[Elecraft] K3 related - non-linear audio transformer behavior

[Jim Brown]

On Sun, 21 Sep 2008 09:11:22 -0400, Paul Christensen wrote:

>the square-wave impulse response 
>of the transformer becomes less meaningful.

As long as there is impulse noise, the square wave response of the 
line out transformer is definitely relevant! As the folks at 
Elecraft have noted, the primary function of the Line Out is to 
drive data decoders of one sort or another. Those decoders see 
signal plus noise. Any distortion in the transformer is additional 
noise as far as the decoder is concerned. The square wave response 
of the circuit is simply another way of LOOKING at those 
distortion products. 

The analysis of the K3 Line Out that I did back in June using band 
noise as a source of excitation show the same problems as Jack's 
analysis using very different signal sources, but my excitation, 
being broadband, exposes the IM distortion as apparent broadening 
of the filter skirts. Jack measures IM using traditional two-tone 
methods. In other words, we both see the same problems using very 
different methods to study them. 

Those of us working in pro audio learned long ago that broadband 
noise (we use pink noise) is a VERY powerful analysis tool. 

73,

Jim Brown K9YC

Audio Systems Group, Inc.