From: schuster@panix.com (Michael Schuster)
Subject: Denon AMAX receiver review
Originator: wdp@gagme
Organization: PANIX Public Access Unix & Internet, NYC
Date: Wed, 4 Nov 1992 09:51:53 GMT


I found the review below posted on the Fidonet shortwave echo.
I thought it might be of interest here:

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>Msg#:53692 *SHORTWAVE*
>10/30/92 11:13:00
>From: AL QUAGLIERI
  To: ALL
>Subj: DENON SUPERTUNER
>Edited excerpts from From RADIO WORLD, 21 October 1992:
 
TUNER TESTS OUT "SUPER"
by Len Feldman
 
At long last, the NAB-commissioned "Super Tuner" has been
produced by Denon and is available for purchase by interested
radio stations - or for that matter by consumers.
 
FEATURES
The Denon TU-680NAB is, first and foremost, a superb AM/FM stereo
tuner, incorporating the universally approved stereo FM system as
well as the Motorola-developed C-QUAM system for stereo AM. Two
settings of bandwidth are available for both the FM and AM bands.
The tuner also incorporates a noise-gating circuit that
significantly reduces interference on the AM band from externally
generated electrical noise, such as that from fluorescent lights,
electric motors, and the like. When using the FM band, noise
reduction in the form of an MPX filter can be switched on.
 
Up to 30 channels of either AM or FM can be stored in memory for
instant recall by number. A remote control, capable of handling
virtually all the control functions of the tuner, is supplied.
The remote also features a "Preset Scan" button that is not
duplicated on the tuner's front panel. A separate AM loopstick as
well as an FM indoor antenna and the usual twin audio shielded
pin-plug cable also come with the product. The AM frequency band
available on this tuner extends from 520 kHz to 1710 kHz, in
conformance with the expanded AM frequency band recently
authorized by the FCC.
 
TEST RESULTS, FM
50 dB quieting in mono with input signals of only 15.3 dBf
Stereo muting below 40 dBf
In mono, THD plus noise at mid frequencies 0.057 percent,
     increasing to 0.085 percent at 100 Hz and just over 1
     percent at 6 kHz.
In stereo, THD plus noise at mid frequencies measured just over
     0.1 percent, increasing to 0.17 percent at 100 Hz and 0.16
     percent at 6 kHz.
In both mono and stereo, lowest THD plus noise was attained with
     little more than a 50 dBf signal strength.
Stereo separation reached nearly 50 dB at 1 kHz and maintaining
     nearly that at 100 Hz. At 10 kHz, separation remained
     greater than 30 dB.
Second harmonic distortion 0.1 percent
 
TEST RESULTS, AM
Wideband selectivity 60 dB, narrowband selectivity 77 dB
Image rejection 85 dB       AM suppression 60 dB
Capture ratio 1.2 dB   IF rejection in excess of 100 dB claimed
Distortion plus noise varied with frequency, using modulation
     levels of 90 percent. At 1 kHz, THD plus noise measured 1.2
     percent in wideband, 1.4 percent in narrowband.
Actual harmonic distortion under 1.0 percent
Ultimate s/n ratio with strong signals: 55 dB mono
Stereo separation at midfrequencies 24.3 dB.
 
SUBJECTIVE TEST
We hooked up an ordinary indoor dipole antenna to the FM antenna
terminal and oriented the dipole towards the west, in the
direction of most of the transmitter antennas in our metropolitan
area. Under those conditions, we were able to receive no less
that 53 acceptable signals in mono. That's nearly a half dozen
more than we usually receive with typical "hi-fi" tuners and
receivers we have tested over the last several years. Switching
to the "Auto" tune more (thereby activating stereo circuitry), we
logged some 43 acceptably noise-free stereo signals on the FM
band.
 
Orienting the supplied AM loopstick for best reception, we then
switched to the AM band and were able to log 26 acceptable
signals. There was little difference in the logged signal count
when we switched from the "Auto" tuning mode to the "Manual"
mode. A few of the stations exhibited less interference when we
switched to the narrowband mode, but even under those conditions,
audio fidelity was better than we have heard from an AM tuner in
many years. (Back in the 1940s and 1950s, AM receivers - then in
the majority - sounded a lot better than most of them do today.
The Denon TU-680NAB is a happy exception to that rule.)
     
Perhaps the most startling revelation occurred when we tuned a
classical music station on the FM band that also simulcasts on
the AM band. The stations were WQXR-FM (at 96.3 MHz) and WQXR-AM
(1560 kHz). This enabled us to switch back and forth between AM
and FM while listening to the same program material. We know
you're going to find this hard to believe, but to our ears (and
to those of several visitors to the lab while these tests were
ongoing), the audio quality of the AM transmission seemed
actually better than that heard when tuned to the FM band.
 
Denon deserves to be congratulated for this effort. The TU-680NAB
may well inspire other audio equipment manufacturers to follow a
similar course in designing future tuners and receivers.
---
 * Origin: Radio FREQS'  SCHENECTADY, NY  (518) 377-7127 (1:267/103)

-- 
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