Cambridge Audio Azur 851C Single-Disc CD Player/DAC/Digital Preamp (Black)

About Cambridge Audio.....

Where It All Began
  • In The 1960s Three Things Happened Simultaneously - British Bands Began To Enjoy Unprecedented Global Success, British Studios Led The Way In Recording Technology And British Manufacturers Started To Make The Best Hi-fi Equipment In The World.
  • Britain Made A Name For Itself In All Three Areas But It Was The Studios And Manufacturers That Began To Develop Systems To Capture And Replay Music As Naturally As Possible.
  • Over Time, This Sound Has Become Recognisably ‘british’. On With Enjoying It.
The Team
  • This Is The Cambridge Audio Team. In Each Picture Is Our Favourite Moment In Our Favourite Song.
  • First And Foremost, We’re All Music Lovers, Musicians, And Gig Goers.
  • It’s This Passion That Drives Our Desire To Make Sure Our Products Make Our Moments Sound Exactly As They Were Made To Be Heard.
  • Everything We Do Is Driven By Our Love Of Music.
  • We Genuinely Believe That Great Things Happen When People Who Love Music Make Audio Products.
We’re Quite Proud
  • It’s Lovely When Others Recognise Our Excellence.
  • We’re Very Proud Of The Many Fantastic Reviews And Awards Our Products Have Received.
Our Technology
  • Our Drive To Produce Audio Equipment That Faithfully Creates A Pure And Natural Sound Has Seen Us At The Forefront Of Audio Innovation Over The Decades.
  • Thanks To Our In-house Design And Engineering Teams, Cambridge Audio Proprietary Technologies Are Only Found In Our Own Products.
Our Culture
  • This Document Started Out As A Presentation, It’s Not Quite A Book, But It Is An Introduction To Audio Partnership And Cambridge Audio.

Product Research

  • Disc Compatibility 
  • Audio Features 
  • Controls 
  • Connections

Disc Compatibility

Single Disc CD Player: 

  • The Cambridge Audio Azur 851C single disc compact disc player/DAC/pre-amp has been designed to play CD-Audio, CD-Text, recordable CD (CD-R) and re-writable CD (CD-RW) type discs.

CD-DA Format Only: 

  • The Cambridge Audio Azur 851C CD player can play only discs recorded in the CD-DA format designed for music reproduction.
  • Do not attempt to play a disc containing other data, such as MP3, WMA, or AAC on this unit.

Audio Features

High-Quality Construction: 

  • The Cambridge Audio Azur 851C CD player/DAC/pre-amp offers high-quality constructions for outstanding performance and reliability.
Wrap-Around Casework Design: 
  • A wrap-around casework design with substantially thick brushed aluminum front panel, and dual layer damped feet, gives enhanced resonance control.
Double-Sided Surface Mount Technology:
  •  All PCBs and DAC stages feature double sided surface mount technology, eliminating wire links and giving ultra short signal paths.
Polypropylene Capacitors: 
  • Low inductance resistors and polypropylene signal capacitors are used for superior audio performance.
Audiophile Grade Toroidal Transformer:
  • Unlike most CD players, who use cheap laminate type transformers, the Cambridge Audio Azur 851C uses an audiophile grade toroidal transformer offering minimal electro magnetic interference and delivering superior audio performance.
Standby Circuit:
  •  This innovative new circuitry design allows compact disc player to consume less than 1 watt of power when in Standby, but itself remains totally isolated and non-detrimental to the sound quality when the CD player is in operation. 

CD Transport: 

  • The Azur 851C uses Cambridge Audio's legendary custom made audio-only, dedicated CD transport that has been tweaked even further using techniques derived from the 740 series.
  • This well-proven transport guarantees incredible rigidity and the CD drawer itself has been designed to offer a smooth, high-end feel.

S3 Custom CD Servo Drive: 

  • Cambridge Audio's CD-only S3 Custom CD Servo employs a custom designed chipset and the latest double-sided surface-mount technology for ultra short signal paths with freedom from wire links.
  • Circuits and software have been meticulously designed, so the S3 can dynamically adjust focusing, tracking, and output level of the laser in real-time, allowing for maximum retrieval of the digital information and jitter minimization.
  • This is all made possible by the implementation of a powerful ARM7 processor and complemented by a highly accurate master clock oscillator and carefully designed impedance-matched clock buffering scheme.

