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5
OPERATION OF THE AMPLIFIER
After all proper connections have been made, you are now ready to turn the
Stereo 90 amplifier on. The power on/off switch is on the front of the amp. Some
preamplifiers and sources can generate dangerous transients that can damage
loudspeakers. To avoid letting dangerous transients reach your loudspeakers turn
your system on in the following order:
1) Turn on all sources (CD, tuner, etc.) that you will be using.
2) Turn on the preamplifier.
3) Wait until preamp has stabilized.
4) Power up Stereo 90 amplifier
5) Select listening source and play music
When powering down your system turn the amplifier off first.
Note – Important! After turning off the amplifier, wait at least one minute to turn
it back on. Do not turn it on then off and then on again in quick succession.
Doing this will not allow the power supply to discharge between on/off cycling
and may result in transient noises.
Triode/Ultralinear switch:
This switch is located on the back panel of the amp. See Figure 2. The output
transformer of a tube amplifier acts as the electrical interface between the very
different impedances of the loudspeaker and the tube circuitry. There are three
fundamental ways that the output transformer can be connected to the tube circuit.
1) Tetrode or Pentode connection – In this configuration, the highest power level
is achieved but at the expense of significantly higher distortion levels.
Practically speaking, this mode of operation is sonically inferior and has been
disregarded in the Stereo 90 design.
2) Triode connection – With this configuration, the lowest level of distortion is
achieved but at the expense of output power. In the case of the Stereo 90, its
power level in triode is high enough that it will likely provide plenty of power
for almost any speaker load.
3) Ultralinear operation – With this configuration, power levels near those of
tetrode mode are achieved with low distortion levels that approach those of
triode operation. For loudspeakers that demand very high levels of power,
ultralinear should provide excellent sound and plenty of power.
The triode/ultralinear switch allows the user to operate the Stereo 90 in either of
the two modes. In general, the sonic differences are subtle but for a given
loudspeaker one mode is likely to sound better than the other. There is a
complex relationship between the output transformer and the crossover network
so try both and see which one works best in your system. This switch can be
operated while the amplifier is playing but you will hear a small relay noise
through the loudspeaker.