The Sound of Silence
In the past couple of months (see "Inadvertent Radio and Other Noises" and "Tracking Down Problems in Your Stereo System"), I've
talked about troubleshooting an audio system to find the source of extraneous noise such
as hum and radio-frequency interference.
While unwanted sounds may bedevil your system on occasion,
their sources are usually fairly obvious. But when all or part of the system quits
entirely, it often takes some real detective work to discover where the difficulty lies.
It doesn't take all that much to interrupt an audio signal, and most problems are easily
fixed, but simply locating the fault can sometimes take a considerable amount of effort. A
process of elimination will help, however.
If the problem affects all sources, for instance, it is
almost certainly in the preamplifier stage or beyond. On the other hand, if only one
source is affected, then the disruption is either in the source component itself, the
input circuitry it is connected to, or in the cables between.
If the problem is in both channels, it probably has nothing
to do with the interconnection, but simply substituting new cables will clear up any
questions on that score. Having eliminated that possibility, plugging the component into a
different input (one you know works) should identify the faulty area as the input
circuitry if the unit now plays, or the component itself if there is still silence. If the
source has a headphone output, monitoring through it should also indicate whether or not
the problem is at that end.
A similar process can be used to narrow the possibilities
if the gremlin turns out to be in the preamplifier, power amplifier, or speakers. If the
silence affects both channels, for instance, it probably has nothing to do with the
speakers (assuming, of course, all switches are in the appropriate positions). If only one
channel has the problem, swap the leads between speakers at the speaker end; if the same
speaker exhibits the fault that's where the problem lies, if the problem is now on the
other side it's earlier in the chain.
Doing the same sort of swap at the amplifier end will
identify whether or not the wiring is at fault. If not, it must be in the central
electronics. In systems built around receivers, there's not much further you can go; with
separates, continuing the elimination process should finally identify which component is
at fault.
Audio equipment is very reliable for the most part, so
chances are that any problems you uncover will be ones of wiring. But if a component
really has an internal fault, at least the troubleshooting process will indicate which
piece of equipment to have repaired, rather than making you drag everything to the shop.
...Ian G. Masters
ian@mastersonaudio.com
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