Mcintosh mac4100 schematic

A CONSUMER'S GUIDE
Preparation supervised by
Robert Long. Harold A Rodgers.
and Edward J. Foster
Laboratory data (unless otherwise rioted)
supplied by CBS Technology Center
Mclntosh's New Receiver: Breeding Tells
Mac 4100 stereo FM/AM receiver, in case with simulated
wood-grain finish, Dimensions: 185/8 by 53/4 inches (front), 14 inches deep plus clearance for controls and connections. AC
convenience outlets: 2 switched plus 1 unswitched (600 wafts
total), 2 for auto on turntable switching (100 watts total). Price: $1,499; optional RMA-5 rack-mounting adapter. $29. Warranty: three-year service contract, free with purchase of the receiver, has provisions comparable to typical "limited" warranties but covers normal wear and tear. Manufacturer: Mclntosh Laboratory, Inc.. 2 Chambers St., Binghamton. N.Y.
13903.
Mclntosh has for some years kept a very low profile vis-a-vis
the press. This hiatus in communications has fostered a po­larization of opinion about Mclntosh: Is the company still de serving of its reputation for superb engineering, or is it trad­ing on past glories? One review can't provide a definitive answer, of course, but the Mac 4100 receiver can be taken as a positive sign of health in Binghamton.
The personality of this receiver is like that of an accom-
plished servant used to coping with pampered aristocrats who
FEBRUARY 1979
demand the finest but are not always technically knowl­edgeable or manually dexterous. Accordingly, it takes respon­sibility in a manner that, paradoxically enough, is unassuming yet quite intolerant of intervention by its master. But once it has taken over, it performs virtually impeccably and can even ward off the consequences of ineptitude without noticeable fuss.
REPORT POLICY Equipment reports are based on laboratory measure
merits and controlled listening tests Unless otherwise noted, test data and measurements are obtained by CBS Technology Center, Stamford. Connecticut, a division of Columbia Broadcasting System. Inc . one of the nation's leading
research organizations. The choice of equipment to be tested rests with the editors of HIGH FIDELITY Samples normally are supplied on loan from the manu­tacturer Manufacturers are not permitted to read reports in advance of pub­hcation, and no report, or portion thereof, may be reproduced for any purpose or in any form without written permission of the publisher. All reports should be construed as applying to the specific samples tested, neither HIGH FIDELITY nor CBS Technology Center assumes responsibility for product performance or quality
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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 conven­tional 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 ac­tually do the signal switching. There are two fundamental ad­vantages to this approach: Switching transients are elimi­nated, and the short, direct signal paths made possible minimize noise pickup, RFI, and crosstalk. In all of these re-
Mclntosh Mac 4100 Receiver
Tuner Section
Capture ratio Alternate channel selectivity THD
+ N
80 Hz
1 kHz 10 kHz
IM distortion
19-kHz pilot 38-kHz subcarrier S/N ratio (at 65 dBf)
stereo mono
L ch
0.25%
0.17%
1.8%
2 dB 76 dB
R ch
0.25%
0.22%
1.7%
0 06%
-63½ dB
-66½ dB
67 dB 71 dB
mono
0.16%
0.15%
0.21%
spects the 4100 is above reproach. We seldom have RFI prob­lems in our area, but we do often find that, for example, some audio from an FM tuner section will "'leak" into the tape-moni­tor 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 sep­aration loss. On weak signals it does work, however—and, like so many features of the Mac, without drawing undue atten­tion 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 oc­curs, 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
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Amplifier Section
Manufacturers rated power Power output at clipping (channels driven simultaneously)
Lch
R ch
Dynamic headroom (at 1 kHz) 1 ½i dB Frequency response
RIAA equalization
Input characteristics (re 0 dBW (1 watt); noise A-weighted)
phono 1, 2 aux 1, 2
tape 1, 2 Phono overload (clipping point) 88 mV at 1 kHz Damping factor at 50 Hz
17¾ dBW (75 watts)/ch.
