Audioclinic (Q and A) (Apr. 1972)

Hum in a Turntable

Q. I am having trouble with an excess of hum in my turntable. I am certain that the hum comes from the turntable because it is present only when the turntable motor is on, vanishing when the motor is off. The hum is not present when playing tapes or listening to the tuner.

I checked the ground on my turntable.

The hum is about the same whether the ground is connected or not. I tried grounding the amplifier to things in the room, like the radiator, the a.c. outlet box, etc. This did not help either.

The position of the cartridge relative to the record does influence the hum.

The further in the cartridge is moved toward the center of the record, the louder the hum becomes.

Any advice you can give me would be appreciated.

-Harry Hastings, Pullman, Wash.

A. The fact that the amount of hum varies with the position of the tonearm indicates that the problem is the result of induction from the windings of the motor into the pickup. Either the shielding of the pickup is defective or the shielding in your particular model is insufficient when used with your turntable. If you can obtain some magnetic shielding material, wrap it around the cartridge, leaving room for the stylus and to be sure that the shielding material does not come into contact with the record. I have done this. It did help to some extent. It did not eliminate the problem entirely, however.

I would say that you need to try another cartridge, with the understanding that, if the hum does not cease, you can return the cartridge to your dealer and try a different one. I believe there is no other solution to your problem.

Insufficient Loudspeaker Output

Q. I recently purchased two rather inexpensive outdoor speakers for use in my music system. They are identified as Wald Sound T-3 Tune Toater.

I am using them in conjunction with a Fisher 500TX stereo Receiver. The speakers are located approximately 40 to 50 feet from the amplifier. They are equipped with self-contained volume controls.

My problem is that the volume I get from these speakers is virtually nothing compared to the volume I get from the indoor speakers at the same amplifier volume control setting. Can you shed some light on what my problem might be?

-Thomas A. Mantini, Havertown, Pa.

A. As I have no data about your outdoor speakers, I cannot discuss them with certain knowledge. If you have literature which was supplied with them, check it to see if perhaps their impedance is something like 500 ohms or perhaps designated as "70 volts." If this is true, you must remove the matching transformers which are inside the speakers. Further, you must then hope that the basic impedance of the speakers is at least 8 ohms so that they will not load down the amplifier when used in conjunction with the main speakers in your listening room.

Assuming that the speakers are of the correct impedance, I suggest that you use No. 16 gauge zip cord as the interconnecting cable between them and your amplifier. That will keep down losses to an absolute minimum.

You indicated that you have a distance of 40 to 50 feet between amplifier and speakers. Sometimes this distance is longer as regards the amount of interconnecting line required. You know what happens. The line must go around moldings and follow baseboards. That can add quite a few feet. Therefore, if it happens that you have 50 to 60 feet of actual interconnecting line, use No. 14 gauge zip cord.

You should check to see whether there are other terminals on the rear of the-speaker. Some speakers provide for various arrangements of jumpers which must be connected or disconnected depending on whether you are going to use internal volume controls, etc.

I am not sure just how loud your outdoor speakers do play. More volume will be required when speakers are located outdoors than would be true when they are located indoors. Furthermore, if these speakers are inefficient, and if the indoor speakers are efficient, the indoor speakers will definitely sound louder than the outdoor speakers, even when nothing is wrong with them.

(Audio magazine, Apr. 1972, Joseph Giovanelli)

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