Built up the PCB's

I'm sorry I seem to have misled people, this project has required all of my skills to complete, I have been in Engineering for 42 years, and my hobby was electronics before I started my craft engineering apprenticeship in 1968, you will need a great deal of DIY skills to build a clone for yourself, even if you have the necessary components.

I have made the clone , using the dimensions of the original synth they are H 44cm x W 43cm x D 42cm.

The panels sizes are upper W 40cm x H 32cm x 2mm and the lower panel is W 40cm H 30cm x 2mm.

The Phutney clone wiring is complete on 16/03/2010, but still needs needs fully calibrating, as there are some differences with the pots and internal wiring.

I have finished the track layouts of the three main PCB's.

I have finished wiring up Board X's connections to the Patch Panel and I/O, and have tested my original Synthi A board in that position, I was a little bit nervous as I powered up, but all was well, and I measured the +12V and -9V d.c. supply, and confirmed that they checked out to within tolerance. Board Y connector is completely wired up, I tested both boards X & Y, I had a problem with the reverb circuit, but soon realised where I had gone wrong, and corrected the error, finished the wiring to Board Z, tested all the boards, but have issues on all three Oscillators.

As you can see I have used plastic conduit to guide the wires, as I don't have wire mans skills, and I didn't want the wires to look untidy, so I have just run them in the conduit, when I have finished, I'll put the top covers on, and should I need to add any further wires, the process will be very easily accomplished.

I have adopted to use a Ghielmetti 20 x 20 patch bay, this is because a 16 x 16 matrix is classed as a "custom" patch bay and cost double the price of a standard 20 x 20, but changing the 20 x 20 to a 16 x 16 is a relatively easy task, but I chose to use the 20 x 20, as I plan to add some extra features, which were planned on the original, like voltage control of oscillator wave shape, and filter response, but as the 16 x 16 matrix were cheap and available, the additional features were shelved.

I didn't like the white finish of the Ghielmetti Matrix Panel. so I ordered a piece of Black poly carbonate and re-manufactured the top panel.

Finishing the wiring, tested all the functions, only a few issues, incorrect wiring to the joystick and Osc 2. now to the manufacture of the 3 PCB's.

I got the PCB's made, the guy quoted me £120, but they actually cost £212, that's just for the three prototypes, well at least the work is done now, and I'm told that if I need any minor changes done, it's going to cost extra.

I've now populated all boards, and after correcting about 10 track errors per board, I managed to get all the boards working. The biggest problem I still have is with the setting up of the Env. Shaper, in contrast the Filter just burst into life, as did most everything else, I had an issue with the Reverberation circuit, any signal passed through became distorted, both on the Wet and Dry mix. I found that the IC was faulty, so I just changed it, problem solved.

I also found that the setting up of all the Oscillator wave shaping, is very difficult, mainly due to the track errors, luckily I have my Synthi A to see which tracks are different.

Still struggling to get the Env. Shaper working correctly, I'm thinking that my method of selecting the Vp values of the FET transistors is wrong, Osc 2 still has issues, I'm guessing that I've still got a trace errors on the PCB tracks somewhere. I had both Osc. 1 and 3 working well at one stage, but in trying to fault find the reason Osc.2 wasn't working, I seem to have stuffed up Osc.3, so I now have only Osc.1 working correctly

I also have worked out how to modify the 18dB/Octave filter, to 24dB/Octave, although people who have a better knowledge than myself, argue that the later filters on the Mk2 synth's were already 24dB/Octave.

An update, the reason for the non working Envelope shaper was simply a bad connection to the PCB edge connector, a repair to the connector was all that was that was required. The oscillators are still proving problematic, although I made the decision to remove all the semi's on both Osc 2 and 3, and test them individually, thus finding a blown 2N5172 and 2N4288, luckily both 2C746 were OK, phew! as these are £30 each, plugging the board back in, Osc 2 started working although the shape is incorrect, the adjusting the shape pot stops the oscillator oscillating, still nothing from Osc 3, but after close inspection I've found more track errors. I was going to purchase a 3 tank PCB unit, to start making my own PCB's, but as the HM Government has put VAT up to 20%, I need to find some more money again.

Keep you posted.