AUDIOCLINIC (Q and A) (Nov. 1974)

Playing Mono Records

Q. Should mono LP reissues purchased since the advent of stereo be played for best results with a mono or stereo stylus? If the monos are cut on a "stereo" cutter, will playing them with a mono stylus cause any damage? If a stereo stylus is the proper one, what kind should be used (i.e., elliptical or conical)?

-Louis I. Goldfarb, New York, New York

A. Most discs will play well when used with the newer stylus designs. There are a few monophonic discs which may be a bit noisy, however. These are discs cut with a groove having a different bottom shape than our present V grooves. The bottom of these grooves is wider than the present quarter-mil radius. This means that elliptical styli will work nicely regardless of whether the discs were reissues or were originals. However, some very small conical tips might not fit these older discs, allowing the tip to ride at the bottom of the groove, thereby adding noise.

While it is true that you can play your mono discs very well with today's styli, you still might want to set your receiver's mode switch to "mono." This will cancel out any vertical stylus motion, and thereby reduce noise to some extent. If your entire record collection is mono, you might want to strap your cartridge for mono in accordance with the manufacturer's instructions.

There is no such item as a "stereo stylus" or a "mono stylus." The stylus does not "know the difference." All that has happened over the years is that the art of making stylus tips has improved.

We are now able to hear more from our discs than was possible years ago. The result is that many of our older discs sound better now than we had ever heard them. Not only have styli improved, but the cartridges themselves are better.

Generally speaking, therefore, play all discs with the most modern equipment. They will sound their best.

Whether or not a disc is cut with a stereo or a mono cutter makes no difference. Most mono discs are cut these days with stereo cutters, but the final result is that the grooves do not "know the difference." The motion of the cutting stylus will be the same as though the disc was cut with a mono phonic cutting system. Therefore, again, there is no problem with the kind of stylus you will use.

Because of the nature of the stereo to be less stiff, especially as regards vertical motion. Again we have a "plus." The decrease in stiffness-or increase in compliance-of the stylus means that we can track at lighter and lighter forces. This enables stylus manufacturers to make the dimensions of the stylus tip smaller and still produce less record wear than was the case with older cartridge and stylus designs.

This decreased record wear takes place in the face of the peculiarities of the stereo disc grooves.

Good stylus design was made necessary by the demands of stereo disc recording, but these benefits are all passed along to those who listen only to monophonic disc recordings.

Noise From a Phonograph

Q. My problem is that I hear a noise (something like a scratch) when a record is playing or whenever the cartridge is held above the surface of a moving record.

This noise is heard only from the turn table. The receiver works without any problems.

-Juan A. Marquez, Gurabo, Puerto Rico

A. It may be that the "noise" you hear when your tone arm is suspended above the moving disc is a result of static charges on the disc caused by friction with the surrounding air. It also may be that the grounding in the arm is not good. The ground may be alternately connected and disconnected as the arm moves into some positions. This can cause a kind of "scratching" sound to be heard from the speakers.

Bass Response from a Dolby Decoder

Q. Please tell me how to get good bass response when using a Dolby noise reduction unit.

-Juan A. Marquez, Gurabo, Puerto Rico

A. Bass response has nothing to do with the use of the Dolby noise reduction system. The use or non-use of one of these Dolby "boxes" will have no effect on bass response. If you have noticed a loss of bass when using your Dolby system, something is wrong with your equipment.

Perhaps the output of the device is feeding into some equipment whose impedance is lower than the unit was designed to "see." Perhaps the input impedance of the device is too low to handle the device being fed into it.

Check all this. If all of this checks "negative," you must then make a frequency response run with the Dolby system. Use a "flat" oscillator or at least have a means of maintaining flat oscillator output. The oscillator must feed in signal at the level you would normally use when operating the Dolby unit. Turn the Dolby decoding portion of the unit off, and make the run. A voltmeter, of course, must be connected to the output of the unit, and should produce a flat frequency response. If it does not, you will either have to make a stage by stage check of the device or return it for servicing.

If you do obtain a "flat" response, switch in the Dolby processing unit.

Feed in enough signal to cause the calibration meter to read at "zero" level at 400 Hz. Make another run. If you now see a loss of bass, you must check the unit again, stage by stage.

