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If asked, most audio buffs will cite loudspeakers as the weakest link in the audio reproduction chain. This simply is not true in any sense. The main or primary (literally) deterrent to our reproduction quality is the source.. .records and tapes, with records being the main offender.
In response, the hardware manufacturers have recently designed and marketed a host of noise reduction components for both records and tapes, which is one of my reasons for writing this letter. In the interest of most of us who either own or are purchasing equipment which exceeds the current and potential quality of records and tapes, an article surveying this noise reduction hardware would be a welcome service. Such an article might include a list of the manufacturers, their addresses, a breakdown of which equipment is designed for discs and which for tape, which handles both, and an insight into how each system operates.
I realize that Audio magazine caters to the hardware industry but, as must be obvious, an improvement in software would certainly enhance the enjoyment of the hardware components and their sales.
With this in mind, editorials, articles, polls, and similar devices may serve to arouse reader interest and action, thus suggesting appropriate action by the record and tape manufacturers.
In regards to your January, 1977, "Behind the Scenes" article concerning record quality...I feel that may be able to help in a small way.
The column questions, and justifiably so, the continued use of the "shrink wrap" format in the retail sale of record albums. Bert Whyte pointed out that the shrink-wrap affords the purchaser, more often than not, a factory fresh copy of the recording, which is what the majority of the buying public wishes. However, Mr. Whyte also points out that it is the shrink-wrap which is responsible for record warps capable of inducing seasickness. To quote from the text: "What we need, then, is some new kind of seal that will guarantee the record is virgin, but will not cause warpage." There in Victoria, British Columbia, it is possible to purchase, in some stores, record albums with a clear plastic shrink-wrap which has been cut and sealed approximately 0.5 cm (0.20 -in.) larger than the record jacket. This, naturally, solves both problems as the consumer can purchase a virgin, sealed record, and since the plastic wrap is rather loose fitting, the warp inducing pressure on both the record and the jacket is eliminated.
While this does not totally eliminate warping, it does significantly reduce the possibility of buying an album which is totally unplayable. The albums are from EMI, British imports, in both classical and rock titles. I am unable to inform you whether this "not so -shrink-wrap" is placed on album covers in Britain and Canada both, but, perhaps, you could find out who is responsible for this simple, yet excellent idea.
I can only hope that this particular solution to the problem of record warpage catches on with North America's EMI subsidiary, Capital Records, and indeed with all other record companies too. I think the added cost would be minimal and more than be recovered in the savings on returned defective records, plus it would be a public relations bonanza for the companies...fewer dissatisfied customers.
I need your help, or rather a number of Audio readers need your help.
As with automobiles, people fall in love with vintage magnetic recorders such as: Magnecord, Concertone, Ampex, Stancil-Hoffman, Tapesonic, Webcor, Pentron, Brush, etc.
Hence, with fair regularity I get letters from readers who would like to restore an old "deck" to operation. In the case of automobiles, there are devotees who can breathe life back into any model. I, and your readers, are wondering if similar specialists exist in the audio field. I have spoken to some of my colleagues, but have yet to find anyone to whom I can refer my readers.
Perhaps Audio Magazine can be enlisted in this search. We could sound a call for the names of labs, repairs shops, individuals, et al. that have the knowledge, parts, and willingness to restore old tape decks and, perhaps, other audio components.
Herman Burstein, Contributing Editor
We would like to commend Herman Burstein for this excellent idea, and we will print the names of those repair shops and individuals who repair vintage audio equipment. However, fair warning, we will also print letters from persons who have had unsatisfactory work performed. E.P.
Nulling AM Distortion
For the past several months a number of my counterparts at other broadcast stations and I have been writing to you concerning the capabilities of AM radio. I am certain that we were not trying to create an "AM versus FM" controversy, but after reading Mr. Stephen Waldee's comments in the March Issue of Audio I feel compelled to write you again. I feel that Mr. Waldee has misinterpreted the purpose of my letter and those of others.
While what Mr. Waldee says about AM technical standards is true, there is no reason why a conscientious broadcaster should permit such performance standards in his physical plant. The AM technical standards were composed many years ago when equipment was incapable of the superior performance found on modern equipment. And these standards have never been upgraded. If one examines the minimum permissible performance standards for FM transmission, they are almost as laughable as those for AM. But I am certain that Mr. Waldee would not permit his transmitting plant to drop to the minimum performance parameters, even though he would still be legal in the eyes of the FCC. While it is true that, in AM, a frequency removed from the carrier by 15 kHz or more must be attenuated by at least 25 dB from the unmodulated carrier, one must examine the applicable FCC rule, 73.40 (a) , to really clarify the matter. The rule states: "Any emission appearing on a frequency removed from the carrier by between 15 kc/s and 30 kc/s, inclusive, shall be attenuated at least 25 dB below the level of the un modulated carrier. Compliance with the specifications will be deemed to show the occupied bandwidth to be 30 kc/s or less." Thus, a frequency of 14,999.999... Hz may be legally transmitted at 100 percent modulation.
