NAD is internationally recognized as the value leader inhi-fi, and the new 7155 is the finest stereo receiver NAD hasever made.

The tuner section of the 7155 combines the convenienceand accuracy of digital frequency-synthesis tuning with superiorstereo sensitivity and quieting.

The phono preamplifier, too, is audibly (and in some casesdramatically) quieter than many other preamp circuits, not onlywith moving-magnet pickups but also with low-output movingcoil cartridges. The entire amplifier circuit has ample dynamicrange for every program source, including the widest-rangedigital Compact Discs.

The powerful high-current output stage of the 7155 drivesloudspeakers to surprisingly high volume levels with clean,solid, full-bodied musical sound and a refreshing freedom fro,,-distortion, even in transient peaks. The exclusive NAD imped-ance selector allows you to make maximum use of the amplifi-er's power regardless of the true impedance of your speakers.

The 7155 is conservatively rated at 55 watts/channel in thenormal stereo mode, not only with test resistors but with loud-speakers of any impedance. Its 3 dB of IHF dynamic headroommeans that it will deliver fully twice its rated power (over 110watts per channel) in brief bursts, important for undistortedreproduction of the uncompressed transients in Compact Discsand DBX-encoded recordings. Finally, the 7155's power can benearly tripled by combining it with the matching 2155 poweramplifier in bridged mode.

Circuit Features - Amplifier SectionDigital-ready design. The receiver's line-level inputs will not

be overloaded by high-level signal peaks from a Compact Discplayer or digital tape recorder. The 103 dB signal-to-noise ratioof the 7155 exceeds that of any analog or digital programsource. The low-impedance, low-noise design of the volumeand tone control circuits guarantees that the transparent clarityof the finest analog and digital recordings will be preserved.

Ultra-quiet MM and MC phono preamp circuits. As longas LPs remain a principal music source, there must be nocompromise in the phono preamp. The phono circuit in theNAD 7155 employs ten selected transistors per channel toobtain the widest possible dynamic range with outstandingfreedom from noise and distortion at all signal levels. Adifferential FET input circuit ensures ultra-low-noise operationat the high impedances of M M cartridges, and its linearity inthe MegaHertz range, aided by a custom-wound input filter,provides exceptional rejection of all interference from TV, CBradio, and computers. A separate high-gain MC pre-preampstage uses newly developed transistors optimised for lowestnoise with low MC impedances. A push-pull high-current out-put circuit drives the precision RIAA equalization networkwithout slewing distortion, and its 107 dB dynamic rangecomfortably accommodates all digitally-mastered LP record-ings with room to spare.

High-current output stage. Electrical power is the productof voltage and current-but current flowing through the voicecoil is what makes a loudspeaker cone vibrate and reproducesound. In many amplifiers the output current is deliberatelyconstricted by current limiters (protection circuits), in order toallow the use of smaller, cheaper output transistors. But NADengineers have always known, and other manufacturers havelately begun to realize, that to provide precise electromagneticcontrol of the speaker's motion the amplifier must be able tosupply high peak currents upon demand. The NAD 7155 canproduce peak currents of as much as 40 amperes per channel.

Loudspeaker impedance matching. Standard lab tests ofamplifiers use 8-ohm resistors in place of loudspeakers. Butmost loudspeakers have a lower and more complex impedancethat increases the required amplifier output current. (And if youconnect two pairs of loudspeakers, the effective impedance ofthe pair is halved.) For this reason the 7155, like all NAD ampli-

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fiers and receivers, is designed to deliver its maximum powerinto low impedances of 4 or even 2 ohms. But the exclusiveNAD impedance selector allows you to re-optimise the 7155'samplifier circuit to deliver greater output voltage for maximumeffective power delivery to loudspeakers whose true imped-ance is 8 ohms or hiqher,

, 8A

, 6A

, 2A

2A

4A

6A8A. _Oscillogram of the current flowing through a popular American "8 ohm"loudspeaker, showing peak currents of plus and minus eight amperesduring the reproduction of a sample Rossini overture. A 4-ohm speaker,or pairs of loudspeakers, would require twice as much current.

