noise/hum contermeasures?

[Fraser, Colin J]

> -----Original Message-----
> From: Dan Gendreau [mailto:gendreau at rochester.rr.com]
> Sent: Friday, May 19, 2000 9:30 PM
> To: synthDIY
> Subject: noise/hum contermeasures?
> 
> Okay, I have started making modifications to my TR808 and on 
> my first mod
> (BD tune) I have noticed a significant amount of 60Hz hum 
> getting into the
> BD voice.
> 
> My question is:
>     Am I going about this all wrong? I had planned to run a 
> ribbon cable out
> of the 808 case into an outboard project box with pots. 
> Internally, I have
> used wire-wrap wires soldered from the ribbon cable to 
> appropriate points in
> the circuit.

I had a similar problem with my cloned 808 circuits.
They are based on bandpass filters with high resonance, so if there is any
mains hum picked up and the filter is tuned near the hum frequency, or its
harmonics, it will boost it nicely.
You either need to keep the leads as short as possible, or incorporate a
voltage controlled element, and control it from your external box.

Colin f