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:
- Dynamic Range >130dB
- Headroom >26dB (reference = +4dBu)
- Signal-to-Noise 104dB (reference = +4dBu)
- THD + Noise <0.002%
- Frequency Response +0/-3dB (2Hz-200kHz maximally flat
phase response)
For more information, visit their web site at www.dbxpro.com. | 
