Mark Twain wrote:
I'm sort of a vintage stereo guy,,..
and Harman Kardon is a good name
It's a good set-up and I had to pay
extra for it at the time.
I was thinking,...even though it was
new in the box would the years since
it was made 'oxidize' circuits etc
and that's the cause of the intermittent
I would be interested, if you wanted
to spend the time. Of your opinion
of my stereo system. I bought this
while in the Navy 1979-1980.
Yamaha A-1 Integrated Amp:
Yamaha- T-1 Tuner:
Pioneer Pl-L100 Linear Tracking Turntable:
Teac C-3 Tape Deck:
It is possible for 1/8" connections to act up.
In some cases, there isn't sufficient control of
dimensions, or sufficient spring force, and it's not
making good contact.
I did think of a way for the LineOut to have
DC on it. HDAudio chips support jack re-tasking.
That means an output, can be used as a microphone input,
and the mode changes in software.
To support electret microphones, they take a voltage
source, and maybe a 2Kohm resistor, and bias tip and ring.
There's no particular pattern to what they select for
a voltage source, and it could vary anywhere from 3.3V to
5V or so.
tip ---- 2K ------- 3.3V
|| ring ---- 2K ------- 3.3V
|| sleeve ------------- GND
The idea is, the electret pulls down the
level, when the electret receives some sound
pressure. Basically, the computer provides a
source of power to make the electret work. On
modern enough systems, the microphone is stereo in,
and a separate bias is placed on tip and ring
(for left and right).
The bias source should be switched off by the
software, when the jack is in output mode.
The next time the speakers do it again, try using the
diagnostic output and routing it to the green and black
inputs as a test. And see if that signal source behaves
What you want, is a way to prove it's the computer
that is doing it.
If the volume pot on the speakers was a bit
dirty, it could function as a noise source. But
you'd also notice this, if adjusting the volume
control created all sorts of extraneous noise.
It doesn't take too many twists of a volume knob
to figure out it's a noise source.
And I think you've got me beat on stereo equipment :-)