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Integrated amplifier
Cambridge Audio AZUR 651A

Price (in Poland): 2990 zł

Manufacturer: Audio Partnership Plc

Gallery Court, Hankey Place | London SE1 4BB, United Kingdom


Country of origin: Great Britain

Polish Distributor: Audio Center Poland

Text: Wojciech Pacuła
Photographs: Wojciech Pacuła/Piksel Studio

Report published: in Polish on Jan 16th 2012, No. 93

The original Cambridge Audio company was founded in 1968 and in fact has its roots in Cambridge. What's more it shares such roots with other companies like e.g. Monitor Audio and Arcam (who's name originally was A&R Cambridge [Amplification & Recording Cambridge]) – all these companies had their headquarters in Cambridge (as well as Meridian and Audiolab). People behind first two of above mentioned companies came from a university group called PA Consultants. There were even more connections between Cambridge and Arcam – in 1976 John Dawson, the owner of Arcam, together with Chris Evans designed an A60 amplifier for… Cambridge Audio. Cambridge Audio since 1994 is a part of Audio Partnership Plc, with its headquarters in London. Today it is one of the most important players on low and mid-priced audio equipment market.
Within the UK, Cambridge Audio is only available through Richer Sounds and competes directly with products from NAD and Arcam, and some Japanese manufacturers (Yamaha, Marantz, Denon). Julian Richer owns 51% share of Audio Partnership Plc. As you can read in Wikipedia, Richer Sounds currently funnels 15% of its profits into charitable organizations.
Anyway Cambridge Audio founded almost 45 years ago has now quite comprehensive portfolio with Blu-ray 3D players as well as phonostages; D/A converters and mini speakers. On the other hand we shall not forget that it comes from a once specialized „hi-fi” market – Cambridge Audio manufactured back then mostly amplifiers and for years this brand was associated with this particular device.
Herewith tested Azur 651A amplifier is, in a sense, a descendant of the very first model P40 from 1969. Of course only “in a sense” - it's about the idea behind them both and not a real resemblance. If you check specification you will find mostly differences. 75 W per channel in 651A versus 20 W in P40, phonostage in the latter versus none in the new model, totally different look, and both were manufactured in different places – these all are differences. Another difference is the scale of the enterprise – today CA employees several engineers running their own projects. Back there were only 2-3 people involved.

We tested up to date:

  • Blu-ray Universal Player Cambridge Audio Azur 751BD, review HERE
  • D/A converter DACMagic, review HERE
  • linestage Azur 840E, review HERE
  • CD Player Azur 840C, review HERE
  • phonostage Azur 640P, review HERE
  • integrated amplifier Azur 340A, review HERE


Recordings used during test (a selection):

  • Audiofeels, Uncovered, Penguin Records, 5865033, CD (2009).
  • David Sylvian, Sleepwalkers, P-Vine Records, PVCP-8790, CD (2011).
  • Eva Cassidy, Songbird, Blix Street Records/JVC, VICJ-010-0045, XRCD24 (2010).
  • Jean Michel Jarre, Téo&Téa, Aero Productions/Warner Bros, 2564699766, CD+DVD (2007).
  • Marc Copland & John Abercombie, Speak To Me, Pirouet Records, PIT3058, CD (2011).
  • Pink Floyd, The Dark Side Of The Moon, EMI Records /EMI Music Japan, TOGP-15001, SACD/CD (2003).
  • Pink Floyd, The Wall, EMI Records/EMI Music Japan, TOCP-71142-43, 2 x CD (2011).
  • Pink Floyd, Wish You Were Here, Experience Edition, EMI Records /EMI Music Japan, TOCP-71169-90, 2 x CD (2011).
  • Pink Floyd,The Piper at the Gates of Dawn, EMI Records, 50391929, 3 x CD (2007).
  • Ralf Illenberger, Red Rock Journeys, Stockfisch, SFR 357.1020.2, CD (2011).
  • Sonny Rollins, Plus 4, Prestige/Mobile Fidelity, UDSACD 2006, SACD/CD (2002).

Japanese versions of the discs are available at CD Japan.

