dbx 1650T Mic Pre and Limiter

January 18, 1996 -- The new dbx 1650T is a high-end mic pre and limiter utilizing four 6992 tubes to provide a phenomenal amount of headroom while retaining an unparalleled level of sonic purity.

The 1650T's microphone preamp features an incredibly wide dynamic range of 154 dB, which provides a pristine signal for operation within the confines of digital's 96 dB dynamic range. The mic pre's beefy front end is overengineered to the point that it can accept the speaker output from a 100-watt guitar head through its line input without an attenuator and still not be overdriven.

The processor's four tubes, originally designed for Russian radar, handle three gate stages and a gain-reduction stage. The first two stages are for preamplification, followed by an attenuation stage and an output amplifier. Semiconductors have been utilized to stabilize and bias tube elements free of the expected sonic tradeoffs. The audio, itself, only travels through tubes. The signal doesn't go through silicon until it reaches the output stage, where it passes through a Class A MOSFET output to drive its low impedances.

The dbx 1650T pedigrees a fully-balanced, Class A design from input to output utilizing absolutely no global feedback. Local feedback has been limited strictly to the gain cell and the output stage. The processor features a balanced and floating output which allows either side to be tied to ground with no loss of headroom or voltage.

Extensive precautions have gone into the design of the dbx 1650T to avoid electroplating the rare earths of its tubes. When the unit is initially powered, it waits for the current to drop, indicating that the resistance of the heater has gone down and that electrons are being emitted, before enabling the high voltage. If any anomalies occur in the power supply, the 1650T activates a hard mute on the output. Output mutes are available in all gain stages and power variations. As with the warm-up cycle, the processor also features a cool-down period once the power is turned off to further protect the tubes.

The maximum output level of the 1650T is +34 dBv into 150 ohms. Internal operating headroom is +40 dBv with limiting done at the +4 dB level. The dbx unit can provide an incredible 117 dB of gain from the input to the output.

The microphone pre-amp gain may be adjusted in 10 dB increments. Limiter emulation is available via EMU Card(TM) set by preset or manual. Side chain access and stereo coupling are also available. For microphones requiring an external power source, 48-volt Phantom Power is offered, while a W meter provides signal monitoring.

For more information, visit their web site at www.dbxpro.com.