...off to Forbin

Well it has taken an eternity... or it does seem like it but today i have started on the new Blog about Forbin which is what ORT MkII was to be... see: Forbin

Minimoog Keyboard

Not much activity on the ORT at the moment as I am attempting to finish off the Minimoog. As I noted in a previous post the Keyboard for the Minimoog got effectively destroyed when it was filled with rainwater. The actual mechanisim that was used in the Mini was manufactured by a company called Kimber-Allen, who I believe are not in bussiness any more. The actual design is really very complicated. The actual up/down keystroke movement is transfered through a lot of springs and small arms to move a rather wobbly mechanisim with two gold plated springs upon it. These springs in turn provided the key information and the gate information. Rather than spend a LOT of time rebuilding all of this and probably ending up with a sub-optimal design I decided to find a replacement keyboard. A late 70's Italian Organ proved to be prefect. It was very cheap, the key mechanisim was simple and easy to adapt, the keys looked a little yellow and discoloured so that they looked about the same vintage as the rest of the unit. Each key has single contect and all the keys are tied togther with a diode ORing scheme. I obviously couldn't use the existing method of a voltage divider that was used in the old keyboard. I didn't really want to do that anyway as I wanted a MIDI feed out from the keyboard to control other stuff anyway and it didn't really seem sensible to take a digital signal into the analog domain then back again. I then decided to split the whole thing between two microcontrollers. One in the keyboard that just scanned the keys and sent the information serially to another micrcontroller inside the electronics unit of the Minimoog. I used the AVR microcontroller as it is cheap, easily available, powerful and well supported with various software tools.

Multiple Identity Filter

This is the MIF or Multiple Identity Filter on the ORT. It was the second module that I made for the ORT and it uses a Curtis Electromuse CEM3340 VCF device. The design is by a chap called Craig Anderton who was an electronic music equipment designer who had an article in a magazine called Contemporary Keyboard. This was a big project for the magazine and was spread across 3 editions. You can read the original article at this site (the owner of the site doesn't give his name). I had actually never read the first part until I stumbled upon this pdf on the web! Anyway here is the front panel. It has a very similar layout to the original; which was important for getting the various operating modes right.

The Electronics was again mounted on a piece of veroboard that was attached to the back of the panel. I recently repaired it as you will notice that one of the switches is red. It have been broken for a few years... The module still suffers from a lack of Q or resonance. I suspect that the tantalum capacitor that is part of the AC bypass circuitry has failed but I have yet to actually repair it yet. I have access to a very nice acoustic spectrum anaylser at work so I plan to one day take the filter in and actually measure some of the different modes. It is probably the most complex module in the ORT and probably the most stable, that has probably more to do with the fact that I tinkered less with the design than anything I suspect!!!

Minimoog Serial # 4322

This is the back panel of my Minimoog showing the serial number stamp. It's number is 4322 which places about the middle of all the Minimoogs produced. It hasn't really been in functioning order since the late 80's. It was in my Dad's shed when the roof leaked and unfortunately the keyboard was filled with water. I pulled the keyboard into about a million pieces as it became a little more than a ball of rust. Luckily the electronics survived and is completely intact and relatively original. About a year ago I gave up on rebuilding the Kimber-Allen keyboard that came with it. I had sandblasted and powdercoated the original metal frame but the small springs that form the contact had all fallen to pieces and I considered making a different contact system. I found an old Italian organ at a pawnbrokers quite cheap and that has formed the basis of the keyboard rejuivination. It is of a similar vintage so it dosen't look new and wrong in the cabinet and we are slowly heading towards it being integrated back into the rest of the system.

Symbiosis

Well things are going slowly on the ORT at the moment as I have been distracted by a number of things... One of which is a score by a chap called M.Pointon that was printed in an electronics magazine called Practical Electronics. It is not often that you get a music score in an electronics magazine! This work was in the June and July edition from 1975. It was written to be performed on a synthesizer called the Minisonic, which really is a pretty apalling bit of kit but I suppose at the time was interesting. I have had the article squirreled away for an awfully long time. I bought the magaines, from which it came, sometime in the early eighties. I think from the Save the Children Fund book sale at the University of Western Australia. I have scanned it in and made it into a pdf file which when I find enough space on the net somewhere I will put it so you can all see it. In the meantime I have been having some fun trying to recreate the piece on some software tools that I found on the net. It is quite interesting when you realize some of the problems that exisited trying to record a fairly simple score on equipment in an amateur situation about 30 years ago. If I finsh it I will post an MP3 or OGG of the result for your listening pleasure. It almost certainly isn't going to be easy listening... I can tell that already!!!

Old VCO

This is the Front Panel of the old VCO or Voltage Controlled Oscillator. This module basically converts a voltage into a signal of varying frequency. The relationship between the voltage and the frequency is 1V for every octave over about a 8 octave range. This VCO has a very expensive IC in it which is now kaput so it will not be used again as better designs can be realized more cheaply. I suppose I will recycle the knobs...

This is what is hiding behind the front panel. It is all mounted on a small piece of vero board.

ORT circa Mar 05

Well this is waht it looks like today; it is now the colour that it is supposed to be. It was based quite heavily on an ARP2600. There was a version of the 2600 called the blue meanine which is this quite nice blue. The main difference from the last version is the addition of the MIDI to CV interface (the white section in the secon from left panel). I was told that it wasn't "old school" enough but then anything with MIDI really isn't "old school" anyway...

ORT Circa June 2004

Here is a picture of the ORT end of June last year. The Picture is taken by me collegue Matt. As you can see from the '86 picture the only addition is the sticker from which it draws it's name. You can see the reverberation spring on the top of the unit.

ORT Circa 1985

Here is a picture of the ORT at my Grandparents house around about 1985. I had just bought the Minimoog (at the bottom). It is scanned in from a fairly dogey photo so the colour is fairly iffy. It is amazing how little it has canged to date really! The Minimoog is more different in reality!