Digitech Digidelay Adds Noise On Power Line

[TomCarlos]

Hola Friends...

Ok, this is a strange one. I have a pedal board that I power up from a 6 pack of "C" cells. In total, my power pack is 9 volts!! It works great. Tonight, I noticed an odd noise coming through my effects chain. It was like a breathing type, motor sound. I disconnected effects and isolated the problem to my Digitech Digidelay X-Series.

With the effect removed from the chain, everything works fine. With the Digitech in the loop, I get the noise. If I have this effect connected using the 9 volt line (what I call the power block), it seems to be back feeding noise, through the power strip. I hear the noise coming through the chain, even if the Digital is not activated. If I take it off the power strip and use a 9 volt battery, the effects loop is quiet.

Is it possible that the device is creating an oscillation or noise that can back feed through the power line and thus be picked up by other devices? I have never seen this before.

Thanks, Tom

[J M Fahey]

[B] I disconnected effects and isolated the problem to my Digitech Digidelay X-Series.

With the effect removed from the chain, everything works fine. With the Digitech in the loop, I get the noise. If I have this effect connected using the 9 volt line (what I call the power block), it seems to be back feeding noise, through the power strip. I hear the noise coming through the chain, even if the Digital is not activated. If I take it off the power strip and use a 9 volt battery, the effects loop is quiet.

Is it possible that the device is creating an oscillation or noise that can back feed through the power line and thus be picked up by other devices?

Yes, of course.
By definition anything digital is a noisemaker so it must be properly filtered and isolated.
Faraday cage, separate audio and digital grounds, bypassing caps, ferrite beads on any wire leaving/entering the box, you name it.
That said, Digitech is a good brand, maybe your particular pedal was knocked or something and some filter was disconnected.
Probably some friend more into Digital may suggest some practical solution.

[Mick Bailey]

Has it always done this, or is it a recent development (or you've just noticed it)?

The Vox Delay Lab does the same thing and the only way I've found is to run it off its own supply.

Some digital pedals can be silenced by adding a bypass cap right at the DC connector. I use a 100uf electrolytic paralleled with a 10nf ceramic, spliced into the cable and heat-shrinked. For test purposes I have this arrangement wired to a short plug/socket which can be used to quickly check if this approach works with a particular setup.

Sometimes re-ordering the power can help, particularly in a daisy-chain. Try your delay first in line or last to see if there's any change.

[TomCarlos]

Thank you JM and Mick...

The problem just started. I think something in the Digitech is starting to fail. I am hearing some audio problems with the unit. I'll pull this effect off my board and take a closer look inside. I think you're right- could be a cap failure or something else. I'll see if I can dig up a schematic.

For now, I think I'll pick up a replacement, maybe a Boss or something else. If I fix the Digitech, perhaps it will be donated to a local student.

Thanks again, Tom