High-End DAC: 

  • The Cambridge Audio 851C can be used as a fully fledged, high-resolution, audiophile DAC.
  • Used in this way, it's capable of breathing new life into audio produced by everyday digital components by utilizing its state-of-the-art internal convertors to bring clarity and detail to audio streams.
  • Rather than investing in a separate stand alone DAC, any audio device with a digital audio output (from TVs to computers and digitally docked iPod/iPhone/iPad devices) can benefit from 851C's highly advanced digital audio processing technology.
  • A number of external devices can be attached to the 851C thanks to two S/PDIF (coaxial) inputs, two Toslink (optical) inputs and, for truly high-performance sound quality, a 24-bit USB input capable of up to 192kHz resolution.
  • The latter enables you to experience true studio master quality from the highest resolution music files available.  

Twin Analog Devices 24-Bit DACs: 

  • The Cambridge Audio 851C employs two very high-quality Analog Devices (AD1955) 24-bit DACs in dual-differential mode for excellent stereo imaging.
  • Since each channel has its own DAC to process information, completely separate and symmetrical analog filter circuitry can be implemented.
  • This implementation allows both the left- and right-channel circuitry to operate identically, ensuring the 851C delivers fantastic sound-staging and stereo-imaging properties.

ATF2 (Adaptive Time Filtering): 

  • ATF2 Upsampling allows digital audio signals from virtually any audio source to be upsampled, resynchronised, and retimed for extraordinary levels of detail.
  • In effect, upsampling the digital data stream (up to 384kHz) allows existing "standard" CDs to have the enhanced audio clarity, richness and dynamic range that would normally be associated with SACD or DVD-A Audio discs.
  • Three proprietary technologies are included in ATF2 effectively reduce noise artifacts caused by imperfect digital systems and allow the digital signal to closer represent the true analog sound of the studio mastered audio data.
Adaptive Time Filtering:
  •  Adaptive time filtering allows the system to adapt to small fluctuations in the systems audio master clock.
  • The master clock is the heart of any digital audio system, however as all components that are constructed from physical materials, they will at some point in time deviate from their ideal generalized behavior causing, in this case variation in frequency and system jitter in this important internal timing reference.
  • Typically these variations will not be corrected for, however in ATF2 enabled devices the system automatically adapts to these small fluctuations resulting in perfect "glitch" free analog sound even after endless hours of continuous playback.
Jitter Suppression: 
  • Jitter Suppression allows any incoming audio stream to be resynchronised and retimed to a local very high quality clock.
  • By using a stable-reference oscillator, the negative effects of inter-component jitter can be dramatically reduced.
  • When converting the digital audio to an analogue signal through high performance D/A converters, this reduction in jitter has enormous benefits in the level of detail and clarity in the reconstructed analogue sound.
Time Domain Model: 
  • Combining this process with a time domain model using an advanced cubic interpolation algorithm, the unique ATF2 system upsamples all incoming audio to 24 bits at 384kHz whilst applying noise shaped dither and is able to actually increase the linearity of response of the D/A converters.
  • The end result is tighter, more focused bass, increased stereo imaging, focus and separation for all musical instruments and voices.

 Digital Pre-Amplifier: 

  • Further adding the Cambridge Audio 851C's flexibility, it can be used as a digital pre-amplifier.
  • The 851C can be used to control volume and balance levels when connected directly to an external power amp or active speakers.
  • This clever feature, processed completely using digital technology, facilitates the simplest of audio replays systems and offers amazing flexibility.
  • This function is operated using Cambridge Audio's proprietary DSP (Digital signal Processor) and gives the highest quality of digital volume control, as opposed to analog attenuation or digital bit reduction.


