® 386 Dual Vacuum Tube Preamp w/Digital Out User Manual
IMPORTANT SAFETY INSTRUCTIONS WARNING FOR YOUR PROTECTION PLEASE READ THE FOLLOWING: CAUTION KEEP THESE INSTRUCTIONS RISK OF ELECTRIC SHOCK DO NOT OPEN A T T E N T I O N : RISQUE DE CHOC ELECTRIQUE - NE PAS OUVRIR W A R N I N G : TO REDUCE THE RISK OF FIRE OR ELECTRIC HEED ALL WARNINGS FOLLOW ALL INSTRUCTIONS SHOCK DO NOT EXPOSE THIS EQUIPMENT TO RAIN OR MOISTURE The symbols shown above are internationally accepted symbols that warn of potential hazards with electrical products.
IMPORTANT SAFETY INSTRUCTIONS LITHIUM BATTERY WARNING CAUTION! This product may contain a lithium battery.There is danger of explosion if the battery is incorrectly replaced. Replace only with an Eveready CR 2032 or equivalent. Make sure the battery is installed with the correct polarity. Discard used batteries according to manufacturer’s instructions. U.K. MAINS PLUG WARNING A molded mains plug that has been cut off from the cord is unsafe. Discard the mains plug at a suitable disposal facility.
386 Table of Contents Introduction Section 3 - Digital Applications 0.1 Defining the 386................................................i 3.1 Digital Output Front Panel Functions ...........10 0.2 Service Contact Info.........................................ii 3.2 Digital Rear Panel Connections .....................10 0.3 Warranty............................................................ii 3.3 Sync Input Sample Rate Selection.................11 0.4 Installation Recommendations...................
386 INTRODUCTION INTRO CUSTOMER SERVICE INFO 386 DEFINED WARRANTY INFO ®
386 Introduction INTRODUCTION Congratulations on your purchase of the dbx 386 Dual Vacuum Tube Preamp with digital output capabilities. For over 25 years, dbx has been the industry leader in dynamics processing. With the introduction of the 386, we offer the classic smooth and warmth qualities of tube microphone pre-amplification, combined with the state-of-the-art proprietary dbx Type IV™ conversion system to offer the best characteristics of both analog and digital recording capabilities.
386 Introduction 0.2 Service Contact Info If you require technical support, contact dbx Customer Service. Be prepared to accurately describe the problem. Know the serial number of your unit - this is printed on a sticker attached to the rear panel. If you have not already taken the time to fill out your warranty registration card and send it in, please do so now. Before you return a product to the factory for service, we recommend you refer to the manual.
386 Introduction 0.4 Installation Recommendations Install the 386 in your rack with the provided rack screws. It is essential that when the 386 is being mounted in a rack mounting enclosure, the unit should be positioned with enough room (at least one centimeter at the top and one centimeter at the bottom of the unit) to allow proper ventilation. The 386 should not be mounted above or below anything that generates excessive heat.
386 Section 1 Getting Started Getting Started ®
Section 1 386 Getting Started 1.1 Rear Panel Connections Power Switch Turns the 386 on and off. IEC Power Cord Receptacle This is the power cord receptacle of the 386. An IEC cord is included with the shipped product. AES/EBU Digital Connector The 386 provides AES/EBU digital output formating through the XLR connector. Be sure to use short lengths of 110Ω digital cables rather than standard XLR to XLR cables. Using the correct cables will prevent digital dropouts and other interconnection problems.
386 Getting Started Section 1 1.2 Front Panel Controls Instrument Input This unbalanced high-impedance input connection is used to insert an instrument signal directly into the preamp. Use the LINE switch to make instrument input or the rear panel line input active. Plugging into the instrument jack will override the rear panel 1/4” input jack (line input must be selected).
Section 1 386 Getting Started Meter Select Switch This switch allows you to select display metering of either the digital or analog output signal. The analog level is scaled in dBu, while the digital level is scaled in dBFS. LightPipe™ Meter This meter displays either the analog or digital output signal. Digital Output This knob controls the signal being sent to the A/D Converter, and ranges from -15 to +15dB. 1.
