NAD 3155 User Manual (English)

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3155

Integrated Amplifier

Date of manufacture : Jan 85 - Jan 87

Please note that this document contains the text from the original product brochure, and some technical statements may now be out of date

NAD leads the audio industry in producing amplifiers with high-headroom circuitry and high-current

output stages, precisely the qualities needed for musically accurate reproduction of today’s wide-range

analogue and digital recordings. The 3155 integrated amplifier and the matching 2155 power amp are

the finest in a long tradition of highly praised NAD amplifiers, with increased power, improved reliability,

and numerous small refinements in both sound quality and ease of use.

The 3155 is two products in one. As a preamplifier it matches most separate audiophile preamps in

sonic performance and surpasses them in operating flexibility. As a high-current high-headroom power

amplifier it drives even “difficult” loudspeakers to surprisingly high volume levels with clean, solid, full-

bodied musical sound that remains refreshingly free from distortion even in transient peaks. The

combination of pre- and power amp, sharing one heavy-duty transformer and chassis, offers another

traditional NAD virtue: an impressive ratio of performance to price. The 2155, which is simply the power

amplifier section of the 3155 packaged on a separate chassis, is NAD’s “building-block” amp, offering a

variety of convenient and economical approaches to upgrading a stereo system for higher performance

and power. The 2155 is an obvious choice if you want to step up from a low-powered receiver or

integrated amp, or if you are using a separate preamplifier. If you need still higher power, a pair of

2155s in the “bridged” mode deliver nearly three times as much power output for only twice the cost.

The 3155 and 2155 deliver substantially more than their conservatively rated 55 watts/channel into the

complex and varying impedances of real loudspeakers. In the bridged monophonic mode each amplifier

is rated conservatively at 150 watts continuous output. And these amplifiers maintain a full 3 dB of IHF

dynamic headroom (2.5 dB in bridged mode), meaning that they deliver twice their rated power in brief

bursts: over 110 watts/channel in stereo and about 250 watts in bridged configuration. This headroom

for peaks is crucially important for reproducing the uncompressed transients in modern digital and DBX-

encoded recordings.

When combined as a bridged stereo pair, the 3155 and 2155 function as a 150 W/ch stereo amplifier

with 250 watts per channel of short-term output. That power, together with the remarkable flexibility

and flawless sonic performance of the 3155’s preamplifier section, makes the 3155/2155 combination a

remarkable best-buy system.

High Current and Headroom: Designing For Real-Use Conditions

Since amplifiers are usually rated in terms of a few standard specifications (e.g. 8-ohm power and THD),

many designers concentrate on optimising test-bench performance. But in the real world, amplifiers are

connected to loudspeakers with complex impedances, not to 8-ohm test resistors, and they are used to

play music, not sine-wave test tones. In NAD amplifiers every circuit is designed to deliver full

performance under real-use conditions. While many specific engineering goals follow from this principle,

two have been the cornerstones of every amplifier in NAD history (including the legendary Model 3020):

graceful handling of dynamic transients that exceed the amplifier’s rated power, and the ability to deliver

large bursts of output current to the loudspeakers. Electrical power is the product of voltage and

current, but it is the current flowing through the voice coil that causes a loudspeaker cone to vibrate

and reproduce sound. As NAD engineers have always known, and other manufacturers have lately

begun to realise, to obtain precise electromagnetic control of the speaker’s motion the amplifier must be

able to supply high peak currents upon demand, unconstricted by transistor “protection” circuits. The

NAD 3155/2155 amplifier circuit produces peak cur-rents of up to 40 amperes per channel.

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NAD 3155 Specifications

Pre-Amp Specifications

Phono input impedance (MM)	47kΩ / 100/200/320pF
Phono input impedance (MC)	100Ω / 1000pF
Phono input sensitivity (MM)	2.8mV
Phono input sensitivity (MC)	0.28mV
Phono signal/noise ratio (MM)	78dB ref. 5mV
Phono signal/noise ratio (MC)	78dB ref. 0.5mV
Phono THD (20Hz - 20kHz)	<0.04%
Phono RIAA response accuracy (20Hz - 20kHz)	±0.5dB
Line level input impedance	10kΩ / 220pF
Line level input sensitivity	25mV
Line level maximum input signal	>10V
Line level signal/noise ratio	86dB
Line level frequency response	20Hz - 20kHz / ±0.5dB
Line level output impedance	800Ω
Line level tape source impedance	Z + 1kΩ
Line level maximum output level	10V
Treble control	±7dB at 10kHz
Bass control	±7dB at 100Hz
Bass EQ	+3dB at 70Hz, +6dB at 32Hz
Infrasonic filter	-3dB at 15Hz - 12dB/octave

Power Amp Specifications

Continuous output power into 8Ω	55W (17.4dBW)
Rated distortion (THD 20Hz - 20kHz)	0.03%
Clipping power	65W
IHF Dynamic headroom at 8Ω	+3dB
IHF dynamic power 8Ω	100W
IHF dynamic power 4Ω	100W
IHF dynamic power 2Ω	130W
Damping factor (ref. 8Ω, 50Hz)	>50
Input impedance	22kΩ
Input sensitivity for rated power	1.3V
Bridged mode continuous output power into 8Ω	125W (21dBW)
Bridged mode IHF Dynamic headroom at 8Ω	+2.5dB
Bridged mode IHF dynamic power 8Ω	250W