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NAD 6155 - User Manual

NAD 6155
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6155
Cassette Deck
Date of manufacture : Jan 85 - Jun 88
Please note that this document contains the text from the original product brochure, and some technical statements may now be out of date
THE FIRST SEMI-PROFESSIONAL CASSETTE DECK FROM NAD
The NAD 6155 is the finest cassette deck NAD has ever designed. Its outstanding performance, in both
recording and in playback, places it on a par with the best cassette decks on the market - machines
costing hundreds of dollars more than the 6155. How can such performance be achieved at the 6155’s
modest cost? NAD concentrates its engineering budget entirely on those aspects of design and
manufacturing that affect the audible performance of the recorder, while omitting cosmetic frills and
features that have little or nothing to do with how well the machine reproduces the true sound of
music. The NAD 6155’s superior performance is derived mainly from three design elements. One is an
NAD “first,” and the other two are found in only a few other cassette decks costing far more than the
6155.
A CLOSER LOOK:
Published specifications and test reports confirm that many cassette recorders can deliver accurate, wide-
range response under ideal laboratory-test conditions. But in everyday listening accurate tape playback is
elusive, for several reasons:
Different brands of tape vary widely in high-frequency sensitivity, so even when a recorder’s tape
selector is set to the nominally correct position, different brands of tape may produce sound that is
brighter or duller than the original music.
Because of the slow speed of cassette recording, tape saturation at high frequencies is a universal
problem.
At the slow speed of cassette playback, high-frequency rolloffs will occur if there is even a very small
difference in head “azimuth” between the machine used to record the tape and the deck used for
playback. (“Azimuth” refers to the orientation of the head gap, which must be exactly at right angles
to the direction of the tape motion.)
Treble losses may occur if a tape is accidentally exposed to the magnetic field of a loudspeaker, an
amplifier’s power transformer, or a magnetised tape head.
Despite the standardisation of 120 and 70 microsecond playback equalisation for cassette decks,
there are significant brand-to-brand differences among recorders, so that tapes recorded on one
machine may not reproduce accurately on another deck.
THREE STATE-OF-THE-ART FEATURES:
1. PLAY TRIM - A FIRST FROM NAD
The NAD 6155 is the first cassette deck to feature the new Play Trim circuit, an innovation that corrects
the high-frequency aberrations which, for many years, have limited the fidelity of cassette recordings.
NAD developed the Play Trim circuit in collaboration with Dolby Laboratories, to deal with the variations
in high-frequency response that often occur in cassette recordings - especially in tapes that were
recorded on one machine and are being played on another.
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Overview

The NAD 6155 is a semi-professional cassette deck, manufactured between January 1985 and June 1988. It is designed to deliver outstanding performance in both recording and playback, aiming to rival higher-priced cassette decks by focusing its engineering budget solely on aspects that affect audible performance, rather than cosmetic features.

Function Description:

The NAD 6155's primary function is to record and play back audio on cassette tapes. It incorporates several advanced features to ensure high-fidelity sound reproduction, addressing common challenges in cassette recording and playback.

Key Features:

  • Play Trim (A First from NAD): This innovative circuit, developed in collaboration with Dolby Laboratories, is designed to correct high-frequency aberrations that often limit the fidelity of cassette recordings, especially when tapes recorded on one machine are played on another. These aberrations can arise from tape saturation, mismatched biasing during recording, and differences in equalization and head azimuth between recorders. Play Trim is a special high-frequency playback equalization circuit located ahead of the Dolby NR circuit. This strategic placement allows it to restore accurate playback response before Dolby NR decoding occurs, preventing mistracking of the noise-reduction circuits and resulting in a more accurate and brilliant sound. The Play Trim control is a narrow-band equalizer operating in the top two octaves of the audio spectrum, providing an adjustable boost or cut of up to ±3 dB at 10 kHz and ±6 dB at 20 kHz. It allows users to adjust tonal balance during playback to remove false brightening or dulling of the sound.

  • Dolby HX Pro Headroom Extension: This circuit addresses the problem of high-frequency rolloff and tape saturation at high recording levels, which typically results in a dull sound. The Dolby HX Pro system constantly monitors the level and frequency content of the input signal during recording. It automatically varies the amount of ultrasonic bias to ensure that the total effective bias (including the effect of high audio frequencies) is always optimal. When recording a strong low-frequency signal, the bias level increases to an unusually high value, leading to remarkably low distortion at high recording levels. Conversely, when the input signal has strong highs, the bias decreases, dramatically improving the high-frequency saturation level and preventing dulling of the highs. This feature enhances the useful dynamic range of the 6155, making it comparable to or better than many decks using costly metal tape, even with ferric and chrome tapes. The operation of Dolby HX Pro is fully automatic and works only during recording, meaning the superior quality of the resultant recording will be evident on any playback device (e.g., in a car, a portable player, or the 6155 itself).

  • Amorphous Head: The 6155 features a costly amorphous record/play head. This type of head is remarkably resistant to flux saturation, even at the highest recording levels. In many cassette recorders, the head can saturate before the tape does, limiting the useful dynamic range. The amorphous head allows for recording musical peaks at levels substantially higher than 0 dB (Dolby NR reference level) without distortion. This capability is particularly important for high-bias (chrome) and metal-particle tape formulations, which excel in high-frequency dynamic range. It enables the capture of the full brilliance and power of cymbals, bells, brass, and synthesizers with clear, airy sound.

Technical Specifications:

  • Speed Accuracy: ±1%
  • Wow and Flutter:
    • <0.06% JIS weighted, RMS
    • <0.1% DIN weighted, peak
  • Frequency Response: 30Hz - 20kHz ±3dB
  • MPX Filter Response: Flat within 1dB to 15kHz
  • Harmonic Distortion (at -10dB): <0.3%
  • THD at 0dB:
    • Normal tape: <0.5%
    • CrO2, Metal: <1.5%
  • Signal/Noise Ratio:
    • Dolby off: 59dB
    • Dolby B: 68dB
    • Dolby C: 77dB
  • Channel Separation: 40dB broadband
  • Erasure (at 1kHz): >70dB
  • Input Sensitivity: 110mV
  • Input Impedance: 7kΩ
  • Maximum Input Level: 2.5V
  • Output Level at 0dB: 580mV
  • Output Impedance: 1kΩ
  • Remote: No
  • NAD Link: No

Physical Specifications:

  • Dimensions (W x H x D): 420 x 120 x 250mm (Note: Dimensions are of the cabinet without attached feet; add up to 18mm for total height. Depth excludes terminals, sockets, controls, and buttons.)
  • Net Weight: 4.8kg
  • Shipping Weight: 5.6kg

Usage Features:

The NAD 6155 is designed for ease of use despite its advanced features. The Play Trim control is adjusted during playback to achieve musically correct tonal balance. The Dolby HX Pro circuit operates automatically during recording, requiring no user intervention. While the 6155 is a mid-priced machine, it is engineered to perform optimally with premium-quality tapes, producing first-class recordings. Its wide-range response, low flutter, and quiet electronics also make it an excellent playback environment for high-quality pre-recorded music cassettes.

Maintenance Features:

The document does not explicitly detail maintenance features. However, as with any cassette deck, regular cleaning of the tape heads, capstan, and pinch roller is generally recommended to ensure optimal performance and longevity. The robust design, focusing on core audio performance, suggests a reliable unit.

NAD 6155 Specifications

General IconGeneral
BrandNAD
Model6155
CategoryCassette Player
LanguageEnglish

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