Chord QBD 76 User manual

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Chord Electronics Limited
QBD 76 (Quarter Back DAC)
DIGITAL / ANALOGUE CONVERTER
OPERATING
INSTRUCTIONS

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Contents
Page
1 Title page
2 Table of Contents
3 Input / Output connection diagram for the QBD76
4 Mains connection instructions
Cleaning and care instructions
Initial Start-up
5 Audio Outputs
Digital Input Selection
Using Bluetooth wireless digital audio
De-emphasis coding
6 Setting the RAM buffer
Product Specification
R203WWJN000006

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Chord Quarter Back DAC 76 connection diagram
Left Unbalanced output
Output phase selector
RAM buffer selector
Digital input selector
75ohm SP/DIF2 BNC Coax inputs
AES balanced XLR inputs
Plastic fibre optical inputs
Mains power
input
USB input
Left Balanced output
Right Unbalanced output
Right Balanced output
Bluetooth antenna
Word Clock output
Display

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Chord Quarter Back DAC 76 Operating Instructions
Mains connection instructions
Please ensure that the IEC mains lead is correctly terminated:
UK / Europe Function USA / Canada
Brown Live Black
Blue Neutral White
Green / Yellow Earth Green
WARNING
THE QBD76 MUST BE EARTHED AT ALL TIMES VIA ITS OWN MAINS LEAD.
FAILURE TO DO THIS MAY BE HAZARDOUS.
Cleaning and care instructions
The QBD76 requires no special care other than common sense. Spray window cleaner (clear type) may
be used (if first sprayed onto a soft cloth) to remove surface blemishes such as finger marks from the
metal casing. Never spray directly onto the converter and never use abrasive cleaning, use only a lint
free soft cloth.
There are no user serviceable parts in the QBD76. It should be serviced only by Chord Electronics
Limited or their expressly approved service agents.
NB: This unit must be ventilated at all times with at least 5cm space around and above the unit.
Initial Start-up
If there is no output from the DAC once everything has been connected and the digital source is
playing it may be that the DAC has not set itself. Remove the power lead and wait for 30 seconds
before powering up. This should be enough time for the DAC to configure itself.

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Audio Outputs
There is one pair of Left & Right fully balanced outputs, via Neutrik XLR style connectors and one
pair of Left & Right unbalanced outputs, via gold plated RCA phono style connectors. Each of these
will drive down to a 50ohm load. This means that the QBD76 will work with all known pre-amplifiers
and is able to drive very long audio cables without difficulty. Both audio outputs work at the same
time, this allows the QBD76 to be connected to two pre-amplifiers if needed.
Digital Input Selection
The QBD76 enables you to use any one of five digital input formats. These consist of two 75ohm-
SP/DIF2 BNC (COAX) and two AES balanced XLR input (AES) and two Plastic Fibre Optic (Opt) and
a USB B type connector and Bluetooth using the A2DP format. Each of these inputs can be selected by
using the selector switch on the top panel of the unit. The switch is located directly above the display,
see connection diagram. The sequence of input selection is as follows;
Function Display
Bluetooth - BLTH
75ohm-SP/DIF2 BNC - COAX
AES balanced XLR - AES
Plastic Fibre Optic - OPT
USB B type connector - USB
On powering the unit there should be a coloured glow from the central located glass window, the
display will then scroll the word chord, then display the source that is selected, then the phase mode
(positive or negative), then the level of RAM buffer selected (0BUF if RAM buffer is not in use) and
then will remain displaying the input selected.
Once digital lock has been achieved the word LOCK will be displayed briefly then the frequency that
the lock has been achieved at (either 44K, 48K, 88K, 96K, 176K or 192K to represent 44.1Khz, 48Khz,
88.2Khz, 96Khz, 176.4Khz or 192Khz).
Using Bluetooth wireless digital audio
The QBD76 is capable of receiving the A2DP format of Bluetooth wireless digital data transmission.
To use this function, firstly press the input selection button until “BLTH” is displayed.
Now, referring to your mobile phone’s instructions, search for new paired devices, you should see a
chord unit (it maybe numbered, but it will also say “Chord”), select that device, enter the passcode
when prompted by your Bluetooth device (the passcode is set to “0000”), then confirm that you wish to
connect to the Chord device / connect to the chord device automatically depending on your preference.
The QBD76 should now be locked to your Bluetooth device, and able to receive high quality digital
audio.
Now with Apt-X advanced Audio Codec Installed
De-emphasis coding
The QBD76 will automatically detect when a pre-emphasized recording is being played, and will set
the correct de-emphasis filters in the converter section.

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Setting the RAM buffer
There are three settings for the RAM buffer. The options are as follows;
Buffer applied Display
No buffering - 0BUFF
Minimum buffering - MIN
Maximum buffering - MAX
The receiver chip takes the data from the transport and generates clocks and data in a form that the
filter can accept. This has two major benefits – all digital data extraction and a RAM buffer. This RAM
buffer sequentially takes all the data, retimes it, and sends it out. The RAM buffer allows the jitter free
local clock operation without needing to send back a clock signal to the data source.
There is however a word clock output located by the power connector on the rear of the QBD76.
N.B. When using the QBD76 with the buffer set to anything apart from 0BUFF there is a time delay
from pressing “Play” to hearing music. Whenever switching between the different buffer settings there
is a delay another delay before the music resumes.
N.B. It is important to set the volume on the pre-amp/amplifier to minimum when switching between
digital inputs or setting the Ram buffer on the QBD76.
Product Specification
HARMONIC DISTORTION < -103dB
SIGNAL TO NOISE RATIO >120dB
CHANNEL SEPARATION >125dB @ 1KHz
DYNAMIC RANGE 122dB
DIGITAL INPUTS 2 x Plastic fibre optic
2 x AES Balanced XLR input
2 x 75ohm SP/DIF2 BNC coax
1 x USB B
1 x wireless Bluetooth (A2DP format)
ANALOGUE OUTPUTS 2 x RCA Phono
2 x Balanced XLR
RAM BUFFER SWITCH sequences between; No buffering, Minimum buffering and
Maximum buffering
SAMPLE FREQUENCIES 44.1Khz, 48Khz, 88.2Khz, 96Khz, 176.4Khz or 192Khz
OUTPUT MAX 6V rms. Balanced. 3V rms. unbalanced
OUTPUT IMPEDANCE 75ohm (short circuit protected)
DIMENSIONS IN MM 338 x 60 x 145mm (Width x Height x Depth)
excluding the 14cm antenna
WEIGHT 7Kg