AUDIOCLINIC (Jul. 1991)

Insufficient Phono Output

Q. The output from my phono cartridge is low compared to that of other program sources in my system. The rated output of my cartridge is 0.25 mV. Even with the extra gain provided by the low moving-coil input on my preamplifier, the output from the speakers is still too low.

During some soft musical passages, the volume needs to be turned up to a point where I hear noticeable hiss.

What can be done?-Name withheld A. When you say your cartridge's level is too low, do you simply mean you need to turn the volume up when listening to records? Or do you mean you cannot get enough volume even when you turn your control up all the way? If you can get satisfactory listening levels from the system, it could be that you are served well enough despite the nuisance of having to readjust the level control when changing sources. Just remember to turn the volume up a notch or so when playing phonograph records, and then to turn it down again before switching to other program sources. In any event, a good habit to get into is to turn the volume down completely while switching from one input to another. You'll never "blast" your system or damage your speakers or amplifier by following this rule. This is true even if and when you do match phono level with that of other music sources.

The hiss you hear when you turn the volume up to listen to soft passages might perhaps be on the LPs themselves. When this is the case, the hiss will remain as a constant background--even when you have adjusted the phonograph output to match that of other program sources.

If the background noise you hear in soft passages is electronics noise generated within the preamplifier, you should use a transformer between the phonograph and the preamplifier inputs. The transformer will boost the voltage sufficiently to overcome the background noise. Manufacturers of moving-coil cartridges usually offer transformers designed for use with their units.

There are some "preamplifiers" which are designed to boost the output voltage from a moving-coil cartridge in exactly the same way that the transformer does. Such units serve no other function.

Although using such transformers or preamplifiers will increase the loudness of your phonograph playback, this does not guarantee that phono output will match all other sources.

Keep in mind that some phonograph records are "louder" than others, and the output from some CD players tends to be higher than other input sources.

Recording levels can vary from one CD to the next and from one cassette to the next.

I can recall one correspondent who was sufficiently bothered by this problem that he incorporated a limiter into his system. Every source sounded as loud as any other. Soft musical passages were as loud as loud ones. He was happy! I heard a sample of this "beautifully balanced" system; I was definitely unhappy.

No Bass Punch

Q. My problem: The sound from my system is bland, lifeless-very little stereo separation and very little bass.

When I use headphones, everything seems to jump out and sound great.

My loudspeakers are located about 5 feet apart on either side of my entertainment center-about a foot away from the back wall and about 3 feet from the side walls. There is a rug on the floor. It's a long room, about 12 x 20 feet. My equipment consists of a preamplifier, surround decoder, power amplifier, and four speakers-two mains and two for the surround effect.

What's wrong with my system?

-John B. Smyth, Clinton, Md.

A. If you like the sound from your headphones, it could be that you just don't like your loudspeakers. I say this because your system is the same in all respects when you listen through headphones and when you listen via your loudspeakers.

Before making any impulsive moves, however, first check to determine if the phase between your two main loudspeakers is correct; if it is not, the sound may well be lifeless and lack bass. Before making this check, kill the surround speakers so that all you hear are the main units. Once you have gotten the phase correct, there should be an improvement. If you do have such an improvement, turn on the surround speakers. If the audio quality again deteriorates, maybe your surround speakers are set at too high a volume.

The 5-foot separation between your speakers is a bit small. Move them apart till each one is against both the side and back walls. The increased physical separation should increase the amount of stereo. The corner location should add considerable bass.

This may solve your problems.

I hasten to point out, however, that, in most instances, stereo stands out more when listening with headphones than it does when listening via loudspeakers. The problem is that headphone listening tends to exaggerate the stereo effect beyond what is heard in the real world.

Unusual Phonograph Hum

Q. i have an annoying phono hum which has me perplexed. The hum is present only when in the phono mode; it is low in level and only occurs in the right channel. The ground wire from the turntable is correctly connected to the phono ground on the rear panel of the amplifier. I have noticed that, when I disconnect the ground wire, the hum disappears completely. What could be causing this hum, and why does it go away when the ground wire is disconnected?

-Richard Dunn, Hampton, Va.

A. I have no idea why the hum is heard in only one channel. It certainly suggests poor connections to the ground side of the cartridge's right channel or to the grounds where the tonearm and the main phono cables meet. It could also indicate a loose skirt on the phono plug.

Why the hum disappears when the ground wire is removed is another matter. My best guess is that your turntable has a three-prong NEMA plug attached to its power cord. If so, the turntable will automatically be grounded to the system via the ground pin on the plug (assuming that your amp also has an NEMA plug). Adding the ground wire would produce a ground loop, causing the hum. The cure is to remove the ground wire.

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(Source: Audio magazine, Jul. 1991, JOSEPH GIOVANELLI)

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