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Equalizers & Long Cables
Q. I am thinking about buying an equalizer. I have my stereo equipment in one room and my speakers in another, but I want the equalizer to be in the same room with the speakers, which is at least 30 feet away from the other components. I need to know a way to run the lines that far without changing the frequency response, or adding hum and hiss. I know of only two ways that this can be done ... either by using matching transformers or through the use of integrated circuits. I need to know the answer to this before I buy the equalizer, since the equalizer is of no use to me if I cannot adjust it during each album I play.
-Michael D. Snyder, Pittsburgh, Pa.
A. Most equipment these days has low impedance output and relatively high impedance input. Because of this, it is possible that you can actually run your equalizer with no matching transformers, ICs or other intermediate devices. The signal levels are high enough so that hiss or hum should not be a problem. It is only where the reactance of the shielded cable, interconnecting the equipment, becomes low enough to equal the output impedance of either the equalizer or the equipment driving it at higher audio frequencies, that high frequency attenuation takes place.
If you use a separate preamplifier and power amplifier, then I suggest that you put the equalizer between them because this position will make it more likely that you can operate the equipment with no problems. This will now depend upon the output impedance of your equalizer relative to the capacitive reactance of the cable connecting the equalizer to the power amplifier. Make sure that the equalizer can supply the power amplifier with sufficient signal without becoming overloaded.
However, if you use tape monitor facilities, you must consider both the output impedance of the equalizer and that of the circuitry which drives the tape recorder inputs. These tape monitor output jacks are sometimes of high enough impedance so that the use of long cables might cause some high frequency losses.
Where it becomes necessary to use some other means to achieve your requirements, I suggest that you use a simple emitter or source follower which should work very well providing low impedance and, at the same time, providing good signal level. With the use of matching transformers, the loss of signal, in most cases, will be too great. I see no need to use ICs where one single, discrete component will work fine.
Disc Playback with Dolby
Q. Please explain why the Dolby system cannot be used for the playback of discs. I would certainly think that it could.
-Fletcher King, Andover, Mass.
A. Let us keep in mind that the Dolby system is a complimentary system. It is used where the program is both recorded and then played back with it. Note that recorded tapes are now available that have been recorded with the Dolby system, and you must use Dolby when playing them back in order to obtain the correct frequency response and dynamic range. As for disc recordings, the master tapes are often recorded using Dolby and when these tapes are transferred to discs, the Dolby system is once again used. So the final disc recordings are already properly decoded and further use would not be warranted.
Plastic Record Sleeves
Q. Are records better off stored in their original paper sleeves or in those plastic-lined ones?
-David J. Lee, Wash. D.C.
A. I do not like those plastic-lined record sleeves as they cause more static build up than the paper sleeves.
This static results from the sleeve rubbing against the record when it is withdrawn and reinserted. Static build up means that dust will be attracted to the surface of the disc, and in these days of high compliance phono cartridges and low tracking forces, dust causes more background noise and ultimate damage to the record surfaces than wear from playing the record a number of times.
If you have a problem or question on tape recording, write to AUDIO, 401 North Broad Street, Philadelphia, Pa. 19108, USA.
All letters are answered. Please enclose a stamped, self-addressed envelope.
(Source: Audio magazine, Jan. 1978, JOSEPH GIOVANELLI)
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