6
closing. At this pint the amplifier’s outputs are not connected to the speakers.
After the protection circuits detect that the unit has completely stabilized, the
speaker relays will engage. Another click will be heard at this point. The amplifier
is now ready to use. The amplifier will be at temperature and sound its best after
approximately 15 minutes.
Operation of the amplifier is simple. It is important to note that care must be
taken in the operation of the whole system in relation to the significant power
output of either amplifier. Mistakes, such as switching between active sources
without muting the preamplifier output or bumping/miscuing a phonograph
cartridge, can generate large transients at low frequencies. When this type of
transient activity occurs, the amplifiers can generate enough power-surge to
damage most loudspeakers. All switching of sources should be done with the
preamplifier level either muted or fully attenuated (turned down). Inputs to the
amplifier should never be changed while the amplifier is on.
Care must be taken when setting high playback levels. Because of their
tremendous reserve of clean power, Krell amplifiers safely drive speakers to
higher sound pressure levels than other amplifiers. This often results in driving
the speakers to their limit. Always turn the volume level down at the first sign of
distortion.
When turning off the system, the amplifier should always be first. This avoids the
possibility of a turn-off transient occurrence from some other component to the
speakers.
F. PROTECTION CIRCUITRY
The KSA-150 and KSA-250 have a sophisticated series of circuits that protect
them from dangerous input signals or loads on the output. These circuits also
analyze various amplifier functions to prevent speaker damage that may be
caused if the amplifier fails to function properly.
There are two protection modes: Input and Output. When the Input Protection is
engaged the amplifier will remain on, with the front panel LED illuminated, but it
will not pass a signal. This indicates a problem with the input signal caused by
the preamplifier or source component. This is most often a DC condition. The
amplifier will resume passing signal when the problem is resolved.
When the Output Protection is engaged the amplifier will turn off, with the front
panel LED turning off as well. This usually indicates a problem with the speaker
wires, their connection, or the speakers themselves. Once the problem is located
and resolved the amplifier will turn on normally with activation of the front panel
switch. The Output Protection will also engage if the amplifier fails. If the amplifier
will not turn on with all inputs and outputs disconnected, please contact your
dealer or Krell Service.
