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I recently bought a Kenwood KR-7400 receiver (rated at 63 watts per channel into an 8-ohm load) to which I want to attach my present Pioneer CS-22 speakers and another larger pair to be obtained later. When the new pair is added the Pioneers will be used as remotes in another room. But I'm worried that the Pioneers, rated for 12 watts' maximum input, will be damaged by the Kenwood. Can they be protected? -Tim Brooks, New York. Your concern is well founded: remote speakers may be fed large amounts of power when no one is present to hear their distress. We suggest that you proceed as follows: Wire in series with each of the Pioneer speakers a wire-wound control (50 to 100 ohms with 10-watt power dissipation capability will suffice) and set the controls for a minimum sound level from these units. Next attach the main speakers to the receiver (for the safety of the receiver these should have 8-ohm or higher impedance) and advance the volume to about the maximum level you ever expect to use with the main speakers. Then return to the Pioneer units and advance the controls you have added until the sound is reasonably loud without driving these speakers into any noticeable distortion. Finally, conceal these controls so that they are safe from tampering. It is true that under these conditions the Pioneer speakers do not benefit from amplifier damping, 'but they are well protected again-t burnout. Is it possible to connect a small oscilloscope to a Sony 6055 receiver? Who sells simple, inexpensive scopes? -Art Faner, Salem, Ore. You do not indicate what functions of your receiver you wish to monitor, but yes-since the loading presented by an oscilloscope in put is negligible in comparison with the usual impedance at any audio input or output--it is possible to connect one for analysis of the audio signals. Candidates for the job would include the Pioneer SD-1100, the Heathkit AD 1013 or 10-102, or the Technics (Panasonic) Model SH-3433-or for that matter any service-grade scope of reasonable quality. But be cautious in applying a scope to any internal circuitry on other than a temporary basis unless you are sure what you are doing. And since the Sony has no scope outputs from the tuner circuitry, you would have to resort to internal connection if you want to use the scope as a tuning aid. In your recent review of the Pioneer CT F6161 cassette deck, you stated that: "measured IM runs much higher-and is much more difficult to hear-in tape equipment than in electronics." Why is 7% IM distortion any more acceptable in this deck than it would be in an amp or preamp? -Richard Schram, San Francisco, Calif. We can't really explain it. and neither, as far as we know, can anyone else. We were quoting empirical psychoacoustic fact, deter mined largely from listening tests, that the ear is far more tolerant of some types of non linear (distortion-producing) response in tape equipment-as well as phono cartridges, loudspeakers, and microphones- than in electronics. I own two amplifiers--the Kenwood 8006 and the Harman-Kardon Citation 12-and a pair of Bose 901 speakers. I have been running the 901s from the Kenwood amp, but lately I have felt a need for more power. Could the outputs of each amp be coupled so that I would get greater power from each amp in mono, and then connect each amp to a single speaker?-Jeffrey Klein, Livingston, N.J. While it is possible that a knowledgeable per son with an engineering background could devise a hookup such as that you suggest, the attempt may easily result in destruction of the output transistors. Furthermore, since the procedure would have to be applied to the two amps separately, you would wind up at best with two unmatched amps-a poor choice for a stereo pair. Your best bet is a new amplifier capable of delivering the power you want. I was amused by the item on phase shift in loudspeakers in your November issue ["News and Views"], but I remain unconvinced that the phase response of a loud speaker makes any difference to the listener. Assume a system that is phase coherent throughout. Place it in a listening room (where sound is reflected from walls, furniture, etc.), and where is the phase coherency now? Gone, of course. The only way that a signal with zero phase shift could be presented to the ear is through headphones, and even there reflections from the boundaries of the ear cavities, canals, etc., would create phase shift before the signal ever reaches the eardrum. It seems to me that Bang & Olufsen et al. are wasting a lot of time and effort, but please prove me wrong--if you can. -Howard Bandell, Nashua, N.H. Music is a series of transients, not a steady state phenomenon, so this argument just doesn't apply. Since the ear receives the direct sound from the speaker before any reflection, the phase response of the speaker can easily affect the waveform presented to the ear at the onset of a transient. Whether this is of any psychoacoustic importance or not is (as we indicated) currently a matter of debate. As to the phase response of the ear itself, a case can be made that, since the interpretation of live sounds is accomplished by the brain on the basis of experience, the brain in some sense "knows" what the ear does to phase relationships and adjusts accordingly. Presumably you know what the sound of, say, a xylophone is to you. Some manufacturers, like B&O, are concerned that poor phase response in the reproduction chain may make this--and other transients--less easy to recognize, especially in a complex sonic context. I have a Sansui Model 7 receiver and a Wollensak 8075 cartridge recorder. When I record 8 track tapes there is an audible click at each track change. I would like to install a dual volume control between the amplifier output and the recorder input, to fade the program during clicks. What sort do you recommend? -Forest Butler, Chicago, Ill. Since the clicks arise in the recorder and not in the source program material, the fader system you propose will not eliminate them. And even if you could eliminate all electrical clicks at track changes you'd still have to put up with the mechanical ones made by the head-repositioning system of the Wollensak-or any other 8-track deck we've worked with. Is my Realistic cassette deck, Model STC-7 with Auto-Reverse, the same machine as the Toshiba PT-490, which was evaluated by HIGH FIDELITY in the January 1975 issue? I bought my Realistic deck on sale for $199.95 and wonder if I got a bargain. The Toshiba lists for $349.95. -Charles M. Hudson, Columbia, Mo. Although we have not tested this for our selves, a Radio Shack spokesman informs us that the two machines are substantially the same. He does not rule out, however, "minor differences in manufacture." These differences, such as they may be, could conceivably account for some of the difference in price. I recently bought a BIC 960 turntable with a Stanton 681EEE cartridge, and I am having some problems with the tracking. With the antiskating force and tracking force set at 2, the stylus skates over the first few grooves rather than tracking them as it should. Can anything be done to correct this? Also, the people where I bought the turntable suggest I remove the record-cleaning brush from the Stanton "since it causes undue record wear and static." Are they right? -Michael White, Petaluma, Calif. We assume that you are using the brush on the Stanton and that, therefore, 1 gram of your VTF setting is counterbalancing for the brush while the other gram is the actual net VTF, which would be correct for this cartridge. But the antiskating should be set for the net VTF (1 gram)-which, when you're using a cartridge with the record-cleaning brush, is not the same as the VTF setting on the arm. Also check the arm setdown point on the BIC. As page 12 of your owner's manual points out, the stylus should not land on the outer bead-thereby propelling the pickup down its slope with enough momentum to skate over the first few grooves-but just inside it. (The adjustment knob is just in front of the arm pivot.) Friction between the brush and the disc probably does increase static charge somewhat, but the brush does an effective job of removing any dust attracted by the static, so the point is moot. We can see no way the brush could cause "un due wear" unless you allow it to become contaminated with gritty dirt. ------ (High Fidelity, Feb. 1976) Also see: Behind the Scenes: Treemonisha ... Kalish and Jacobs ... Bishop-Kovacevich |