Non-Switching Amplifiers
Most of the distortion in Class-B is crossover distortion, and results
from gain changes in the output stage as the power devices turn on and
off. Several researchers have attempted to avoid this by ensuring that
each device is clamped to pass a certain minimum current at all times.
This approach has certainly been exploited commercially, but few
technical details have been published. It is not intuitively obvious (to
me, anyway) that stopping the diminishing device current in its tracks
will give less crossover distortion .
Current-Drive Amplifiers
Almost all power amplifiers aspire to be voltage sources of zero output impedance. This minimizes frequency-response variations caused by the peaks and dips of the impedance curve, and gives a universal amplifier that can drive any loudspeaker directly.
The opposite approach is an amplifier with a suffi ciently high output
impedance to act as a constant-current source. This eliminates some problems – such as rising voice-coil resistance with heat dissipation – but introduces others such as control of the cone resonance. Current amplifiers therefore appear to be only of use with active crossovers and velocity feedback from the cone
. It is relatively simple to design an amplifier with any desired
output impedance (even a negative one), and so any compromise between
voltage and current drive is attainable. The snag is that loudspeakers
are universally designed to be driven by voltage sources, and higher
amplifier impedances demand tailoring to specifi c speaker types
0 comments:
Post a Comment
Note: Only a member of this blog may post a comment.