Note that there are often two separate input/output circuits on Dolby "boxes." One is used to supply signal to the tape machine, and the other is used when playing back from the machine, supplying signal into the play back system. Check each one for good response. Ignore the high frequency response. This will not be flat WHEN THE DOLBY SYSTEM IS SWITCHED IN, unless you have set your levels high enough to overcome the action of the system.

Insufficient Phonograph Volume

Q. I recently purchased a turntable and cartridge. I own a reasonably small amplifier/tuner. The phonograph will not play through the amplifier with sufficient volume for my pleasure, but my 8-track tape deck works fine.

What can I do about getting more volume?

-William A. Pasel, Lexington, Kentucky

A. Because you obtained sufficient volume from your 8-track player, it is obvious that your amplifier can supply enough power to meet your needs. Your problem, therefore, involves your There can be more than one reason for your amplifier not delivering sufficient volume when playing phono graph records. Some amplifiers are not designed to work with magnetic cartridges. These amplifiers must be used with ceramic cartridges. If you attempt to use a magnetic cartridge with such an amplifier, there will be insufficient volume. Sound quality will be raspy and lacking in bass.

If the amplifier is designed to accept a magnetic cartridge, it is likely that the output from your present cartridge is not as high as is required by your equipment. The instruction book for your amplifier should state the minimum amount from a cartridge which will drive the amplifier to full output.

If the cartridge does not produce enough output, either obtain a cartridge which can produce sufficient output or obtain a preamplifier which contains the necessary gain and equalization for magnetic cartridges. The preamplifier must be connected to one of the high level inputs of your amplifier, and not into the magnetic phono graph inputs of your unit.

Such a preamplifier need not be equipped with the tone controls, selector switches, etc., which are found on complete stereo control centers. The device need do just one thing, boost the tiny voltage supplied by a magnetic cartridge to a sufficient level for use with a high-level input, plus adding the necessary RIAA compensation.

Even if your amplifier was not de signed for use with magnetic cartridges, the preamplifier will make it possible for you to use one satisfactorily.

"Static" in Speakers

Q. When listening to music with lots of high frequencies. I sometimes get a "static" noise coming from my tweeter. As the music becomes louder, the static is louder.

What is this static? What can I do about it?

-Andrew Coffman, Las Vegas, Nevada

A. The "static" you hear from your tweeters could have a number of causes. If its intensity varies, depending on how loudly you play your equipment, it is probable that your tweeter is defective. The cone may have become unglued from the voice coil, resulting in loss of drive during a portion of each cycle, thus causing the noise. It also could be that the voice coil is no longer centered within the magnetic gap. This would mean that it is rubbing against one of the pole-pieces, at least at times.

If you hear this noise during loud music passages, regardless of the setting of your volume control, chances are that the noise is associated with the discs you are playing. Either the phono graph must be checked or else the discs are over-recorded, as is all too often the case.

If you can borrow speakers, do so. Listen to these speakers to find out if the "static" occurs in the same musical passages. If it does not, you will know that something is wrong with your speakers. If the sound occurs in the borrowed speakers, you will know that the problem lies elsewhere.

It could be that the amplifier is being overdriven during loud passages; this can cause some strange sounds.

If this "static" condition is noted primarily on FM broadcasts, the sound may be caused by a misaligned tuner or by multipath distortion.

Interference with AM Receivers

Q. The AM section of my tuner exhibits strange behavior. Except on very strong signals, I get an excruciating “buzz" which seems to get worse when the dial is tuned to a lower frequency.

Sometimes by turning off my television receiver, the “buzz" is reduced. Physically turning the tuner usually helps. I have attached insulated wire for an external antenna, but this makes the `buzz" worse. There is no heavy machinery nor are there any neon lights in the area which would cause this noise.

Can you help me?

-Dennis W. Brandt, Indiana, Pennsylvania

A. I do not think that you can totally eliminate the interference you hear on your AM radio. In all likelihood it is produced by television receivers and it is not a problem within the tuner itself.

Television sets radiate harmonics from their horizontal deflection circuits. These harmonics extend to perhaps 4 mHz.

Harmonics are more intense as frequency decreases, which fact goes along with your observations.

Even though your television receiver is turned off, the television sets of neighbors remain on, and produce the trouble.

You may be able to shield your own set by placing copper screening around the high voltage area, and also by lining the entire cabinet with this screening.

The screening should be grounded to the chassis. The a.c. line of the set should be by passed to prevent the interference from being radiated into the power line.