The upper limit for stereo FM is 15,000 Hz, but who's counting? Incidentally, how many recordings do you know that contain enough high frequency information in the region of 15,000 Hz to modulate the transmitter 100 percent? Or, for that matter, even 25 percent? 10 percent? As to his cases of 17 percent inter modulation distortion in an AM transmitter, I suggest that there is something very basically wrong with a transmitter that produces that kind of a figure. Perhaps a defective power supply transformer, capacitor, or choke. Maybe a defective modulation transformer or reactor. Even something not the fault of the transmitter could be responsible, such as insufficient power mains. Perhaps, even, the detector in the distortion analyzer is not linear.
Concerning low frequency phase shift, once again I suggest that there is a deep seated problem in any transmitter that shifts phases excessively in the audio. Some phase shift is inevitable when audio passes through any transformer, but a high quality transformer will produce a minimal amount of phase shift, well within acceptable limits.
It is true that the new Harris MW -1 transmitter eliminates phase shift because of the absence of a modulation transformer and reactor. However, in 1957, RCA developed their "Ampli phase" transmitter utilizing a phase to -amplitude modulation system.
There is no modulation transformer and reactor involved in this system, consequently, no phase shift. Several years ago Gates Radio (now Harris Corp.) developed their line of "PDM" transmitters which utilize a Class-D pulse-width modulation system. Once again, the modulation transformer and reactor have been eliminated, thus phase shift is also eliminated. The technology necessary to eliminate audio phase shift in AM transmitters has been around for a long time in regular use.
What all this boils down to is the fact that with a good solid signal, transmitted properly by the station, a good receiver can recover as high a fidelity audio signal from an AM station as from an FM station. However, sloppy engineering will destroy fidelity no matter what type of modulation is used.
While it is true that modulation mad program directors and managers exist, they are not exclusive to AM radio. I once worked for an FM -only station whose manager insisted on seeing the modulation meter hovering near 100 percent at all times. It did, but at the expense of fidelity. He had the loudest sound in town, but also the dullest sounding one.
I am as happy as anyone else to see the new state-of-the-art equipment make its appearance, and I hope more manufacturers will get the message that they must produce better equipment to remain in business.
But don't dismiss AM as a hopeless case. It's still a very much alive medium, and soon to be stereo. If better receivers were produced by manufacturers, AM radio might even become a serious listening medium. Incidentally, I'm 28 years old, hardly a "radio old timer." Robert I. MacDonald, CE Village Broadcasting Radio Station WCHL Chapel Hill, North Carolina
Equations in Error
Thank you for publishing my article "Simple Pink Noise Filter" in the March, 1977, issue of Audio. Unfortunately, Fig. 4 of the article contains a few minor errors which I thought I should bring to your attention. Specifically, the equations should read:
e2 (Ra + Rb + Rc\ (1+j f/fH) e, \ Ra / (1+j f/fL)
fL 1 27rRc C, 1H 1 21-Rp C, and Rp _ (Ra + Rb) Rc Ra + Rb + Rc
Dr. Robert Mauro
Asst. Professor of Electrical Engineering
Manhattan College Riverdale, N.Y.
We are both die-hard quadraphonic enthusiasts. Through reading Audio magazine, we know that this enthusiasm is shared by many other devoted fans.
Quadraphonic is a very exciting format, but let's be realistic about the subject; four-channel is dying. Sure, we've all heard of the newest technological advances in encoders, decoders, demodulators, etc., but where are the results? Not in our local hi-fi shop, and certainly not in the bins of our favorite records stores.
We can throw the blame at whomever we want, the hardware/software manufacturers, or the public, but let us stop harping on who should take the blame. It's time to make a positive move straight ahead. We now have the proper technology and the means for properly educating the audio salesmen, the record dealers, and the general public.
Here is what this letter is leading up to, a plea for anyone interested in the future of quadraphonic to form a Quadraphonic Club. All that is needed is a group of people rallying around four -channel to get this "turkey" up and changed into a "race horse." Why not? Please send us any thoughts, notions, inspirations, anything at all to help keep quadraphonic alive. All the major companies have adopted a "wait and see" attitude. We're tired of waiting, so let's see, or better yet HEAR some results. It doesn't matter what you prefer: QS, SQ, CD -4, it's all quadraphonic. If you think four -channel is a fantastic idea, send us your ideas and opinions.
