"Phil Allison" wrote in message
...

"Arfa Daily"


I fired it up again, and put a sine wave in, then hooked up two channels
of my 'scope, one to the "A" output and one to the "B", both with the
same polarity, and was surprised to find that the two signals were
completely anti-phase,


** When servicing audio, knowing the polarity of the test signal and if
there is significant phase shift is important. A scope triggering off the
incoming wave will it not reveal this in single channel mode - so AF used
both channels.

A much better way is to use the External Synch input on your scope and
link it to a fixed output on your bench audio oscillator ( create on if
you have to). This way, you see instantly if the signal's phase has
reversed or has a large phase shift.

Also, triggering will be rock steady with nearly any kind of distorted,
noisy or contaminated signal on the scope screen.

Try it out for a day or two - you will never go back.


... Phil



Interesting. Are you squaring up the generator's sine output, to give a good
sharp transition for syncing the scope ? I was looking at the phase
reversals on this particular unit, by using 2 of the channels on the scope,
and using internal auto trigger derived from CH 1. The sync circuitry on
this Hitachi scope is very good, and will produce a perfectly stable trigger
point from virtually any waveform, no matter how complex or scruffy, but I
can see where it would be useful to be able to have a fixed known trigger
point, and from there, be able to look at relative phasing between amps, and
phase shift within an amp, using a single scope channel.

Arfa