Synth-DIY Yahoo! Groups Archives

Thread

Q: a strange issue

2012-05-16 by evening1

Found a couple of odd issues after I sorted out my panel membrane problem.

(I needed new connectors.)

OSC1 & 2 seem to be affected by pulse with modulation even when they are set to saw.

The OSC2 pulse width mod slider is controlling the sweep speed, but the sweep slider doesn't do anything.

I haven't dug into the schematics yet or done any calibration but I just thought that I'd throw this out to the list.

I'm suspecting ICs have failed in some kind of odd way.

jmw

PS: My Polaris has metal faders, are there any suggested replacements?

RE: [chromapolaris] Q: a strange issue

2012-05-16 by Paul D. DeRocco

> From: evening1
>
> Found a couple of odd issues after I sorted out my panel
> membrane problem. (I needed new connectors.)
>
> OSC1 & 2 seem to be affected by pulse with modulation even
> when they are set to saw.

That's a feature, not a bug. It's really a "saws" shape, as in the original
Chroma, where the width controls the phase between two sawteeth. This gives
you the inverse comb spectrum of the corresponding pulse. If you want a
plain saw, set the width to zero.

> The OSC2 pulse width mod slider is controlling the sweep
> speed, but the sweep slider doesn't do anything.
>
> I haven't dug into the schematics yet or done any calibration
> but I just thought that I'd throw this out to the list.
> I'm suspecting ICs have failed in some kind of odd way.

If any other sliders are mismatched, it could be one of the bits into the
4051 multiplexer that scans the sliders. Or it could be the 4051 itself.
This sort of thing usually makes itself obvious as soon as you poke a scope
probe into it.

> PS: My Polaris has metal faders, are there any suggested
> replacements?

Are any of them bad? The symptoms you describe don't sound like they
indicate bad sliders.

--

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

Re: [chromapolaris] Q: a strange issue

2012-05-16 by evening1

That's a feature, not a bug. It's really a "saws" shape, as in the original
Chroma, where the width controls the phase between two sawteeth. This gives
you the inverse comb spectrum of the corresponding pulse. If you want a
plain saw, set the width to zero.

OK - that's good to know

If any other sliders are mismatched, it could be one of the bits into the
4051 multiplexer that scans the sliders. Or it could be the 4051 itself.
This sort of thing usually makes itself obvious as soon as you poke a scope
probe into it.

Thanks for the tip.
Yeah - OSC1 PWM level doesn't seem to do much of anything either, so it may be related.

> PS: My Polaris has metal faders, are there any suggested
> replacements?

Are any of them bad? The symptoms you describe don't sound like they
indicate bad sliders.

The volume slider is intermittent but I may be able to refurb it.
It's probably best to sort out the slider mismatch before blaming the faders.

jmw

-

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