Soft Clipping. NAD's trademarked Soft Clipping circuitgently limits the waveform when the amplifier is driven beyondits maximum power rating. By preventing the output transis-tors from being driven fully into saturation, the Soft Clippingreduces the harshness that is normally heard when an ampli-fier is overdriven. Because of this and the amplifier's high dy-namic headroom, the sound of the 7155 remains clean andmusical at high sound levels, rather than being distorted asin other amplifiers.

Bass EQ. A special equalization circuit provides 6 dB ofboost at 32 Hz in order to strengthen and extend the deep-bassresponse of closed-box loudspeaker systems. A typical book-shelf speaker that rolls off below 50 Hz will have strong outputto 30 Hz when used with the NAD 7155, providing the sort ofauthentic bass "feel" that might otherwise require a costlyseparate subwoofer system.

Infrasonic filter. Precise infrasonic filtering is included toeliminate signal contamination from turntable rumble, recordwarps, tonearm/stylus resonances, vibration and acoustic feed-back. This guarantees the cleanest possible handling of signalswithin the audible range and eliminates the excessive woofer-cone excursions that can cause intermodulation distortion andmuddy bass in systems without filtering.

Bridging. If still more output power is needed, a bridgingswitch immediately converts the 7155's stereo amplifier into amonophonic unit conservatively rated at 150 watts, and thematching NAD 2155 power amplifier (also bridged) can beused for the second stereo channel. With an IHF dynamic head-room of +2.5 dB in the bridged mode, the 7155 and 2155 canproduce peak levels of over 250 watts per channel formusical transients.

The combination of the 7155 and 2155 in bridged modebecomes, in effect, one of the world's most powerful stereoreceiver while retaining all of the operating simplicity of the7155 receiver alone. Since the 7155 has independent preamp

NAD 7155S

DIGITAL AM/FM-EREO RECEIVER

outputs and power amp inputs, it can also be used with anelectronic crossover for bi-amplification with either full-rangespeakers or a separate sub-woofer. This flexible "buildingblock" approach ensures that the 7155 can serve equally wellat the heart of the simplest or most elaborate audio systems.

Circuit Features - Tuner SectionDesign for real-world conditions. Tuner specifications are

measured with a medium-strong signal (65 dBf, i.e., 100 ~V into300 ohms), but in the real world a tuner must perform well withsignals of widely varying strength and quality. For example, anFM tuner's resistance to multi path interference depends onits ability to "capture" the desired signal and reject weakerreflected signals; the lower the tuner's capture ratio, the moreefficiently it rejects the interference and captures clean stereo.The capture ratio of the NAD 7155 is consistently excellent, notonly at the medium signal strengths where other tuners per-form well, but also over the 100-to-1 range in signal level from25 to 65 dBf, allowing many more stereo broadcasts to bereceived without distortion.

Optimum gains and losses. In the I.F. section of any tunerthe signal is both attenuated (by the high-selectivity filters) andre-amplified, by high-gain ICs. But the final signal-to-noise ratiocan never be better than at the point where the signal isweakest. By optimising the filter design to reduce losses, NAD'sdesigners were able to eliminate an entire stage, reducing I.F.gain, and still deliver the optimum signal level to the PLL MPXdecoder-obtaining an 80 dB stereo SIN ratio at 75 dBf!

Sharp selectivity and clean stereo. The digital tuning cir-cuits control a MOSFET input circuit that can accept a full volt(i.e., a million microvolts) of signal, meaning that strong-signaloverload will no longer be a problem in urban areas. The I.F.circuit contains three linear-phase ceramic filters selected forthe optimum combination of sharp selectivity (to get cleanseparation of closely-spaced stations) and low phase-shift de-lay (for minimum distortion and crosstalk in stereo). The bal-anced linear quadrature detector ensures consistently low dis-tortion, even with over-modulated broadcasts. The compositestereo signal is phase-compensated to ensure that the PLLmultiplex decoder delivers wide separaton at all frequencies,not just in the midrange.

