LACHAPELL AUDIO Model 992 Vacuum Tube Preamplifier for Microphones and Instruments Operating Manual
Introduction: Congratulations on your purchase of the LaChapell Audio 992, a fully balanced pure class-A vacuum tube preamplifier and instrument input amplifier. LaChapell Audio has gone to great lengths in making sure this preamp not only deliver world class performance numbers but more importantly, deliver them with warmth and character while using only the finest components.
• SERVICE/REPAIR- WARNING: With the exception of tube replacement (see below) the user should NOT attempt to service this unit. Due to the risk of electrical shock and the presents of lethal voltages inside the chassis. Only LaChapell Audio or other highly qualified personnel are to perform maintenance and service activities. Tube replacement: Turn the unit off, disconnect the power cord and let the unit stand for at least 20 minutes.
• SAFETY PRECAUTIONS: Never operate the 992 with the top panel removed. The top panel’s perforations provide more then enough ventilation for cooling. The top panel also plays an important role in maintaining good signal to noise ratio performance. Always provide a source to ground (earth.) Never under any conditions should a power cord that has the 3rd prong for ground missing or defeated be used.
Controls: FIGURE 2.1 the five LED tipped toggles on channel 1 are (from left to right) Meter, 48v, -20db, Polarity Reverse and Mute. The two lower knobs on the inside are for input gain and the two upper knobs are for output gain. • INPUT GAIN: The user is given separate control of the input signal strength via a dual ganged potentiometer.
• -20dB: If needed the user can pad the microphone inputs using the -20db attenuator. This adjustment takes place before the first input tube. This function is defeated while the Hi-Z inputs are engaged. • POLARITY REVERSE: Some of the more common reasons to use this would be to reduce feedback in a live environment, enhance the stereo image of certain content or to assist in eliminating headphone signal bleed through during a recording session.
