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Фрагмент инструкции
Your Bryston preamplifier has been engineered to provide many years of trouble-free, highly musical listening enjoyment. This instruction manual refers to the Model 12B. With the exception of the phono inputs, the Model 11B preamplifier is identical, and the instructions pertain to it in exactly the same way. Where a difference occurs, it will be noted in the text. The Model 12B is a basic signal preamplifier with switching facilities for all the sources likely to be used by even the most elaborate domestic sound system, including dubbing capability for two tape recorders, and the convenience of recording from any source while simultaneously listening to any other through the speakers. The included diagram will illustrate the switching functions of the Bryston Model 12B preamplifier. Phono Inputs; Including Moving Coil The Model 12B is supplied with an internal moving-coil step-up transformer. This extremely wideband transformer, with almost no added noise or distortion, increases the voltage gain through the phono section by 22.5dB, and adjusts the input impedance to suitthe vast majority of moving-coil cartridges. (It is available on special order with 6dB less gain, and a higher input impedance, for those few high-output MC cartridges which may perform better with these settings). The 12B will also accept moving-magnet cartridges by switching the MC transformer out via a switch on the front panel. In this case, the cartridge is plugged into the MM inputs on the rear panel. The MM inputs (only) are equipped with input loading capacitors of about 275 pf per channel. When added to the normal turntable wiring capacitance, this yields about 300-400 pf, which is in the optimum range for most cartridges. (This internal phono capacitance may be special-ordered to any value at no extra charge). The Model 11B is identical to the Model 12B except that it is not equipped with the MC transformer. Thus both .phono inputs become MM inputs, as above. They may be selected between Phono 1 and Phono 2 via the switch on the front panel. (The MC tranformer may be retrofitted at any time, converting the preamp to a 12B). Since the phono stage on the Model 12B inverts absolute phase, the MC transformer is connected to invert phase also. Thus, MC cartridges play in proper phase with no special connection necessary. In case of MM cartridges, reversing the hot and ground leads on the cartridge pins is a convenient way of obtaining the same function. Tape Monitor Function Although the 12B’s tape monitor function is arranged differently from most standard preamplifiers, it is not complicated to use. The two selector switches operate independently, and affect only the outputs to which their labels refer. Thus the “MAIN OUTPUT” switch is used as the tape monitor, also. Include yourtape deck in the preamp’s tape loop in the normal way (i.e., its record head is connected to Tape 1 output, and its playback head is plugged back into Tape 1 input). To monitor the recording, just move the MAIN OUTPUT switch to “Tape 1 ” A second tape deck may be included in the tape loop in a similar manner, using Tape 2 input and output, and “Tape 2” selector position for monitoring. Two Tape Recorders; Dubbing Facility Plug in the playback and record heads of the two decks to their respective tape inputs and outputs, as above. Normally, both decks will receive the same signal for recording. When “Tape 1” is selected on the TAPE OUTPUT switch, however, the playback head of deck 1 is connected to the record head of deck 2, via Tape 2 output. This obviously allows direct dubbing from Tape Deck 1 to Tape Deck 2. Selecting “Tape 2” on the TAPE OUTPUT switch allows dubbing in the opposite direction by reversing these connections. External Equalizer, Noise Reduction, or Other Audio Processor An equalizer, noise reducer, etc., may be included in the tape loop (as shown in the diagram) by connecting its input to one of the tape outputs, and its output back to (the same numeral) tape input. Turn the MAIN OUTPUT switch to (that numeral) “Tape” position whenever you wish to use the audio processor in the signal path. During that time, the TAPE OUTPUT switch is used as the selector for wh ichever source is to be processed. Turning the MAIN OUTPUT switch back to this source position will bypass the processor. Headphone Jack The Model 12B is equipped with a headphone jack for convenient, private listening. The signal is taken directly from the output circuit which normally feeds the power amplifier, and is thus controlled by the volume knob. This output will drive headphones of any type, but lower impedance headphones may require somewhat more volume control rotation for the desired loudness. To facilitate headphone listening without disturbing others, the preamplifier automatically disconnects the direct feed to the power amplifier. (This is indicated by the green pilot light on the front panel changing to red whenever the output relay is opened). This...
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