Details. Acute attention to small details is often the finalingredient of a superior design. For example, the 75-ohm coaxinput bypasses the internal 300/75-ohm balun transformer andgoes directly to the r.f. amplifier for best sensitivity. By meticul-ous analysis of the layout and component interactions, the fulltheoretical performance of the circuit has been achieved inproduction, avoiding the internal interference that often ariseswhen adjacent circuit parts "broadcast" to each other at radiofrequencies. A dual-notch low-pass filter completely suppres-ses the 19 and 38 kHz stereo subcarrier signals and also pro-vides extra filtering of SCA interference. (This is especiallyimportant now that FM stations use SCA subcarriers to trans-mit computer data.) A special low-leakage capacitor maintains

programmed station frequencies in memory for over 3 weekswhen the tuner is off or unplugged.

Dynamic Separation. Conceived by Larry Schotz, thisdynamic high-blend circuit cancels the out-of-phase portionof the high-frequency hiss in weak stereo signals. Maximumhigh-blend occurs only during quiet moments (when it is mostneeded, because that is when noise would be most audible).and wide stereo separation is restored whenever the musicitself contains significant stereo separation and is loud enoughto cover the background hiss.

Superior stereo sensitivity and quieting. In most tunersand receivers the 50 dB stereo quieting sensitivity is about 37dBf (39 ~V across 300 ohms). The 7155's refined front-end andI.F. circuits improve this figure by 3 dB, to 34 dBf (27 ~V), andDynamic Separation provides another 2 to 3 dB gain in quietingsensitivity, to 31 or 32 dBf (19-22 ~V), making the 7155 twice assensitive in stereo as other receivers. 60 dB of stereo quiet-ing is achieved at less than 70 ~V (42 dBf). This reflects thesuperior ability of the 7155 to extract truly quiet, clean soundfrom weak FM signals.

Quiet AM tuning. The 7155's AM section is based on an ICthat was especially developed for use in digital tuners. While itadds little to the tuner's cost, it is surprisingly sensitive, and itsexceptional freedom from noise and static makes it unusuallypleasant to listen to.

Exceptional Performance and ValueThe 7155 receiver represents the kind of value that has

made NAD world-famous. With its outstanding FM sensitivityand quieting, convenient and accurate digital tuning, flexibleand musically useful controls, very low noise and wide dynamicrange, very powerful high-current output stage, unique speaker-impedance matching for maximum power transfer, "buildingblock" expansion options, and superbly musical sound quality,the NAD 7155 is a strong contender for the title of the beststereo receiver in the world today.

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Specifications,NAD 7155 Stereo ReceiverNote: Measurements referenced to 8 ohms are taken with the SpeakerImpedance selector set to "80 (High)." Measurements for 4 and 2 ohmsare taken with the impedance selector at "40 (Normal)." Specifications aremeasured in accordance with EIA Standard RS-490 (IHF A-202) for amplifi-ers and ANSI-IEEE Standard 185(1975) (IHF T-200) for tuners. Tuner sensitiv-ity is measured via 75-ohm coaxial input and converted to equivalent300-ohm values.

ControlsTrebleBassSpeaker Equalization

±7 dB at 10 kHz±7 dB at 100 Hz+3 dB at 70 Hz,+6 dBat 32Hz-3 dB at 15 Hz,12 dB/octave-20 dB

Infrasonic filter (switchable)

Audio muting (low level)

FM Tuner SectionInput sensitivity

Power Amplifier Section, Stereo ModeCONTINUOUS AVERAGE POWER OUT- 55 W (17.4 dBW)

PUT INTO 8 OHMS (min. RMS powerper channel into 8 ohms, 20Hz-20kHz,both channels driven, with no morethan the rated distortion)

Rated distortion (THD), 20Hz-20kHzClipping power (max. con-

tinuous power per channel)IHF dynamic headroom at 8 ohmsIHF dynamic power

(max. short-term powerper channel)

