November 21, 2008

getting my modules together

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?


xart said...

Where do we send our $?

Wavedeform said...

Yeah, are you making these for sale?


skkatter said...

I'll take one of each please!

Reed said...

I always wished both CV inputs for the 258 had fine tune controls, but even more useful than that would be fine tuning on the voltage processor. Every time I use a 257 I wind up tapping that first knob because blowing on it never seems to work very well.

Quad said...

Oh yes, i'm very interested in these modules!

buchlajoe said...

Ill take one of the 258s. great work.

darkness said...

definitely one of each. and one asr too please :-)

matmitchell said...

Great Work! I'm interested in getting in on a 258 either complete or as parts. Patiently waiting.. :)

mark verbos said...

I'll make a few of them.

Dual Oscillator $1000 (4 for $3500)
Quad Voltage Processor $800
Programmable Pulser $1500

Reed and I have talked and come up with some new ideas. So I'm redesigning the Shift Register/Quantizer to include scales. We'll see how complicated it becomes after that.

I'm also almost ready to do a clone of the Buchla 288. I have redesigned the digital memory section to use RAMs instead of the shift registers that rendered all the real ones useless.

email me in private about any interest in this stuff and make it quick because I need to know how many panels to make.

I will not make any panels, PCBs or documents available. Sorry.

wavingpalms said...

Also, since info on the Time Domain Processor is even less than SCANT, how about a briefer on what your update does, exactly?

mark verbos said...

The 288 is an awesome multi-tapped voltage controlled delay module. From the front, it appears to have 8 taps, but inside it actually has 16 and the presets section can access 8 at any one time. These are then globally voltage controlled. There's a built in sawtooth oscillator to make the delay act as a rough pitch shifter. It also has some looping/sampling modes.

The unit never really went into production, I know of 2 units in existence. I don't believe either works. The delay was implemented with metal can shift register chips that Intel made for memory in very early computers. These are now impossible to find in quantity and sell for more than $40 each if you do find them. The 288 uses 40 of them. I have kept all the control stuff as is and just replaced that memory with sixteen 64k RAMs. All the changes are in the digital memory section, not anything in the analog domain, so it won't change the sound or feel of the unit.

I have all the design work done on this, I just need to build a prototype.

wavingpalms said...

Jiminy Christmas!

That's what I call answering a question!

And now this is probably the only place anywhere that tells anybody what the 288 does!... (now if only somebody will cobble together info on the 300/500 stuff, and that weird hex-field patch bay that pops up in photos here and there).

I've already commented here on the quality of your posts- so here's my chance to thank you for the quality of your responses!

stretta said...

I can't seem to find your contact information to email you privately. :( Interested.

mark verbos said...

verbos2002 (at)

matmitchell said...

Hey Mark

Patently following your progress, again Great Work!

I am still interested in getting my hands on one when you have them available.