Audioclinic (Nov. 1984)

Tuner Antenna Connections and Pilot Lamp

Q. My tuner is connected to a 75 ohm outdoor FM antenna via a balun transformer attached to the tuner's 300-ohm input. Recently, while reconnecting the tuner to the cable, I accidentally connected it to the 75-ohm input. When I turned the unit on, the dial light flashed on and, a moment later, off. The light has not worked since. The tuner itself works perfectly.

What made this happen? Is it likely that any other damage has been done? And would I get better performance if I took the balun out of the circuit and connected the cable directly to the 75-ohm input terminals?

-Patrick J. Callery; Massapequa Park, N.Y.

A. You will be glad to learn that the lamp's burning out and the accidental connection of your cable directly to the tuner were coincidental events. Replace the lamp and all should be fine.

The balun serves as an impedance matching device when placed between the 300-ohm input and the 75 ohm transmission line. It also creates the balanced condition needed by the tuner's 300-ohm input and the unbalanced arrangement required by the transmission line. However, considering that you have a 75-ohm input, you should connect the transmission line directly to this input. It is unbalanced and of the proper impedance for matching the transmission line. Eliminating the balun removes a device which introduces a small amount of signal loss. As long as your tuner can live without it, don't use the balun.

Disc Stabilizers and Turntable Speed

Q. I have used a disc stabilizer for some time. When I do so, I see that the platter drops about 1/16 of an inch. I am concerned this drop can harm my direct-drive motor. Do you think the disc stabilizer is too heavy? (It weighs about 600 g.) When the stabilizer is used, will it change the speed of the turntable?

-C. K. Chan; Long Island City, N. Y.

A. On direct-drive turntables, the platter and the motor are one unit; so if the platter sinks, the motor is sinking with it. If you check your turntable carefully, you'll probably find that the extra weight is either making the entire base sink on its suspension or making the motor and platter assembly sink slightly on its shock mounts. There should be no immediate harm, as long as no rotating parts are made to rub against the base and the arm and turntable remain rigidly coupled so that their relative positions do not change.

In the very long run, there might possibly be extra wear on the motor bearings; check with the manufacturer of the turntable on that.

On other types of turntables, additional problems could occur if the weight made the platter sink or tilt relative to the motor; bearing wear would affect platter motion, but not the motor.

The stabilizer should not affect turntable speed. Its added mass may make the turntable take somewhat longer to come up to proper speed.

But once it is running at speed, no adverse effects should be noticed.

Tonearm Wiring

Q. My question relates to phonograph wiring: Why is there a separate left-channel ground and a right-channel ground? Would not one common ground suffice? Electrically, it is all the same at the phono inputs. Additionally, one less wire in the tonearm would be beneficial from a mass/pivot-friction standpoint.

-Nicholas A. Sisco, Jr.; Columbus, Ohio

A. You are correct about tonearm wiring regarding the reduction of mass and drag, but the grounding situation is something else again. If a common ground is used for both channels, there is a risk of hum resulting from a ground loop. By using two separate grounds, it is possible to keep electrical grounding as close to its corresponding input as is practical, eliminating this ground-loop problem.

Eliminating Static from Phonographs

One problem which has been brought up again and again with turntables is static electricity. It is an inevitable, but unwanted, byproduct of cleaning and playing your phonograph records.

Since I purchased the Discwasher Zerostat, I have eliminated this problem to a certain extent. But, there always seemed to be a static charge remaining on the record and the turntable mat. In the end I still had a statically charged record and a statically charged mat-both of which draw dust, further complicating things.

I was particularly interested in removing static electricity from the turntable mat without having to purchase an additional mat. After I "sprayed" the stationary disc (about 12 inches above its center), I would touch the center tip of the Zerostat to the center spindle and slowly squeeze the trigger. This effectively removed any static electricity from the turntable mat.

Since a static charge could enter the ground system and damage the phonograph preamp, amp and possibly the loudspeaker systems, you should turn the volume down and set the program selector to a position other than phono before using the Zerostat.

In summary, by using a Zerostat gun on both the record and the turntable platter, static electricity can be effectively controlled.

-Fred Botway, North Merrick, N.Y.

Noise Generators and RTAs

Q. What's the purpose of a real-time spectrum analyzer and a pink-noise generator in an equalizer?

-Elmer F. Maye, Jr.; Coram, N.Y.

A. The spectrum analyzer and pink noise generator help determine the frequency response of a sound system (including the room's acoustics), while the equalizer is used to correct any deficiencies thus discovered.

In use, the pink-noise generator provides a signal having equal energy in every octave of the sound spectrum.

The real-time analyzer shows the system's output level in each of several (usually 10) frequency bands, so you can tell in which bands the signal should be boosted and in which it should be cut to obtain flat response.

Phonograph Hum

Q. Two or three times a week I hear a low-frequency hum produced by some disorder in my turntable. When it occurs, it is accompanied by the loss of one channel. I can cure the problem by tapping on my phono cartridge, but I am afraid of damaging the cartridge. Is there a wiring problem?

-Bill Bales; Roanoke, Va.

A. There are several possible causes for your problem. The most likely is that one of the slide lugs which fit over the terminals of your cartridge is loose and intermittently fails to make good electrical contact. It is probably a ground connection. (When a "hot" lead is intermittent, it does not tend to produce hum.) Remove the slide terminal, gently squeeze it with pliers, and then replace it. If you have not squeezed the lug too much, it will now fit snugly over the terminal and the hum should disappear.

A similar problem involving the cartridge terminals can occur if the electrical connection from the coil to the terminal within the cartridge is not properly attached. This problem cannot be fixed; you will need to replace your cartridge or have it repaired by the manufacturer.

Intermittent contact can also occur where the shell's contacts mate with those within the tonearm. A little squirt of contact cleaner on these terminals will generally cure problems that result from oxidation but not those caused by weak spring tension. If the springs are a part of the shell, all that is needed is a new shell. If, however, these contacts are within the tonearm, then the arm must be repaired by its manufacturer.

The final possibility is less likely, but I am including it for the sake of completeness. Check all of the connections on the cables which connect your turntable to the rest of the sound system. Sometimes the plugs' skirts will widen with repeated insertions and withdrawals. Squeeze them gently and reinsert them into their sockets. All should then be well. There is also the chance of a cable defect, usually found at the connector. Although rarer, it can happen that the "hot" connector inside the equipment has enlarged, resulting in an intermittent connection.

The equipment must be opened, the connector on the offending socket squeezed a bit, and the plug reattached.

Direct to Digital Disc

Q. Is it necessary to make a digital tape of a performance before producing a Compact Disc? Or can we expect a few "direct-to-digital discs"?

-Karl E. Landgren; Smithfield, N.C.

A. I doubt that any direct-to-digital disc recordings will be produced. The equipment needed to make a CD recording is not portable. It requires a special, "clean-room" environment, where positive air pressure keeps dust from being deposited onto the surface of the master.

Further, digitally made tapes should be virtually identical in audio quality to CDs. This takes away any advantage that direct-to-digital disc recording would otherwise have had.

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

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