Dear Editor (Feb. 1977)

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Contented Mac Owner

Dear Sir:

I was pleasantly surprised to find you reviewing the McIntosh C-28 Preamplifier. I've had the joy of owning one for almost four years now, and it looks and works like the day I brought it home. And your note that it weighs 25 pounds really brought a point home to me, ruggedness of construction is something I value just as much as performance. I would never think of trading my "28" for anything else on the market because of its quietness and incredible versatility.

How about reviewing one of their new super cool-running amps, like the MC-2205? You'll be amazed at the clarity of sound and the incredible metering/overload system. Or how about a unique product like the MPI4 Maximum Performance Indicator? I've really raised my awareness about power levels with the dual vertical line readout that indicates power output in real time, averages or displays the last highest peak. And the huge multipath display (fed from their MR 78 tuner, of course) is the first I've seen that's truly easier to use than meters and much more informative.

have one question to ask your manufacturer/advertisers: When, oh when, will someone please make a CD-4/SQ/QS Super-Deluxe Demodulator combination for us poor, frustrated top-of-the-line component owners? I'm gonna sit tight with my $8,000 two-channel until somebody sees the light. Come on, let's get going!

J.H., Detroit, Mich.

Editor's note: There are several good demodulator/decoders which have recently come onto the market.

While they may not be on a par with your equipment, they are nonetheless a step in the right direction.

AM Fidelity

Dear Sir:

As chief engineer of an AM/FM station I read with interest Eric Norberg's letter in the November 1976 issue of Audio relating his experiences with high grade AM broadcasting and requesting the inclusion of AM tuner data in your Equipment Profiles. Here's my two-cents worth on the "low fidelity" AM band. AM broadcasters have been using studio equipment that delivers at least 50 Hz-15 kHz response with low distortion for quite a few years. Usually they are monaural versions of audio equipment used for FM broadcasting.

In some cases, the same studio is used for both AM and FM origination, with the monaural AM feed developed through a simple summing of the left and right channels through a bridging amplifier.

It has been routine to find 50 Hz-15 kHz response with reasonable distortion in even 10to 15-year-old transmitters. Current AM transmitters are starting to use various forms of pulse code modulation to improve their phase linearity. With these transmitters, it is not unusual to find frequency response, transient response, THD and IM distortion quite close to the FM transmitters available five years ago.

The major limiting factor in transmitting a high quality AM signal has been the bandwidth of the transmitting antenna. Recently broadcasters have realized that any response limitation in the antenna system has a direct effect on the amount of audio power reaching the air.

When you add this to the realization that many broadcasters are becoming more audio conscious in order to have a competitive edge in a tight marketplace, it is easy to see why many AM broadcasters are broad banding their antennas to give good audio response up to 15 kHz and even beyond.

An AM station with a reasonably broadband antenna can actually broadcast a better top end than an FM station, since AM is not saddled with the 754S pre-emphasis curve used in FM broadcasting. This means that properly received broadband AM can sound like Dolby encoded-decoded FM broadcasts.

While there are some operators, on both AM and FM, who use signal processing as an end in itself, most responsible broadcasters want to put out the best signal they can. Most of the "sins" committed by the average AM broadcaster in the area of signal processing are attempts to compensate for the extremely poor performance of current AM tuners. It is not unusual for a so-called "high fidelity" AM tuner to have a high frequency roll-off that starts around 3-4 kHz while "boasting" a distortion figure of 5-10 percent at 85 percent modulation. Since the AM band is crowded in many areas, it should also have switchable 5-8 kHz low-pass and 10-kHz notch filters for use when needed. Good sensitivity would be around 0.5-1 mV for a 20-dB signal-to-noise ratio. To date, the only receiver I have found that approaches these figures is a vintage tube-type McIntosh MR-55, which I use for home AM listening.

You will notice that I used 85 percent modulation as the reference point for my distortion figures. Since the FCC specifies this as the minimum peak modulation level, it does not make sense to use 30 percent modulation as a reference. Even if there was not this FCC requirement, I don't know of any station that would consistently modulate at this low level.

When you consider the advances made within the past decade in FM tuner performance, it is sad and frustrating to me to realize that the current AM tuners are solid-state versions of the receivers used during WW II. I would like to second Mr. Norberg's request for the inclusion of AM tuner data in your Equipment Profiles, if for no other reason than to shame manufacturers into making a high quality AM section available, if only as an option.

Lou Schneider, Chief Engineer KTIM/KTIM-FM, San Rafael, Cal. USA

Jailhouse Musicians

I am writing with the hopes that Audio Magazine will print this letter. I am a member of an organization known as the C.C.I. Music Association which is composed of both professional and amateur musicians. There are four different types of music groups: Jazz, Rock/Blues, Soul, and Country & Western. The difference between this and other musical organizations in the music field is that members of the C.C.I. Music Association are serving time at the Chillicothe Correctional Institute.

We would like to expand our membership to include outside people, whether they are professional or amateur musicians, or people who just like to listen to good music. You don't have to play an instrument, or even know how to read or write music to become a member. As a group, we can get a lot done if we have an outside membership.

If any of the Audio readers are interested, please write to either George Williams, President, or to me, Steve Griffith. We will see to it that you receive a copy of our constitution and by-laws, plus a fact sheet explaining what we are trying to accomplish.

If you don't wish to join, but know of someone who would like to donate musical instruments to our organization, please put them in contact with us. I hope that there are people interested in joining our organization.

Thank you.

Steve Griffith, #144-539 P.O. Box 5500 Chillicothe, OH 45601, USA

Reissue Suggestion

Every month the hi-fi and record magazines carry reviews of the reissues of old records.

May I make a suggestion for consideration by those responsible for selecting these records of historical or artistic value: reissue those famous early electrical recordings by the Associated Glee Clubs of America.

L.K. Crabtree, Vineland, Ont. Canada

Editor's Comment: Are there any other suggestions for reissue? E.P. Prof. Lirpa Exposed

Dear Sir: I am new to this country and I was recently thumbing through some back issues of Audio Magazine, among them the April 1976 issue.

Who are you trying to kid with your zany accounts of Prof. I. Lirpa? I don't know if you've divulged this to your readers, but I. Lirpa is Eaotin Shirdlu backwards-you don't fool me.

Rishiyur Nikhil, Phila., Penna., USA

(Source: Audio magazine, Feb. 1977)

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