Analogue systems

Hey peter, thanks for the reply.

Important things to note: The VCOs I am using are model 15s not
doepfer brand vcos so the detailed instructions you gave will be
confusing at best to apply to these. Also, I can hear the VCO "noise"
from any jack of any module connected to the doepfer bus. I also have
Asys modules installed and i can NOT hear any bleed through when
monitoring those modules' jacks. Revealing observation?

I want to say this is a problem with the Asys doepfer buss, but I
haven't heard widespread accounts of this and if it is the problem
then there should be a solution, as you are thankfully trying to persue. 

Any ticks I should try with the model 15s.. that is if you're at all
familiar with them ;]

-Zach

--- In analogue_systems@yahoogroups.com, "(i think you can figure that
out)" <peter@...> wrote:
>
> 
> 
> It sounds like the ground is daisy-chained on the power buss board.
> Doing this opens the potential for the noise caused by one module to
> bleed down any module to it's right on the rack, and if severe enough,
> to every module in the system - even those powered by different PSUs 
>  It's especially prevalent with systems with a lot of LEDs unless a
> separate return line is run specifically for those grounds (ala
> Buchla, which is why he has a dedicated 'noisy' ground buss and
> partially why he went with an altogether different patchcord system
> for control voltages - it keeps the noise out fo the audio path). 
> 
> There are a few things you can try, two of which won't require
> modification. Please understand making electrical mods will void your
> warranty...so think twice before you do them!):
> 
> 1. Try mounting the VCOs of the far left of the rack.  This keeps the
> daisy chain short as possible
> 
> 2.  Move the PWM pot on the Doepfer VCOs so they fall silent (full
> positive or full negative) then have a listen again to see if it's
> still there.  PWM circuits are hard on power supplies, if you don't do
> it right they will bleed into the return line which can be picked ff
> by other modules.  Dieter's an excellent engineer, I'm sure he handled
> this correctly.
> 
> 3) On the Doepfer VCOs yo will see two 10uf caps somewhere close to
> the power connector.  Replace those with a larger value - something
> like 33 uf.  Make sure the caps you put in there have 16 volt or
> higher voltage rating above or they'll blow about 10 seconds after
> power is applied.  You;ll know when they do - it sonds like a
> firecracker and leaves paperpulp all over the PCBA and insdie of the
> rack.  The module won't suffer any damage if this happens, but it's a
> pain to deal with.
> 
> 4) Are you monitoring from the same module when you're hearing the
> noise?  Is the same module going to the speakers?  Have you trie
> monitoring form a different module?  If you have one module you use fr
> your outputs, you may need to do the same cap replacmen on that one.
> 
> 5) Another mod which will fix this is running the power to the module
> through a lowpass filter BEFORE that power goes the module itself. 
> Not so easy retrofit however as you've got to insert this mod in right
> at the point the power comes into the board from the buss, before it
> goes anywhere int the module.  What you do it calculate the maximum
> power consumption of the module and divide that by the voltage (in
> this instance, 12).  This gives you the resistor value (this is OHMs
> law, btw).  What you'll need to do it cut the line where the power
> leaves the connector and insert a series resistor there that's just a
> bit under the value you came up with in your calculation.  I
> understand this is a pain - but it will fx the problem.
> 
> 5) Although not at all practical, another thing you may want to try is
> running separate wires from the ground terminals on each of the module
> power connectors on the rack that's powering the VCOs and run all
> those lines directly to the ground tap of the rack's power supply. 
> You won't have to cut the ground lines already there.  If they are
> daisy chained together, this wil take take of it.
> 
> hope this helps???
> 
> 
> - P
> 
> 
> 
> --- In analogue_systems@yahoogroups.com, "TacocaT" <zpardos@> wrote:
> >
> > Hello,
> > 
> > I just recieved my rs15 case and I put a couple of doepfer style VCOs
> > into th case and I can hear one VCO's output (faintly) through the
> > other's output (no patches). This shouldn't be happening. Does it
> > happen for anyone else? Is there also crosstalk when using the ASys
> > power connectors?
> > 
> > I wonder if the doepfer racks have this problem at all.
> >
>