Most Cambridge Audio devices, at least those I listened to, delivered rather precise, dynamic sound. Not all of them, but definitely most. And I don't mean it as it was a bad thing, not at all. Simply they all had it in common. Similar sound characteristic can be found in Denon and Marantz amplifiers. My point is – each time I reviewed one of those I had to chose matching speakers carefully to achieve a result I wanted to. But recent experiences suggested that this general rule might have started to change a bit. First symptoms were noticed during reviews of Azur 840C preamplifier, or Azur 640P phonostage that delivered rather warm side of sound, but these two were still unique exceptions in CA portfolio.
Azur 651A is now a third device from this manufacturer, after Blu-ray 751BD and D/A converter DacMagic Plus (test in „Audio”), that in my opinion has an overall rather warm tonality balance. It is not “warm” per se – the presentation is still airy, as it always used to be with CA products, upper and lower frequencies are also nicely extended. But I think that designers put more attention to the presentation of midrange now, that seemed to be slightly rolled off in the “older” devices. This resulted in producing much more versatile device – the above mentioned change might not seem like much, but from my point of view it was a significant improvement.

It is easy to enjoy the sound of Cambridge amp from the very first moment. In my opinion it could be used with almost any loudspeakers, except maybe for bright sounding ones. Surely some will be a better match than others, but the performance differences should not be too big.
I started my listening session with some guitar music – very impressive sounding Ralf Illenberger's Stockfish recording, and fantastic, but poorly recorded music of Marc Copland & John Abercrombie. In most cases when I listened to these recordings using some inexpensive devices the one of them sounded great and the other one not so good, or the other way around. Cambridge delivered them both in a very nice way – nice dynamics, quite good instruments differentiation and with ability to show each instrument's own character.
So I had a very nice inside view into Illenberger's acoustic guitar sound, accompanied by low sounding bass guitar. The contrast between those two instruments was obvious, natural, but without over-exposing them (like some older CA devices did) – at least basing on my experience as sound engineer on some live concerts, and comparing 651A's performance with my reference system. On the other hand Abercrombie's electric guitar, with its rather warm, dark timbre, was shown bit deeper on the soundstage surrounded with some noise and room's acoustics. This performance was shown as a quite rounded, not too well differentiated (but it was in fact recorded this way). Yes, it was really nice performance.

As I said I particularly liked the contrast between bass and acoustic guitar. The former had a nice timbre with well extended and differentiated low end. I think it was one of the most important features of previous generation of this company's amplifiers - differentiation. Here it is accompanied by richness, saturation. Sound is not as rich as delivered by Music Hall's devices (a15.2 and a25.2), just to be clear. But all these amplifiers represent now similar level of performance – CA delivers more open, better differentiated sound, and MH offers richer sound, also general impression or character of the sound is more similar that it ever was before (between devices of those two brands).
651A deals very well not only with some extremely well realized recordings like a very energetic Plus 4 by Sonny Rollins, but also with rather rough sounding Téo&Téa by Jarre. The latter recording was meant to be rather kind of club music and both high and low frequencies were “enhanced” accordingly.
High performance systems are able to “extract” unusual depth, lots of layers and threads in this recording which makes it quite special. Entry level systems have to deal with such recording in their own way as they lack the resolution of more advanced systems.
Cambridge's presentation was simply enjoyable. Sound wasn't rough – it seemed that some treble was rolled off. That makes this presentation bit darker, not really dark but darker than what older models ‘600’ series models delivered.
Maybe that's why everything seemed to be... just right. Listening to Pink Floyd's recordings, The Dark Side of the Moon most of all, with vocal usually showed deeper on the soundstage, blending somewhere between instruments, I could simply enjoy the music – nothing was overexposed, nothing was “obscured” - the whole presentation was pretty clear and transparent. On this price level resolution is never too good, but that's why I noticed this particular feature of the sound so easily.

Bass is nicely extended and has also quite some body. It won't be the most impressive bass you've ever heard but you simple can only dream about it at this price level. What's important is that each kind of bass – electric, acoustic or electronic – is always nicely integrated with the rest of the range.
What I found interesting was that Cambridge offered better performance with loudspeakers that were easier load. This amp doesn't lack power with its (according to the manufacturer) 75 W @ 8 Ω, but it's never only about output power. So it's going to perform better with loudspeakers from Chario, some Dynaudio, Monitor Audio from Reference (former Bronze) line, Monitor Bronze BX (I'm mentioning this brand more than once simply because same distributor here in Poland sells Cambridge and Monitor Audio so chances are you will hear such a setup in showroom you go to), also with Electra 2 Divine Acoustics and so on. The most important factor is an easy load – if you provide that, you might also chose some speakers from higher price level like e.g. Acoustic Energy Radiance 2 I tested some time ago but also some very inexpensive ones like Pylon Pearl.

