AUDIOCLINIC (Q and A) (Feb. 1975)

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Mixing Tube/SolidState Equipment

Q. I know that one can do almost anything with a high-fidelity system-but is it wise to mix tube and solid state components in such a system?

-Name withheld.

A. There is nothing wrong with mixing tube and solid-state gear. One thing to watch out for with transistor amplifiers is to be sure that the speaker (output) terminals have one side returned to chassis ground, to which all input signal grounds are made (some solid-state amplifiers have "floating" outputs).

The input impedance of solid-state equipment is usually much lower than that of tube equipment. And the output impedance of tube tuners and preamplifiers is generally so much higher than the input impedance of transistor units that the signal output from the tube unit is inadequate to drive the transistor component. However, there's generally little problem driving tube amplifiers from transistor units.

Bi- and Tri-Amplification

Q. I am seriously considering the purchase of an electronic crossover system so I can bi-amp or tri-amp my speakers. Must my power amplifiers all have the same power output, or can I use smaller amps for the tweeters and mid-range than for the woofers? Can I get as good sound using standard loudspeakers with one heavy-duty power amplifier (only) for each channel?

-Name Withheld.

A. The bass frequencies account for the greatest proportion of acoustic energy in a music system. Therefore your most powerful amplifiers should drive the woofers, the next largest amplifiers connect to the midrange (if you're tri-amping), and the tweeters can be driven with the smallest amplifiers.

There are a number of different input-output phase relationships possible between the three (or two) control centers (preamps), the crossovers, and the power amplifiers in each channel. This means that speaker phasing must be worked out by careful, aural testing, not just by the normal connection of the high (+ or 8 ohm) speaker terminals to the high amplifier output terminals, and the common (or ground) terminals to the commons. Listening tests may even dictate reversing some of the connections.

Because an electronic crossover divides the signals into two (or three) frequency bands before they're fed to the power amplifiers, the amount of intermodulation distortion will be reduced. This will improve the sound. In addition, some high level (conventional) crossovers, such as are found in most normal speaker systems, tend to ring at or near the crossover frequencies. This is distortion also, and is obviously undesirable.

Properly designed electronic crossovers do not ring. Just how much improvement can be gained from bi- or tri-amplifying (using two, or three power amplifiers from each channel, plus the electronic crossovers) depends on how much IM and ringing is in your present system before you upgrade it in this way. Sometimes the improvement can be quite dramatic.

15 Degree Tracking Angle

Q. I know that a phono cartridge must track at a 15 degree angle. I am not sure that mine is doing so. Is there a way that I can check this parameter?

-Ronald L. Ambrogi, Brooklyn, N.Y.

A. If a cartridge is properly installed in its tonearm, it is almost always automatically tracking at the proper angle, as this is generally a function of the stylus and how the jewel is set into the shank. Be sure that the cartridge is mounted correctly.

Check the instructions which are included with both the cartridge and with your tonearm. Follow them carefully, and that should be all you need to do.

(Source: Audio magazine, Feb. 1975, JOSEPH GIOVANELLI)

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