If by chance, some of the interference is being picked up by way of the power line, you may be able to eliminate some of this problem by using line bypassing to the tuner's chassis. The entire tuner should be grounded to a good earth ground.

Frequency Response of Phonograph Records

Q. In the book DISC RECORDING AND REPRODUCTION by Mr. P. J. Guy. 33 1/3 rpm "fine-groove" records are reported to have a frequency response of 40 Hz to 15 kHz. Is this the maxi mum frequency range for all 330 rpm discs? If so, is this because cartridges cannot track above and below these frequency limits? Is it because of a restriction imposed by the groove width?

-Douglas F. Cook, March A. F. B., Calif.

A. A disc with a frequency response of 40 Hz to 15 kHz is actually unusually good. We generally do not find this wide response. Lows are often rolled off. Because of the heavy modulation impressed on all too many discs these days, highs are often rolled off above perhaps 12 kHz. It is possible to produce discs having a wide frequency response, down to perhaps 30 Hz and above 16 kHz. The highs will gradually be lost, however, as the inner groove diameters are approached during playback. Very little can be done about this loss because of a parameter of the stylus which cuts the disc, and the tip radius of the play back stylus. At the inner-most diameter of the disc, high frequencies are not likely to exceed 10 kHz. Any highs which may be present above this will not be flat.

If one were to attempt to reproduce 16 Hz found on some large pipe organs, very large groove excursions would be required. Hence, a disc side would be reduced in length. If such pedal tones were present for most of the recording, the disc side might be 10 minutes long.

Bass response at really low frequencies will cause some tonearms to skip grooves, especially in the cheaper, home phonographs which are commonly used.

FM Stereo Versus Stereo Record

Q. I have compared recordings played on FM stereo with the same recordings played on my turntable. I notice a loss of highs on the FM/ stereo version when compared to my own recordings. Is this the fault of the tuner portion of my receiver or is this the FM station itself? (When I say "loss of highs," I do not mean a complete loss as there are still some high frequencies in the music on FM.) The overall sound quality of FM is acceptable.

I am using Cable TV for an FM antenna. Could this be part of the problem? Would an FM-only antenna be better? Also, when there are extremely loud passages, I hear a rattling sound, especially in high frequencies, on violins (over-modulation in the recording?)

-Larry K. Cook, Albany, Georgia

A. All too many FM stations do not sound as they could. The FCC requires a flat frequency at the transmitter, but this never takes into account the studio equipment, telephone links between transmitter and studio, etc.

Also, in order for many FM stations to make any money, they often operate completely automatically, with no announcer on duty. This means that virtually everything is recorded on tape, often played at slow speeds to obtain maximum time per reel. All of this adds up to a loss of quality.

Your receiving antenna will not alter the sound quality of the received signal, at least not in terms of loss of highs. A poor antenna can produce multipath distortion.

The distortion you have heard on high level passages could either be a fault in the discs being played, or you are hearing multipath distortion. A directional antenna can reduce this kind of interference.

Noise from an Equalizer?

Q. I have a quadraphonic receiver which does not include tone controls for the rear channels. As my room acoustics are poor, I use my front tone controls to adjust the sound to my liking. After this is done, my rear channels seem weak and masked by the front channels.

To correct my problem, I purchased a five-band equalizer to correct the condition of my rear channels. Since the equalizer was installed, however. I notice more hiss from my rear channels than I heard from the front ones, I am not sure whether the equalizer is at fault or whether the boosted frequencies merely cause hiss to become more dominant. I would appreciate your advice in this matter.

-Larry Titchenal, Belleville, Illinois

A. To determine whether your equalizer produces the hiss or whether it is generated in some portion of your remaining equipment, disconnect the input of the equalizer. Set all controls on the equalizer as usual, with the equalizer turned on. If the hiss is present, turn off the equalizer. Note whether hiss This may take a few seconds if the capacitors in the equalizer maintain a charge for a time. If the hiss disappears, you will know that it is generated within the equalizer. It may be that your volume controls after the equalizer are set too high, causing you to hear more of the inherent noise than you should.

If your equalizer has input level controls, perhaps they should be set to a more advanced position so that you can then back down on the amplifier controls, thereby eliminating the hiss.

Perhaps the equipment driving the equalizer produces the noise. The added treble boost would make that noise more apparent.