386 Section 2 ANALOG APPLICATIONS ANALOG APPLICATIONS ®
Section 2 386 Analog Applications 2.1 Basic Analog Connection of the 386 • Turn off all equipment before making any connections. • Install the 386 in your rack with the provided rack screws. It is essential that when the 386 is being mounted in a rack mounting enclosure, the unit should be positioned with enough room (at least one centimeter at the top and one centimeter at the bottom of the unit) to allow proper ventilation.
386 Analog Applications Section 2 2.3 Direct Connection to a Recorder 1). Make microphone connections, being careful to keep the DRIVE control in the minimum (+30 dB) position. 2). Connect the 386’s Line outputs directly to the audio inputs of your recorder. 3). Enable the record function of the specific track of the recorder and open the specific tape track return in the console which corresponds to the track to which the 386 is connected.
386 Section 3 DIGITAL APPLICATIONS DIGITAL APPLICATIONS ®
Section 3 386 Digital Applications 3.1 Digital Output Front Functions of the 386 Dither Switch This switch is used to select the dither type algorithms including: TPDF, SNR2 , or None. Dither is random noise that is added to the audio signal which effectively eliminates the harmonic distortion created by truncation. See the“Truncation” graph in section D.2 of the Appendix. The LED will be lit RED for the SNR2 or GREEN for the TPDF dither algorithm. When the LED is off, dithering is not in use.
386 Digital Applications Section 3 AES/EBU Digital Connector The 386 provides AES/EBU digital output formating through the XLR connector. Be sure to use short lengths of 110Ω digital cables rather than standard XLR to XLR cables. Using the correct cables will prevent digital dropouts and other interconnection problems. S/PDIF Digital Connector The 386 provides S/PDIF digital output formating through the RCA coaxial connector.
Section 3 386 Digital Applications 3.4 Direct Connection to a DAW (CPU) S/PDIF Rear Panel Connections • • Connect the source to the desired 1/4” TRS or XLR input. Connect the AES/EBU or S/PDIF output of the 386 and run into the AES/EBU or S/PDIF input interface of the DAW (CPU). Front Panel Digital Output Features 1). 2). 3). 4). 5). 6). Use Use Use Use Use Use the the the the the the METER switch to select digital output metering. DITHER switch to select the desired dither algorithm.
386 Digital Applications Section 3 3.5 Direct Connection to a Digital Mixer (insert) THRESHOLD THRESHOLD - + - CHANNEL ONE 2:1 -40 -20 SC Enable 3:1 -20 1.6:1 -60 O -10 GAIN REDUCTION dB + 30 OverEasy 0 27 24 21 +10 2:1 SC Mon 1.2:1 8:1 RATIO EXPANDER / GATE 12 9 4 2 -24 1 -18 50 -12 -6 0 +6 +12 THRESHOLD 12.5 -10 Auto I/O Meter +8 +10 1:1 :1 RATIO 3 dB/mSec .
Section 3 386 Digital Applications 3.6 A/D Conversion S/PDIF or AES/EBU Rear Panel Connections • • Connect the source to the desired 1/4” TRS or XLR input. Connect the AES/EBU or S/PDIF output of the 386 and run into the AES/EBU or S/PDIF input interface of the DAW (CPU). Front Panel Digital Output Features 1). 2). 3). 4). 5). 6). Use Use Use Use Use Use the the the the the the METER switch to select digital output metering. DITHER switch to select the desired dither algorithm.
386 Digital Applications Section 3 3.7 Multi-Tracking to Digital -24 SYNC AES/EBU or S/PDIF Rear Panel Connections • • Connect the source to the desired 1/4” TRS or XLR input jack. Connect the AES/EBU or S/PDIF output of the 386 and run into the AES/EBU or S/PDIF input of the digital mixer. Front Panel Digital Output Features 1). 2). 3). 4). 5). 6). Use Use Use Use Use Use the the the the the the METER switch to select digital output metering. DITHER switch to select the desired dither algorithm.
