REAR PANEL CONNECTIONS
1. PHON011NPUT. This input is designed for use with "high-output" moving-coil cartridges such as the NAD 9000, Dynavector (Ultimo) 10A and 10X, Satin M18 and M117, Adcom XC/LT, et al.
This input may also be used with cartridges of other types which have lower-than-normal output voltage, such as the B&O MMC series and Audio-Technica models AT-22 through AT-25. The Phono 1 input has a standard input impédance (47K ohms résistance, 100 pF capacitance) but is 10 dB more sensitive than the Phono 2 input.
Moving-coil pickups with low output voltage should be used with an external transformer or pre-preamp. The output from the step-up device may then be connected to either Phono 1 or Phono
2. CAUTION: Some step-up devices may produce a high enough output level to overload the Phono 1 input, yielding distortion; in case of doubt, use Phono 2. Here’s one way to tell: if you find that the amplifier is driven to full power (as indicated by the peak-reading front-panel LED display) with a volume-control setting of 12 o'clock or lower, then you should switch to the less sensitive Phono 2 input. Conversely, if you must turn the volume control up beyond the 3 o'clock position in order to drive the amp to full peak power, then the extra gain of the Phono 1 input will be beneficial.
2. PHONO 2 INPUT. This input is intended for the majority of phono cartridges of the moving magnet, induced magnet, moving flux, and moving iron (variable reluctance) types.
Plug the signal cables from your turntable into these jacks. If the cables or plugs are color-coded, refer to your turntable's instruction manual to learn which cable or plug is for the Left channel and which for the Right. Be careful to insert each plug fully into the socket so that the plug's metal skirt fits tightly over the exterior of the socket. If necessary, carefully crimp the plug's metal skirt slightly so as to obtain a tight fit with the socket.
3. CAPACITANCE SELECTOR. This switch selects the input capacitance for PHONO 2 on/y. It enables you to optimise the load capacitance for those cartridges whose frequency response is affected by this parameter.
If you are using a low-inductance pickup (such as a Grado or Micro-Acoustics), or a moving-coil cartridge with a transformer or pre-preamp, then the setting of the Capacitance Selector is unimportant. But with many high-inductance magnetic pickups, the capacitance setting will audibly alter the sound of the pickup.
In order to select the best value of preamp input capacitance you must first determine the total capacitance recommended for the cartridge. This will usually be included in the maker's specifications, and may also be mentioned in magazine reviews of the cartridge. Next, subtract the capacitance of your turntable's tone-arm wiring and signal cables. (Check the specifications supplied with the tonearm, or write to the manufacturer of the tonearm, or as a last resort assume a typical value of 150 pF.) After this subtraction, what remains is the desired value of preamp input capacitance. Set the Capacitance Selector to the nearest value. It is not necessary to match the computed value exactly : with most phono cartridges a variation of 50 pF one way or the other will produce only a very slight change in frequency response.
Example: suppose you are using a Stanton 881S pickup cartridge in a Pioneer turntable. Stanton specifies a recommended load capacitance of 275 pF for the cartridge, and the Pioneer turntable has a cable capacitance of about 100 pF. 275 minus 100 equals 175 pF, so you should set’ the Capacitance Selector to the nearest value, 200 pF.
It you prefer, you may simply set the Capacitance Selector by ear while listening to recordings which are strong in high-frequency overtones. Typically, when the capacitance is too low the upper-midrange (the soprano voice range) will be softened and the response at the highest frequencies will be peaky, leading to edgy
violin tone and increased surface noise. Too high a value of capacitance will bring the upper-midrange forward while rolling off the extreme highs.
4.GROUND. If your turntable is equipped with a grounding wire (usually a green wire terminating in a U-shaped spade lug), connect it to this terminal. Turn the thumb-nut counter-clockwise, place the spade lug under the nut, and tighten the thumb-nut clock-wise to secure the lug. If the grounding wire has no terminal lug, strip off a half-inch (1 to 2 cm) of insulation to expose the bare wire, twist the wire strands tightly together, insert the wire through the small hole in the shaft of the Ground terminal, and tighten the thumb-nut to fasten the wire in place.
5.TUNER. Connect the signal cable from a radio tuner to these jacks. As with ail of the other input/output jacks, the upper one in each pair is for the left channel and the lower jack is for the right channel.
6.AUX. These auxiliary input jacks are for any "line level" signal source—such as a spare tape player, a television sound tuner, the audio line output from a videocassette or videodisc player, or a child's record player containing a high-output ceramic pickup cartridge.
