is that they are all transistor and don't have the characteristic Vactrol mushy attack. Everything has it's place after all.

I have a loop going, so the envelope keeps triggering, while I work on it. I started with function generator 1 in looping mode and it's trigger out plugged into the trigger in on function generator 2. In this patch, both are triggering at the same time, and I'm taking the voltage out of the combiner section at the bottom. It is a diode combiner and not a mixer, so it puts out whichever is the higher of the 2 voltages at any given time. If the second function generator is set with a slow attack, you can create a cool, compressed drum type sound, where there's an attack followed by a swell in the decay portion. If you put the switch into AR mode on function generator 2 you can play this from a keyboard with sustain.

Then I put the 281 into quadrature mode. The pulse output from function generator 2 plugged back to the pulse input of function generator 1. This gives you a AHDSR of sorts. The Attack control of function generator 1 controls the attack time. The attack control of function generator 2 controls the peak hold time. The decay control in function generator 1 and the pot in the combiner section control the decay and sustain (unfortunately decay is the time of decay AND sustain so you have to massage them to get what you want). The decay control on function generator 2 controls the release. This setup is good for making hard punching sounds, because of the peak hold. Again, put the switch into AR mode on function generator 2 for sustain.

The final option I can come up with right now, is to invert the second function generator. The first function generator's pulse input is where the envelope is trigger from. The quad mode is on. The cv out of function generator one is plugged into a voltage processor and turned up to 100%. The CV out of function generator 2 is sent into the voltage processor and inverted, it's inverted gain will then be the sustain control. It should be in AR mode. The attack control on function generator 1 is the attack, the attack control on function generator 2 is the decay. The decay control on function generator 1 is the release and the decay control on function generator 2 should be all the way down (it's sort of a delay until the next envelope fires if this is all looped). What I like about this is how it always completes the full attack and decay faze before it starts the release, unlike a "normal" ADSR. That makes it great for sending a pulse from a sequencer and getting percussion envelopes with full control.

Oh, and you can tweak the shape of the segments with feedback too...

Music Easel Oscillator

2008-10-23T19:24:00.004-04:00

The oscillator section in the 208 module can be seen as a rest stop on the way between the 258 and the 259. The "timbre" section is introduced as well as a switch to select waveforms. It's the first time Don implemented a dedicated modulation oscillator and trimmed keyboard CV inputs.

Interestingly, the original version of the 208 used a totally different design than the 258 or the 259, with Vactrols in the oscillator core. I don't know how many of these were made, but it was fazed out in favor of the 259-like design you can find schematics for on the web.

The "Timbre" control introduces wave folding on the sine wave, but does not effect the other waveforms at all. There is a separate, unlabeled knob above the waveshape switch that controls the mix between sine and the other shapes. The wave folder's effect disappears at the full CW position of this control.

I built a clone of this oscillator about 6 years ago, using 2 single sided photo etched boards. I modded a few things to make more sense in a dedicated module. There are a few lessons I learned, that I would do differently, if i did it again. It is a nice design and I think it has validity, even alongside other Buchla oscillators.

Going through my box of abandoned old PCBs, I got the idea that maybe this would be a cool module to throw together, considering the hype surrounding the Music Easel. Maybe it's time to revisit this one....

Musings on Voltage Processors

2008-10-23T18:16:00.006-04:00

Some time in 2007, the idea of "building a better voltage processor" came up between Reed and me. The problem goes like this....

256
pros: good for mixing, inverting and scaling. Huge output voltage swing possible, for black knob era systems where you really need 15 volts to open some parameters.
cons: All it can do is mix and invert. Only 2 sections. No indicators. All black banana jacks. (just kidding Rick)

257
pros: able to mix, scale, invert, crossfade, manually offset, VCA
cons: no gain, can only mix 2 CVs. Because it uses PWM for the crossfade, it doesn't like audio rate CVs. Only 2 sections. Confusing nomenclature.

256e
pros: able to crossfade. invert, scale, mix (kinda). Breakpoints!
cons: only will work with up to 10 volt CVs. No real mixing.

The first idea was to make a quad voltage processor module that had 2 sections of 256 clone and 2 sections of 257 clone. That seems like a cool enough idea, but then I thought, "what about making a design that can do what both do and including 4 of those?"

The idea is to have the ability to mix 3 CVs, crossfade, scale (from a knob or another CV), offset. It should have an LED to show it's state. I had a design made up and a front panel worked out, then my laptop was stolen by a Gypsy in Barcelona. These print outs are all that remain. Anyway, I am ready to dive back in and I will get something together.

