May 11, 2013

Video of the new Verbos 247v sequential voltage source


Here's a quick video of my 247v module in my Buchla 200 cabinet. It shows some of the sequencing features. The 247v is connected to a 259, 281 and 292. The 281 is in sustained mode to get the benefits of the variable pulse length on the 247v. To start, I run it from it's internal clock and switch around the stages' on-off-slide switches. Then, I run it from an external pulse from the 281. This shows how the TIME MULT control acts like a pulse length/slide length control. I then show some tricks with patching stages into the strobe input and send in voltage to the analog input from an off stage 254 to select which stages are playing. There are loads more features, using the yellow inputs to make envelopes and stuff. I hope this starts to show it off...

April 17, 2013

The 247v Sequential Voltage Source

I have been working on a new Sequential Voltage Source. It is only a single module space and packs a big punch. It does most of the things a MARF or ARF does, but without any menus. It can act as an 8 stage sequencer with two rows, voltage control of the clock/slide rate, switchable slides/pulses, pulse outs on each channel and the ability to loop from any stage to any stage.  It can act as a multi-stage envelope, up to all 8 stages with any stage as a sustain stage or any stage pausing unless a key is held. It can act as ADSR, AHDSR, HADSR, AD, AR, AHD, LFO saw, pulse, square, triangle, something more complex, LFO that only runs when a key is held, LFO that only runs when a key is lifted.

I wanted a small sequencer with every function on the panel. I wanted to do TB-303/MC-202 type sequences with slides selectable per stage, where the pulse output holds the whole stage on a slide stage but only pulses 25% of the stepped stages. I desperately scrambled to complete two for my performance during the NAMM show. I made panels from PCBs because they take less time to manufacture. I only got one finished and then it didn't work when I got there! Anyway, it's working now. It's pretty fun.

misc. banks on the 263v

The 263v has been a lot of fun. When I programmed the scales, I had a bunch of left over memory spaces. I filled those spaces with random voltage sequences that are similar to the ones in the middle sections of the 266. Of course they are addressed by control voltage instead of pulses, so they have different uses. I threw in a set of 16 smooth random patterns. If you send in an LFO, you get back something like the fluctuating randoms in a 266, well not "random" but fluctuating. Finally, I through in some pulse sequences and some melodic sequences. Using the random sequences and the melodic sequences is a bit like dropping a sample loop into music (you have to trim the start time and length using a voltage processor).  I hope that these functions add something useful to the toolkit.

BTW. I also got it to track 2 volts/octave for the old Buchla guys who need that.

November 21, 2012

Quantizer/Analog Shift Register take II

In 1972 as a resident at CalArts, Fukushi Kawakami made four modules as additions to the school's rather extensive Buchla 200 system. The modules are a Control Voltage Switching Matrix, two Control Voltage Integrators and what I believe is the world's first Analog Shift Register.

Since then, the world has fallen into disarray, computers have taken over, analog modulars have gone in and out of favor several times and those four Fortune Modules have ended up in Grant Richter's hands. Somewhere in the middle of all that, Serge made an analog shift register and wrote about it (under the nom de plume Arpad Benares) in Synapse. Even before the Fortune Modules, Buchla had made a rather amazing Control Voltage Integrator called the 155, but that's another post.


Analog Shift Registers are a bank of Sample and Holds. In fact, using only the first output, it is a Sample and Hold. When a pulse is applied, the CV on the input is stored on output one. Whatever was on output one is moved to output two, and so on. 

In 1997 I made 2 copies of a module that was a dual four stage analog shift register as well as an 8 channel voltage quantizer. One of these is still in daily use over at OSI music and the other is rotting on a shelf in my shop. When this photo went around the forums and blogs some people suggested that rearranging the panel to allow the analog shift register outputs to be quantized via shorting bars would be a good idea. Point taken.


I had a couple of ideas of my own that could make it a better module. Sadly, it got back-burnered and never saw the light of day until now. The new version has rotary switches to select the scale to quantize to. The ASR outputs can be plugged into the quantizer with  shorting bar. There is no longer a "slave" switch to chain the two ASR's together, but a cable and shorting bar can now do that too. Some new ideas have come up as well, like using the quantizer to look-up the voltages from the "random" voltage sequences from the 266. It's obviously not as glamorous as an oscillator or filter, but it will come in useful to some people.

Spring Chickens

In the golden age of analog synthesizers, everybody had a spring reverb in their system. In fact, sounding like the Radiophonic workshop is often as easy as adding spring reverb to simple sine and square wave sounds. Buchla was no exception including the 190, 275 and part of the 212, 208 and 227. The 275 in particular is a rare and interesting beast, offering voltage control of the wet/dry mix as well as simple EQ on the dry signal. 

The module itself sends out and receives a line level signal to an external reverb unit. Most likely, the signal is sent to a 17" x 7" x 3" box that has the reverb drivers and recovery amplifiers built inside, along with 2 15" dual spring tanks.  Any line level in/out unit could be used with the module though. The brochure reads, "The reverberation electronics and delay elements are remotely mounted. Interconnections are at line level, permitting the use of the control module with reverb units of alternate origin (E.M.T.'s, for example)." In the case of the module in my hand above, the "remotely mounted" electronics were not included. Rather than connect an "E.M.T.", the owner and I decided to whip up some electronics to use a couple of reverb tanks pulled from a 190 unit.

The electronics inside the remote unit for a 275 have a discrete amplifier, envelope follower and a variable gain recovery amplifier. In other words,  a compander is built in.  The slowed down attack makes a bit of a pre-delay on the reverb and the gain reducing as it decays takes out some of the noise from the spring reverb. Sadly, the amplifier uses +/-24 volts, which I wanted to stay away from. I created a similar circuit, using the same amplifier IC that is used in the 208 and 227, LM380, with a 275-like compander. I attached it to the back of the module and ran pigtails to the tanks, mounted on the back of the cabinet. The trims control how much action the compander has. I just trim them to have unity gain out when the signal is full strength. I wish I had made a sound clip once it was installed.

This unit could be built inside a box with the springs like the original one was. Since it has line level in and line level, 100% wet output, it could be put on a send of an analog mixer or on an insert of a DAW, like the vintage Roland and RCL units I have right now on my ProTools rig. I use them in my sessions and since they don't have any controls on the front to change, everything comes up the way I left it. Kinda cool I think. 

October 2, 2011

Harmonic Oscillators

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).

March 18, 2011

Prototype Music Easel!?

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.