Very tittle of the receiver's special quality is immediately
apparent from the outside, though in hooking it up you get a
clue from the convenience outlets. In addition to the conven-
tional switched (black) and unswitched (red) ones, there are
two green ones marked TURNTABLE, plus an AUTO/MANUAL
switch. If you use the AUTO setting and a turntable plugged
into one of the green sockets is turned on, the receiver and
any outboarded equipment run off the switched outlets will
come on automatically, even when the receiver's power switch
is off, and all will turn off again when the turntable shuts
down. Thus an automatic model can be made to turn off the
whole system unattended. Since the feature works by sensing
current drain through the turntable outlets, the switch serves
to override it should the turntable be one of those that draw
some current even when they are off.
The receiver's switching is handled by DC control voltages,
actuated by the front-panel controls and fed to FETs that ac-
tually do the signal switching. There are two fundamental ad-
vantages to this approach: Switching transients are elimi-
nated, and the short, direct signal paths made possible
minimize noise pickup, RFI, and crosstalk. In all of these re-
spects the 4100 is above reproach. We seldom have RFI prob-
lems in our area, but we do often find that, for example, some
audio from an FM tuner section will "'leak" into the tape-moni-
tor signals; none was detectable in the Mac.
The FM section is unusual in that—in addition to conventional
automatic stereo/mono switching—it has an automatic-blend
feature that progressively reduces stereo separation (and
hence out-of-phase noise) as signal strength drops. Since the
full audio band is blended, the resulting stereo image may be
a bit stabler than in the more usual high-blend solution, but
the hiss seems a little more intrusive for a given degree of sep-
aration loss. On weak signals it does work, however—and, like
so many features of the Mac, without drawing undue atten-
tion to itself. Similarly, the Automatic Frequency Lock gently
holds onto an FM station that has been tuned correctly; were
it not for the front panel AFL LED, which lights when lock oc-
curs, you would be unaware of its action. This LED acts as a
tuning aid; when the muting is on, the LED announces arrival
at a receivable station before the unmuting action (which is
gentle and slightly delayed) allows any audio to pass. The
34
HIGH FIDELITY MAGAZINE
Mclntosh Mac 4100 Receiver
Capture ratio
Tuner Section
Alternate channel selectivity
THD
+ N
80 Hz
1 kHz
10 kHz
IM distortion
19-kHz pilot
38-kHz subcarrier
L ch
0.25%
0.17%
1.8%
S/N ratio (at 65 dBf)
stereo
mono
2 dB
76 dB
R ch
0.25%
0.22%
1.7%
0 06%
-63½ dB
-66½ dB
67 dB
71 dB
Amplifier Section
Manufacturers rated power
mono
0.16%
0.15%
0.21%
17¾ dBW (75 watts)/ch.
Power output at clipping (channels driven simultaneously)
Lch
R ch
20 dBW (98 watts)
20 dBW (98 watts)
Dynamic headroom (at 1 kHz) 1 ½i dB
Frequency response
RIAA equalization
+ V,, -V, dB, 20 Hz to 20 kHz
+
V»,
-3 dB, 13 Hz to 35 kHz
±1 dB, 20 Hz to 20 kHz
Input characteristics (re 0 dBW (1 watt); noise A-weighted)
phono 1, 2
aux 1, 2
tape 1, 2
Sensitivity
0.27 mV
30.0 mV
30.0 mV
S/N ratio
76½ dB
80 dB
80 dB
Phono overload (clipping point) 88 mV at 1 kHz
Damping factor at 50 Hz
100
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