Rhodes Chroma Polaris

I have a Polaris which works well except for one problem I hope is an easy fix.

The problem is that I can not completely turn off one oscillator.

I have no problem to disable oscillator #2 by selecting pulse and setting the pulse width to minimum (0%).

However when I do the same on oscillator #1, I can still hear the pulse wave as it turns on and then off again at a very slow rate. The pulse width slider works and affects the pulse width however it is not shutting completely off at "0".

I get the same effect if the pulse width is set to minimum (0%) or maximum (100%) and on all six oscillators.

Is there an adjustment I need to make to the pulse width slider?

Thanks

> From: ktfiz
>
> I have a Polaris which works well except for one problem I
> hope is an easy fix.
>
> The problem is that I can not completely turn off one oscillator.
>
> I have no problem to disable oscillator #2 by selecting pulse
> and setting the pulse width to minimum (0%).
>
> However when I do the same on oscillator #1, I can still hear
> the pulse wave as it turns on and then off again at a very
> slow rate. The pulse width slider works and affects the pulse
> width however it is not shutting completely off at "0".
>
> I get the same effect if the pulse width is set to minimum
> (0%) or maximum (100%) and on all six oscillators.
>
> Is there an adjustment I need to make to the pulse width slider?

Could be a bad slider. If you have a meter, you could measure the voltage on
the wiper, and compare it to another slider. They're all static 0 to 5
voltages. You might also redo the ADC RANGE adjustment detailed in the
manual, just in case.

--

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

Hi Paul,

Thank you. I played around with it some more and this is what I discovered...

As I move the Pulse Width Slider towards "0" the saw or pulse wave starts to narrow (as it should) but then another saw or pulse starts to mix in and cycles between the pulse/saw wave and this new wave. So, at the center I only hear the pulse or saw wave but as I move the slider towards "0" or "100" it starts to alternate on/off with this new wave. At "0" you are left with just this other wave. It sounds like this other wave is an octave lower.

What's weirder is the frequency of the oscillation between the two is controlled by the Sweep Rate slider and type (sine/square). This is with the scratch patch and is not affected by Sweep Depth. Again this is only occurs on Oscillator 1.

It also seems to be intermittent as this morning it worked again but this evening it came back.

Does that make sense? Does it still sound like a faulty slider?

Thanks.

--- In chromapolaris@yahoogroups.com, "Paul D. DeRocco" <pderocco@...> wrote:
>
> > From: ktfiz
> >
> > I have a Polaris which works well except for one problem I
> > hope is an easy fix.
> >
> > The problem is that I can not completely turn off one oscillator.
> >
> > I have no problem to disable oscillator #2 by selecting pulse
> > and setting the pulse width to minimum (0%).
> >
> > However when I do the same on oscillator #1, I can still hear
> > the pulse wave as it turns on and then off again at a very
> > slow rate. The pulse width slider works and affects the pulse
> > width however it is not shutting completely off at "0".
> >
> > I get the same effect if the pulse width is set to minimum
> > (0%) or maximum (100%) and on all six oscillators.
> >
> > Is there an adjustment I need to make to the pulse width slider?
>
> Could be a bad slider. If you have a meter, you could measure the voltage on
> the wiper, and compare it to another slider. They're all static 0 to 5
> voltages. You might also redo the ADC RANGE adjustment detailed in the
> manual, just in case.
>
> --
>
> Ciao, Paul D. DeRocco
> Paul mailto:pderocco@...
>

> From: ktfiz
>
> Thank you. I played around with it some more and this is what
> I discovered...
>
> As I move the Pulse Width Slider towards "0" the saw or pulse
> wave starts to narrow (as it should) but then another saw or
> pulse starts to mix in and cycles between the pulse/saw wave
> and this new wave. So, at the center I only hear the pulse or
> saw wave but as I move the slider towards "0" or "100" it
> starts to alternate on/off with this new wave. At "0" you are
> left with just this other wave. It sounds like this other
> wave is an octave lower.
>
> What's weirder is the frequency of the oscillation between
> the two is controlled by the Sweep Rate slider and type
> (sine/square). This is with the scratch patch and is not
> affected by Sweep Depth. Again this is only occurs on Oscillator 1.
>
> It also seems to be intermittent as this morning it worked
> again but this evening it came back.
>
> Does that make sense? Does it still sound like a faulty slider?

Are these two waves that you sometimes hear concurrently independent of each
other in pitch?

And, no, it doesn't sound very much like a bad slider. Like I said, try
swapping ICs between channels.

--

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

There is a difference in pitch between the two sounds, but both track with the corresponding note.

I have turned off the voices and tested them one by one. They all exhibit the same behavior so I'm not sure if swapping out the ICs would make a difference. I assume by ICs you mean the CEM3374 and CEM3372?

--- In chromapolaris@yahoogroups.com, "Paul D. DeRocco" <pderocco@...> wrote:
>
> > From: ktfiz
> >
> > Thank you. I played around with it some more and this is what
> > I discovered...
> >
> > As I move the Pulse Width Slider towards "0" the saw or pulse
> > wave starts to narrow (as it should) but then another saw or
> > pulse starts to mix in and cycles between the pulse/saw wave
> > and this new wave. So, at the center I only hear the pulse or
> > saw wave but as I move the slider towards "0" or "100" it
> > starts to alternate on/off with this new wave. At "0" you are
> > left with just this other wave. It sounds like this other
> > wave is an octave lower.
> >
> > What's weirder is the frequency of the oscillation between
> > the two is controlled by the Sweep Rate slider and type
> > (sine/square). This is with the scratch patch and is not
> > affected by Sweep Depth. Again this is only occurs on Oscillator 1.
> >
> > It also seems to be intermittent as this morning it worked
> > again but this evening it came back.
> >
> > Does that make sense? Does it still sound like a faulty slider?
>
> Are these two waves that you sometimes hear concurrently independent of each
> other in pitch?
>
> And, no, it doesn't sound very much like a bad slider. Like I said, try
> swapping ICs between channels.
>
> --
>
> Ciao, Paul D. DeRocco
> Paul mailto:pderocco@...
>

> From: ktfiz
>
> There is a difference in pitch between the two sounds, but
> both track with the corresponding note.
>
> I have turned off the voices and tested them one by one. They
> all exhibit the same behavior so I'm not sure if swapping out
> the ICs would make a difference. I assume by ICs you mean the
> CEM3374 and CEM3372?

