> From: c.puidokas@...
>
> I just finished restoring a Chroma Polaris and have noticed a
> digital / computer noise in the background of my output.
>
> It isn't effected by any of the controls other than master volume.
>
> It is my understanding, from other conversations in this
> group that there were different grounding solutions for
> different revisions of the Chroma Polaris.
>
> Has anybody had this issue, and if so, what was your solution?

If you're talking about the headphone output, is there a green wire going from that jack back to the power supply? I've found that it's better to remove that, and connect the jack's sleeve terminal to the unused brown wire in the harness that goes to the output board.

But even then, on all outputs there's a tiny bit of computer noise. In fact, there are several different sources of noise. There's noise on the ground. There's noise on the power supply. There's noise on the DATA AUD line. There was noise radiated from the keyboard matrix that coupled into the channel circuits, until they put that cardboard and foil shield under the keyboard. There was noise from the noise generator picked up on the CD4053 switch sections that route the channel outputs between MAIN OUT and ALT OUT. This last one was dealt with by doing a new layout that rearranged the switch sections, but in the earlier units this was mitigated by cutting a trace in each channel, lifting a pin on the CM3372 filter chip, and hand-wiring the pin down to the board. I'm curious which version you've got.

If you want to diagnose further, I might be able to help a bit.

--

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