It will be like a 257, but with 2 reversable CV inputs. The PWM crossfader will be made from newer, faster parts. So the cutoff frequency will not be so low. The 257's triangle oscillator, for the PWM, is 21kHz. I think I'll try to take it up to 100kHz or so. This shouldn't be a problem for modern analog switch chips. I think I'll use center detented pots for the reversing CV inputs. Here's the 257 schematic, BTW.

With this configuration, you can mix 3 signals, one with voltage controlled gain. It's not the 4 signals of a 256, but it's close. It can do everything a 257 can do, with a bit more speed. It's 4 processors in one module space. It'll have LEDs on the outputs. the output will not swing a full 15 volts, because I don't want a 24 volt supply line (200e and many 200 systems don't have one). It won't even try to do the breakpoints, we'll leave that to the 256e.

Desoldering Station

2008-10-23T18:10:00.003-04:00

Last week, I became the proud owner of a Hakko 472D desoldering station. This amazing device heats up a solder joint and vacumes out the molten solder. I had been using the Soldapult large size hand pump sucker thing up until I got this thing.

This allows me to reclaim chips and other parts from a circuit board, rather than resorting to cutting off the legs. It is a work of genius. Thank You Reed!

LEDs for Lamps

2008-10-18T16:54:00.004-04:00

I dug into the 280 quad envelope generator's indicators. Originally, Buchla used lamps for the indicators on his modules. This evolved into the use of LEDs in later and current modules. Don couldn't decide how to mount LEDs either, some modules had them mounted to a "motherboard" PCB, some had them mounted to terminal strips bolted on the panel. The owner of this 280 decided to have me replace the lamps with LEDs, so they would be faster as well as last longer. I decided to change all four, even though only two were blown.

The offending lamps are sealed into a panel mounted enclosure that was intended to be disposable. Sadly, 40 years have passed since they were installed and they are no longer being manufactured. The only solution that will keep the aesthetic of the panel is to cut off the back of the enclosure and put a new light inside it. This is the cute lamp that was inside.

Luckily, a 5mm LED fits inside perfectly. I have chosen to use RED diffused type. They light up nicely with no extra resistor! Here is the job partially finished. The sawed off lamp on the left and an unaltered one on the right.

And here all done.

I forgot to snap a picture of the LEDs lighting up, but they look great. Now the fast, "blip" type envelopes can be seen, which was not the case with the original lamps.

Garage Sale 259

2008-10-16T16:06:00.007-04:00

Today's project was a broken 259. The modulation oscillator was not putting out anything in the sawtooth position of the switch. The Harmonics Order control was doing nothing, but voltage was effecting it. Judging simply from the outside of this module, I can assume it was not built at the Buchla factory, but was a kit purchased at the garage sale a few years ago. The blue LEDs (yuck!) and the black big knobs were the first tip off.

Once I had this guy open, I was treated to confusing extra wires, which I came to see were there to get around using the remote switch as intended and to use it to engage some extra trim pots. I guess that the switch puts the trimmed CV ins into 1.2v/oct mode to work with a 200e system. Why the builder didn't just add some fixed resistors and make the CV ins ALWAYS 1.2v/oct is beyond me.

The Harmonics Order control problem was just some bad soldering. During assembly the iron was held on one of the pot's pads for too long and it lifted off the board. Finally, the pad tore away from the trace.

The modulation oscillator turned out to be putting out a sawtooth wave, but it wasn't getting to the output. The LF13331 is the switching chip that I always HOPE isn't blown, since it is hard to come by. In this case, the working saw wave told me that the chip was fine. It turned out to be a faulty 4555 decoder. I think if the LF13331 had been the problem, the LED on the panel would have been showing the saw mode, but it wasn't.

Upon re-assembly I tried everything out and came to notice that the lower order harmonics were coming out as just a sin wave. When I tweaked the trimmer I got a little action, but only about 25% of the total that is normal for the wave folder section. It turns out, the 2N3958 dual FET transistor that is supposed to be there was substituted with 2 2N4339 FETs. These FETs don't have as much gain I guess, because they weren't doing the job. Rather than tweak resistor values, I put in the real thing and it worked perfectly!

Now it's working properly. I even added some rubber caps to the switches(not in the picture). I don't mind the black knobs, in fact I prefer them to the unskirted ones I got, but I HATE the blue LEDs.

