Palmer DREI Manual De Usuario página 10

2) SINGLE-ENDED VS. PUSH-PULL
In similar fashion to solid state and tube rectifiers both the Single
ended and push-pull amplifier designs have found their place with gui-
tar players for their distinct sonic qualities. Actually referring to the
amplifier's output stage the single ended type provides complex tones,
rich even order harmonics and overall „warmth" while the push-pull design
has become famous for its efficiency, immediate articulation and extended
dynamics.
Single ended amps use only one output tube (or multiple tubes in parallel
to increase power). They operate at full power all the time irrespective
of the presence or absence of an input signal - in other words they are
always „on". This kind of operation is also called Class A.
The push-pull design requires a pair of output tubes (or multiple pairs
in parallel to increase power). The input signal to a push-pull amp is
split into two - one that is in phase with the original signal, and one
that is phase reversed. The opposite signals drive the output tubes, i.e.
While one side is busy with the in-phase signal (i.e. it is „on") the
inverse signal side is „off", and vice versa. The difference between the
two sides is taken for the output. This is why push-pull amplifiers are
also called „differential" amplifiers. They usually operate in Class AB.
Alternating between „on" and „off" states produces distortion in the
push/pull transition area. This is generally known as crossover distor-
tion, and its aggressive, gritty quality is a favorite with many players.
Other than in single ended (i.e. „always on") designs there is no contin-
uous load on the output transformer of a push-pull amplifier. The result
is less saturation and improved fidelity. Also, push-pull amplifiers are
more efficient due to the „off" periods of the power tubes which permit
higher output levels when they are „on". However, even order harmonics
generated in the output stage are cancelled out by the push-pull opera-
tion while they are emphasized in single ended amps.
The choice remains a matter of taste. Many professional guitar players
use small single ended amps for recording while the more powerful push-
pull design is preferred on stage.
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