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Фрагмент инструкции
For these reasons, and for the more important reason of avoiding low frequency transient overshoot, ringing and phase misalignment, the low filter is a “minimum” type, with a 6dB/octave slope below cutoff. This is quite effective in reducing subsonic woofer-wooble and its attendant intermodulation effects, however, since the most problematic turntable and warp-induced rumble frequencies, in the area of 2-5Hz, are reduced an average of about 20dB or a factor of 100 in terms of power demand. The low filter switch is active in the In’ position, and affects only the phono inputs. Mute Switch The listener often is called momentarily away from critical listening, to answer the phone for-example, and wishes to reduce the gain for a short time without disturbing the volume control setting. The mute switch reduces preamp gain by 20dB. Thus thfe music may still be heard, but at a background level. This is also useful for changing records, cueing the stylus manually to a particular song, cleaning the stylus with a brush, etc. The mute switch is active in the In’ position and affects only the main outputs without disturbing the tape outputs. Mono Function Occasionally a system will display some offset in gain favouring one channel over the other due to slight differences in speaker efficiency, differences in room loading, or a somewhat off-center listening position dictated by room decor. Thus it is convenient to “mo.no” the signal to obtain the most unambiguous center image, convenient to adjust- ing the balance control. For reasons of simplicity, rather than having a separate switch for this function, the “Mute” switch also connects the two channels in Mono. Obviously, the listener may wish to advance the volume control to provide sufficient level for establishing center image. Do not forget to reduce the volume control again before deactivating the mute switch in this case, or you may be startled by the sudden increase in sound level. The balance control is a tailored inflection type which has very gradual action near the center of rotation for fine adjustments to the left-right balance of the stereo image. Turn On Delay The Model 12B contains an output relay with an approximate 3-second delay at tu rnon, to allow any transient thumps to settle. The relay opens instantly when the preampis switched off to prevent any power-supply decay artifacts from appearing at the outputs. The relay is hermetically sealed in an inert atmosphere to completely eliminate contact contamination and provide nearly infinite lifetime (rated in tens of billions of cycles). This same relay is employed in the automatic amplifier disconnect function which is part of the headphone circuit, and in the protection mechanisms connected into the power supply. Whenever the preamplifier is under power, and the relay is open for any reason, the green pilot light on the front panel changes to red. (Since the power-supply filter capacitors are quite large, the red LED indication will fade slowly after the preamp is switched off). Accessory Outlets The 12B includes three 3-prong grounded, 120 volt receptacles on the rear panel, two switched, one unswitched. Please observe the caution printed below the receptacles regarding maximum power draw from these outlets. Large power amplifiers, especially including the Bryston Models 3B and 4B should not be plugged into these receptacles. To do so may damage the preamp’s power switch. It is permissible to plug the Bryston 2B-LP into these outlets, however, or any class AB amplifier up to 50, (or class A amplifier up to 15) watts per channel. In general, it is inadvisable to switch large power amplifiers on and off by the switch in a preamplifier, for the above reason, and also because it is likely to cause a fluctuating voltage-drop on the preamplifier's line cord, which in worst case conditions can become an audible problem. DC Power-Supply Output On the rear panel of the Model 12B (and 11B) there is a DIN connector which provides ±24V DC of regulated power. This is provided for future Bryston products, such as equalizers, electronic crossovers and the like, which will be available with or without power supply, for reasons of economy. This output is fully protected, and contains a circuit which opens the output relay automatically if excessive current is drawn. The Twelve-B has been designed from a rational, function-oriented ideal of maximum musical accuracy, with an absolute minimum of useless gadgetry or extraneous controls. The signal-handling circuit is novel and fundamentally correct, both electrically and more important, sonically. We believe you will find a renewed sense of awareness of the listening pleasure in your music collection, played through your Bryston preamplifier. All your signal sources will sound cleaner and more muscially transparent than you may have experienced before. Please do not hesitate to write us if you have any questions or comments about any of our products. Your op...
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