This ol' 281

2008-10-15T23:08:00.003-04:00

There are two versions of the 281 Quad Function Generator. I have one of each in my system. The older version has blue PCBs and circuitry for remote control. The newer, yellow PCBs and the "remote" switch does nothing more than turn on the LED. I received this older one as part of a trade, in dysfunctional condition. Just one of the 4 envelopes was working. The panel is beat up, some of the silk screen has come off, presumably from stickers being stuck to it for 30 years. The knobs were discolored and the arrows had worn off. One switch was broken and one was missing.

I replaced the switches and all the knobs. Then, I attacked the circuitry. After some song and dance, I found that the CA3080s on all three and the LF356s on two were not working. The odd part is that 4 out of 5 of these were already in sockets (not all the chips were) and all 5 were metal cans. It seems so much less cool to put in plastic DIP chips, but whatever works. Aren't these bad boys supposed to be MORE robust?

This design has resistor values on the schematic for 15volt systems or 10volt systems. i came to find out that mine is set up for 10volt systems, which makes it match my yellow board version. Anyway, it's nice to have it working.

Early To Rise

2008-10-14T16:25:00.007-04:00

A while back, in the Buchla Yahoo Group, I got involved in a discussion about why some 200e modules will not advance a 245/246 Sequencer and subsequently my 243 Programmable Pulser module. I suggested that it was the slow rise time of the 249e, and likely every other 200e module, that caused the problem. Ezra wrote that he thinks it's the voltage level of the pulses, since they only peak at 10 volts, not 15 volts like the old black knobbed modules from the 246 era. Well, I am not one to let sleeping dogs lie, so Reed and I did a little research on as many modules as we had available and my scope. This is what we found.

249e - 8.5 volt peak - 300µS rise time - does not step the 246
281 - 15 volt peak - 10µS rise time - steps 246
230 - 15 volt peak - 5µS rise time - steps 246
257 pulse from 281 sent through - 10 volt peak - 80µS rise time - steps 246
248 all pulses out - 14.75 volt peak (no spike, just gate) - 500nS rise - steps 246
248 CV out alternating between high and low - 200µS rise - steps 246
225e modded for bigger pulses - 12.75 volt peak - 150µS rise time - steps 246
259 square wave out of mod oscillator - 10 volt peak - 5µS rise time - steps 246
259 saw wave (falling even though the panel shows rising) - 10 volt peak - 5µS rise time - steps 246

The 246 schematic specifies that it's "input sens." is 3V, 100µS rise. The 284 schematic specifies it's "nominal input sensitivity: 5V (5 pulse, 3V sustain)" and "required rise time (15v):3ms.). Interestingly, the 284 would trigger from the 249e. Where does that leave us? Why does the 225e modded to have a higher gain on the output opamps work if it's not about gain? Why is 10 volt enough coming from the 257, but not the 249e? Why is 10 volts not enough if the "sens" of a 246 is 3v? These are all very good questions. I have a guess.

The issue is not wither the rise time or the voltage level, it's both. Specifically, The rise time to the threshold. In the 246's case, the rise time from 0 to 15v needs to be 100µS. On the scope, the rising voltage slope is not linear. It appears to be an RC curve, rising quickly at first and slowing as it approaches the asymptote. So the "rise time" is not actually the issue, but the speed of the rise. If the pulse's total voltage is 15v (WAY above the threshold), it will be moving much faster as it passes 3v than if it is only rising to 8.5v.

My assumption is that the output of the microprocessor in the 249e is PWM that is filtered to make continuous voltages and there's no way to raise the cutoff frequency of that filter to speed up that rise time.

The gain on the pulse outputs could be pumped up, like I did to that 225e, or an opamp comparator could be added between the pulse input jack and the circuit of the sequencer/pulser. A 281 could be triggered with very short time constants and it's big daddy pulse output used to step the sequencer. A banana to 1/8" lead could be used to send the sluggish pulse into a 230 to sharpen it up. I'm considering changing the input section of the Pulser to be more understanding.

I'll close with a quote from the 242 clock schematic. I have not tested any 100 series modules for rise time, but they seem to be way faster than anything 200e...

"pulse width: ~50µS
risetime: ~3µS
[<10µS required to operate models 123, 146 sequencers. when these are phased out, we may increase to ~20µS]"

My first 280

2008-10-14T00:57:00.004-04:00

Today I worked on my first 280 Quad Envelope Generator. I was told that the top envelope seemed to get confused when it got pulses from certain modules. Once it got into this confused state, it was inconsolable. I didn't understand this condition at all. 2 of the 4 lamps are burned out as well.

