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AM Buff No. 1 … Dear Sir: How do you express demand for tuners with good AM performance? I have been looking for one ever since the days of E. H. (not H. H.) Scott. I agree with Mr. Herbert's letter in your July, 1972 issue. Most people today don't know how good AM can be and those who do can do nothing about it because no manufacturer now builds a quality AM tuner. -R. N. Servaas; Grand Rapids, Mich. AM is not, as commonly supposed, inherently inferior to FM in terms of bandwidth or distortion. In Australia, where there is no FM, wide-band, low distortion tuners are used extensively. However, AM is subject to electrical interference, and there is not much room in the present AM broadcast band. (AM on VHF? Well, that would be a different story!) Signals on the broadcast band travel great distances particularly after dark so the tuner bandwidth would have to be restricted to avoid interference effects from stations on adjacent channels. In England, before the FM network was established, top-quality AM tuners had to have 9 kHz whistle filters or variable-bandwidth controls and the net result was often pretty poor. And how about stereo. It can be transmitted on AM but.... Having said all that, it must be conceded that many AM/FM tuners have low sensitivity AM sections. For instance, I like to listen to the news from Canadian AM stations, but I get better reception from my car radio than I can from quite expensive tuners! -ED. And No. 2 Dear Sir: I read David P. Herbert's letter (July, 1972) with great interest. It would indeed be nice to see quality AM tuners with quality specs, features, and component parts. Mr. Herbert has done audio science a great service with his letter. The only problem is that his comments will most probably be ignored! Let's hope not. Besides the four items Mr. Herbert recommends, I'd like to see the following:
-Joe Frandeka; St. Louis, Mo. Distorted Rock Recordings Dear Sir: In doing a bit of review work, I just noted a tape recording problem described in Herman Burstein's March, 1970 Tape Guide section of AUDIO. I have just finished fighting the same problem in a PA system and my experience might be helpful to many tape recording situations. The problem described by Ben Miller is excessive distortion in live tape recordings of rock groups. Burstein correctly listed the three possible causes: 1) Too high recording level at the tape, 2) poorly designed first stage of the tape recorder, and 3) overloaded microphone. I would emphasize reason #2 rather than the other two. The problem is created by the high sound level of rock music performances and is similar to the PA system problem when the entertainer or lecturer "eats the microphone." A good dynamic microphone can put out (at the secondary of the transformer) about a volt (that's right, a whole volt) under these conditions. Usually, this is applied to the input of a transistorized stage directly and the output of this stage fed to the level control. For normal levels, this is the best arrangement because the level control cuts out pre-amp noise when the level control is at a low setting. But, when the microphone signal hits a volt, the distortion is gross and no tinkering with the level controls will make the least bit of difference. This explains why Miller's recordings from a large barn-like auditorium had less distortion. The sound intensity was less because the same acoustic power radiated by the rock performers had to fill a larger volume and supply the losses at a much larger surface area. This meant the microphone output was lower and overloaded the input stage by less. What is the cure? Probably the simplest is to wire up a 20 dB attenuator with cable connectors which match the microphone connectors being used. This 20 dB pad is placed between mike and tape recorder input for loud level situations. There will still be plenty of signal going into the tape recorder to achieve good signal to noise ratio. Most of the newer machines which have only one level adjustment afford a simple way to achieve this end. The "auxiliary" input, meant for levels of a volt or so (from pre-amps, tuners, etc.), is actually an attenuator which goes between this input and the microphone amplifier stage. Thus, by plugging the microphone into the AUX input instead of its normal input, the chances of overload are greatly reduced. -Prof. J. Robert Ashley; University of Colorado, Colorado Springs, Colo. Construction Suggestion Dear Sir: Being a devoted listener to orchestra and classical church music, I like to work on improvements and extensions of my stereo system. Thus, I would like to see articles on construction projects which would improve an already good sound system or basic building blocks to up-grade or build a system. My personal need is an 18 dB per octave crossover at 300 to 500 Hz and also at 3000 to 8000 Hz to be used with Altec Lansing or University high frequency horn and a Klipsch type low frequency horn. This is simply a suggestion, though I can well imagine that many hobbyists have a similar requirement. -F. Machmuller; Kalthof, Germany Miklos Rozsa Society Dear Sir: There has been increased interest of late in the music of Dr. Miklos Rozsa, both the music he has written for films and that he has written for the concert hall. Inasmuch as some of us feel that his music is unjustly neglected, we have founded, in his name, the Miklos Rozsa Society, the main purposes of which are to promote his music and to disseminate news and information about it to music lovers. Those interested in such a society may write: J. F. Fitzpatrick, 2604 Davidson Ave., Bronx, N.Y. 10468. If you would print this notice in your letters column, we would be most appreciative. -Mark Koldys; Dearborn, Mich. (Source: Audio magazine.) = = = = |
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