Audioclinic (Jan. 1984)

Record Damage from Water

Q. I have an unusual problem. Roughly two years ago there was a slight flood in my basement apartment. My record collection, to say the least, was damaged. How do I remove the white residue left on my discs?

-Benjamin L. Smith; Newark, N.J.

A. If the residue is not mold, I believe you can remove it with, of all things, water!! I know that your recordings already saw their share of that, but the water stayed on their surfaces for some time. Thus, the residue is probably material which was transferred onto the discs from the sleeves and jackets--aided by the wetness.

To apply the water, use it under high pressure, such as obtainable from a garden hose or kitchen sink sprayer.

You will probably want to mask the label first, to prevent further staining.

When the discs have been thoroughly wetted, you must then wipe them vigorously and completely with a lint free cloth. Even if there is some residual staining, I believe that the background noise created by the white material deposited on the surface of your discs will be reduced-hopefully to very low levels.

This procedure is designed to avoid the use of any soap compounds. Some detergents can cause more problems than they solve.

If mold is involved, you will need to investigate various fungicides, with the hope that you can find one which will not damage your recordings still more.

To make this trial-and-error investigation, I believe you will have to try various fungicides on one or two recordings which are not of value to you. That way, if a disc is ruined by this research, you won't feel too bad.

I hope a reader with more experience with this sort of problem will write in to share his knowledge with us.

Impedance and Sensitivity Matching

Q. Is there any reason for matching the impedance and sensitivity of phono, tape and AUX inputs of a receiver to the outputs of components providing signals to those inputs?

-Roger Ross; Peshastin, Wash.

A. No. Regarding sensitivity, if a device can supply more signal than is needed by a second device, there is no need to lower the source's output.

At one time, if a phonograph cartridge produced more output than was called for by the phono input, overload of the phono circuits was likely. This is no longer true.

It is sometimes a good idea to keep the output signal level from a preamplifier close to what is called for by a power amplifier, to maintain a good signal-to-noise ratio and allow easy volume adjustment. If the power amplifier has input level controls, there is no problem with a preamplifier having too much output.

Impedance matching is of little concern and, in fact, is not even desirable in most circumstances. With small-signal devices such as tape recorders, tuners and the like, the general rule is that the device being driven must have an impedance at least 10 times that of the device driving it. Even loudspeakers are not matched to the output impedance of the amplifier (but within limits, to prevent overloading of the output stages). A moving-magnet phono cartridge usually should be loaded by a 47-kilohm resistance, not for impedance matching but for reasons having to do with the O of the resonant circuit formed by the inductance in the cartridge and the capacitance of turntable wiring, interconnecting cables and phono input circuit capacitance.

Loudspeakers and Increased Dynamics

Q. How will the impending digital equipment, with its increased dynamic range and frequency response, affect my purchase of electrostatic loudspeakers? Specifically, will my new speakers be able to cope with the dynamic range of the new digital discs/sources?

-Jim Spahr, Oradell, N.J.

A. Your electrostatic speakers (or any speakers, for that matter) can handle some maximum amount of input signal or power. This, in turn, permits that speaker to produce some given SPL (sound pressure level). If the dynamic range has been increased, two conditions can take place: We can keep the softest musical passages at their present values or we can lower them and keep the loudest sound levels at their present values. The choice is yours to make.

If the speakers you plan to purchase can produce sound at a level loud enough to be painful, you do not need a speaker capable of more. In this instance, you would keep your highest listening levels at or below those obtainable at the speakers' full output, and allow the softest passages to be heard at much reduced volume.

On the other hand, if the speakers you are considering are not capable of producing sufficiently loud sound, even when they are being driven by a sufficiently powerful amplifier, the softest passages might well, with greater dynamic range, virtually disappear. In that case, you should consider purchasing speakers capable of producing more sound volume.

Tuner to Monophonic Amplifier

Q. I plan to purchase a digital FM tuner, a preamplifier, a power amplifier, and a pair of loudspeakers. My budget will not allow me to buy all of these components at once, but I could purchase the tuner and enjoy it now.

Would it be possible for me to connect the tuner to a mono amp with a Y- connector and a potentiometer between the two components? If so, what value should the potentiometer have? Should the potentiometer be wired after the Y-connector, or should there be a potentiometer for each channel before the connector?

-Jeff Taylor; Johnson city, Tenn.

A. If your new tuner has provisions for monophonic operation (many of them do), simply switch the tuner to "mono" and connect one channel to the input of your monophonic amplifier.

All will be fine unless your power amplifier does not have an input potentiometer and your tuner lacks an output pot. If that is the case, you will have to wire one between the output from the tuner and the input to the power amp.