There are 2 versions of the 280 module. I'm not sure what the deal is, since they were designed only 3 months apart, on March 23rd and June 21st of 1971. I guess this means the first one was a dud of some kind, and I don't know how many, if any are out there. This one was of the second type. (I'm guessing there was a third design as well, since the pictures I got from www.electricmusicbox.com show one with no lamps or pulse outputs and both schematics I have show these.)

Anyway, the problem turned out to be that someone had replaced the input comparator opamp with an LM307 instead of a uA741! I never would have guessed that this would be a problem, but when I opened it and saw that only the weird channel had a different opamp, obviously I was suspicious.

The lamps are still dead. Since they are enclosed in a lens apparatus that is panel mounted, they are not an easy replacement job. I have been told that cutting the back off and sticking another lamp inside the lens is the only way to keep the look. The owner and I have decided to replace all 4 with LEDs inside the lens, since the lamps are so slow they don't even light on short envelopes. Plus, I really don't want to replace them again.

Oddly, the 292 on the bench today had a bad uA741 as well. They must suck. ;)

Overall, I have developed a fondness for this module. On the surface, it would seem that a 281 is better than a 280 or 284, and capable of all of their tricks plus more. But, this little guy does his job with a swagger that can't be duplicated. Oh, and the output swings a FULL 0-15 volts.

The Good Thing About Standards: So Many To Choose From

2008-10-07T12:47:00.002-04:00

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.

107 voltage Controlled Mixer

2008-10-05T15:56:00.003-04:00

In a lot that I bought, I ended up with a PCB from a 107 Voltage Controlled Mixer and a 114 Touchplate Keyboard, shown below. I also have a 160 Noise Source panel that I haven't done anything with yet, but that's not important to this post. I ended up selling the 114 on ebay because I could not imagine making a panel and touchplates that would be convincing and anyway I don't really care for that module. However, I was fortunate enough to find a Buchla owner who had a 107 panel in their system, backwards, as a blank space filler. So I had both the panel and the PCB, I needed only to get the pots and jacks and wire it up.

Assembling this module was an easy enough task. Since the schematic is on the list of ones I WISH I had, I found myself asking around if anyone had this module and would take a picture of the inside and tracing out the PCB to make up my own schematic. Soon enough, I realized that the pots on the panel don't control the VCAs on each channel! They are actually input volume controls.That means that you can't open up a channel without sending external voltage. Totally weird. I guess that's par for the course with Buchla 100 modules.

After some reverse engineering of my PCB and a picture that I got of someone else's 107 guts, I came to realize this module is the equivalent of ten 110 gate modules tied to two output channels and those 2 then mixed. The nice thing about having a 110 VCA in a 200 system is that it has a much snappier attack than a 292 and allows you to cheat nature a little and make sharp percussive sounds. A 107 let's you do a whole drumkit like that!

As it turns out, the PCB was totally functional as soon as I wired it up. This system is coming together slowly but surely.

That 214 Booster Board

2008-10-04T21:14:00.007-04:00

In my post about the Music Easel, I mentioned my clone of the 214 power booster board. Here's a picture of it.

Here is the original.

And, here is the reverse engineered schematic I made.

Since I traced this, I have seen another one that had most of the values changed, but you get the idea. Here it is inside Reed's 300 cabinet. Notice the red velvet trim on this bad boy.

The 266 project

2008-10-04T20:49:00.011-04:00

The Audities Foundation got whatever parts were left in Don's archives during the garage sale about 6 years ago. Included in that lot were 2 unused 266 Source Of Uncertainty panels. I built this one and am working on the other.

Obviously, this is a very popular module and every Buchla user wants to have one, but without any circuit boards nobody was jumping at it. A couple "kits" for this module went out the door at the same time. So I was fortunate to track down some scans of the circuit boards without any parts installed. Then came the long process of cloning them. This module has 3 PCBs inside. The motherboard (with all the panel components on it), A and B.

I know, I know. "They're not blue!" Well, I didn't feel that it was necessary to make the PCBs the same color as the originals. The second cry is, "But there are no orange banana jacks on MY 266!" True, the original release of the 266 used red banana jacks for both pulse input and pulse output jacks, but since Don changed to orange for pulse inputs in the late 70s and is still using that standard today I went with the new standard. It turned out that I made several errors in my cloning of the PCBs, leaving short traces between pins on ICs off. It's ended up working after a little stress and now lives happily between a 265 and a 266e. Long live the Source of Uncertainty.

