Synth-DIY Yahoo! Groups Archives

CEM Rev's and tuning?

2017-09-09 by listmicrocode@...

I have a Prophet 600. It's not very well known that if you use the Rev G 3340 (instead of original issue Rev F) that you will need to mod the synth to ensure performance within spec.

I have been sending my Polaris back to my tech a whole lot over the last few years, and have a long outstanding tuning issue on what would seem to be two voices now, it used to be one voice, but now I believe I have two that will not properly tune (always too high or too low by about 10ct+/-). I am wondering if the Polaris has the same concerns with different Rev chips?

Here is the link to the P600 issue: Example on page 41 -http://www.synfo.nl/servicemanuals/Sequential/SEQUENTIAL_PROPHET-600_SERVICE_MANUAL.pdf

thanks!

Robert

RE: [chromapolaris] CEM Rev's and tuning?

2017-09-09 by Paul D. DeRocco

> From: Robert
>
> I have a Prophet 600. It's not very well known that if you
> use the Rev G 3340 (instead of original issue Rev F) that you
> will need to mod the synth to ensure performance within spec.
>
> I have been sending my Polaris back to my tech a whole lot
> over the last few years, and have a long outstanding tuning
> issue on what would seem to be two voices now, it used to be
> one voice, but now I believe I have two that will not
> properly tune (always too high or too low by about 10ct+/-).
> I am wondering if the Polaris has the same concerns with
> different Rev chips?

I doubt it's the oscillator chips. It's more likely leakage in the sample-and-hold circuit, which can be a bad analog switch, a bad opamp, a bad cap, or contamination on the board. If it's a bad chip, you can find that out by swapping chips between good and bad channels. I had an oscillator that was persistently off by that much, which was solved by washing the S&H area of the board with plenty of alcohol.

I think the Prophet problem was that those chips fell outside the range that the auto-tune could compensate for, with the original resistor value, so the auto-tune would fail completely, not just produce sour notes.

--

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

Re: CEM Rev's and tuning?

2017-09-12 by synthparts@...

I've been selling and using CEM3374s with the latest 1993 date codes without any probs in my Polaris and Matrix-12. I still have a few available if you need any.

Doug

synthparts.com