DBX 676 Owner's Manual

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Owner’s Manual

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Warranty

1. Please register your product online at www.dbxpro.com. Proof-of-purchase is considered to be the responsibility of the consumer. A copy of the original purchase receipt must be provided for any warranty service.

2. dbx warrants this product, when purchased new from an authorized U.S. dbx dealer and used solely within the U.S., to be free from defects in materials and workmanship under normal use and service. This warranty is valid to the original purchaser only and is non-transferable.

3. dbx liability under this warranty is limited to repairing or, at our discretion, replacing defective materials that show evidence of defect, provided the product is returned to dbx WITH RETURN AUTHORIZATION from the factory, where all parts and labor will be covered up to a period of two years. A Return Authorization Number must first be obtained from dbx. The company shall not be liable for any consequential damage as a result of the product’s use in any circuit or assembly.

4. dbx reserves the right to make changes in design or make additions to or improvements upon this product without incurring any obligation to install the same additions or improvements on products previously manufactured.

5. The foregoing is in lieu of all other warranties, expressed or implied, and dbx neither assumes nor authorizes any person to assume on its behalf any obligation or liability in connection with the sale of this product. In no event shall dbx or its dealers be liable for special or consequential damages or from any delay in the performance of this warranty due to causes beyond their control.

Technical Support & Service

If you require technical support, contact dbx Technical Support. Be prepared to accurately describe the problem. Know the serial number of your device – this is printed on a sticker attached to the chassis.

Before you return a product to the factory for service, we recommend you refer to this manual. Make sure you have correctly followed installation steps and operating procedures. For further technical assistance or service, please contact our Technical Support Department at (801) 566-8800 or visit www.dbxpro.com. If you need to return a product to the factory for service, you MUST first contact our Technical Support Department to obtain a Return Authorization Number.

NO RETURNED PRODUCTS WILL BE ACCEPTED AT THE FACTORY WITHOUT A RETURN AUTHORIZATION NUMBER.

Please refer to the Warranty information, which extends to the first end-user. After expiration of the warranty, a reasonable charge will be made for parts, labor, and packing if you choose to use the factory service facility. In all cases, you are responsible for transportation charges to the factory. If the product is still under warranty, dbx will pay the return shipping.

Use the original packing material if it is available. Mark the package with the name of the shipper and with these words in red: DELICATE INSTRUMENT, FRAGILE! Insure the package properly. Ship prepaid, not collect. Do not ship parcel post.

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Table of Contents

Overview �� 2

Introduction �� 2 Features �� 3

Installation �� 4

Installation Recommendations �� 4 Making Connections �� 4 Applying Power �� 4

Quick Start �� 5

The User Interface & Connectors �� 6

Front Panel �� 6 Rear Panel �� 7

The Preamp Section ��8

Preamp Example Settings �� 9 Setting The Preamp �� 9

The EQ Section ��10

EQ Example Settings ��11 Setting The EQ ��11

The Compressor & Limiter Section ��12

Compressor/Limiter Example Settings ��16 Setting The Compressor/Limiter��17 Parallel Compression ��18

Application Guide �� 19

Direct Instrument Recording Application��19 Mic Preamp Application ��20 Sidechain Application ��21 Using The 676 Compressor At Mixdown ��22

Technical Information �� 23

Block Diagram ��23 Compression Graphs ��24 EQ Plot ��24 Audio Cable Diagrams ��25 Replacing The Tube ��26 Replacing The Fuse��27 Specifications ��28

Recall Sheet �� 29

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Overview

Introduction

The dbx® 676 is a single-channel tube microphone preamplifier and channel strip processor with 3-band semi-parametric EQ, compressor, and PeakPlus™ limiter. When used at the front of a digital audio workstation, tracks will take on more analog warmth and sheen when compared to preamps built into standard audio recording interfaces.

The 676 preamp is a Class A, high-voltage (250V) vacuum tube design that can accommodate microphones or direct instrument connections thanks to the front-panel Hi-Z instrument input. Use the PRE TUBE GAIN control to dial in just the right amount of tube drive, then adjust the POST TUBE ATTENUATION control to set your gain back to unity. Keep the PRE TUBE GAIN low and raise the POST TUBE ATTENUATION for an open, clean sound. Or, turn the PRE TUBE GAIN up and lower the POST TUBE ATTENUATION for a tone that’s rich in harmonics and analog warmth. The 676 provides up to 60 dB of low-noise gain, a 20 dB pad, +48 volt phantom power, and polarity inversion, making it well suited for a wide variety of recording and live sound applications. Use the insert jack to patch in your favorite outboard compressor, EQ, or any other signal processor post the preamp.

