|[AMRadio] Class AB and B audio XFMRS|
John E. Coleman (ARS WA5BXO)
wa5bxo2005 at pctechref.com
Mon Mar 13 13:30:27 EST 2006
Thank you Larry,
I don't know the math either, but I think you gave a much better explanation
than I did.
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Larry Will
Sent: Monday, March 13, 2006 12:25 PM
To: Discussion of AM Radio; 'Discussion of AM Radio'
Subject: RE: [AMRadio] Class AB and B audio XFMRS
As I dimly remember from Motors and Machines 1 and 2, THE TRANSFORMER
IS A HIGHLY NON-LINEAR DEVICE. WE USE THESE SIMPLE FORMULAS for TR
and ZR but in reality YOU NEED ADVANCED CALCULUS TO adequately
explain BOTH THE Hysteresis and eddy current losses and
distortions. The open circuit and short circuit tests can get that
info out of a particular device, I haven't done these in years but it
is a valuable tool for analyzing any transformer. You need power and
the correct frequencies however. Its the hysteresis losses that
result in the poor LF response. The secondary voltage lags the
primary current (I think I remember that correctly) more and more as
the frequency is decreased. The problem is especially acute at the
polarity change, ie the zero crossing where the magnetic field must
reverse instantly. The non linear effects generate a discontinuity
in the waveform and the harmonic components and odd phases are the
result. What is happening the primary power is converted to a
magnetic flux which is then converted back to power in the
secondary. Its the medium - the IRON that causes the problems. This
cannot be analysed except by non-linear mathematics Messy at
best. The DC current, if present polarizes the magnetic field making
the effects worse. MacIntosh got around this with his patented
transformer and circuit which greatly minimized the magnetic
non-linearity, circuits which are still used in MacIntosh audio amps today.
BTW audio analog tape recorders minimized this problem with the head
by using a high frequency bias, say 22 kcs, to keep the flux
constantly changing and allowing good LF response while making the
recording. The HF signal is filtered out on playback either by the
playback head or immediately before the first preamp.
Some folks on here surely can amplify this and correct my fuzzy
memory if needed.
The problem is the energy transfer medium - THE IRON.
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