Some Initial Demos

Once I had built most of the circuits I did a couple of video demonstrations with the kit set up in an improvised fashion. This was around February 2016.

Much improved waveshaper with 16 steps and improved anti aliasing:

wave shape demo from Tom Richards on Vimeo.


System set up in improvised fashion and able to control pitch and waveshape only:

Mini Oramics Demo from Tom Richards on Vimeo.

Finalizing the other circuits

I still needed to transfer all the test circuits into soldered permanent circuit boards, and also design and construct some simple utility circuits for combining CV and audio signals.

These were:

• Main VCO
• 2x Multiplexer/Waveshaper Circuits
• 2x Voltage Controlled Filter
• 3 Channel Motor Speed Control (Drive / Wind / Rewind)
• DC Mixer for combining the Pitch/Octave/Vibrato control voltages
• VCAs and simple audio mixer for combining the two different waveforms and allowing for the spring reverb send/return. (I completely cheated on the spring reverb and just used a Doepfer modular unit. I had totally run out of money and time, and I already had this unit in my studio.)

Most of these I made on stripboard, except the waveshapers which I designed PCBs for. Some images below give the general gist.

Twin VCF circuit based on an R.A. Penfold design:



Multiplexer based 16/32 step waveshaper board:

Slider PCB for waveshapers:



3 channel stepper motor control for transport mechanism:

Turning drawings into control voltages

This part of the design took months and months. Turning felt tip pen drawings into digital logic is unfeasibly difficult! I went through about three or four prototypes on breadboard with varying degrees of success. I had a lot of very generous free assistance from Robin Iddon and Roger Dealtry, who coached me on the necessary logic and prioritisation circuitry through these experiments, and I got very close, but not quite close enough. I was trying out different types of flip-flop circuits: SR, JK, and D-type. Essentially I needed a circuit which would read and latch onto the last read input, but that would also reliably reset all the other inputs so that only one input would be 'read' at any one time. From there I could use analogue switches and resistor ladders to select and output control voltages, which would then be used to control pitch and volume etc. In the end I had to go back to the drawing board and old fashioned logic timeline graphs to analyse what was going wrong, and then what needed to happen instead, and finally the penny dropped and the optical reading circuits were born. I wanted them to be simpler with a reduced gate count, but as I had finally something working properly I just went with it rather than trying to make it less complex first. Once the circuit was working I took the time to design proper PCBs, as I would need seven of them for the final machine. This was by far the most complex circuit I had ever designed and also by far the most complex PCB design I had made, so I had my fingers firmly crossed as I switched on the PCB version for the first time. I had about three hours of exasperation as it just would not cooperate, and then I realised I had not soldered one tiny resistor which was essential for the start up process (a simple RC sub-circuit to overcome start-up glitches and to make sure the machine came on silent awaiting the first instruction). After fixing that, and a doing a bit of calibration on the optical inputs it finally worked. I made some small adjustments to the layout and then ordered one PCB for each of the input parameters of my Mini-Oramics machine.



The first optical reader PCB. The multipin header sockets connect to the phototransistor readers and also the indicator LEDs which allow you to monitor if the drawn inputs are being read correctly:




Last of the breadboard prototypes:

Improved Transport Mechanism

After I built Legoramics, and after building a few unsuccessful test logic circuits, I decided that I should prioritise building the final transport mechanism in order to be sure that any further circuitry I built would be made for the actual mechanical framework I was to finish up using. So I enlisted the generous help of Christian Nyampeta, as I am useless at CAD and technical drawing. Together we came up with the framework for the final machine, in which Christian's drawings were later transformed into laser cut perspex. The design was to use standard OHP cellophane rolls. I tried to design the machine to be mechanically simple, and capable of both 'reel to reel' and closed loop operation.

This is what we came up with:

Mini Oramics Transport Mechanism - first test from Tom Richards on Vimeo.

Transport prototype and initial light reading circuits

I then needed a way to test some initial light reading circuitry designs. I had yet to build the transport mechanism so I built a small lego prototype with four LED/ light-sensor pairs to test my initial logic circuits. I named this Mini-Mini-Oramics prototype Legoramics.

Legoramics from Tom Richards on Vimeo.

Waveform Building Strategies

I decided that using a separate oscilloscope and feedback set-up (as per Oram's design) was too much of a rigmarole for an 'intuitive interface' and that due to the variety in analogue scopes it would have required quite fine calibration and frequent adjustments and also may have not ever worked on some types of oscilloscopes. 

This left two options for my design:

• Build the whole CRT / Photomultiplier set-up into Mini-Oramics like Oram's original machine.

OR

• Come up with another strategy.

The first option had a few issues, the main one being that small CRTs are only now available as 'new old stock' and are expensive and limited in supply - I wanted my new design to be a bit future proof. Also I have little existing expertise in valve technology or associated high voltage analogue electronics, so I opted for a totally different strategy.

The new strategy had to be in keeping with my design goals of building something which would have been technically feasible in the early/mid 1970s. 

After some discussion with my supervisor Mick Grierson I opted for the 'sped up analogue sequencer' type of wave shaper. This works by sequentially switching through a series of adjustable voltages very quickly creating a stepped waveform. This type of waveshaping strategy has been described in Peter Manning's Electronic and Computer Music. And also in Forrest Mims' Circuit Scrapbook Volume II. 

In fact when I started prototyping my wave-shaping oscillator I hadn't realised you could buy one off the shelf, so I must give fair mention to Ian Fritz's Double Deka VCO. 

This video shows my early ten step prototype in action:

unfiltered scans from Tom Richards on Vimeo.

And this video shows the same prototype with sound, played through a basic low pass filter in order to reduce the 'stepping' or aliasing noise:

first wave scans from Tom Richards on Vimeo.

Shortly after making those videos I performed with the new system, nerve-wrackingly still in breadboard  for the Nonclassical label's Pioneers of Electronic Music festival. If you look closely I am adjusting tiny preset pots with a screwdriver live on stage at the Macbeth in Hoxton!

Picture courtesy of Nonclassical

Sound from that gig here:

Beginnings

Oram planned to use a simple op-amp feedback circuit and an external oscilloscope to become the waveform scanning oscillator. This design from an electronics magazine was to become the basis:

I reconstructed the circuit and used it with my analogue oscilloscope and found it to be quite slow and unresponsive. Often it would only scan the top half of the waveform. On interrogating the text a little further, the authors state that it is only good up to about 500 hz. The following image is the scope hood I constructed to test the circuit.

This post by nick's world of synthesizers illustrates the idea working really well using a vacuum tube based photomultiplier like the original Oramics Machine, instead of an LDR like the above circuit.