Azur 651A is a well equipped amplifier. It also looks good. It's sound is well balanced and presented in orderly fashion. It's open but also quite rich – that's its clear advantage over previous models. Both frequency extremes are strong but they don't dominate over midrange – smart move. Resolution is typical, for this price level, so nothing really worth mentioning. Dynamics on the other hand is quite good and only with very “flat” recordings like mono version of Pink Floyd's The Piper at the Gates of Dawn Pink Floyd dynamics was rather flat.
Important advantage of this amplifier is its reliability – this might not be the most impressive feature when it comes to music reproduction but it is really important. If you are attracted to the device itself you are at the same time distracted from music – that doesn't happen here.
On this price level competition is enormous - NAD, Arcam, Music Hall, Marantz, Denon, Yamaha, Advance Acoustic, Xindak, Fatman, Cyrus – just to name a few competitors that come immediately to mind. And each person looking for his own sound will surely find it depending on his preferences, listening room and the rest of the system.
Cambridge Audio 651A seems to be worth special attention because of its ability to play well each kind of music. Hook it up with Oyaide cables (I used those), put it on some Vibrapods and you will enjoy it!
And there is a bonus – you can use it with some nice headphones. Signal to headphone output comes directly from amplifier, which is not the best solution, but with certain approach you should get quite a satisfying result. To make it work you will have to use “bass” and “treble” knobs to turn bass bit up and treble bit down. When I listened via loudspeakers I preferred listening without touching bass and treble knobs. Sound was than internally richer, deeper, seemed to have more layers. But it was at the same time also bit brighter. But as I wrote in my leader for No. 93, Jan 2012 issue, what matters is the goal, methods to achieve it as not that important. So if somebody thinks he needs more bass or treble (greetings Przemek!), he should not hesitate. He can start with neutral setup just to know the basic sound, but than he could try to adjust it to his expectations. When listening via headphones it might be the best way to achieve enjoyable, uncolored, clean sound.
Let's not forget about USB port – sound quality is maybe not to impressive but it is surely enough to get to the world of music played from files, and you don't really have to pay for it.


Amplifier landed on the top shelf of my SolidBase IV Custom stand but also on Vibrapods and Acoustic Revive RHB-20 Hickory platform.
I used Oyaide Black Mamba power cable with P/C-004 plugs, that was plugged into Oyaide
MTB-4 power strip. I used Oyaide Tunami Terzo RR interconnect for connection with my CD Palyer and some other sources (e.g. D/A converter KingRex UD384). Unfortunately my own Acrolinks have too big plugs to fix them in sockets that are placed quite closely one to another. One of the sources that I used to deliver signal via USB port was my HP Pavilion dv7 with 2 core CPU, 320 HDD, 2 GB RAM, running under Windows Vista, with software players like foobar2000 and JPLAY. USB cable used was Acoustic Revive usb-5.0pl.


Cambridge Audio Azur 651A is an integrated amplifier. Aluminum front panel, aluminum side panels and top, plus a very nice overall design and very handy remote control called Navigator – these are its main advantages. Manufacturer offers it either in black or silver finish. Amplifier is equipped with four plastic legs with rubber washers.

There is a large volume control knob exactly in the middle of front panel dividing it thus into two halves. This one and three other, smaller knobs (treble, bass and balance) are also made of aluminum and they all have blue spots on them that indicate present position of each knob. Remote offers only volume control function. On the right side of front panel except for balance knob, there are couple of push buttons allowing to chose inputs. Above each button there is a small, blue LED. There is a mini-jack (Ø 3,5 mm) allowing to plug in some remote devices (players). On the right from “volume” knob there are two more - “bass” and “treble”, and a push button that allows to shorten signal path by bypassing a preamp section. Above there are two blue LEDs indicating which speaker output is in use (A, B, or none). When headphones are plugged in speakers outputs are automatically disconnected. Next to above mentioned LEDs there is one more „Protect”, that indicates that protection circuits work properly, or indicate particular kind of malfunction. Its a part of advanced system called CAP5, that was implemented already in previous models. There are also two single RCA sockets (Control Bus) – these are not digital inputs but sockets for communication between CA devices in the system. Plus there is a IR Emmiter socket.

