AUDIOCLINIC (Nov. 1988)

Tube Receiver with Solid-State Equipment

Q. I recently acquired an old tube type H. H. Scott receiver. The AM section works quite well, outperforming my newer tuner's AM section. If I wanted to use only the tuner section of this receiver with my stereo system, could I hook it up to my integrated amp without causing any problems?

-Gary Semnoski, Southington, Conn.

A. You can connect the Scott receiver to your present gear by using the tape outputs on the Scott to drive one of your amp's high-level inputs. If the receiver is monophonic, use a Y connector between the tape-out jacks and the high-level stereo inputs on your integrated amp.

The amount of signal produced by tube equipment is higher than is usual for all 'solid-state gear except for some CD players. This means you must turn down the volume before switching to this program source. It is possible that the tube equipment's signal will be sufficient to overload the circuitry ahead of the integrated amplifier's control volume. If this happens, place an attenuator between the Scott and the inputs of your equipment. (These attenuators are available because of overload problems with CD players.)

Speaker Fuse Size and Amplifier Power

Q. I have a receiver capable of 50 watts per channel, and my speakers are rated at 6 ohms impedance. I notice that the back of my amp has speaker fuses rated at 5A/250 V. Does this mean that only 5 amperes of power flow through my speakers, even though my amplifier can produce 50 watts? Will this be enough power to permit my speakers to reproduce very low frequencies, even though the impedance of my speakers dips well below 6 ohms?

-Gary C. Powell, East Orange, N.J.

A. Because power is measured in watts and not amperes, the 5-amp fuses will work well. If 5 amperes were fed into your loudspeaker, it would mean that (at 6 ohms) about 180 watts of power would be supplied.

If your system provides you with sufficient volume and bass, there is no need to make changes. The fact that the impedance of your loudspeakers falls at low frequencies will not come into play. If you have enough overall volume but lack bass at really low frequencies, you may be able to improve this somewhat by adding an equalizer-which is much less expensive than replacing your amp.

Wow and Flutter With Digital Recordings

Q. I have read various equipment reviews of CD players and, recently, of a few DAT recorders. I would like to know why wow and flutter specifications are not listed for these devices but are listed for turntables and cassette recorders. Is it possible that CD players and DAT recorders have no wow and flutter?

-Wesley S. Mayeda, Oxnard, Cal.

A. Yes! It is true that CD players and DAT recorders don't have wow and flutter. Because of the digital format, slight speed variations of their mechanisms are not reflected as the small changes in musical pitch which we call wow or flutter. Even severe speed variations will not result in such pitch changes. Rather, these fluctuations will cause dropouts or other sounds that are not program related.

The reasons for this are difficult to explain. Remember that analog systems are very direct. The pitch of the music relates directly to the lengths of the magnetic fields impressed on tape or the lengths of successive LP groove undulations. A wave's frequency depends on the length and velocity at which it passes the playback head or the stylus. You can see that speed variations must change the wave's frequency, which the ear perceives as a change in pitch.

With digital recording, wave information is not directly set down on the tape or disc; only a string of numbers is stored. When a sufficiently large group of these numbers has been "studied," the nature of the waves can be reconstructed. Speed variations will increase or decrease the quantity of numbers being detected. To oversimplify, there is a clock in the CD player or DAT recorder which must be in step with the material being reproduced.

Each number is presented for a given amount of t me (a matter of microseconds). Slight speed variations will still permit the clock to receive the pulses and recognize them. If the speed change is too great, however, the clock may get ahead of (or fall behind) the stream of numbers. This can cause errors, but they will not be heard as wow and flutter.

Loose Speaker Mounting Screws

Q. Can acoustic suspension speakers be harmed by occasional, but not extreme, tightening of all the driver mounting screws? I serve as a DJ at dances and notice that, after long periods of loud bass, the mounting screws seem unusually loose, so I tighten them cautiously. Will this cause trouble?

-Alan Harper, Seattle, Wash.

A. There is no harm in tightening speaker mounting screws. If they are coming loose, and you permit them to do so, eventually the drivers will separate from their mounts and perhaps be damaged when they fall.

Be sure that you tighten these screws evenly, however. Do not tighten one fully and then go on to the next.

Rather, tighten each screw a bit, working your way around until you have tightened all of them securely.

I do wonder why the screws are loosening in the first place. Have any of the drivers been replaced, and were lock washers lost in the process? If the drivers are mounted with nuts and bolts, lock washers are important. If the screws are wood screws, perhaps the holes into which they fit are stripped. Fill the holes with plastic wood and re-drill them when the plastic wood has set.

Setting Component Levels

Q. I recently purchased a component system for my car, consisting of a tuner/cassette deck, an equalizer, and a power amplifier. The system sounds great! I am not sure, however, that I am getting the best sound possible from it, because each piece of equipment has its own level controls. The tuner/cassette deck has output adjustments, the equalizer has both input and output level controls, and the power amplifier has input level controls.

My problem is that I do not know how to set these levels for optimum performance, and the owner's manuals do not provide explicit directions.

Please give me an accurate way to set the level controls. How important is it for these controls to be set correctly?

-Kevin Miller, Lenoir, N.C.

A. I do not have an absolute answer to your question, though I don't believe that these settings are critical. If the controls you mention are not properly set, you may have some background noise even with no signal present, or you may experience distortion even when the power amplifier is not driven to anything like maximum power. On the other hand, you might discover that all of the controls can be set wide open with no problems. What could happen, in that event (even if the sound is clean), is that the actual volume control might be touchy; turning it up to perhaps one-third of its full rotation could produce more volume than you want.

If your volume control works properly, if you don't hear background noise in the absence of a signal, and if you can drive your system to as loud a listening level as needed, you probably can leave well enough alone.

If faced with your problem, I would start out this way: I would turn down the input level control on the equalizer to a point where I could no longer produce enough volume from the speakers. I would turn up the cassette system until it became distorted. (Of course, that might not even happen.) Then I would back its volume control down to a point where the sound once again was clean, and then back it down just a bit more so that "super hot" program material would not cause distortion.

I would next turn up the equalizer's input level control until I once again had as much sound as I could stand.

Then I'd turn down the equalizer's output level control so that I could not obtain enough volume from the speakers (as with the input control). I would next turn up the input control on the equalizer (with the equalization settings I found useful), listen for distortion, and then back the input down until that distortion cleared up.

Next, I would do the same with the equalizer's output controls. I would turn down the amplifier control until the sound level was too low, and then I'd advance the equalizer until I heard distortion. (You might never hear any; this will surely be true if the output volume control is located right at the output terminals and if the level controls on the power amplifier are located right at the input.) If you do, continue as above.

If no distortion were heard, then I would back the equalizer's output volume down somewhat, perhaps to a bit more than half open, and advance the level controls on the power amplifier until I had enough volume, without overdriving the power amplifier.

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(Audio magazine, Nov. 1988, JOSEPH GIOVANELLI)

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