7.TAPE 1 REC/PLAY. Two types of connectors are provided for use with a stereo tape recorder: separate pairs of RECORD and PLAY phono jacks, and a five-pin DIN socket. If your recorder has only DIN-type plugs, use the DIN connecter. If your recorder has both a DIN plug and pairs of phono jacks, it is preferable to use the phono plug connections. (Do not use both the phono plugs and the DIN plug simultaneously.)
The TAPE 1 connections may be used with tape recorders of ail types: cassette, micro-cassette, open-reel, eight-track, digital, etc. To make recordings, connect a stereo patch cord from the RECord jacks to the LINE or RADIO input jacks on the recorder (not to ils microphone inputs). To play back tapes, connect a stereo patch cord from the recorder's LINE output jacks to the amplifier's PLAY input jacks.
8. TAPE 2 REC/PLAY. These jacks enable connection of a second tape recorder of any type, and the amplifier is wired to permit copying tapes from one recorder to the other. Connect a cable from the RECord jacks to the tape deck's LINE or RADIO input jacks, and another cable from the amplifier's PLAY jacks to the recorder's LINE outputs. The upper jack is for the left channel and the lower jack for the right channel.
The TAPE 2 jacks may be used for a signal-processing accessory instead of a second tape machine. Examples of such accessories include a dynamic range processor, a dynamic noise filter, an impulse noise ("tick and pop") suppressor, and any other processor whose operation depends on the setting of a signal threshold. Connect a patch cord from the REC jacks to the processor's inputs, and another patch cord from the PLAY jacks to the processor's outputs.
Other signal processors, such as a graphic equalizer or the special equalizer supplied for use with some loudspeakers (e.g. Bose, Electro-Voice, KLM), may be connected either to the tape jacks or at the output of the preamp. The choice is a matter of convenience.
9. PRE-AMP OUT, NORMAL IN, LAB IN. Each channel of the amplifier is comprised of two independent sections or stages: the control preamplifier (including the phono preamp and most front-panel controls), and the power amplifier (which provides the power to drive loudspeakers). In normal operation the preamp and power amp are connected together via U-shaped metal jumpers; check to be sure that they are fully inserted into the jacks and that nothing is touching them.
Two sets of power amp inputs are provided. The LAB inputs have wideband frequency response extending uniformly from low infrasonic to high ultrasonic frequencies, and may be used for laboratory tests and special applications. The NORMAL inputs are equipped with infrasonic and ultrasonic filters; these reject any
interference which occurs outside of the audible frequency range, in order to prevent intermodulation distortion and preserve the amplifier's power for music.
For conventional operation the PRE-AMP OUTjacks are connected to the NORMAL IN jacks by means of the metal jumpers. Removal of the jumpers (with the POWER switched OFF) enables various signal-processing accessories to be connected in the signal path between preamp and power amp: an equalizer, a time-delay ambience reproducer, a stereo image enhancer, etc. To use a signal processor, connect a stereo patch cord from the PREAMP OUT jacks to the processor's line-level input jacks, and a second patch cord from the processor's output jacks to the amplifier's NORMAL IN jacks. (Note: any signal processor whose operation depends on the setting of a threshold, such as a dynamic noise filter or a DBX decoder, should be connected to one of the sets of TAPE REC/PLAY jacks—where the signal levels are unaffected by volume and tone controls—rather than to the PRE-AMP OUTjacks.)
If you remove the metal jumpers, save them in case you may want to disconnect the signal processor and return to normal operation at a later time. If the jumpers should be lost, a conventional stereo patch cord can be used to connect PRE-AMP OUT to NORMAL IN or LAB IN.
The NAD 3140 can be used as the heart of an elaborate audiophile sound System. For example the PRE-AMP OUT jacks may be connected via a stereo patch cord to any high-quality separate power amplifier. To use a separate high-power amplifier for one set of loudspeakers while continuing to use the NAD 3140's built-in power amp for headphones or another set of loudspeakers, simply install Y-connector adapters to split the signal from the PRE-AMP OUTjacks. The preamp stage is capable of driving several power amplifiers in parallel, or driving the long signal cables required to connect to power amps which are located near the speakers, or to "powered" loudspeakers with built-in power amps. The preamp output can also be fed to a time-delay ambience sys-tem, with the 3140's built-in power amp used to drive either the main stereo speakers or the time-delayed ambience speakers. In a bi-amplified System the preamp output is fed to the input of an electronic crossover; the low-frequency output of the crossover unit is fed to the amplifier which drives the woofers, while the high-frequency output of the crossover unit is fed to the 3140's NORMAL IN or LAB IN jacks, and the speakers' tweeters are connected directly to the 3140's SPEAKER terminals.
