reported
by: Mr. Jibby Jacob
Secretary (Term
1997/98)
Once again the AES Singapore
Section gathered to hear Mr Stephen Low lecture on "Understanding
Amplifier Jargon". This subject which is shrouded with myths was explained
by Mr Low on Friday, 6th Feb. 98 at the Ngee Ann Polytechnic. He is a
founding member of the Singapore Section. The die-hards crowd of audio &
hi-fi enthusiasts included 5 AES members and 7 guests.
Mr Low clearly explained
the basics of audio amplifier design, its desirable characteristics.
Starting with the basic definition of an amplifier, he moved on to how the
amplifier evolved from Valve circuitry to operational amplifiers.
| He then went on
to discuss the performance criteria, among which good subjective
performance i.e. realistic sound quality, low noise, distortion free,
adequate bandwidth & quick transient response. Mr Low then went
on to discuss in depth on the different amplifier classes by operations
and their distinct features. Many listeners felt that this was excellent
because it helped them recall these important amplifier theories which
they had studied long ago. |
The speaker Mr
Stephen Low at the Lecture on "Understanding Audio Amplifier Jargon" |
Mr Low then moved on to the
different types of distortions that occur in an amplifier and these included
the harmonic & IM distortion, Crossover and Transient Intermodulation
Distortion (TID) to name some. Mr Low was lucid in discussing the
thermal noise output as a function of the circuit impedance.
|
Stephen Low (far
left) speaking passionately to an appreciative audience. |
Interference was always a
bane in a practical amplifier system and Mr Low then covered some
of these factors which included spurious noise intrusions from radio
pickups, ESR, loudspeaker interference and microphonic feedback. However
the most controversial issue dealt with was the ubiquitously used term
of PMPO (Peak Music Power Output). |
Mr Low was emphatic enough
to explain that this is a misnomer and a ridiculously large output is often
quoted by salesmen as an advertising gimmick to sell their products to the
consumer or to ridicule their competitors product. Technically this term is
meaningless if load impedance, distortion limits and frequency response are
not defined. Giving examples, Mr Low explained that instead the term
"RMS power" was therefore more meaningful although electrical engineers
would more accurately use "Average Power" to measure power amplifier
output.
|
The speaker Mr
Stephen Low (5th from the left) with 10 members and guests among the
audience at the Lecture on "Understanding Audio Amplifier Jargon" on
Friday, 6th Feb 98 at Ngee Ann Polytechnic, Singapore. |
Mr Low then touched on
advanced designs for power amplifiers and the need to compromise in
practical situations, the output power stages, voltage amplifying circuitry,
protection circuitry & well stabilised power supply system. He illustrated
many of the concepts with circuitry from commercial amplifiers.
|
The speaker, Mr
Stephen Low (right) receiving a plaque of appreciation from Dr Roland
Tan, Chairman AES Singapore Section. |
In closing he also mentioned that
AES Inc. has published several monographs on amplifiers and on related
topics written by various experts. Non-members were also informed that
these were available for purchase and they included many of the actual
specifications for the AES standards. |
|
