MOTM

Just theorizing here: could a faulty cap across one of the lines  
cause swings in voltage?

Recently I shuffled some units around, pulled the 960 out of the  
system and put it back. I've noticed that now the + voltage takes an  
eternity to settle after powering up. It will swing up to 15.6v and  
then drift randomly between that and 14.8v for maybe 15 minutes  
before finally settling on 14.9, while the - voltage heads right to  
-14.9 and stays there, rock-solid. I've had a meter hooked up for the  
last few days trying to figure out the pattern.

I'm inclined to say that the problem isn't due to the PSU, which is a  
dotcom NOS by Power One, because my dotcom VCO doesn't drift in pitch  
at all but the two MOTM vcos do, together, and along with the +  
voltage. The 960 is the only thing between the PSU and the MOTM  
units, so it's the only thing that appears wonky.

Matthew

On 23-Nov-09, at 8:19 PM, Paul Schreiber wrote:

> a) technically, they are not 'bypass' caps, they are 'bulk' caps. A  
> 'bypass' cap is a small value cap (like 0.01uf) that is very close  
> to an IC's power pin. It is there to 'bypass' RF frequencies to  
> ground cause by the lead inductance of the part. The caps used in  
> the '960 are there to reduce voltage drop when wiring large  
> cabinets, where the '960 is say 20-30" away from the main supply  
> (or if you are wiring say 2-4 of them up in a big cabinet.
>
> b) the caps are across the +-15V lines, so every connector "sees"  
> the caps.
>
> Both bypass caps and bulk caps are needed in 'real systems' to  
> counter effects of the 'real world'.
>
> Paul S.
>

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