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Thread

Volume envelope question

2015-03-13 by Dylan Wahl

Hi all,

I'm getting close with my Chroma Polaris restoration, but I have a question. How abrupt should the decay on the Volume Envelope be? I feel like I never hear a smooth decay to zero, it is like it drops off abruptly, which seems unusual, at least compared to other synths I've ever owned, but I didn't know if it's a feature...

One thought I had was to probe the opamp output for example Z503 pin 7, disable the other voices, and watch an envelope decay waveform at different settings. But it seems unusual to me that the voices would all cut off similarly. I should mention that it properly tunes five of the six voices, I'm waiting for a CEM3372/74 to repair the 6th channel. So that suggests to me that the DAC chain works properly.

I also should probably reload some preset voices, maybe I'm just missing something with the patch programming.

--Dylan

Re: [chromapolaris] Volume envelope question

2015-03-13 by w.james.meagher@...

I had this issue . . . I seem to recall it was solved with a full recalibration.

Sent from my iPhone

On Mar 12, 2015, at 20:43, "Dylan Wahl constanw@... [chromapolaris]" <chromapolaris@yahoogroups.com> wrote:

Hi all,

I'm getting close with my Chroma Polaris restoration, but I have a question. How abrupt should the decay on the Volume Envelope be? I feel like I never hear a smooth decay to zero, it is like it drops off abruptly, which seems unusual, at least compared to other synths I've ever owned, but I didn't know if it's a feature...

One thought I had was to probe the opamp output for example Z503 pin 7, disable the other voices, and watch an envelope decay waveform at different settings. But it seems unusual to me that the voices would all cut off similarly. I should mention that it properly tunes five of the six voices, I'm waiting for a CEM3372/74 to repair the 6th channel. So that suggests to me that the DAC chain works properly.

I also should probably reload some preset voices, maybe I'm just missing something with the patch programming.

--Dylan

RE: [chromapolaris] Volume envelope question

2015-03-13 by Paul D. DeRocco

> From: Dylan
>
> I'm getting close with my Chroma Polaris restoration, but I
> have a question. How abrupt should the decay on the Volume
> Envelope be? I feel like I never hear a smooth decay to zero,
> it is like it drops off abruptly, which seems unusual, at
> least compared to other synths I've ever owned, but I didn't
> know if it's a feature...
>
> One thought I had was to probe the opamp output for example
> Z503 pin 7, disable the other voices, and watch an envelope
> decay waveform at different settings. But it seems unusual to
> me that the voices would all cut off similarly. I should
> mention that it properly tunes five of the six voices, I'm
> waiting for a CEM3372/74 to repair the 6th channel. So that
> suggests to me that the DAC chain works properly.
>
> I also should probably reload some preset voices, maybe I'm
> just missing something with the patch programming.

James is right, calibration will fix it. Since there's a small variable
offset in the zero point of the VCAs, the firmware includes a calibration
adjustment so that the envelope smoothly decays to that value, and then
suddenly forces the envelope to a negative value so that the note won't
bleed through if the calibration is off. You need to do the Volume Offset
adjustment, described in chapter 15 of the Owner's Manual. Then you won't
hear that sudden cutoff any more.

--

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

Re: [chromapolaris] Volume envelope question

2015-03-13 by Dylan Wahl

Thanks. Actually I am having a new problem, the CPU freezes after ~8 minutes operation. Power cycling doesn't work until it cools. I checked the digital 5V supply, looks okay. Wondering if either CPU, RAM, or ROM is going corrupt...

On Thu, Mar 12, 2015 at 11:43 PM, 'Paul D. DeRocco' pderocco@... [chromapolaris] <chromapolaris@yahoogroups.com> wrote:

> From: Dylan

>
> I'm getting close with my Chroma Polaris restoration, but I
> have a question. How abrupt should the decay on the Volume
> Envelope be? I feel like I never hear a smooth decay to zero,
> it is like it drops off abruptly, which seems unusual, at
> least compared to other synths I've ever owned, but I didn't
> know if it's a feature...
>
> One thought I had was to probe the opamp output for example
> Z503 pin 7, disable the other voices, and watch an envelope
> decay waveform at different settings. But it seems unusual to
> me that the voices would all cut off similarly. I should
> mention that it properly tunes five of the six voices, I'm
> waiting for a CEM3372/74 to repair the 6th channel. So that
> suggests to me that the DAC chain works properly.
>
> I also should probably reload some preset voices, maybe I'm
> just missing something with the patch programming.

James is right, calibration will fix it. Since there's a small variable
offset in the zero point of the VCAs, the firmware includes a calibration
adjustment so that the envelope smoothly decays to that value, and then
suddenly forces the envelope to a negative value so that the note won't
bleed through if the calibration is off. You need to do the Volume Offset
adjustment, described in chapter 15 of the Owner's Manual. Then you won't
hear that sudden cutoff any more.

--

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

RE: [chromapolaris] Volume envelope question

2015-03-13 by Paul D. DeRocco

> From: Dylan
>
> Thanks. Actually I am having a new problem, the CPU freezes
> after ~8 minutes operation. Power cycling doesn't work until
> it cools. I checked the digital 5V supply, looks okay.
> Wondering if either CPU, RAM, or ROM is going corrupt...

Does the DC OK signal turn off? If you have the original PS that has the
DC OK adjustment, then it may simply be a matter of turning that trimmer a
little.

The only digital parts I'd worry about are the EPROMs, because after 30
years some of the 0's could have leaked down close to the 1 level. The
solution to that is erase them and reprogram them.

--

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