Matrix Quad Light

Q. My FM tuner has a "stereo light," indicating the obvious. Matrix 4-channel is being broadcast by some FM stations. I have not seen a matrix decoder, however, or tuner or receiver with a "matrix light." Why not? Such a light would be a great convenience in verifying for the listener that the program being broadcast is in matrix quadraphonic.

Certainly the matrix decoder that am using "knows" when the program material is encoded. Could it latch a light on in this case? How might I hook one up?

-Andrew D. Keller, Wappingers Falls, New York

A. It would be almost impossible to provide a "matrix light" similar to the stereo indicator light found on most receivers. You say that your decoder "knows" when it is decoding matrix quadraphonic as opposed to conventional stereo. Actually, this is not true.

It happens that some discs, though not intentionally recorded to have matrix effects, still possess this characteristic.

The decoder will process them with some rather exciting results. The de coder only "knows" when it is getting difference information with which it can work its "magic." This difference information is important even when reproducing conventional stereo.

The stereo light found on most FM equipment is operated because of the presence of a 19-kHz pilot signal, which the FM stations do not transmit unless they are broadcasting in stereo or matrix quadraphonic, which is exactly the same technical process as far as broad casting it is concerned.

This pilot signal is not present merely to turn a light on in a distant receiving set. It is there to provide a reference for the stereo information, thereby enabling proper decoding to take place. The designers of FM equipment have taken advantage of this situation and have made it perform the extra function of operating a "stereo light."

Evaluating Phonograph Cartridges

Q. Can you explain the relationship between decibel output and frequency response? How does one go about subjectively comparing the frequency response of various phonograph cart ridges when the measurements were given in different ways for each product? As an example, we might have three different cartridges with these specifications: 1. with a 10-10,000 Hz plus or minus 1/2 dB rating; 2. with a 20 20,000 Hz plus or minus 1 dB rating; 3. with a 50-10,000 plus or minus PA dB rating. Is there a way to convert one specification to the others, so that I could know which cartridge is the best one? Will I be able to determine, in other words, which one has the flat test response? Is there some mathematical formula which can be used to convert different "decibel outputs" into "equal out puts"?

-Neil T. Shade, Dugway, Utah

A. You can determine the frequency response of one cartridge by comparing it with that of another cartridge. Suppose we have a cartridge whose frequency response is stated as being plus or minus 1 dB from 20 to 20,000 Hz. This, in itself, is a good specification, at least for a stereophonic cartridge. (It would not be satisfactory for a CD-4 cartridge unless we knew more about its characteristics above 20,000 Hz. We would have to assume that, with no data given for the higher frequencies, this cartridge would fall "short of the mark.") Now take a cartridge which is plus or minus 3 dB between 50 and 10,000 Hz. We can immediately assume that this latter cartridge is not nearly as good as the first one in terms of frequency response. Here we have a cartridge which covers a narrower range of the audio spectrum than the first one and which is less flat than that of the first cartridge. Thinking once again of the first cartridge, somewhere in its response, above and below its specified limits, there is a point at which this cartridge will be plus or minus 3 dB. (More likely this will occur as a minus 3 dB point, but not necessarily.

There could be a peak somewhere, which could mean a rising response.) These frequencies could be minus 3 dB at 15 Hz and plus 3 dB at 25 Hz, and minus 3 dB again at 30 kHz. (I did not arrive at this by any mathematic work, but merely by familiarity with the behavior of some cartridges.) These are arbitrary figures. Here we have a minus 3 dB at 15 Hz and minus 3 dB at 30 kHz. With the second cart ridge we have a response of minus 3 dB at 50 and perhaps minus 3 dB at 10 kHz. Actually, from this data, we can not know about the high frequency response for certain. It could be at 10,000 Hz we are plus 3 dB, and minus 3 dB at 17,000 Hz. We do not know, and cannot know this unless we can actually measure the frequency response of the cartridge. We can, how ever, make good guesses that the first cartridge will out-perform the second one by a wide margin.

Suppose we have one cartridge which is said to have a frequency response of plus or minus 1 dB from 20 Hz to 20,000 Hz. Suppose we have a second cartridge rated as being plus or minus 13 dB from 10 Hz to 30,000 Hz.

It could be that the two cartridges have much the same overall response, but we cannot know this for certain unless measurements are made.

(Audio magazine, Nov. 1974, JOSEPH GIOVANELLI)

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