Tuesday, December 15, 2009


Well another Panel is awaiting the drill press! This is the much needed MIDI interface and a real bast from the past in the Elektor Formant RFM (Resonant Filter Module). This thing has always interested me since I read the acticle in Elektor over 30 years ago... I still have the Magazine as well! Reading the Electro-Music forum there was some scorn poured upon it, but it was less specific than "rfm is crap". Will very soon find out what sort of crap it is! Could be excellent crap... or maybe not... Perhaps I should have gone with the Jürgen Haible Polymoog Resonator as it is similar in nature?
Posted by Picasa

Sunday, November 15, 2009

Cabinet Creations

Poor old Forbin has been very neglected as all manner of stuff has revolved around him... We have however got the cabinet glued up to-day. It is going to be a fair size at about 1m x 1m -- I can squeeze in 4 x 9 panels at my standard size. You can see one of them sitting in the frame. There is a fair amount of sanding and coats of varnish to go but it shouldn't be too long before we can start screwing in the panels for real.
Posted by Picasa

Thursday, September 24, 2009

NOS Toobz

These arrived from TubeDepot today. I think that we have an average age here of about 40... There is another couple of pencil tubes to do the Mean VCF, three 2D21's for a VCO and a Thermonic Noise source. To finish off a 6BN6 for a beam modulator... also a collection of ceramic tube bases for the PCB... should be fun!
Posted by Picasa

Wednesday, September 9, 2009


Bought this NOS valve, a 6ME8, to make a Sheet-Beam Modulator as per Ken Stones site where he hosts some of Eric Barbour schematics and articles. On closer inspection I can see that he inside of this one has become a bit munted... Not really sure how this is going to effect the sound but I suppose that we shall just have to give it a go...
Posted by Picasa

Monday, September 7, 2009

Mirrored VCO...

Further to Previous post -- here are the two PCB's (the one on the right has the copper on the top so the IC's are underneath!) The right hand board is configured as the squarewave output and the one on the left is the sawtooth -- this was the subject of the earlier postings.
Posted by Picasa

The Saga Continues!

Been a bit busy with the mundane part of life (you know family, work, that sort of stuff) so Forbin has been somewhat neglected but I have been trundling along with a few bits and pieces. This is our old favourite the Buchla 258 VCO clone... I have been doing a bit more work and have made a second PCB for the wave shaping section only. I have also taken some aspects of a Cat Girl design and worked it into the Waveshaping control along with some buffering and amplification of the output waveforms to boost them to +-5V so they are in line with the other VCO's in the Choir. This picture is to try and help out ericcoleridge with the FET placement. Good plan to write on the board the GDS of the pins just to make sure! It is a bit odd and confusing, you can see the squarewave board mirrored on the right (got the press and peel printed back to front yet again....) There has been some discussion about the pots used and I have used 100K's BUT my waveshape control input has an extra summer and buffer... I will draw up what I have done and try and get it up here soon. It does allow me better control of the wave shape as I was finding that most of my control was up at one end of the travel (more so with the squarewave than the sawtooth).
Posted by Picasa

Sunday, August 2, 2009

Forbin LFO comes to Life...

Well the PCB has been made (back to front -- hence IC's on the copper side) and slowly it is coming to life... This dsPIC will give me 20 MIPS and I suspect that I will need more! Certain aspects of the behavior that I had considered will perhaps be saved for later revisions...

Tuesday, July 21, 2009

Forbin LFO

Goodness Gracious! A front panel! This is the Front Panel for my new LFO! It has 4 outputs which can be phase modulated (and being digital it can do the Through Zero trick without batting an eyelid!). Currently designed for 100Hz to 0.01Hz with the choice of 6 waveforms. What you can see here is the four outputs and the three waveform selections that can be mixed between. The one on the left is down to -5V and the middle is at 0V and the right is at +5V. We should be able to get interesting waveshapes by feeding the outputs back into the controlling inputs! The 4 outputs have measured well and being 12bit it is next to impossible to see any steps on the CRO. Still have some code to write but we shouldn't be toooooo far away.....

Uncertainty Levels > 75%

This is an older board, but Board #4 of the Source of Uncertainty collection is reaching completion! I have even started on front panel layouts and it is looking a bit like two boards on one panel and two on the other or one Mega panel. I also have started on a better version of the AVR noise source. I have decided on a dsPIC version with Grey and Brown noise. It will also support the original noise pattern of the noise generator from National Semiconductor along with a longer, less chuggy version of a 48bit sequence. The dsPIC is probably overkill for the project and I am slightly tempted to do the Grey noise in the DSP! I have a nice SPICE model of an Analog filter design that I have generated but it depends if I can get three outputs from the DSP in a reasonably simple manner...
Posted by Picasa

Thursday, July 9, 2009


It has all been a bit quiet recently. The rest of life has intruded a little bit on Forbin activities but I have been slowly working away on a little project which is a LFO with some fairly unique aspects. Not really sure how well it will actually work but we are pretty close to a press'n'peel PCB. Found a couple of poggs ups and I keep adding functionality so that I can use the PCB for some other things as well (an Envelope Generator maybe?) When it is all finished I will probably upload it to some of the forums (well assuming that it works!). I have tried to keep everything "free" so the PCB is layed out with Eagle and kept within the limited capabilities and the development tools are all the free versions of those as well. The PCB is all single sided but it is going to be a fairly careful etch if it is going to work well. Oh and this site has just passed it's first Birthday!