If you can’t quite achieve the tone you’re after with mic selection and placement alone, use the built-in semi-parametric EQ to fine-tune the tone of the source. Engage the 80 Hz low cut filter to help keep the mix clean and maximize headroom by eliminating subsonic plosives, hum, and microphone vibration noise.

The 676’s VCA compressor design was taken from the revered dbx 162SL and delivers smooth, low-distortion compression characteristics, as well as very fast attack/release capabilities for shaping drum transients. Sources can be compressed gently by engaging the OVEREASY switch (soft-knee mode) or aggressively by disengaging the OVEREASY switch (hard-knee mode). Use the compressor to beef up instruments and voices, smooth out level fluctuations, and make your tracks more ‘mix-ready’. Compression attack and release times can be set manually or be program-dependent by engaging the AUTO switch. Use the compressor’s sidechain jack to insert an outboard EQ for frequency-weighted compression, such as de-essing, or for other creative sidechaining applications. The PeakPlus limiter can be used for level-critical applications, where you want to keep the output level under control no matter how loud the source gets.

PREAMP and COMPRESSOR / LIMITER outputs are provided for parallel compression applications or for recording an uncompressed backup, so there’s no need to worry about over-compressing a recorded track. An option slot can be fitted with the digital output option card for high-quality onboard A/D conversion and direct connection to an AES or S/PDIF input on a digital mixer or recording interface.

Whether you’re working in the studio or on the stage, the 676 adds harmonically-rich, warm analog tones to your sound sources, at a fraction of the cost of other comparable products in its class.

Thanks for choosing dbx.

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Features

• Discrete, Class A, High-Voltage Tube Microphone Preamplifier

• 60 dB of Preamplifier Gain

• +48V Phantom Power

• 20 dB Pad

• Polarity Invert Switch

• 80 Hz Low Cut Switch

• Pre-Tube Gain & Post-Tube Attenuation Controls for Varying the Amount of Tube Drive

• 3-Band Semi-Parametric EQ with Sweepable Mid Frequency

• Built-In 162SL-Style Compressor

• dbx PeakPlus™ Limiter

• LED Backlit VU Meter with Selectable Meter Source

• Front-Panel Hi-Z Instrument Input

• 1/4˝ Preamp Insert Jack

• 1/4˝ Compressor Sidechain Jack

• Electronically Balanced XLR & TRS Preamp & Compressor / Limiter Outputs

• Slot for Optional AES / S/PDIF Digital Output Card

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Installation

Installation Recommendations

FOR RACK MOUNT USE ONLY. Install the 676 in a standard 19” rack with the provided rack screws. The 676 should not be mounted above or below anything that generates excessive heat. Ambient temperatures should not exceed 95ºF (35ºC) when equipment is in use.

Making Connections

The 676 has balanced line outputs that can be connected to any balanced or unbalanced line-level device. To connect the 676 to your system:

1� Ensure the power is turned off on all interconnecting equipment and the 676 before making audio connections.

2� See ‘Application Guide’ on page 19 for application system diagrams and notes which can be used for reference

when connecting the 676 to your system.

3� Make audio connections via the XLR or 1/4˝ TRS connectors according to application needs (see ‘Audio Cable

Diagrams’ on page 25 for additional information on cable wiring). Either the XLR or 1/4˝ output connectors for

each output (i.e., PREAMP or COMPRESSOR / LIMITER output) can be used for balanced or unbalanced connections. Connecting to both XLR and 1/4˝ outputs simultaneously (as shown in the below diagram) is perfectly acceptable as long as the combined parallel load is 5kΩ or greater. This is typically not a problem since most modern-day audio devices have been designed with high-impedance line inputs. If desired, parallel resistance calculators can be found online and used to verify if the parallel load meets this criteria. Simply enter the input impedance for the two receiving devices into the calculator to calculate the combined parallel load. Note that connecting both XLR and 1/4˝ outputs to an unbalanced and balanced input simultaneously will cause the balanced line to become unbalanced.

To Device 1 Input

To Device 2 Input

Combined Load

5kΩ or Greater

Combined Load

5kΩ or Greater

To Device 1 Input

To Device 2 Input

Applying Power

1� Ensure your monitoring system is turned down before applying power to the 676.

2� Connect the power cord to the AC power inlet on the 676’s back panel and route the AC power cord to a convenient

power outlet away from audio lines.

3� Turn the 676 power switch to the on position.