DFSTN Display: 

  • To ensure simple operation, a high contrast reverse black DFSTN (Double Film Super Twisted Nematic) display offers excellent feedback of the 851C's playback features, which now include CD-text support. On inserting a disc, the CD player will take a few seconds to read the Table of Contents (TOC) information from the disc.
  • The display will then show the number of tracks on the CD and the total length of the CD.
  • If the CD incorporates CD-text, the name of the album will scroll once (the number of tracks remains stationary throughout).
  • Once playback of an individual track begins, the track number, total number of tracks, and playtime will be displayed.
  • On a CD containing CD-text, the track name will scroll once.

Power On/Off: 

  • The 851C compact disc player/DAC/pre-amp's main power on/off switch is located on the rear-panel.
  • Once the CD player's rear-panel main power switch has been turned On, you can switch the 851C on/off using the front-panel Standby/On button.

Front-Panel Controls: 

  • The Cambridge Audio compact disc player/DAC/pre-amp offers the following front-panel controls.
  • Standby/On
  • Open/Close tray
  • Play/Pause
  • Stop
  • Skip/Scan
  • Menu/Select
  • Filter

IR Remote Control: 

  • The 851C compact disc player/DAC/pre-amp is supplied with an Azur Navigator remote control that operates both this CD player and Cambridge Audio Azur-series amplifiers.
  • The Azur 851AC Navigator remote control can also control the basic functions of Apple devices, such as Apple TV and Apple's iPod/iPhone/iPad when docked in a Cambridge Audio or Apple dock (sold separately). he remote operates off of three "AAA" batteries (supplied).

Auto Play Setting: 

  • The Cambridge Audio Azur 851C can automatically start playback of a disc inserted into its drawer without the unit's "Play" button being pressed.

Playback Functions: 

The 851C compact disc player offers Repeat, Random, and Program playback controls.

  • Repeat: You can repeat a specific track or an entire disc.
  • Random: You can play all the tracks on a disc in random order.
  • Program: You can program up to 30 tracks on a disc to play in a specific order.

Phase Filter Select: 

  • The 851C's ATF2 Upsampling technology employs Cambridge Audio's own proprietary digital filter algorithms with three different filter options available - Linear Phase, Minimum Phase, and Steep. Controlled from one switch on the front-panel, they are extremely clever audiophile topologies specifically developed for audio playback and all offer excellent sound quality, but differ slightly to appeal to a wide range of listening tastes.
Linear Phase Filter: 
  • The Linear Phase Filter is the same as used in Cambridge Audio's flagship Azur 840C upsampling CD player.
  • It uniquely features 'constant group delay' which delays all audio signals at all frequencies by the same amount - meaning all audio is fully time-coherent at the output.
Minimum Phase Filter: 
  • The Minimum Phase Filter does not feature constant group delay, but rather has been optimized without feed-forward so that the impulse response exhibits no pre-ringing in the time domain.
  • Many audiophiles have argued that the pre-ringing, as seen in nearly all digital filter designs, may affect the transient attack of percussive instruments.
  • Minimum phase implementation eliminates this and is a technology only seen previously in some extremely high-end CD playback systems
Steep Filter: 
  • The steep filter removes undistinguishable artifacts via re-calibration for a very slight roll-off at 20kHz, but an ultra-steep drop to the stop-band just after 20kHz.

Digital Preamp Mode:

  • The Digital Preamp Mode is used to connect the 851C directly to a separate power amplifier or active speakers.
  • The 851C is supplied as default with Digital Preamp mode enabled.
  • In this mode, the output from the Unbalanced and Balanced audio outputs is controlled by the front-panel Volume control. 
  • If you wish to disable this mode (and have fixed line-level level output from the Unbalanced and Balanced Audio outputs) switch the 851C off, then push and hold the Volume control in while switching the 851C on.

Ground/Lift Switch: 

  • When Grounded, the 851C is connected to the earth connection of the PC directly.
  • When Lifted the ground connection is made via a network designed to break any hum loops that may be caused by the source equipment.
  • The Grounded setting is recommended, unless audible hum is experienced

Auto Power Down: 

  • If desired, the 851C can shut itself down if not used for a period of time. Power down after an inactive period (no disk playback or any functions of the player used) of 5, 10 or 15 minutes can be selected.


