Maximizing Music And Minimizing Noise; Ground Hum - Kurzweil K2500 - PERFORMANCE GUIDE REV F PART NUMBER 910252 CHAP 9 Maintenance And Troubleshooting Manual

Maintenance and Troubleshooting

Maximizing Music and Minimizing Noise

adjustments, it's best to increase the output level digitally (by editing programs) instead of
increasing the gain of your amplifier or mixing board. This is because a digital gain increase is
completely noiseless whereas an analog increase will proportionally increase hum and noise
from the connecting cabling and from the K2500 itself.
Increasing the volume digitally can be accomplished in three different ways. You can increase
the volume of all programs assigned to a given MIDI channel by selecting the CHANLS page in
MIDI mode and setting the OutGain parameter to the desired level (in 6dB steps). For multi-
timbral sequences (on multiple MIDI channels), you will 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 finer adjustment, the Adjust parameter on the F4 AMP page can be used.
Increasing the level too much can cause clipping distortion when multiple notes are triggered
with high attack velocity. For dense sequences all played through the same outputs, you will
probably only be able to increase the volume by 6dB 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, the individual outputs should be used. 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 all mixed mixed together, and the signal must travel through more circuitry
to reach them.
Programs that are routed through the K2500's global effects processor (Output Group A) will
also be slightly noisier than programs routed to Output Groups B, C, or D. As with an external
effects unit, maximizing the input signal level (using the methods described above) will
improve the signal-to-noise ratio of the effects processor. When in Effects mode, you'll see an
internal Wet/Dry mix parameter; in the Effects Editor you'll find numerous parameters for
setting the level of the various effects. Your best signal-to-noise ratio will be achieved by setting
the effects level parameters to maximum and adjusting the Wet/Dry Mix parameter to set the
overall effects mix. If you are only using the effects unit for EQ functions, one of the EQ or Tone
Control functions accessible through the Program Editor will produce quieter results then the
global effects processor's EQ functions (Parametric EQ, Para Bass, Para Mid, or Para Treble, for
example).

Ground Hum

A common problem with all electronic musical gear is the hum that can occur in connecting
cables due to AC ground loops. Although "3-prong to 2-prong" AC adaptors are frequently
used to break ground loops, they also break the safety ground that protects you from electric
shock. Using these adaptors is dangerous, and SHOULD NOT be done! Furthermore,
although using these adaptors may reduce low-frequency hum, high-frequency line noise (such
as motor switching noise) is likely to get worse in this case, since the K2500's AC noise filter
will have no outlet for the noise it filters if you disable the ground.
To reduce ground hum, you can increase your output signal levels as described earlier in this
section. Other safe procedures include plugging your mixing board and amplifier into the same
outlet as your K2500, and making sure that all 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.
A 75-watt transformer is sufficient for the K2500.
For studio applications, where the utmost signal purity is required, using audio unbalanced-to-
balanced line transformers will give you the best results. Each of the K2500's audio outputs can
easily drive a 600-ohm transformer.
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