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Quick Start

Follow these steps to get up and running fast:

1� Turn the POST ATTENUATION control all the way down.

2� Engage the INSTRUMENT INPUT button if connecting a bass or guitar to the INSTRUMENT INPUT jack on the front

panel. If connecting to the MIC INPUT jack on the rear panel, disengage the INSTRUMENT INPUT button.

3� Engage the +48V button if using a condenser microphone which requires it, otherwise, disengage the button.

4� Set the remaining preamp buttons for the application (i.e., 20dB PAD, POLARITY INVERSION, and 80 HZ LOW CUT), see

‘The Preamp Section’ on page 8 for further information on these buttons.

5� Set the GAIN and POST TUBE ATTENUATION knobs for the desired amount of tube drive and output level. For a cleaner

tone, use lower GAIN settings and higher POST ATTENUATION settings. For a tone with more harmonics and warmth, use higher GAIN settings with a lower POST ATTENUATION setting.

6� Once microphone selection and position have been decided, enable the EQ with the EQ ENABLE button then adjust the

EQ settings to taste if any further tone shaping is required. If no EQ is required, leave the EQ ENABLE button in the off position. See ‘The EQ Section’ on page 10 for further information on using the EQ.

7� Compression and limiting can be used to smooth-out overly dynamic source signals. If you wish to use compression and/

or limiting, you must be connected to the COMPRESSOR / LIMITER output. You can then enable the compressor/limiter with the COMP/LIM ENABLE button and adjust the compressor/limiter settings to taste. For more information on using the compressor/limiter, see ‘The Compressor & Limiter Section’ on page 12. For information on using both the PREAMP and COMPRESSOR / LIMITER outputs, see ‘Parallel Compression’ on page 18.

The User Interface & Connectors

Front Panel

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CLASS “A” VACUUM TU BE WITH HIG H VOLTAG E GAI N

+40

+25 +50

+55

∞

GAIN

INSTRUMENT INPUT

ENABLE

-30 -5

PEAK

∞

POST TU BE

ATTEN UATION

20dB PAD+48V

POLARITY

INVER T

21 4 5

-15

LOW CUT

-15 +15

LOW

80 Hz

-15 +15

MID

-15 +15

ENAB LE

200 2k

100 8k

NARRO W

HIG H

FREQ

METE R SE LECTI ON

INPU T OUTPUT G.R.

COMP/ LIM

ENAB LE

CONTOU R

-20

-30 +10

–

-400+20

THR ESHOLD

200 10

SIDE CHAI N

ENABL E

-10

OVERE ASY

dB/msec

400

ATTACK

2:1

1.5:1 3:1

1.2:1 8:1

1:1 ∞:1

RATIO

400

1.5k 70

dB/sec

4k 10

RELEA SE

AUTO

-10 +10

-20 +20

MAKE UP

GAIN

+10

+2 +18

dBu

-4

OFF

LIM ITER

PEAK

POWER

DIGI TAL OUTPUT

LIMIT

RED: 96kHz

GREEN: 48kHz

YELLOW: 44.1 kHz

7 8

1. Preamp

This is the preamp section, see ‘The Preamp Section’ on page 8 for further information.

2. EQ

This is the EQ section, see ‘The EQ Section’ on page 10 for further information.

3. Meter

This LED backlit VU meter displays input signal level, output signal level, or the amount of gain reduction applied by the compressor and/or limiter.

4. Compressor

This is the compressor section, see ‘The Compressor & Limiter Section’ on page 12 for further information.

5. Power Switch

This switch turns the power to the 676 on and off.

6. Meter Select Buttons [INPUT, OUTPUT, G.R.]

These buttons select what will be displayed in the VU meter, the selections are: INPUT (input level), OUTPUT (output level), and G.R. (gain reduction applied by compression/limiting).

7. Limiter

This is the limiter section, see ‘The Compressor & Limiter Section’ on page 12 for further information.

8. Sample Rate Select Button [96 kHz, 48 kHz, 44.1 kHz]

This button selects the desired sample rate frequency for the digital output signal when the Digital Option Card is installed. Note that this button will serve no function if the Digital Option Card is not installed.

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Rear Panel

4 5 7 86

1. Power Connector

Connect the included IEC power cord to this connector and the other end to an available AC outlet.

2. Fuse Drawer

This drawer houses the main power fuse as well as a replacement fuse, see ‘Replacing The Fuse’ on page 27 for further information.

3. Option Card Slot

This option card slot can be fitted with the 676 Digital Option Card (sold separately) which adds AES and S/PDIF digital outputs. The Digital Option Card is equipped with high-quality A/D converters and our proprietary dbx Type IV™ conversion system to prevent the A/D converters from accidental clipping.

