Amplifier Burst Testing
"John L Stewart"
Phil A points out that the average audiophool does not know what to do
with that kind of information nor does it matter. But none of us in this
discussion is an average audiophool far as I can tell.
** Very careless misquote:
" None of which matters one a HOOT to a hobbyist audiophile.
Cos he can use music programme and a scope to see what is really
going on."
And the audio
gate still provides a lot of information without the advantage of
switching at zero crossing.
** Without zero crossing and equal half cycles, you get low frequency
transients that spoil the shape of the burst so the wave peaks are not all
the same amplitude. Big problem
This technique can be used to test loudspeakers & room acoustics as well
as amplifiers. So worth having for those involved in that kind of work.
** A " tone burst gate" is a very handy tool for *speaker* testing -
I built a kit version as published in ETI magazine ( ETI 124) about
30 years ago and it gets regular use. The circuit consists of just three
4000
series CMOS and two op-amps - plus a +/-15V psu.
Input can be any frequency from 5Hz to 50kHz.
With the aid of an omni condenser mic and suitable pre-amp you can learn
a great deal about the transient and frequency performance of a speaker,
even when tested in a room, as the direct reflected sounds are easy to
separate since the latter can be seen to arrive after the burst on a scope.
.... Phil
|