USB Port:

  • A rear-panel 24-bit/192kHz USB (type-B) port enables the 851C to be connected to your Windows PC or Mac computer.
  • The 851C will act as a very high-quality DAC/sound-card with very low jitter for your computer, offering genuine Hi-Fi-quality playback from your stored music and Internet radio.
  • The 851C is both USB 2.0 (Hi-Speed) and USB 1.1 (Full-speed) USB port compatible.
  • It will also work with the new USB 3.0 ports where the PC will simply treat the 851C as if it were a USB 2.0 or 1.1 device.
PC Compatible: 
  • With the 851C switched to USB Audio 1.0 (this is the default setting), the 851C will work with the native Windows XP, Vista or 7 Audio 1.0 driver (no need to load any new driver) and accept audio up to 24-bit/96kHz. With the 851C switched to USB Audio 2.0, the 851C needs the Cambridge Audio USB Audio 2.0 Driver to be loaded and can then accept up to 24-bit/192kHz (and support ASIO and WASAPI Exclusive if required).
Mac Compatible: 
  • No extra drivers are required to connect your Mac computer. With the 851C switched to USB Audio 1.1,  the 851C will work with the native Mac OS-X 10.5 (Leopard) or above Audio 1.0 driver and accept audio up to 24/96kHz.
  • With the 851C switched to USB Audio 2.0, the unit works with the native Mac OS-X 10.5 (Leopard) or above Audio 2.0 driver and can accept audio up to 24/192kHz.

Digital Inputs: 

  • The 851C is fitted with two rear-panel 24-bit digital inputs. Each digital input consists of an optical and coaxial digital connection.
  • The optical and coaxial digital input allow a wide range of digital source (CD, DVD, Game Console, etc.) to be connected to the 851C.
  • Only one of the two types (optical/coaxial) of each digital input should be connected at any one time.
  • If both the optical and coaxial inputs have connections made to them, neither will work.
  • This unit only decodes two-channel LPCM digital audio (Dolby Digital 2.0). If you connect a DVD or similar device, please ensure that the audio output of the player is set to two-channel PCM.

Digital Output:

  • A rear-panel digital output (optical/coaxial) allows pass-through of the selected digital source for recording purposes (no up-sampling performed).
  • These outputs loop or pass-through unprocessed digital audio from the selected digital input.
  • Both the optical and coaxial digital outputs are always active and can be used to connect and run equipment at the same time.
  • A 5.1 Dolby Digital or DTS signal can be passed through the unit's digital outputs.
  • The 5.1ch signal is not decoded or processed (only pass-through).

Balanced & Unbalanced Outputs: 

  • The Cambridge Audio 851C features both balanced (XLR) and unbalanced (RCA) audio outputs to connect to a wide variety of home stereo receivers and amplifiers.
  • The 851C features an unbalanced stereo analog RCA audio output for connecting your stereo receiver or amplifier.
  • The 851C features true balanced XLR analog audio outputs to connect high-end home receivers and amplifiers.
  • XLR is a higher-quality output that can reject noise and interference with equipment with balanced inputs.
  • It is possible to use the unbalanced stereo RCA output and the balanced XLR outputs at the same time for connecting two different amplifiers or multi-room operation.
  • The analog audio outputs are muted, if the 851C receives a 5.1 Dolby Digital or DTS signal.

IR Emitter Input: 

  • The 851C features a IR Emitter input (3.5mm) which allows modulated IR commands from multi-room systems or IR repeater system to be received by the CD player/DAC/Pre-amp.

Control Bus Input/Output: 

  • The 851C features a Control Bus Input & Output (RCA), which allows un-modulated commands from multi-room systems or other components to be received by the player and loop out to another unit.

RS232 Port: 

  • The player's RS232 port is used for control of the 851C in custom install situations from an external controller.
  • A full protocol is available for the 851C onCambridge Audio's website.

Detachable AC Power Cord: 

  • The Cambridge Audio 851C operates off of standard household AC current using the supplied detachable 6' AC power cord.
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