4. Compressor Line Output Connectors

This output carries the signal post-compressor/limiter. Both 1/4” and XLR balanced COMPRESSOR / LIMITER outputs are provided. The COMPRESSOR / LIMITER output can be used by itself or along with the Preamp output for parallel compression applications, see ‘Parallel Compression’ on page 18 for additional information.

5. Compressor Sidechain Insert Connector

Connect an insert cable to this unbalanced connector to patch in another device for processing the signal feeding the compressor’s detector circuit. For example, an external EQ could be connected and used for frequency-weighted compression, such as de-essing. See ‘Sidechain Application’ on page 21 for more information on using this connector.

6. Preamp Line Output Connectors

This output carries the signal post EQ and pre compressor/limiter. It provides a slightly more minimalistic signal path than the COMPRESSOR / LIMITER output. Both 1/4” and XLR balanced Preamp outputs are provided. The Preamp output can be used by itself or along with the COMPRESSOR / LIMITER output for parallel compression applications, see ‘Parallel Compression’ on page 18 for additional information.

7. Preamp Insert Connector

Connect an external signal processor to this unbalanced connector to process the signal just after the preamp section and before the EQ.

8. Mic Input Connector

Connect a microphone or stage D.I. box to this balanced XLR input connector.

The Preamp Section

987654

1 2 3

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-30 -5

PEAK

∞

POST TU BE

ATTEN UATION

20dB

PAD+48V

POLARITY

INVER T

-15

LOW CUT

-15 +15

LOW

80 Hz

-15 +15

MID

-15 +15

ENAB LE

200 2k

100 8k

NARRO W

HIG H

FREQ

METE R SE LECTI ON

INPU T OUTPUT G.R.

COMP/ LIM

ENAB LE

CONTOU R

-20

-30 +10

–

-400+20

THR ESHOLD

200 10

SIDE CHAI N

ENABL E

-10

OVERE ASY

dB/msec

400

ATTACK

2:1

1.5:1 3:1

1.2:1 8:1

1:1 ∞:1

RATIO

400

1.5k 70

dB/sec

4k 10

RELEA SE

AUTO

-10 +10

-20 +20

MAKE UP

GAIN

+10

+2 +18

dBu

-4

OFF

LIM ITER

PEAK

POWER

DIGI TAL OUTPUT

LIMIT

RED: 96kHz

GREEN: 48kHz

YELLOW: 44.1 kHz

CLASS “A” VACUUM TU BE WITH HIG H VOLTAG E GAI N

+40

+25 +50

+55

∞

GAIN

INSTRUMENT INPUT

ENABLE

1. Gain Control

This control adjusts the amount of input gain applied to the preamp and how hard the tubes will be driven. Use lower values to achieve a cleaner, more transparent sound. Use higher values for tones with more analog warmth, harmonics, and sheen.

2. Peak LED

This LED lights when the input circuit is driven into clipping. Turn down the POST TUBE ATTENUATION control if this LED begins to light.

3. Post Tube Attenuation Control

This control adjusts the amount of attenuation applied post the tube preamplifier and is meant to be used in conjunction with the GAIN control. For cleaner tones, leave this control fully clockwise and raise the GAIN control until the desired level is achieved. For richer tones, lower this control and raise the GAIN control.

4. Instrument Input Enable Button

This button enables/disables the INSTRUMENT INPUT. When enabled, the signal connected to the INSTRUMENT INPUT will be passed through the 676. When disabled, the 676 will pass the audio from the MIC INPUT connector located on the back panel.

5. Instrument Input Connector

Connect an electric guitar or bass directly to this unbalanced, Hi-Z input.

6. +48V Button

This button enables/disables +48 volt phantom power. Enable it for condenser microphones which require an external power source. Leave this button disabled when connecting a dynamic or ribbon microphone, or a condenser microphone which is powered internally or using its own dedicated power supply.

7. 20dB Pad Button

Engage this button to attenuate the input signal by 20 dB. Use it to prevent the MIC INPUT from being overdriven by loud source signals or high-output microphones.

8. Polarity Invert Button

When enabled, this button inverts the polarity of the MIC INPUT signal. Use it with multi-miked applications where polarity inversion is required to match the polarity of the MIC INPUT signal with another miked signal – for example, when using top and bottom mics on a snare drum.

+ 22 hidden pages

DBX 676 Owner's Manual

Specifications and Main Features

Frequently Asked Questions

User Manual