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Extracted text from Nad 3140 Owners Manual (Ocr-read)
FRONT PANEL CONTROLS
1. POWER. Depress to switch on the amplifier and any other equipment plugged into the SWITCHED convenience outlet on the rear panel. To switch off the power, depress the button again and release it.
If you prefer, you may leave the 3140's POWER switch per- manently engaged and use an external switch (such as a clock timer) to turn the power on and off.
2. PHONES. Plug stereo headphones in here. The circuit will provide proper drive signals for ail conventional stereo head phones regardless of their impedance, with just one exception: electrostatic headphones usually are supplied with an adapter unit which must be connected directly to the speaker terminals on the rear panel.
Before plugging conventional headphones into the PHONES Jack, turn down the VOLUME control for safety. And when you are not listening to the headphones it is wise to unplug them from the PHONES jack. Otherwise, when listening to loudspeakers you might turn up the volume to a level which would feed excessively strong signals to the headphones and damage them.
You may freely use headphone extension cables. If you want to use a headphone Y-connector to drive two headsets simultaneously, they should be identical models. Connecting together two headphones which differ widely in impedance usually will produce a substantial loss of volume in the headset having the higher imp edance (or in both).
3. SPEAKER SELECTOR. When this switch is set to "A", sound is heard only from the speakers connected to the SPEAKERS A terminals on the rear panel of the 3140. When the switch is set to "B" the SPEAKERS A terminals are shut off and sound is heard only from the speakers connected to the SPEAKERS B terminals. At the "A+B" setting the amplifier's output power is fed to both sets of speakers; they are wired in parallel by the switch. At the "OFF" setting, both sets of speakers are shut off.
Thus if you have your main stereo speakers wired to the "A" terminals and a set of extension speakers wired to the "B" terminals, you can choose to hear only the main speakers (A), only the extension speakers (B), or you can activate both (A+B).
The amplifier's output signal is present at the PHONES jack at ail settings of the SPEAKER SELECTOR switch. When using headphones it normally is advisable to switch OFF the loudspeakers; then the VOLUME control may freely be used to adjust the loudness level in the headphones with no fear of overdriving the speakers or disturbing neighbors.
If you have connected the adapter unit for electrostatic head- phones to the SPEAKERS B terminals, you can use the SPEAKER SELECTOR to switch between your main stereo speakers (A) and the headphones (B).
If you have connected speakers wired for "ambience recovery" to the SPEAKERS B terminals, you can use the SPEAKER SELEC TOR to listen to conventional stereo (A), to switch off the main speakers and listen to only the stereo L-minus-R "difference" signal in the rear speakers (B), or to listen to spatially-enhanced stereo (A+B). You will find that the stereo difference signal is usually lacking in bass. If the difference signal is very weak, the recording lacks stereo separation.
4. SPEAKER EQ. The lowest octaves of deep bass sound are seldom experienced at their full level in stereo playback, for three reasons:
(1) Most loudspeakers are designed for uniform response down to
a planned System resonance frequency (usually in the 40-70 Hz range)
and roll off rapidly in response below that frequency.
(2) The low bass is often rolled off by filters when records are made in order to limit groove-modulation levels and increase playing times.
(3) Standing waves bias the distribution of low-frequency
energy in listening rooms, weakening the low bass and reinforcing the
mid-bass at typical listening positions.
The NAD SPEAKER EQUALIZER compensates for these losses by providing a 12 dB/octave boost below either 45 Hz or 70 Hz. Since ail closed-box (acoustic-suspension and infinite-baffle) loudspeaker Systems roll off in response at 12 dB/octave below the woofer/cabinet resonance, the NAD SPEAKER EQUALIZER precisely compensates this rolloff and extends the useful response of the speaker a full octave lower in frequency. Note: while the SPEAKER EQ can be used with "vented" speakers (bass-reflex, tuned-port. auxiliary bass radiator, et al.), these designs usually exhibit a much more rapid rolloff below the system's planned cutoff (typically either 18 or 24 dB/octave); consequently the SPEAKER EQ will not produce the same dramatic benefit with these designs as it does with acoustic-suspension Systems.
If you have full-size speakers with strong response down to the 40-50 Hz range, the 45 Hz setting of the SPEAKER EQ is theoretically "correct." Nevertheless you should feel free to use the 70 Hz setting (instead of the BASS control) to bring up the rolled-off bass in recordings to a satisfying level; let your ears be your guide.
Three CAUTIONS should be observed in using the SPEAKER EQ:
(1) This circuit is intended for use with loudspeakers having woofers eight inches (20 cm) or larger in diameter, preferably those with "long-throw" voice-coils and acoustic-suspension enclosures. It is not recommended for use with small "mini" speakers having woofers smaller than six inches; in most cases they are not designed to accept high power input at low frequencies and will only distort or suffer damage as a result.
(2) Be prepared to reduce or switch off the equalization when playing recordings (especially digitally-mastered ones) which contain unusually potent recorded bass. The SPEAKER EQ boosts deep bass levels by 12 dB (i.e. by a factor of 16 in power). A bass- heavy input signal may Overdrive the amplifier into clipping and Overdrive your woofers beyond their safe excursion limits causing the voice-coils to clatter against their magnet back-plates. As long as it sounds good it probably is OK; but distorted or unmusical sounds are a sign of distress in a woofer.
(3) We recommend that you use the Infrasonic Filter, in order to avoid amplifying inaudible frequencies below 20 Hz, and to preserve the amplifier power and available woofer excursion capacity for the genuine bass energy in the music.
5. BASS. The Bass control adjusts the relative level of the low frequencies in the sound. The electrical response of the amplifier is flattest when the control is set in the detent at the 12 o'clock position. Rotation of the knob to the right (clockwise) increases the level of low-frequency sounds, and rotation counter-clockwise decreases their level. Adjust it to achieve the tonal balance which sounds most natural to you. You will note that at moderate rotations the effect of the Bass control usually is subtle because its action is confined to the lowest audible frequencies. Only at large rotations away from center is there a substantial boost or cut at the mid-bass frequencies which are prevalent in music.
6. TREBLE. The Treble control adjusts the relative level of the high frequencies in the sound. The electrical response of the amplifier is flattest when the control is set in the detent at the 12 o'clock position. Rotation of the knob to the right (clockwise) increases the level of high-frequency sounds, and rotation counter-clockwise decreases their level. Adjust it to achieve the tonal balance which sounds most natural to you. You will note that boosting the Treble increases the brilliance and clarity of details in the sound, but also makes any noise more prominent. Cutting the treble makes the sound mellower and suppresses hiss and record surface noise, but too much Treble cut will make the sound dull.
7. INFRASONIC FILTER. The signal from a record player usually contains strong infrasonic energy (due to disc warps, tone arm resonance, and vibrations reaching the turntable) which, if amplified at full strength, will waste amplifier power and produce excessive woofer cone excursions, muddying the sound. This