Gee, I guess I'm having trouble imagining what you're hearing. If you have a
way of posting a recording of it somewhere, maybe we could tell something
from that.

--

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

I've uploaded a short video that shows the problem. Audio quality is not great but it should give you a better insight into the issue I am having. Hoping someone has an idea of what could be wrong.

http://youtu.be/iJbBRya_MlE

--- In chromapolaris@yahoogroups.com, "Paul D. DeRocco" <pderocco@...> wrote:
>
> > From: ktfiz
> >
> > There is a difference in pitch between the two sounds, but
> > both track with the corresponding note.
> >
> > I have turned off the voices and tested them one by one. They
> > all exhibit the same behavior so I'm not sure if swapping out
> > the ICs would make a difference. I assume by ICs you mean the
> > CEM3374 and CEM3372?
>
> Gee, I guess I'm having trouble imagining what you're hearing. If you have a
> way of posting a recording of it somewhere, maybe we could tell something
> from that.
>
> --
>
> Ciao, Paul D. DeRocco
> Paul mailto:pderocco@...
>

> From: ktfiz
>
> I've uploaded a short video that shows the problem. Audio
> quality is not great but it should give you a better insight
> into the issue I am having. Hoping someone has an idea of
> what could be wrong.
>
> http://youtu.be/iJbBRya_MlE

The sweep signal is a pure software signal. The only way it can manifest
itself in the hardware is if it is used to modulate one of the six control
voltages that go to the channel. One of the things it can modulate is pulse
width. Therefore, I suspect there is some interaction between the PULSE
WIDTH slider and the PULSE WIDTH MOD slider. It could be a short somewhere,
or a broken ground, or a bad 4051 multiplexer on the panel.

--

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

Paul, I think you are on to something!

The PULSE WIDTH MOD slider does affect this. When the PULSE WIDTH MOD slider is in the center position the modulation goes away. As I move the slider down it increases the modulation I hear until it is fully on at the bottom. However, as I move the slider up just past center it goes to fully on. I assume that is a faulty or dirty PULSE MOD WIDTH slider?

I also realized that I get the same effect on OSC 2 as well. However the PULSE WIDTH MOD slider does slowly increase the modulation I hear from center to the bottom and from center to the top. So, it seems at least that the bi-polar slider works correctly on OSC 2.

So, I guess my question now is...

In a perfectly functioning Polaris, if the PULSE WIDTH is all the way at the bottom and you move the PULSE WIDTH MOD slider either up or down away from center, should you hear this modulation? So in order to completely turn off an oscillator, PULSE WIDTH needs to be at "0" and PULSE WIDTH MOD needs to be at center?

If so, then I am only looking at a faulty bi-polar slider.

--- In chromapolaris@yahoogroups.com, "Paul D. DeRocco" <pderocco@...> wrote:

> The sweep signal is a pure software signal. The only way it can manifest
> itself in the hardware is if it is used to modulate one of the six control
> voltages that go to the channel. One of the things it can modulate is pulse
> width. Therefore, I suspect there is some interaction between the PULSE
> WIDTH slider and the PULSE WIDTH MOD slider. It could be a short somewhere,
> or a broken ground, or a bad 4051 multiplexer on the panel.
>
> --
>
> Ciao, Paul D. DeRocco
> Paul mailto:pderocco@...
>

> From: ktfiz
>
> Paul, I think you are on to something!
>
> The PULSE WIDTH MOD slider does affect this. When the PULSE
> WIDTH MOD slider is in the center position the modulation
> goes away. As I move the slider down it increases the
> modulation I hear until it is fully on at the bottom.
> However, as I move the slider up just past center it goes to
> fully on. I assume that is a faulty or dirty PULSE MOD WIDTH slider?
>
> I also realized that I get the same effect on OSC 2 as well.
> However the PULSE WIDTH MOD slider does slowly increase the
> modulation I hear from center to the bottom and from center
> to the top. So, it seems at least that the bi-polar slider
> works correctly on OSC 2.
>
> So, I guess my question now is...
>
> In a perfectly functioning Polaris, if the PULSE WIDTH is all
> the way at the bottom and you move the PULSE WIDTH MOD slider
> either up or down away from center, should you hear this
> modulation? So in order to completely turn off an oscillator,
> PULSE WIDTH needs to be at "0" and PULSE WIDTH MOD needs to
> be at center?

If the width is at zero, you'll hear half the bipolar sine wave modulation
and all the unipolar square wave modulation. If the width is at 100%, you'll
hear the other half of the bipolar sine wave modulation and none of the
square wave modulation. If you dial in enough width that you don't clip the
modulation, you'll hear all the modulation.

> If so, then I am only looking at a faulty bi-polar slider.

I think it's more likely to be a bad 4051 chip (Z3) than a faulty slider. If
they're socketed, you could try swapping Z3 and Z4 to see if the problem
moves to different sliders.

--

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