2008-10-04T19:25:00.002-04:00

This is a Music Easel I had for repair. That's a suitcase type case with a 218 touchplate keyboard, a 208 stored programmable sound source and a 214/215 power supply. The power supply was not working on this unit. It was designed to be operable from 12 volts in batteries as well as from the wall AC. It takes the 117 VAC and sends it through a huge 12 volt transformer. This 12 volts is filtered with a GIANT capacitor. Then that unregulated 12 volts is plugged in where a battery would have also worked. There's a circuit that takes the 12 volts in and spits out +/-24 volts. That is then regulated down to +/-15 and +5 by the normal 215 power supply card. I have cloned that "voltage booster" card and I think I'll use it in my 203 cabinet if I ever need to power a 24 volt module. By the time Don made the 203 cabinets, he had stopped using 24 volts in his designs. Those cabs have Power One brand single output supplies accross the back. Mine is 8 spaces wide so it has doubles of the positive and negative 15 volt supplies. The top two boats get their own.

Why Buchla?

2008-10-04T18:45:00.004-04:00

Since this is the first post, I'd like to start by explaining why I vote Buchla.

The Buchla 200 is the best modular electronic instrument ever made.

1. Don Buchla designed the front panel of his instruments first and the electronics second. A musician himself, this means that each module was an idea for a musician's tool rather than an engineer's.

2. Audio paths and control paths are totally divided. The control path uses unshielded stacking banana cables. The audio path uses 1/8" mini cables. On early modules the control paths and signal paths even used separate power rails! The audio signals are line level, just like all the signals in a recording studio, so patching in and out of the system is seamless. The stacking bananas are great for control signals, they mult simply. The EF Johnson banana jacks come in a variety of colors, which Don used to code what the jacks are used for.

3. Controls sweep within a musically useful range. This is in some ways related to #2. Because audio processing modules never have to concern themselves with CV signals and vice versa, the controls don't have half of their rotation representing useless values, like a Serge.

4. "Unencumbered by engineering expediency or presumed musical asthetics..." Taken from the 248 catalog page.

5. Circuit boards are all mounted parallel to the panel, making the system take up less space behind the panel than most modulars. This allows for the suitcase cabinets and folding 203 cabinets. I will never understand the MOTM/Moog/Blacet/whatever system of mounting PCBs sticking way out back.

6. Sound design emphesis taken away from "fat" and "juicy" 24dB/Oct. lopass type sounds and into more interesting textures. Sure, you can do FM, AM, whatever audio rate modulation on any modular, but Buchla really pushes the user that way. The 259 has a switch and VCA internally patched for FM. It has a dedicated modulation oscillator!

7. Analog address of sequencers. Most of the time a sequencer is simply going to be pulsed along linearly. But having the CV in to sweep through the range of steps allows the sequencer to be used in several new ways including as a quantizer, tracking generator and more.

8. Harmonic Generator. No other modular ever had an oscillator module with the first 10 harmonic sine waves available. Don updated his 148 module for the 200 series too, but only made 2 as far as I know.

9. Source of Uncertainty. These days, all modulars have noise and sample & hold modules, but nobody ever made so many specific and musical options available to make sounds randomly shift and evolve. All hail the 266!

10. Quadrature mode on the 281. After a while, the ADSR became de facto for the whole of the synth industry. The 281 module allows all of the modes on a 284 or a 280 to be achieved, with voltage control of each stage. It's the quad mode that allows a quadrature LFO to be created, for quad panning or whatever. However, this mode can also be used to creat ADSR and DASR envelopes. I like the ADSR that you get from this because it follows through the whole decay and release cycles, even when it only gets a short pulse.

11. "Timbre." No, I don't mean the sound of the machine, at least not in this case. I mean the "timbre" circuit that is inside the 208 and the 259. It involves wave folding similar to the Serge wave multiplier (totally different circuit) attached to the sine wave output from the oscillator. The 258 already had the ability to sweep from a sine wave to either a saw or square wave, which is a bit like lopass filtering. A sweep of the "timbre" sounds unlike any other synth and is amazing.

12. Voltage Controlled Panning. The 207 allows 2 channels to be sweeped around via a CV. The 227 and 204 allow quad panning from 2 CVs. Simple yet wonderful.

13. Tunable Touchplate Keyboards. Those users who have no interest in playing a piano keyboard can rig up a 217 to do lots of things that no other system has ever allowed.

14. VTL5C3. The vactrol used in the 292 lopass gate has a characteristic slew to it. It makes the attack of any note from a Buchla 200 a little round. The "woodiness" of the sound is a key reason that the Buchla's sound has been discribed as natural.

I'm sure there are more reasons that will come to me as soon as I post this, but it will do for now.