Ground Hum - Kurzweil K2600 Musician’s Reference

Maintenance and Troubleshooting
Maximizing Music and Minimizing Noise
in MIDI mode and setting the OutGain parameter to the desired level (in 6dB steps). For songs
that use multiple MIDI channels, youÕll need to do this for each channel. Alternatively you can
increase the volume of a single program by going to the OUTPUT page in the Program Editor
and setting the Gain parameter to the desired level, again in 6dB steps. For Þner adjustment,
thereÕs the Adjust parameter on the F4 AMP page.
Increasing the level too much can cause clipping distortion when multiple notes are triggered
with high attack velocity. For dense songs played through the same outputs, you will probably
be able to increase the volume by only 6 dB or so without risk of distortion. For monophonic
instruments (lead guitar) or single instrument tracks (such as drums), a substantially greater
boost is generally possible.
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
K2600 into a stage or studio environment is to use the K2600Õs balanced audio outputs, and to be
sure that the mixing board, ampliÞer, or other equipment receiving the K2600 audio signal has a
balanced input circuit.
If you canÕt use the K2600 audio outputs in a balanced manner, there are a few things you can do
to reduce ground hum. Although Ò3-prong to 2-prongÓ 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; donÕt 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 K2600Õs AC noise Þlter will have no output for the noise
it Þlters 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 ampliÞer into
the same AC output as your K2600, and making sure that all of your gear is properly grounded.
If youÕre 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 canÕt use the K2600Õs balanced outputs.
A 75-watt transformer is sufÞcient for the K2600.
Use the shortest possible cable, with the heaviest possible ground (shield) wire, to connect your
K2600 to the mixing board or ampliÞer. This helps to reduce the potential difference between the
chassis of the K2600 and the chassis of a mixing board or ampliÞer that has unbalanced inputsÑ
thus reducing the level of ground hum.
Finally, magnetic Þelds can be a source of interference. The area surrounding the K2600Õs Alpha
Wheel and alphanumeric buttonpad is sensitive to Þelds from large transformers in power
amps; keep them at least a foot away from the K2600Õs front panel. Smaller gear like drum
machines and hardware sequencers can also cause interference.
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