Back panel
Looking on the front panel one has to realize its a XXIst century device – there is mp3 input, but also a push button marked as USB. And in fact there is an USB 1.0 port on the back panel, which might be used to deliver signal from a computer directly to the amplifier. Unfortunately manufacturer used quite an obsolete chip that accepts only 16 bit, 32 kHz/44,1 kHz/48 kHz signal so you can forget about hi-res files. But there is an USB port and someone who never played music from files before now has an opportunity to play with it.
Of course there are also 5 line inputs, including one that doubles the function of mp3 input on front panel. What I find interesting is a lack of phonostage – most competitors treat it as a must nowadays. And P40 was also equipped with one… Maybe the answer is a range of external phonostages that CA offers. NAD also prefers to offer external ones. There are two record outs, one pre-out, and one mono ‘Sub’ (output from preamplifier for active subwoofer). Sockets are not gold-plated, only GND is.
There are two pairs of solid, gold plated speaker binding posts, one placed above the other. So the easiest solution is to use speaker cable terminated with banana plugs. There is also an IEC socket plus mechanical on/off switch. Next to them there is a description of CAT5 system, explaining messages delivered by LED located on the front panel.

Looking inside the casing is a pleasure, as usually when it comes to Cambridge Audio devices. The whole setup is build up of modules – separate PCBs. The first of them contains input circuit. There are just standard, not gold plated inputs soldered directly to the PCB. Behind every input there is a NE5532 chip that acts as a buffer, but also does a preliminary amplification. Standard solution is to switch the signal first and than to amplify it – that's a cheaper solution. But this solution is a better one – first buffer and amplify and than switch, as in such case source impedance does not matter any more. Toshiba's selector is soldered on the opposite side of the PCB. It receives signal either from inputs or from USB port. The latter is mounted on a small, separate PCB, which sports also a Burr Brown PCM2704 chip (that's been on the market for quite some time). It is a USB-S/PDIF converter and DAC at the same time. Other elements are soldered using SMD technique. After selecting an input signal it is firstly amplified by another NE5532 chip and only than send forward. Same PCB contains quite advanced power supply circuit – some voltage regulators, rectifier and some smoothing capacitors.

Another PCB is a proper preamplifier. Writing on it says: „Hi-Fidelity Linear Preamp Stage”… . Signal amplification, as well as bass and treble adjustment are carried out by next NE5532 chips. Volume control is done with black Alps pot, placed on small PCB. Signal from there goes with shielded cables to power amplifier. The latter is based around complementary pair of STD-03N and STD-03P Darlington by Sanken. These are two bipolar transistors in cascode setup with a diode in one enclosure. There are bolted to a large radiator. Power amplifier works in Class AB.
Smoothing capacitors are placed on the same PCB – there are 8 capacitors (4 per channel) with CA logo, obviously these are above standard quality. Next to it there are large diodes in the diode bridge circuit. Large toroidal transformer has 4 taps – two for right and left channel and two for preamplifier section.

Specification (according to Manufacturer):
Power output: 75 W (8 Ω)
THD (unweighted):
- <0,002%, 1 kHz, 80% of rated power
- <0,03%, 20 Hz – 20 kHz, 80% of rated power
- <0,02%, 20 Hz – 20 kHz, 10 W
Frequency Response: 5 Hz – 50 kHz (-1 dB)
S/N ratio (ref 1 W): >92 dB (unweighted)
Input impedance: 47kohms
Damping factor >100
Max. Power Consumption: 600 W
Standby Power Consumption: <1 W
USB input: USB Audio 1.0 | 16 bit, 32 kHz/44,1 kHz/48 kHz
Dimensions (H x W x D): 120 x 430 x 350 mm
Weight: 8,4 kg

Polish Distributor:
Audio Center Poland

ul. Malborska 56, 30-646 Kraków
tel.: 12 265 02 85 | 12 265 02 86




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  • Power strip: Acoustic Revive RTP-4eu ULTIMATE
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