The Torturous Path Through
Your Audio System
It seemed to be an unusual feature. I
was watching a friend operate her stereo system, and I noticed that when she switched from
CD to tape, or back again, she didn't have to change any of the controls on the receiver.
Whichever component's play button was pressed, that one was heard with no further ado; in
fact, she jumped the gun once or twice, and both sources were audible. The receiver seemed
to be fairly ordinary, and not particularly new, but it did have this mixing facility,
which I had not encountered before.
I started wondering about it, however, when my friend
pointed out that the feature prevented her from recording. Putting the deck into its
recording mode produced no effect on the level indicators, and flipping the tape switch on
the receiver to its monitor position killed the sound from all sources (but taped sounds
were audible when the monitor function was switched out!).
All of this seemed very peculiar, and for a time I was at a
loss to explain it, but eventually the little light went on above my head. I pulled out
the receiver, and looked at its rear panel; my friend had very logically connected the
outputs of her tape deck to the "tape out" jacks on the receiver (which would
have the effect of mixing the taped music with whatever other source was selected) and the
tape deck's input to the receiver's "tape in" jacks (which would produce nothing
at all).
The problem was caused by a lack of standards in labeling:
Had the appropriate jacks been marked "playback" and "record" there
would have been no confusion. Instead, the manufacturers had chosen to label inputs and
outputs (i.e., output to tape on the receiver, but output from tape
on the deck). In doing so, they had made even more confusing an aspect of audio that many
newcomers already find hard to grasp.
For the most part, the signal path through an audio system
is easy to understand. Source components, such as FM tuners and CD players, are plugged in
at one end, and "destination" components -- speakers and headphones -- at the
other. The signal travels more or less directly from the source through the control center
(the amplifier or receiver) to the speakers. But a tape deck is both a source and a
destination, and it has to be accommodated in a special way. Virtually all preamplifiers
and preamp sections incorporate at least one "tape monitor loop" for this
purpose.
To understand it, think of the receiver as three blocks:
First there's an input section, with jacks, a source selector switch, and usually a phono
equalization circuit. This is fed to the second block -- the monitor loop itself -- and
thence to the third: the rest of the system.
In its simplest form, the circuit consists of a pair of
jacks that constantly feed to the tape recorder whatever input signal has been selected in
the first block. This is also fed to the tape monitor switch. Another set of jacks
receives the signal from the tape recorder's output, and this is also fed to the monitor
switch. In one position, often marked "Source," the monitor simply allows the
first-block input to pass to the rest of the system, so you can listen to it (and record
it at the same time). In the other position, "Tape," it cuts off this input
signal and feeds only the tape deck's signal to the rest of the system. If you happen to
be recording, this signal will be the same as the input signal, but routed through the
tape deck's electronics; otherwise, the same position enables you simply to listen to a
tape.
Things may become a bit more complicated if you have a
three-head tape deck: You may be listening to the signal fed to the tape or what
has already been recorded a moment before, depending on the settings on the recorder
itself. And dealing with multiple loops that facilitate dubbing may take some
experimentation. And -- dare I say it? -- it's usually a good idea to check the owner's
manuals of both receiver and recorder to make sure things are hooked-up correctly.
But once you have figured out just what's going on behind
the panel, you should have little trouble.
...Ian G. Masters
ian@mastersonaudio.com
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