Doepfer

Hi all

I have two of these modules (bought 6 weeks ago) and only just got round to checking the second VCA of the second module. There's a fault: It doesn't shut down fully. With both the CV and gain controls at zero I can still here an oscillator patched directly into it. My other 3 VCAs all fully shut off the input at this setting as expected.

Is this something that I can fix by adjusting a pot somewhere or do I need to think about returning it as faulty?

Thanks

Rich

--- In Doepfer_a100@yahoogroups.com, <yahoo@...> wrote:
>
> > Hi all
> >
> > I have two of these modules (bought 6 weeks ago) and only just
> > got round to checking the second VCA of the second module.
> > There's a fault: It doesn't shut down fully. With both the CV and
> > gain controls at zero I can still here an oscillator patched
> > directly into it. My other 3 VCAs all fully shut off the input at
> > this setting as expected.
> >
> > Is this something that I can fix by adjusting a pot somewhere or
> > do I need to think about returning it as faulty?
> >
> > Thanks
> >
> > Rich
> 
> There is nothing to trim on this module. In the first series of the module
> (manufactured until ~ September 2008) this behaviour was discovered now and
> then due to tolerances of the dual VCA circuit (CEM3360). From September
> 2008 the value of two resistors have been changed to avoid that (R10 and R24
> = 220k instead of 270k). If you are a bit familiar with electronics please
> take a look at your module: R24 is the resistor at the bottom edge of the pc
> board (below the switch). If the value is 270k (red-violet-yellow) it's from
> the first series. If it's 220k (red-red-yellow) it's from the second series.
> I'd recommend to return the module for modification (or to replace the 270k
> resistors by 220k if you dare to do that and you have these values
> available) or replacement of the CEM3360.
> 
> Best wishes
> Dieter Doepfer
>

Thanks for the quick reply Dieter, I'll check resistor values when I get home.

Is it true that this would just affect the lower VCA on the module while the upper one works correctly?

Thanks

Rich

> Hi all
>
> I have two of these modules (bought 6 weeks ago) and only just
> got round to checking the second VCA of the second module.
> There's a fault: It doesn't shut down fully. With both the CV and
> gain controls at zero I can still here an oscillator patched
> directly into it. My other 3 VCAs all fully shut off the input at
> this setting as expected.
>
> Is this something that I can fix by adjusting a pot somewhere or
> do I need to think about returning it as faulty?
>
> Thanks
>
> Rich

There is nothing to trim on this module. In the first series of the module
(manufactured until ~ September 2008) this behaviour was discovered now and
then due to tolerances of the dual VCA circuit (CEM3360). From September
2008 the value of two resistors have been changed to avoid that (R10 and R24
= 220k instead of 270k). If you are a bit familiar with electronics please
take a look at your module: R24 is the resistor at the bottom edge of the pc
board (below the switch). If the value is 270k (red-violet-yellow) it's from
the first series. If it's 220k (red-red-yellow) it's from the second series.
I'd recommend to return the module for modification (or to replace the 270k
resistors by 220k if you dare to do that and you have these values
available) or replacement of the CEM3360.

Best wishes
Dieter Doepfer

> Thanks for the quick reply Dieter, I'll check resistor values 
> when I get home.
> 
> Is it true that this would just affect the lower VCA on the 
> module while the upper one works correctly?
> 
> Thanks
> 
> Rich

This may happen due to the tolerances of the two VCAs inside the CEM3360.

Best wishes
Dieter Doepfer

Bleedthrough from one of the VCAs to the other, or just each one not fully closing?  Because I thought I had the latter issue, but it turned out I had the input gain / sensitivity set far too high on my breakout box's input.  D'oh!

Sorry if it's a far more advanced problem.  I just thought I'd try to rule out the obvious first.  I'd overlooked it myself for far too long.

> Hi All
>
>
> Sorry to be resurrecting such an old thread but I can't find any more recent discussion on this topic elsewhere. I am
> also experiencing this bleed issue in both VCAs, like others worse in EMP mode, but still there in Lin mode. It is V2
> with the SSM2164. Looking at the back of the PCB there are some modifications (see images here). Are these an attempt to
> resolve some of the bleed issues? I have read the info on swapping resistors but not sure if this is necessary on this
> module or has it already been done (I also wasn't sure which resistor was R24). As the bleed is still there is there any
> further modifications that can be done?
>
>
> Thanks
> Alan

Indeed we modified the module a bit by adding a 10M resistors between -12V and pin 9 of IC3 to add a small negative offset voltage
to make sure that the VCA closes when the CV sum is 0V. Maybe 10M is not sufficient for your individual module and has to be lowered
again.

Best wishes
Dieter Doepfer