Ground Hum - Kurzweil K2661 Musician’s Reference Manual

Maintenance and Troubleshooting
Maximizing Music and Minimizing Noise
For the absolute maximum signal quality (with the exception of digital output, of course), use
the separate analog outputs. These are connected almost directly to the 18-bit digital-to-analog
converters with a minimum of noise-inducing processing circuitry. A total dynamic range of
over 100dB is available at these outputs. The MIX outputs are naturally somewhat noisier
because they represent the noise of the individual outputs mixed together, and the signal must
travel through more circuitry to reach them.

Ground Hum

A common problem with all electrical musical gear is the hum that can occur in connecting
cables due to AC ground loops. The best way to avoid ground loop noise when integrating the
K2661 into a stage or studio environment is to use the K2661's balanced audio outputs, and to be
sure that the mixing board, amplifier, or other equipment receiving the K2661 audio signal has a
balanced input circuit.
If you can't use the K2661 audio outputs in a balanced manner, there are a few things you can do
to reduce ground hum. Although "3-prong to 2-prong" AC adapters are frequently used to
break ground loops, they also break the safety ground that protects you from electric shock.
These adapters can be dangerous; don't use them! Furthermore, although using these adapters
may reduce low-frequency hum, high-frequency line noise (such as motor switching noise) is
likely to get worse in this case, since the K2661's AC noise filter will have no output for the noise
it filters if you disable the ground.
You can effectively reduce hum by increasing your output signal levels as described in the
previous section. Other safe procedures include plugging your mixing board and amplifier into
the same AC output as your K2661, and making sure that all of your gear is properly grounded.
If you're using an external SCSI device, plug it into the same outlet as well.
AC isolation transformers are extremely effective at eliminating ground loops, and are
recommended for critical installations in which you can't use the K2661's balanced outputs.
A 75-watt transformer is sufficient for the K2661.
Use the shortest possible cable, with the heaviest possible ground (shield) wire, to connect your
K2661 to the mixing board or amplifier. This helps to reduce the potential difference between the
chassis of the K2661 and the chassis of a mixing board or amplifier that has unbalanced inputs—
thus reducing the level of ground hum.
Finally, magnetic fields can be a source of interference. The area surrounding the K2661's Alpha
Wheel and alphanumeric buttonpad is sensitive to fields from large transformers in power
amps; keep them at least a foot away from the K2661's front panel. Smaller gear like drum
machines and hardware sequencers can also cause interference.
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