20 dBW (98 watts) 20 dBW (98 watts)
+ V,, -V, dB, 20 Hz to 20 kHz
+
V»,
-3 dB, 13 Hz to 35 kHz
±1 dB, 20 Hz to 20 kHz
Sensitivity
0.27 mV
30.0 mV
30.0 mV
100
S/N ratio
76½ dB 80 dB 80 dB
HIGH FIDELITY MAGAZINE
range of the signal-strength meter is well chosen as an aid in antenna orientation for best reception of problem stations.
The amplifier section, too, exemplifies the extra care that sets the receiver apart. Whether the option that enables switching in three speaker pairs simultaneously requires them or not, it has three distinct protection systems. The most conventional is triggered by a heat sensor and shuts down the output until the heat sink has cooled to within safe operating limits. The Sentry Monitor circuit reacts to abnor­mal current conditions by restricting the drive to the output transistors. And the Power Guard circuit responds to over-
drive that normally would create hard clipping by shaving off the potentially dangerous harmonics—"softening" the clip ping, so to speak. None impinges on normal operation; all
minimize the effects—aural, thermal, or electrical—of abnor­mal operation.
The Power Guard, for example, limits peaks so smoothly that you are unlikely ever to hear this receiver overload, as such. The top LEDs in the front-panel power display—the one possible concession to fashion in the design—are Power
Guard pilots; below that, the display is calibrated from 100 watts down to 0.1 watt in 5 dB steps. As we've said before,
we're not convinced of the utility of such indicators, but the calibration points do seem relatively well chosen.
Two unusual features of the front panel are the equalizer/ tone controls and the "loudness" knob. The latter might bet­ter be marked "contour" since it does not adjust midband level like most loudness controls, but simply adds boost in the deep bass plus some in the upper treble to compensate for low listening levels. Like other separate-knob schemes, this frees the loudness compensation from the volume control
and makes it adjustable to the actual listening levels through the system; unlike some, the appropriate setting must be de­termined by ear alone—which is arguably the most reasonable approach.
The equalizer's five bands have maximum ranges of ap-
proximately ± 13 dB and are marked for center frequencies of 30, 150, 500, 1,500, and 10,000 Hz—making them, re-
spectively, controls for subbass, bass, midrange, treble, and
sparkle. The 30-Hz control is most effective as a rumble-fil-
ter/boom-boost control; the top one might be used as a hiss
filter, though its maximum cut setting dulls the upper treble a
good deal. As an ensemble, they offer genuinely useful flex-
ibility; all have detented center "flat" positions.
While the lab measurements give little clue to the "extras"
from which the receiver's special qualities derive, they docu-
ment its very solid performance. Mclntosh appears to be thinking in terms of listening quality rather than specsman­ship (an attitude we applaud), so distortion, for example, is only vanishingly low—not infinitesimally low. The frequency response has been intentionally cut off beyond the audio band to help maintain clean sound by inhibiting inter­modulation with infrasonic and ultrasonic "garbage" (a de­sign criterion that applies to the tuner section as well as the amplifier); though this, similarly, may dismay those who judge
an amplifier by its square waves, the results with music seem all the better for it. Tuner data are likewise very good—even superb—with no offsetting cause for complaint of any kind.
It is obvious, too, that Mclntosh has a clearly formed idea of
the sort of user it is designing for: someone who, while he is
uninterested in playing the "pro," cares very much about
quality and craftsmanship. The cosmetics, the "feel," and the
sound quality of the Mac 4100 are all superb; the controls are minimal for the degree of useful flexibility they provide, with little if any concession to users who simply like to putter. This truly is a receiver for music lovers.
CIRCLE 136 ON PAGE 89
FEBRUARY 1979
In making comparisons between current reports and those published in the past, readers are cautioned to pay particular attention to the reference levels and similar test criteria cited S/N ratios tor electronics, in par­ticular, are measured very differently now that we have adopted salient features of the new IHF amplifier-measurement standard While we be­lieve that the new technique (which also implies a saner approach to
loading of all inputs and outputs) will result in measurements that more perfectly reflect audible, in use effects. they cannot be compared directly to the numbers resulting from the former, more conventional lab meas­urements
NEW MEASUREMENT STANDARDS
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