Palmer FAB5 Manual De Usuario página 8

1) BEFORE SWITCHING THE AMP ON FOR THE FIRST TIME
—
Make certain that the voltage selected next to the rear panel pow-
er connector of the FAB5 (mains voltage selector) matches the mains
voltage in your country.
—
Make certain that the amp is positioned safely and secured.
—
Ensure sufficient air circulation through the cooling slits of the
FAB5.
PLEASE MAKE CERTAIN THAT YOU READ ALL OF THE SAFETY INSTRUCTIONS CON-
TAINED IN THIS MANUAL BEFORE YOU BEGIN USING YOUR FAB5!
2) SINGLE-ENDED OR PUSH-PULL
Like tube and diode rectifiers, both "single-ended and "push-pull" am-
plifiers have a fixed place among guitarists because of their varying
tone characteristics. Both terms actually refer only to the output stage.
Single-ended amplifiers produce a complex, warm tone with distinctive
harmonics, while push-pull amplifiers stand out because of high efficien-
cy, direct response, and high dynamics.
Single-ended circuits usually use only one power tube (or multiple tubes
connected in parallel for higher output). They always run at full power
regardless of whether or not an input signal is present - in other words,
the power tube is always "on". This mode of operation is also called
"Class A".
The push-pull circuit requires a pair of power tubes (or multiple pairs
connected in parallel for higher output). The input signal of a push-pull
amplifier is split into a signal with the same phase as the original and
a signal with the phase reversed by 180°. The two opposing signals now
drive the power tubes alternately, i.e., while one tube amplifies the
in-phase signal ("on"), the tube driven by the phase-reversed signal is
"off". The difference between the two sides is picked up as the output
signal. For this reason, push-pull amplifiers are also referred to as
differential amplifiers. They are usually operated in "Class AB".
The constant alternation produces distortion in the transition area
("on", "off"). Many guitarists love this aggressive, scratchy transition
distortion.
Unlike the single-ended circuit ("always on"), the output transformer of
a push-pull amplifier is not constantly under load. This means that it is
less saturated and attains higher sound fidelity. Push-pull circuits are
also more efficient, since the rest periods of the power tubes ("off")
permit higher output levels when they are "on". However, odd overtones
generated in the output stage are cancelled out by the push-pull func-
tion, while they are clearly predominant in single-ended amplifiers.
In the end, the choice is a matter of taste. In the studio, professional
guitarists like to use small single-ended amplifiers, while more powerful
push-pull amplifiers are preferred on stage.
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