> From: dmxkrew@...
>
> I have this too, very quiet and not making the synth unusable
> but it would be good to get rid of it. Did anyone find a solution?

There was an early version of the main board that had a bleedthrough issue, which was fixed in the later version by swapping two of the switches in Zx08 in each channel. If you have the old version, and this is the type of bleedthrough you're getting, there is a way to modify the board, and indeed they did this in production on some of the early units.

The problem is that the output of oscillator 1 goes over to oscillator 2 for the sync function, but also goes to one of the switches in Zx08 to short it to ground to disable the sync. This line runs right next to the MAIN OUT bus. When SYNC is turned on, this has a strong sawtooth on it, which you hear in the output. When SYNC is turned off, this mostly goes away, but I believe there was still some residue. If you have the old board, and the level of the bleedthrough is affected by SYNC, then you've encounted this particular problem, and I can describe how to mod the board.

But even on the new board, the output is a bit noisy. This can be improved by lifting the entire MAIN OUT bus, and running it on a wire above the board. This line ties all the Zx08-12 pins together (or Zx08-5 in the early version), and routes them to the output connector. Lifting these pins out of the sockets and tying them together with wire in the air moves this bus away from some of the noise on the board. It's best to use shielded wire for this, but for mechanical reasons you should try to find some very skinny lightweight shielded wire, like the kind used for phono cartridges.

Beyond that, the grounding of the output is a bit iffy. Some units have a green ground wire added between the main output jack and the power supply. I haven't experimented with this grounding, but there may be alternative ways of grounding things that reduce the noise. But I believe this was primarily computer noise that was getting in through the ground, not oscillators.

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Ciao, Paul D. DeRocco
Paul mailto:pderocco@...