Thursday, June 4, 2009

Buchla 258 Sawtooth

Well after a lot of mucking around and changing the FET's quite a few times we have the "sawtooth" that looks pretty much like the one that was captured from the original.

This was a picture that is from the synthesis technology website. I tried linking directly to it but the Blogging software didn't work so I have copied it here. You can see all the original information at Synthesis Technology.

Mark Verbos, from who's design & PCB layout i used, has also done a more accurate clone from which he garnered this picture:

You can read his full blog posting here. Strangely I did end up securing the original FET that Don used, a 2N4339...

Wednesday, June 3, 2009


Not much Forbin action recently but I have been putting together a speaker so I can hear the sound ring out clearly... We have here a speaker from the Italian organ from beside the road and a speaker from the $50 Japanese Hammond Organ from the Quokka... Current outlay is about $18 for the MDF
Posted by Picasa

Monday, May 25, 2009

Bits & Pieces...

Been a bit quiet recently but there have been some boards building up... Need to sort out the front panels and some Cliff sockets...
Posted by Picasa

Sunday, April 26, 2009


A new Power Supply for Forbin. This is an adaption of the Elektor Formant one. It hasn't been finished off quite yet...

Friday, April 10, 2009


Yet More Source of Uncertainty -- this is board number 1; but the 3rd of the boards that I have built. It has one rather old CMOS part in the 4006 -- for some reason this particular part has become very hard to get hold of but it is actually fitted here. All it needs is quite a few more resistors and we should be away! This one is a random Quantizer, from my rather brief look at the schematic it might be better called a Random Attenuator! Anyway I still need to finish it off and give it a real test to be more sure...

Friday, March 20, 2009

Organ Donor

More stuff from the Organ from beside the road! Now we have a rather nice spring reverb -- the actual spring is in turn isolated from the frame by another spring assembly and there is a nice acoustic bag for the whole thing. A bit tempted to investigate a valve (tube if you must) option! There is still booty to be rescued what's more!

Sunday, March 15, 2009

Some new Ideas...

Possible keyboard scanning/arpeggiating for the organ keyboard, with velocity of course...

Saturday, March 14, 2009

...and the Sound Comes out of There...

Back to get more organ waste... Seems in resonable condition despite the water stain -- probably good enough for my ears anyway!

Tuesday, March 10, 2009

Top Octave

The fruits of the Organ salvage... a top octave generator... these are becoming inceasingly hard to find. I have a design that i made that uses a PLD to act as a top octave generator but it is expensive, very power hungry and a pain to program...
Posted by Picasa

Monday, March 9, 2009


Well got a new keyboard from beside the road! Forbin will be pleased... Not the best action but it does have the kimbell allen style springs that are stretched between two contacts. We may be able to do some velocity sensing? The mind starts to wander...

Wednesday, March 4, 2009

More Uncertainty

This is the Gaussian distributed noise. The steps are much finer on this output as it is summed from 15 resistors instead of the 8 from the linear distribution.
Posted by Picasa

Source of Uncertainty 3

This is the stepped output which has a linear distribution. It is running from a 1000Hz clock and giving a nice 0->10V range.
Posted by Picasa

Source of Uncertainty 2

The board being tested. Note the addition of a 10V reference to the CMOS sections at the bottom.
Posted by Picasa

Source of Uncertainty

Have made two of the boards for the Buchla Source of Uncertainty. This board is the SRV or Stored Random Voltages. It is basically a Pseudo Random Sequence that is created from a couple of shift registers. The pseudo random sequence is 15 bits long and cycles every 32767 clocks. If you look carefully you can see the results of some simulation of the circuit on the paper behind the board. The resistor values that Don Buchla choose are a closest approximation from standard resistor values, hence the jaggies. The board is a layout by vtl5c3 and can be found here. I have found a couple of mistakes which I am currently fixing up and will post back to the newsgroup when I have verified the fixes.

Saturday, February 28, 2009

Thursday, February 26, 2009

Friday, February 20, 2009

258 Tweeks

The Verbos/Buchla 258 Clone requires a few tweeks -- if your using the SSM2220 you will need to turn it around a hack off the two unused legs. See the picture above, after I sort out the mixing FET I will put in the proper Tempco.

Thursday, February 19, 2009

Busy Week

Whilst not much bloggin there has been a fair amount of activity in the background. I have added four new boards recently, there is a power supply based upon the Elektor Formant design (PCB by Jörgen Bergfors for the Bergfotron), two PCB's of the four PCB set for the Buchla 266 Source of Uncertainty (PCB by vtl5c3) and finally a voltage controlled HADSR based on a design by Jürgen Haible and again a layout by Jörgen Bergfors. I am waiting for a couple of resistors, a 4030 and the 2N3055 power transistors and we should be smoking!

Thursday, January 29, 2009


Found this layout for Thomas Henry's LM-VCO from the Analog Synthesizer for the 21st Century. Seems to work fine with the exception of the Sinewave output which is rather lumpy at any setting... My substituted transistors are probably sub-optimal... I have also used a different matched pair, which leads to the interesting sculpture in the corner...

The layout is here: http://electro-music.com/forum/viewtopic.php?p=225947#225947

Thursday, January 8, 2009

Spiced up...

Various attempts at working out the optimal FET for the sine converter on the Buchla 258 VCO - I am going to try a NTE133 and at a pinch a 2N5484 should also work. I am unable to easily source the original one at all..