Mesa/Boogie 400 manual Input Circuitry, Outputs, LED Power Indicators, Power and Standby Switches

INPUT CIRCUITRY

The Strategy 400 Stereo offers extremely sensitive input circuitry: 0.2 volts will produce full power when the Level control is turned fully up. This means you can actually plug in many signal sources directly without needing a preamplifier. The output from virtually any effect unit is strong enough -- as is any keyboard, CD player, cassette deck... even electric bass plugged in direct produces full power with incredible tone. Electric guitar needs more tone shaping to sound right but can still be plugged in direct for testing purposes. When using the Strategy with a preamp you should turn down the Level controls for best signal-to-noise performance and easy controllability from the preamp knobs. With the MESA/Boogie Quad preamp, settings from 2 to 5 are recommended for the Strategy Level controls. With the Level set at 7, input sensitivity is reduced to 1 volt for full power out. With the Level at 6, 2 volts are needed; and at 5, 3 volts of signal deliver full power. Input impedance of each channel is 75K ohms which becomes 37.5K when using the Parallel Input jack, still high enough to be perfectly compatible with virtually any signal source.

OUTPUTS

Each channel of the Strategy 400 offers two 8 ohm plus two 4 ohm quarter inch jacks for connection to speaker cabinets. Unlike transistor amps, the 400 will produce full power at either 4 or 8 ohms, and mismatching of speaker impedance will not cause damage or severe loss of power (extreme mismatches will decrease tube life however). Avoid running either channel without a proper load or damage may result. When using more than one speaker cabinet on a single channel, remember that the total impedance goes down as more cabinets are hooked up. For example, if you use one 8 ohm cabinet, use one of the 8 ohm jacks. But if you use two 8 ohm cabinets on the same channel, they will be operating in parallel and the total load will be 4 ohms. Therefore plug each cabinet into a 4 ohm jack.

LED POWER INDICATORS

The output power of each channel of your Strategy 400 is continuously monitored by simple LED indicators. Reflecting the logarithmic relationship of loudness and power, the first LED comes on at 12.5 watts (-12 db); the second at 50 watts (-6 db) and all three at 200 watts. Due to the 400's large dynamic headroom and predominately second-order harmonic distortion, it is quite possible to light up all three LED's very strongly before objectional clipping distortion is heard. A more complete explanation of distortion appears later in this manual.

POWER AND STANDBY SWITCHES

AC Mains power is turned on via the Power switch and indicated by the pilot light. Before switching on the power, place the other two front panel switches in the Standby position. Allow 20 to 30 seconds of warm-up time before switching the Standbys to On. This helps extend tube life by preventing a high-voltage turn-on surge, however, all amplifiers are tested to withstand this extra stress in case you neglect to follow the best procedure.

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