Slew factorSlew rateDamping factor (ref. 80, at 50Hz)Input impedanceInput sensitivity for 1W/55W outPower amp gainTHD (Total Harmonic Distortion, 20Hz-

20kHz, from 250mW to rated output)SMPTE I.M. (Intermodulation Distortion,

60Hz + 7kHz, 4:1, from 250mW to ratedoutput)

IHF I.M. (CCIF 1M Distortion, 19+20 kHzat rated output)

Bridged (Monophonic) ModeCONTINUOUS AVERAGE POWER OUT-

PUT INTO 8 OHMS (min. RMS powerinto 8 ohms, 20Hz-20kHz, with nomore than the rated distortion)

IHF Dynamic Headroom at 8 ohmsDynamic power (max. short-term output,

8 ohms)

Preamplifier SectionPhono InputInput impedance

Mono, - 30 dB THD + NMono, 50 dB SIN

Stereo, 50 dB SINStereo, 60 dB SIN

Capture ratio at 25, 45 and 65 dBfAM rejectionSelectivity Alternate channel

Adjacent channel

9.8 dBf (1.7 1.N/3000)13.2 dBf (2.5 ~V)32 dBf (22 ~V)42 dBf (70 ~V)<1.5dB>65 dB70 dB8 dB85 dB70 dB90 dB70 dB60 dB1 kHz 100Hz-6kHz0.09% 0.2%0.09% 0.3%82 dB75 dBtypo 80 dB at 75 dBf±0.5 dB50 dB40 dB

0.03%75W90W+3 dB110W130W150W>5020 V/~sec>5022kO.175V/1.3V25 dB<0.03%

8 ohms4 ohms

a ohrns40hms20hms

Image rejectionR.F. intermodulationI.F. rejectionSeA rejectionSubcarrier suppression (19+ 38 kHz)THD at 100% modulation

MonoStereoMono

StereoSignal-to-noise ratio A-

weighted, 65 dBf

<0.03% Frequency response, 30-15 kHzStereo separation 1 kHz

(Dyn Sep off) 30Hz-10kHz

AM Tuner SectionUsable sensitivity

. SelectivityImage rejectionI.F. rejection

Physical SpecificationsDimensions (width x height x depth)

<0.03%

300 uv/rneter35 dB50 dB50 dB

150 W (22 d BW)

42 x 10.8 x 38 cm.16.5 x 4.25 x 15 in.9.18 kg./20 lb. 4 oz.10.6 kg./23 lb. 6 oz.50/60 Hz at 110, 120,220, or 240 VAC340W

+2.5 dB250W

Net weightShipping weight

- Power consumption

R=47kO; ~C = 100/200/320 pFR= 1000; C = 1000 pF0.4 mV for 1 W out2.8 mV for 55 W out0.04 mV for 1 Wout0.28 mV for 55 W out18mV/170mV /1.5V1.8mV/17mV /150mV<0.04%

MM:

Industrial Design: REINHOLD WEISS DESIGN/CHICAGOMe:MM:Input sensitivity (1 kHz)

Me:

Input overload at20Hz/1kHz/20kHz

THD (20Hz-20kHz) and 1M Dist.at +30 dB level

RIAA response accuracySIN ratio, IHF A-weighted,

with cartridge connected

MM:Me:

±O.5 dB78 dB re 5 mV78 dB re 0.5 mV

MM:Me:

Line Level Inputs (Aux, Tape)Input impedanceInput sensitivity

R= 10kO; C = 220pF25 mV for 1 W out180 mV for 55 W out>10V86 dB re 1 W103 dB re 55 W±0.5 dB

Maximum input signalSignal to noise ratio, A-weighted

Frequency response, 20Hz-20kHz

OutputsPreamp output impedanceMaximum output levelTape output impedanceTape output infrasonic filter

1N,A, D I, NAD (USA), INC.675 Canton StreetNorwood, Massachusetts 02062Telephone: (617) 769-7050

800 ohms10V1000 ohms (buffered)-3 dB at 15 Hz, 12dB/octave e 1984 BY NAD 265 PRINTED IN U,S,A