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reliability and replacement of Mag ribbon tweeters?
wrote:
I finally figured it out and it's even stranger than I thought.
The CDR-630 causes this distortion whenever it's in the tape loop,
turned off. The moment I turn it on, the distortion goes away.
Turning it on must power up the input stage changing the impedance or
grounding. I've had a lot of different units in my tape loop and this
one is the ONLY one that's ever done this. VERY VERY strange. But the
behavior is consistent and repeatable.
Has anyone encountered this? Can anyone explain this?
I posted a reply to your earlier message, and it had not shown up yet. I
was asking whether the problem went away when the CD recorder is turned on.
The reason why you are seeing this "problem" is because of clamping
diodes from the input terminals to the supply voltages. These may be
discrete diodes on the PC board, or diodes inside integrated ciruits
(e.g. analog switches or op-amps). When the recorder is turned on, the
supply voltages are at the nominal levels, and the diodes will not
conduct unless the input voltage exceeds the supply voltages in
magnitude. However, when the CD recorder is turned off, the supply
voltages drop to ground level, and effectively the inputs are clamped to
ground by diodes. Whenever the input voltage gets higher than a few
tenths of a volt, you will see appreciable clipping due to the diodes
starting to conduct, since the source impedance is not zero (in other
words, distortion current flowing throught the source resistance and
appearing as a distortion voltage).
The solution is either to always turn on the CD recorder, or disconnect
the CD recorder when it is not used. You can also isolate the CD
recorder by putting a switch in series with its inputs.
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