dbx 786 Solid State Mic Preamp

January 16, 1997 -- Companion to the new dbx 160S Blue Series Stereo Compressor Limiter is dbx Professional Products' 786 Solid State Mic Pre-Amp. Truly a "precision" microphone pre-amplifier, the dbx 786 is designed to provide the purest reproduction of the microphone source as is electronically possible.

Featuring ubiquitous +48V phantom power, 20dB pad and phase invert functions, the mic pre-amp also includes a switchable "super low Z" setting which optimizes the preamp's performance for microphones with very low source impedance. An 11-position coarse gain switch sets the gain between +10 and +60dB (in 5dB steps), while the fine gain control varies between -3 and +3dB. Levels may be monitored on peak-program VUmeters with adjustable reference levels.

The dbx 786's signal path consists of a transformer-coupled, discrete-design premium input stage utilizing the proprietary dbx M8(TM) Mic Pre-Amp Module. This module exhibits extremely low noise (-132dBu EIN), low distortion (THD <0.002%), wide bandwidth (>200kHz) and wide input common mode range (Input CMRR >100dB).

"Spectrum", a unique variable high-frequency equalization circuit employed in the mic pre-amp enhances the high-frequency spectral content of the signal while maintaining phase integrity. The "Detail" control varies the amount of high-frequency shelving boost at the frequency determined by the Spectrum control. The combination of the Spectrum and Detail controls allow pristine high-frequency equalization adjustments without the added "hash" of traditional high-frequency EQ topologies. The minimum signal path design routes the amplified signal directly to a patented high output drive circuit. Each stage throughout the mic pre-amp is small-signal square wave compensated to assure precise phase alignment at all audio frequencies.

Two output options are available for the dbx 786; an analog card that parallels one extra high drive output per channel acting as a premium signal splitter, and a digital Type IV Conversion System card that provides proprietary analog-to-digital conversion for both channels with both AES/EBU and S/PDIF outputs.

The Blue Series microphone preamplifier offers patented high-precision, high-drive, transformer-coupled output stages capable of performing with incredible accuracy and sonic transparency in virtually any audio environment. The custom designed transformer, coupled with a discrete distortion-canceling driver circuit, is capable of driving 1000 feet of Belden 8541 cable terminated with a 150 ohm load at remarkably low distortion levels, and maximum drive levels exceed +30dBm.

Overall unit specifications include: