It was 1968 when the company Cambridge Audio was formed by legendary designer Stan Curtis. Responsible for such classics as the Cambridge Audio CD2 & CD3 these designs were radically  innovative of their time. The CD3 used 4x Philips TDA1541A and 16x oversampling to push quantization noise higher above the audio band and enable a simpler analogue filter.The auction is for the modification only and does not include the Cambridge Audio Azur 640C CD player which must be purchased separately.

30 years on Cambridge Audio’s innovation has evolved to produce some excellent products which include the Azur range. At the top of this strong line up is the flagship 840C but here we turn our attention to the ward winning budget 840C V2.  The glowing testimonies of this player have earned 5 star rating and best CD player under £500 from What Hi-Fi, the “Gold Award” from Hi-Fi choice to name a few.

So What’s Under the Bonnet?

At the heart of the 640’S analogue circuits we find 2 x Wolfson WM8740 24-bit/192kHz DACs in dual differential configuration. These dual DACs have been arranged in a symmetrical formation and Cambridge claims this helps improve sound staging and stereo imaging. Features also include a low resonance, acoustically damped chassis, high-specification toroidal transformer and a claimed low jitter clock. Budget kit has probably never looked better and with and all for an absurd giveaway of £250.00.

Under Scrutiny

The 640C sets new standards in its price class but at £250.00 one would expect the 640C to have short comings and realistically it does. These shortcomings are highlighted in a TNT audio review where the reviewer explains these shortcomings; “Treble isn't completely clean. Loud piano tones in busy parts do sound a bit hard and the sound can become a little bit brittle at times. Bass lacks some control and a fraction of bass detail is lost because of his. Bowed double bass sound a little rough with less feeling of an actual physical instrument than I know to be possible” ...”The whole mid and treble actually sound a little bit 'bleached”...”the tendency of this player to make things sound 'fast' makes slower fragments sound a little bit hurried and unnatural.”

As will all reviews the perception of sound quality is subjective but the TNT review does paint an honest picture of the 640’s limitations and concludes with a positive remark... “One thing is absolutely certain: for the money this is one hell of a player, and if you want something better you will have to pay much, much more.” The auction is for the modification only and does not include the Cambridge Audio Azur 640C CD player which must be purchased separately.

More Marvellous Magic

Like other Cambridge Audio products gone before it, the 640C’s excellent circuit topology means serious improvements can be unlocked. With a justifiable and practical expenditure the 640C V2 loses its foibles and becomes a thoroughly capable and refined CD player.

The 640C is divided in to two main PCB’s, the servo PCB (digital) and main PCB (digital & analogue), it is the main PCB which is the focus of the Level-1 upgrades. Containing main power supplies, regulation, master clock, DAC & analogue output stage this PCB is certainly where most of the action happens.

First off we replace the ‘cooking grade’ capacitors used for power supply reservoir (smoothing AC) for Panasonic FC type. The FC series although not selected as “audio grade” outperform several types of electrolytic pitched at the audio market. The main PCB contains several fixed voltage regulators for the +/- 15V analogue supply, +5V DAC supplies. High grade bypassing is essential to reduce noise and impedance on the power supply lines; here more general purpose capacitors are upgraded to Rubycon ZA type, excellent for their ultra-low impedance, E.S.R, and sound quality.

The master clock in the 640C hides underneath a screening can and is labelled ‘low jitter’. Beneath the can we find a TCXO which is powered by a 7805 regulator. The output of the TCXO is buffered by a 14-pin CMOS inverter and the outputs from this sent directly to the Wolfson WM8740 DAC’s.

This arrangement has several drawbacks, the limited power supply rejection of the 7805, output noise of the 7805, CMOS gate oscillator in the TCXO has poor signal to noise ratio; the selected crystals inside the TCXO have low Q and a used in parallel mode, a method which is highly susceptible to digital noise injection.

To attain the highest level of sound quality from these circuits the OEM clock is removed and replaced with the Superclock 4 Ultra-low jitter master clock. The virtues of Superclock 4 can be found here; http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=300150205626

The post DAC filter in the 640C is a little unusual, it uses what is called a ‘double balanced’ filter rather than the normal low-pass filter. A total of 6x NE5532 operational amplifiers follow the Wolfson WM8740 for filtering and buffering. The 5532 is an ordinary consumer grade op-amp, a great workhorse in its day but it can be significantly better by modern op-amps. Here we use a mix a top spec op-amps costing 20x the price of the 5532 to wring the most out of the WM8740 DAC’s. This is more than icing on the cake, sonically it proves a revelation.

The signal output of the 640C is capacitor coupled to ‘block’ DC, a pair of capacitors lie in the signal path of each channel, a 100µF general purpose non-polar electrolytic bypassed with a 2N2 film capacitor. This combo of capacitors dirties and degrades the audio signal, a real offender to the now excellent analogue stage. These capacitors are removed and replaced with a single, Black Gate N series capacitor for each channel. The N series are the highest grade Black Gate capacitors and keep the total amount of distortion down to -150dB or less. Comparable with high-performance film capacitors, these new capacitors provide exceptional transparency, clarity and signal purity.

The finishing touches are made with a sheet of Sontech SFRT-AL resonance control panel for the lid to remove unwanted vibrations from entering the sensitive electronics. The SFRT-AL is designed to remove specific bands of vibration/noise turning into heat.

Showdown

The 640C V2 already ranks as the best player under £500.00 so what does spending an extra £250.00 bring in real terms? We left the Level-1 modded 640C on repeat 24/7 for 100 hours before making our assessment.

To hand we had a couple of unmodified CD players, the Marantz SA-7001KI and Cambridge Audio's own 840C.

Having another unmodified 640C to hand we sat down and made the comparisons. Listening in to the unmodified 640C we started out with a man who knows how to play piano; Ludovico Einaudi and his recent album Divenire was set to play. On the title track ‘Divenire’, this excellent piece can be beguiling and the stock 640C managed the intro well but as soon as the track became more complex the highest treble notes started to harden and the recordings leaner balance did not bode well with the 640C.  Moving to the modified 640C the same track ‘Divenire’ showed an enormous shift in music making ability, the modified 640C was streets ahead. The piano sounded that much more real and 'live', the timbre and tones of instruments were more believable. The music flowed effortlessly with superb coherence keeping control and poise during the intricate shifts in tempo. 

Sting’s Sacred Love album puts any CD player through its dynamic paces and the unmodified 640C fared much better with this album. The sound was lively and intelligible throughout and ‘Forget About The Future’ conveyed and excellent sense of feeling. However, the powerful notes on this track were understated, thinner, blander the sound compressed with less space.

Switching to the modded 640C and with the first track ‘Inside’ Sting had yet to sing and the realisation of extra power, depth and spatial qualities felt. Stings voice was strikingly real, full of meaningfulness; raspy and rich in character. Behind the voice the instruments surged with energy, control; details and nuances uncovered; the sound shimmering with passion and life.

The modded 640C’s finest achievement is that it maintains an open and uncluttered perspective on all recordings, even those CD’s in the ‘don’t play’ box get a look in!

The Level-1 modification delivers an outstanding upgrade to an already fine player wringing out performance trapped in the OEM player’s circuits. The improvements made to the stock 640C were shockingly good, its ability to remain intelligible even when pushed, energetic when other players are listless; all this and no right to sound as musical and natural at the price means it easily rivals players costing £1K.

If you are an existing owner of the 640C and have the itch to upgrade, spending £250.00 on this upgrade will give you the biggest bang for your buck, consider it unreservedly a bargain.

The modification work is completed with 4-5 working days from receipt of the CD player. The Level-1 modification is covered by a 2 year parts & labour guarantee, this guarantee excludes any OEM parts such as laser & LCD display.