Doepfer

> Hello
>
> First time on this forum.
>
> I've just bought a Doepfer modular and I'm have a slight problem
> with the A101-1 Vactrol filter.
>
> Whenever I connect anything to one of the CV inputs I get a lot
> of background noise/interference.  This happens even when the
> corresponding CV control is zero and even when connecting to
> sources with no control voltage output (e.g. mixer input or reset
> on LFO)- so its not CV opening the filter.
>
> Any ideas anyone?
>
> Cheers
>
> Carter

That's a very unusual behaviour because zero CV should be the same as an
open CV connection. I'd recommend to return the module for repair. I have
never heard of such a behaviour (i.e. connecting zero Volt CV that affects
the sound) and have no idea what could be the reason (maybe it a problem
with a GND loop ?).

Best wishes
Dieter Doepfer

Here is the first online review for the Dark Energy. It's valid also for the
A-111-5 module (except the USB/Midi interface comments)

http://www.sonicstate.com/news/2009/07/17/sonic-lab-doepfer-dark-energy-anal
og-synthesizer/

Best wishes
Dieter Doepfer

> -----Ursprüngliche Nachricht-----
> Von: Doepfer_a100@yahoogroups.com
> [mailto:Doepfer_a100@yahoogroups.com]Im Auftrag von yahoo@doepfer.de
> Gesendet: Montag, 20. Juli 2009 10:17
> An: Doepfer_a100@yahoogroups.com
> Betreff: AW: [Doepfer_a100] Is my filter faulty (A101-1 Vactrol)?
>
>
> > Hello
> >
> > First time on this forum.
> >
> > I've just bought a Doepfer modular and I'm have a slight problem
> > with the A101-1 Vactrol filter.
> >
> > Whenever I connect anything to one of the CV inputs I get a lot
> > of background noise/interference.  This happens even when the
> > corresponding CV control is zero and even when connecting to
> > sources with no control voltage output (e.g. mixer input or reset
> > on LFO)- so its not CV opening the filter.
> >
> > Any ideas anyone?
> >
> > Cheers
> >
> > Carter
>
> That's a very unusual behaviour because zero CV should be the same as an
> open CV connection. I'd recommend to return the module for repair. I have
> never heard of such a behaviour (i.e. connecting zero Volt CV that affects
> the sound) and have no idea what could be the reason (maybe it a problem
> with a GND loop ?).
>
> Best wishes
> Dieter Doepfer
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>

--- In Doepfer_a100@yahoogroups.com, <yahoo@...> wrote:
>
> > Hello
> >
> > First time on this forum.
> >
> > I've just bought a Doepfer modular and I'm have a slight problem
> > with the A101-1 Vactrol filter.
> >
> > Whenever I connect anything to one of the CV inputs I get a lot
> > of background noise/interference.  This happens even when the
> > corresponding CV control is zero and even when connecting to
> > sources with no control voltage output (e.g. mixer input or reset
> > on LFO)- so its not CV opening the filter.
> >
> > Any ideas anyone?
> >
> > Cheers
> >
> > Carter
> 
> That's a very unusual behaviour because zero CV should be the same as an
> open CV connection. I'd recommend to return the module for repair. I have
> never heard of such a behaviour (i.e. connecting zero Volt CV that affects
> the sound) and have no idea what could be the reason (maybe it a problem
> with a GND loop ?).
> 
> Best wishes
> Dieter Doepfer
>



Thanks for the help Dieter.

I have noticed that the problem only happens when connecting the A101-1 to the modules on the MIDDLE row of my 9u cabinet. I have removed all the modules from the middle row and tried them individually and the problem still occurs.

The excessive noise from the filter happens if I connect the filter to ANY point on the middle row.  It does not happen on the top or bottom rows.  

I am concerned that it may be the power supply or would you still suggest that the filter is faulty.

Many thanks

Carter

> Thanks for the help Dieter.
>
> I have noticed that the problem only happens when connecting the
> A101-1 to the modules on the MIDDLE row of my 9u cabinet. I have
> removed all the modules from the middle row and tried them
> individually and the problem still occurs.
>
> The excessive noise from the filter happens if I connect the
> filter to ANY point on the middle row.  It does not happen on the
> top or bottom rows.
>
> I am concerned that it may be the power supply or would you still
> suggest that the filter is faulty.
>
> Many thanks
>
> Carter

What kind of 9U cabinet is used ? If there's only one power supply in the
cabinet it should make no difference. Double check if one of the supply
connections (between PSU und bus boards) is loose or broken.

Is the noise like a white noise (e.g. like the A-118) or hum noise with
50/60Hz ?

Best wishes
Dieter Doepfer

--- In Doepfer_a100@yahoogroups.com, <yahoo@...> wrote:
>
> > Thanks for the help Dieter.
> >
> > I have noticed that the problem only happens when connecting the
> > A101-1 to the modules on the MIDDLE row of my 9u cabinet. I have
> > removed all the modules from the middle row and tried them
> > individually and the problem still occurs.
> >
> > The excessive noise from the filter happens if I connect the
> > filter to ANY point on the middle row.  It does not happen on the
> > top or bottom rows.
> >
> > I am concerned that it may be the power supply or would you still
> > suggest that the filter is faulty.
> >
> > Many thanks
> >
> > Carter
> 
> What kind of 9U cabinet is used ? If there's only one power supply in the
> cabinet it should make no difference. Double check if one of the supply
> connections (between PSU und bus boards) is loose or broken.
> 
> Is the noise like a white noise (e.g. like the A-118) or hum noise with
> 50/60Hz ?
> 
> Best wishes
> Dieter Doepfer
>

It is the LC9 case. I have checked for loose connections but I will have another look.  The noise is like if you turn the gain up full on a mxing desk with no input - just amplified circuit noise/interference. Certainly not pure white noise.

I do not think there is any mains hum but I will check tonight.

Cheers