Kurzweil PC3x weird noises

[diydidi]

I have this unit here for repair. All is fine and in good order, except that when connected to an external PA/ amplifier, there is a strange digital type noise. This noise is also reacting to certain button presses etc.
If I remove the mains earth from the Kettle plug used to power the unit, the noise goes away.
Any ideas to a solution?

[Mick Bailey]

Don't know about that specific piece of kit, but a lot of audio uses separate digital and signal grounding paths. If the digital grounding goes high resistance at some point then noise can leak onto the signal ground. I'm thinking you may have a connector or grounding point (bracket, screw or something) that isn't making good contact.

[doctor]

Don't know about that specific piece of kit, but a lot of audio uses separate digital and signal grounding paths. If the digital grounding goes high resistance at some point then noise can leak onto the signal ground. I'm thinking you may have a connector or grounding point (bracket, screw or something) that isn't making good contact.

The separation of the analog and digital grounds that Mick Bailey describes is inside the device and cannot exist outside.

The problem, which you have is a “ground loop”, i.e. you made connection to the ground in the few points (at least two) instead of in the single point. The fact that the noise disappears when you remove one grounding cable confirms this assertion.

Check multiple ground connection and fix it.

[diydidi]

So you guys think its an outside problem? The unit has balanced trs output ports. So technically speaking noise cant be on the balanced lines cause they are balanced right? (CMRR)
So, a DI BOX with a ground lift switch should do the trick?

[Mick Bailey]

The separation of the analog and digital grounds that Mick Bailey describes is inside the device and cannot exist outside.

What would be the mechanism for digital hash getting onto the chassis ground if it can't exist outside?

If there's a grounding issue that isn't the result of a fault then I usually try a signal lead that has the ground disconnected at one end.

[Jazz P Bass]

For what it is worth, I have seen a number of manufacturers that went to an offboard power supply.
For whatever reason.

I have also seen , from the factory, a three prong IEC mains input connector, and the ground wire is not connected to anything.
Never was.
Virgin ground connector.
No solder in the hole.
No ground tabs on the chassis.

Makes you wonder what that's all about.

[Mick Bailey]

Last year I had a complex setup including a Roland GR-33 guitar synth. Everything was powered fine and grounded. Take out the synth completely and no problem at all. Reintroduce it and lots of digital hash and series of noises associated with button presses and pedal movement. Tried the synth on its own as the only thing connected to the pedal board PSU and the same noise. The thing that fixed it was using the synth's OEM power supply, which didn't have a ground connection.

I never did resolve why grounding would introduce noise like that. A humming ground loop I can understand.

I've also seen the unconnected ground on three-pin IEC inlets.

[Jazz P Bass]

I've also seen the unconnected ground on three-pin IEC inlets.

Yeah, and they are shipped out with a 3 prong cord.

[diydidi]

Anyways. Thank for all the replies. Told customer to get a passive DI with ground lift. Bob's ur Uncle....