Section 3 386 Digital Applications 3.8 Analog and Digital Output Application MONITOR SOURCE ANALOG OUTPUT S/PDIF or AES/EBU The 386 gives you the unique option of utilizing the analog and digital outputs simultaneously. This option is ideal for using the analog output section as a reference monitoring signal of the digital signal.
386 Appendix APPENDIX APPENDIX Sync Input Info Block Diagram dbx Type IV™ White Paper Noise-Shaping Algorithms Truncation Specifications ®
Appendix A 386 Sync Input Info Sync Input Info The dbx 386 comes with the word input 75Ω terminated. For certain configurations, you may wish to have the sync input be unterminated. Certain "house sync" configurations will require you to change the default position of the termination jumper on the main circuit board.
Front Panel Instrument Input Rear Panel Line Input Insert - + Digital Output Level +48V Analog Output Level Microphone Input Digital Analog 20dB Pad Analog Outputs Phase Invert dbx TYPE IV Conversion System Bargraph Meter Low Sample Rate Word Length DSP Dither Drive Output Format Shape dbx Pulsar Chip Line/Mic Word - Out Word - In Low Cut Peak LED 12AU7 Tube S/PDIF Output AES/EBU Output 386 Block Diagram Appendix B Block Diagram ® 386 User Manual 19
Appendix C 386 Type IV™ White Paper Type IV™ White Paper dbx Type IV™ Conversion System White Paper by Roger Johnson The dbx Type IV™ Conversion System is a proprietary analog-to-digital (A/D) conversion process that combines the best attributes of digital conversion and analog recording processes to preserve the essence of the analog signal when it is converted to a digital format.
386 Type IV™ White Paper Appendix C to-noise performance since the signal is now closer to the noise floor. Because users of digital equipment have to be extremely careful not to exceed 0 dB FS (full-scale), they must use peak-reading headroom meters. On the other hand, the forgiving nature of analog tape allows users of analog recording equipment the luxury of only needing to monitor the average level using VU meters, often having no peak indicators whatsoever.
Appendix C 386 Type IV™ White Paper Input Signal Level TYPE IV™ Over Region +12 +8 +4 0 dB FS 0 -4 dB -4 A/D Converter Linear Region Noise Floor Figure 2 - Input Signal Levels Mapped to Type IV Over Region Fig. 2 illustrates the mapping function in a different way. Input levels are shown on the left of the graph, while converted levels are shown on the right. Notice the mapping of large signal excursions to the 4 dB “Type IV™ Over Region.
386 Type IV™ White Paper Appendix C Amplitude Time Figure 3a - Signal Having Low and High Frequency Content Amplitude A/D Clip Level Time A/D Clip Level Figure 3b - Signal of Fig.
Appendix C 386 Type IV™ White Paper Amplitude High-Frequency Information Completely Lost High-Frequency Content A/D Clip Level Low-Frequency Content Time A/D Clip Level High-Frequency Information Completely Lost Figure 3c - Disproportionate Loss of High-Frequency Information Due to Clipping Amplitude 0 dB FS } -4 A/D Clip Level TYPE IV™ Over Region Time -4 } 0 dB FS TYPE IV™ Over Region A/D Clip Level Figure 3d - Type IV Mapping Preserves High-Frequency Information Now you’re probably wo
386 Appendix Appendix D D.1 Noise-Shaping Algorithms D.1 16-Bit TPDF dither. (a) Shape “off”, (b) with shape set to “S1”, (c) with shape set to “S2.” Parameters: Input -60dBFS, 1 kHz; FFT Length= 2048, Sample Rate= 48 Khz, Averages= 32; Graph Steps= 1024. D.2 Truncation D.2 (a) 24-Bit word, (b) 16-Bit truncated output, no dither. Parameters: Input -60dBFS, 1 kHz; FFT Length= 2048, Sample Rate= 48 Khz, Averages= 32; Graph Steps= 1024. .
Appendix D 386 Appendix D.
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