[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.

John, WA5BXO

-----Original Message-----
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

Hi all,

As I dimly remember from Motors and Machines 1 and 2, THE TRANSFORMER 
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.

Larry W3LW

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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