10. BRIDGING MODE SWITCH. This switch "bridges" the NAD 3140's two power amplifier channels to form a monophonic amplifier with more than double the output power. To convert to bridged operation, the following procedure should be followed.
(1) Disconnect the metal jumper or signal cable from the left-channel input to the power amplifier section of the 3140. In the bridged (monophonic) mode the amplifier is driven through its right-channel input only (either the NORMAL or LAB input socket). If you need stereophony reproduction, the left-channel PRE-AMP OUT signal can be used to drive a second, separate power amplifier and loudspeaker, (If another 3140 in bridged mode is used for the second channel, it too will be driven through its right channel power amp input regardless of whether it is used for the right or left speaker.)
(2) Disconnect any speaker wires from both the SPEAKERS A and SPEAKERS B terminals. From the speaker which is to be driven by the 3140, connect its positive lead to the red R+ terminal, and its negative lead to the red L+ terminal, in the SPEAKERS A group of terminals.
NOTE; do not connect any wires to the black (R- and L-) terminals.
If you want to drive two speakers in parallel, connect the second speaker's leads to the red (R+ and L+) terminals in the SPEAKERS B group; make no connection to the black (R- and L-) terminals. NOTE: in the bridged monophonic mode, the loudspeaker's impedance appears to be halved as "seen" by the amplifier. An 8-ohm load looks like 4 ohms, a 4-ohm load looks like
2 ohms, and a pair of 4-ohm speakers operated in parallel will look Iikea1-ohm load. Driving a pair of such speakers to high levels may cause the amplifier to overheat, activating its protection circuits.
CAUTION: In the bridged mode the speaker wires must be "floating" with respect to ground. Do NOT connect the speaker wires to anything which shares a common ground between stereo channels (such as a headphone adapter) nor a common ground with the 3140's inputs (such as a switching comparator or a distortion analyzer).
(3) After the preceding conditions have been satisfied, use the bridging switch. It is normally covered by a metal bracket to prevent its accidental use. Loosen the screw which holds the bracket in place and swing it out of the way or remove it altogether. Press and release the BRIDGING button. The button has two settings:
IN—normal stéréo mode OUT—bridged monophonic mode
To return the 3140 to normal stereo operation at a later date, simply depress the BRIDGING button to engage the normal stereo mode, fasten the metal bracket in place over the button to prevent accidental re-setting of the switch, feed stereo signals into the left and right channel power amp inputs, and connect loudspeakers to the appropriate terminals as described below under SPEAKERS A and SPEAKERSB.
11. SPEAKER LEAD COMPENSATOR (SLC™*). When a speaker is connected to an amplifier through a length of wire, the résistance of the wire will affect the signal reaching the speaker terminals. If the wire is sufficiently short or sufficiently large in diameter, its résistance will be negligible. As a general rule, 18-gauge or heavier wire should be used for lengths of up to 20 feet (6 meters) and 16-gauge or heavier wire for lengths of up to 30 feet (10 meters). But if you use thinner wire, or greater lengths, the wire résistance may have a directly audible effect on the speaker's sound—especially with low-impedance speakers, or pairs of speakers wired in parallel. This effect is of four kinds:
(1)Some power is dissipated in the wires, and the signal delivered to the speaker is slightly reduced in level.
(2)Since the speaker's impedance varies with frequency, the reduction in signal level varies in proportion; i.e. the tonal balance of the signal is altered.
(3)Typical speaker impedances are complex, varying with signal level (for example, the voice-coil inductance varies as the coil moves in and out of the magnet gap), and may become non-linear at high volume levels. The resulting non-linear current flow produces a non-linear (i.e. distorted) voltage across the résistance of the speaker leads. Thus the audio signal may be completely distortion-free at the amplifier's output terminals, yet exhibit several percent of distortion at the far end of the leads where they connect to the speaker terminals.
(4)Finally, the wire résistance reduces the amplifier's
damping factor.
The Speaker Lead Compensator (SLC) cancels the effects of the wire résistance, eliminating the distortion and restoring the performance which would be obtained if the wire had no résistance. The SLC is calibrated for a specific amount of wire résistance, corresponding to the following lengths of standard wire sizes:
GAUGE |
FEET METERS |
|
1 |
97 |
30 |
4 |
61 |
19 |
16 |
38 12 |
|
18 |
24 |
7 |
20 |
15 |
5 |
22 |
1 |
4 |
24 |
2 |
3 |
26 |
10 |
2 |
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