Because many power amplifiers require a considerable amount of signal to drive them to maximum power output, you should be certain that the tuner can supply sufficient voltage to drive the amplifier to a reasonably high sound level. If it cannot do this, you must find a way to introduce gain between the tuner and amplifier. This might take the form of a "power booster" sold by dealers specializing in musical instruments and accessories.

These boosters have input potentiometers, so you need not provide your own.

If your new tuner has no manual stereo/mono switch, you will need to feed both its outputs to your amplifier. However, hooking them both together with an ordinary Y-connector can cause problems: Distortion, lack of bass and sometimes even damage to the tuner's output circuits. For that reason, it's best to wire each channel's "hot" (center) conductor through a 10-kilohm resistor, with the free ends of each resistor wired together and connected to the "hot" input terminal of the amplifier.

Appropriate shielded cable and grounding practice must be followed.

If the power amplifier was inadequate with just the tuner connected, it will be even less so with the resistors wired into the circuit. The booster is almost certain to be required.

These boosters are generally designed for battery operation. You may wish to use an appropriate power supply for the booster rather than use batteries.

If the booster is unnecessary, you will have to connect the "high" side of the potentiometer to the junction of the two 10-kilohm resistors, and the slider of the potentiometer to the "hot" input terminal of the amplifier, with the low end of the potentiometer grounded.

Turntable Hum

Q. My turntable hums--not much, but it is audible. I checked the ground by unhooking the ground wire, and the hum increased dramatically. The hum changes in pitch with changes in volume: The higher the volume control setting, the louder the hum. Is my grounding ineffective or is my turntable defective?

-Benjamin Blacque; San Francisco, Cal.

A. The fact that the pitch of the hum changes with volume suggests that this is not ordinary 60-Hz hum. Apparently, something is oscillating. The most likely cause of such oscillation is the proximity of the speaker leads to the phonograph input leads. There are other combinations of input/output leads which could possibly cause this, but this is at least a starting place.

Separate all input leads from all output leads and, while you're at it, from the a.c. power leads.

It is also possible that the oscillation is the result of problems within your preamplifier, the most likely of such possibilities being a defective decoupling capacitor. Such a conclusion is at least partially supported by the statement in your letter in which you say that the "hum" is not very dramatic.

There is yet another possibility, and this is that your "hum" really is hum!

You mention a change of pitch with changes of the setting of the volume control. If such changes are, in fact, changes of intensity rather than pitch, then you do have some hum. Whether or not this hum is significant is impossible to tell from my vantage point. I can say that if the hum is audible during the softest passages of music to which you listen, then the hum in your system is too great. This hum may be the result of a cartridge with insufficient shielding or perhaps of a turntable located too near to a motor or heavy-duty power transformer, which results in hum being induced into the cartridge.

Low-Pass Filter

Q. What is a low-pass filter?

-William Kay, Yonkers, N. Y.

A. A low-pass filter is used to reduce background hiss from tapes or discs. It will also reduce record "scratch." This is done at the expense of the higher audio frequencies. Modern disc recordings are relatively quiet, so this filter might not be required. If you intend to play 78s, you will find this filter helpful. In most instances, you will not sacrifice much in terms of high frequency response because highs were lacking on most 78s.

Amplified TV Signals

Q. A friend of mine has the amplified signal from his TV receiver patched into his Yamaha receiver. This signal is again amplified. What damage could occur?

-Michael E. Chapman; Concord, N.C.

A. There probably is no harm in having a TV set connected to the input of a receiver. You say that the TV signal is amplified before it gets to the Yamaha receiver. By this I believe you mean that it is being extracted from the speaker terminals of the TV receiver. Although this is sometimes not the best way to obtain good sound quality, it is often the simplest way of extracting the sound.

The resulting sound quality is likely to be better than the sound provided by the internal speaker of the TV set.

If the person has the necessary understanding of circuitry, he will know when to do this and when it should not be done. Your friend either understands the problems involved or was fortunate that the low side of the speaker line in the TV set was grounded.

None of this, however, relates to amplified sound. Rather, it relates to matters involving the output stage of the TV set and whether or not the low side of the speaker line is at true ground potential. Where this terminal is not truly grounded, damage to all equipment is possible with the connections you have described.

Even where grounding is not a problem, there is still the situation of the hot chassis. (I do not see one very often these days.) When it is present, using such a set connected to audio equipment can cause very dangerous shocks to the user and possible damage to the equipment.

(adapted from Audio magazine, Jan. 1984; JOSEPH GIOVANELLI)

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