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Humm

DenisDenis Posts: 163
Hi

In my demo store, I include a NI3000 with MVP8400

When I'm connecting control cable ( RS232) between NI3000 and Rotel preamp I get a humm in sound.

The humm is present when the preamp is on or off. Power amp (Rotel) isON

Somebody can help me ?

Comments

  • Jimweir192Jimweir192 Posts: 502
    Sounds like a ground loop via the control cable screen, is the cable moulded or homemade? Is the shell connected to pin 5? If it is break this connection. The other option is if the case of the preamp is in contact with the case of the NI3000
  • ericmedleyericmedley Posts: 4,177
    Denis wrote:
    Hi

    In my demo store, I include a NI3000 with MVP8400

    When I'm connecting control cable ( RS232) between NI3000 and Rotel preamp I get a humm in sound.

    The humm is present when the preamp is on or off. Power amp (Rotel) isON

    Somebody can help me ?

    Rotel's are notorious for having ground hum. Try cutting the gournd wire off the RS-232 cable. (pin 5) It's probably already getting a connection to ground off the chassis.
    If it still persists, try removing all the other devices connected to the Rotel one by one and see if you can isolate a possible loop through the other gear connected to it.

    Good luck on this one. Ground loops blow chunks!!!
  • RS232 Isolation

    Hi Dennis,
    We tend to end up with 4 or 5 RS232 devices connected an NI-4000 on some sites, and no matter how carefully we cable them we always end up with ground loops. The best solution I have found is to use RS232 Optical Isolators. These units are self powered (by the control lines) and electrically isolate the two systems. They still pass data as normal. Ground loop goes away - Problem solved!

    Just Google RS232 Optical Isolator - they're fairly rare animals but worth the cost.

    Cheers

    Brent
  • SergeyMSergeyM Posts: 22
    Some years ago I found, that Neutal pin of power cord of PSN 2.8 is connected to minus 12V out pin (!!!). So my master works with only +12V wire connected (master was connected to other equipment with interface wires). So try to use other power plug orientatation (invert Phase - Neutral pins). Also check grounding in all of your equipment.
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