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reliability and replacement of Mag ribbon tweeters?
wrote:
I finally found it -- it's not the amp either!
It's about the very strangest thing I've ever seen.
It happens only when my CD Burner is plugged in to my passive pre's
tape loop.
Each source device driving the passive pre drives the CD Burner in
parallel with the amplifier. Total impedance seen by the source is
about 9 kOhm for both, or 10 kOhm if it's the amp only (CD Burner RCA
jacks unplugged).
Whenever the CD Burner is in the loop, there is distortion on each of
the 3 inputs. Whenever I take the CD Burner out of the loop,
distortion goes away. So something about the CD Burner being in the
loop, causes the distortion.
My first hypothesis was that the CD Burner had a short and the input
impedance was too low, overdriving the source and causing distortion.
But I measure between 50 kOhm and 100 kOhm for its inputs, so that's
not the issue.
So how is this possible? Any ideas? I can think of only 3, all equally
unlikely:
1. The output stage of my CD Player (Rotel RCD 1070) is fried and it
can't drive a 9 kOhm load? But it can drive a 10 kOhm load. Yet its
output impedance is 100 ohms, so it should have no problem.
I had a tape deck with 50 kOhm input impedance for over a year before
the CD Burner, and the problem started about when I added the CD
Burner (a few weeks ago). So (1) is highly unlikely. This leaves (2)
and (3).
2. The CD Burner's analog input is fried somehow and its input
impedance at musical frequencies is very low, overdriving the sources.
Yet it's 90 kOhm for DC (e.g. my multimeter).
3. Some kind of weird grounding issue. All of the RCA inputs & outputs
are grounded together at the passive pre (left & right channel
grounded separately). And the left channel is grounded to the frame.
Thanks in advance for any help with this very strange problem.
Does the problem go away when the CD burner is powered up?
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