Jay Frank 23757 Canzonet St. Woodland Hills, CA 91364; Steve Walker 4028 N. Yankee Dr., Agoura, CA 91301
As a long time professional in the audio art, FCC First Class License No. P1-11-41380, and a motion picture and television sound mixer whose credits include everything from the now -defunct "I Spy" series through many feature motion pictures, the recently popular "Family" series on ABC, and the pilot film for "Charlie's Angels," I read with a great deal of interest the article in the January 1977 issue of Audio on the vintage E. H. Scott AM receivers. As one who remembers the Scott, but could not afford one, it was a very pleasant trip through "nostaligia land." Coincidentally, in Edward Tatnall Canby's Audio ETC column in the same issue, regarding "miniaturization," Canby mentions the Fisher Series 80 tuners. However, he failed to mention that those Fishers did have a "broad" and "narrow" i.f. bandwidth, controllable from the front panel. This writer is still using a Fisher 801 with a new, home -built IC preamp section, and an outboard solid-state multiplex adaptor all of which works very well indeed.
The main point of this letter, however, is to shed a little more light on the state of the art in the 30s. The writer has had for a number of years a vintage 1936 Sparton all -wave receiver sitting on the shelf of my shop. It was purchased in 1937 when the Sparks Withington Co. was on the verge of bankruptcy. A department store in Portland, Oregon, sold them as a "loss leader" for $85.00. It had five wave bands, tuned from 150 kHz to 60 mHz without skips, had an r.f. stage on all bands, a separate oscillator and mixer, two stages of i.f., and a diode detector-first audio. This was followed by a "switchable" volume expander and an electronic crossover. Bi-amped, if you please, in 1936, with a single-ended 6F6 pentode, driving two six-in. tweeters, and a pair of class AB 2 6L6s providing about 45 W rms to a 15-in. woofer.
A few months ago, a very slight interest in listening to "CB" prompted me to tune in the "old girl" to see what it could do on about 27 mHz.
Alas, it had sat on the shelf for too many years ... dried out capacitors, tired tubes, and coils which had absorbed too much moisture, all had taken their toll. However, a visit to the science section of the Los Angeles Public Library yielded the original schematic from one of the old Ryder Service Manuals.
So, the old Sparton was stripped down to the bare chassis and tube sockets, then completely rewired, bad capacitors replaced, and the coils dried out and lacquered. A visit to friends at some of the studios supplied from the "obsolete" shelves the necessary 6K7s, 6L7s, 6J5s, 6J7, and 6Q7, even a 6E5 tuning eye. The bi-amped output stages had long ago been replaced by a pair of 6550s and a modern output transformer. Even the volume expander was rebuilt to factory specifications and works just fine.
Today, this 40 -year -old receiver sits on a rack in the shop, together with an ancient Pilotuner for FM, a couple of 35 watt, Williamson -type tube amplifiers, a Type-A Garrard turntable with a Shure V15-II cartridge, and an old PT 6 Magnecorder tape deck. The speakers are, a 30-year-old 15 -in. Jensen co-axial and, on the other side, an even older 18 -in. Jensen Theater woofer with a 5Y3 rectifier tube on the side, combined with an eight -in.
midrange, and a resurrected Kelly ribbon tweeter. And for their age, they sound remarkably good, even by today's standards. So, the newest is not necessarily the best.
Lest the writer be accused, or a -"cussed," of living in the past with a "tin ear," let me hasten to add that the main system in my house is all solid state with large bi-amped JBLs, and since this writer, because of his work, has access to sophisticated measuring equipment, the entire system is equalized to be "flat" ±1 dB in the listening room from an honest 20 Hz to at least 18.5 kHz, above which it is hard to make a meaningful measurement.
Before ending this letter, let me add one note of "self protection" if you will about the atrocious quality of the sound usually heard on television. It is not the fault of people, like myself, who do the recording and engineering. By the time a filmed TV show, for example "Charlie's Angels," reaches the broadcasting network, it has been through many skilled hands, listened to by many trained ears, and put through the best sound equipment the "state of the art" can provide.
The real culprit is the inexpensive TV audio system, and the downright cheap four to six inch speaker used in the average television receiver. This has long been a sore spot with, many of us who know how good TV audio should sound.
Burdick S. Trask Sherman Oaks, Cal.
I just saw your April issue with the test of the Lirpa-1 Receiver. It was hilarious. Where do you guys get all those neat ideas? I looked all over the issue trying to find a credit for the constructor of the prototype, but I couldn't find the name. Was it by chance, Karl Kofoed? I remember that he built the Ultima One amplifier that fooled all those people two years ago. If it was, indeed, Mr. Kofoed's work he should be congratulated for another fine job.
Keep those Kofoed Kovers Koming, please.
Congratulations are due you, also, for having the exquisite taste and humor to liven up a basically dull field with gems like the Ultima and Lirpa. Good show!
Jim Wilson Phila., Pa.
Editor's Note: Yes, Karl Kofoed designed the Lirpa I for the April cover of Audio, but he has taken a better paying job as a union jackhammer operator in the oil fields of Shake NimaIdi somewhere in Lower Saudi Iran.
Dear Sir: After reading your Equipment Profile on the Lirpa I Receiver while simultaneously perusing the AKAI advertisement on page 43 with my x-ray vision, I cancelled my subscription to the National Lampoon.
Charles J. Oeler Pittsburgh, Penn.
(Source: Audio magazine, Jun. 1977)
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