Cambridge Audio 651P Review

Many amplifiers and preamplifiers made today lack an internal phono stage. It used to be a common feature of the amplifiers of yesteryear – most, if not all, proudly boasting at least 1 if not more phono inputs. And these stages were no slouches, either – many had options for cartridge loading, and if your amp was of the higher end variety, you got capacitance and MM/MC options as well.

Now, however, this has changed. Many amplifier manufacturers favour internal DACs over internal phono stages. And, when an amplifier does include a phono stage, it’s often an afterthought – an extra feature to advertise on the front panel. If you’re serious about vinyl, these phono stages won’t cut it – so external stages are the only way to go.

However, many phono stages on the market are simply too expensive for the budget-conscious audiophile. An audiophile phono stage can cost more than a reasonably priced integrated amp – and then some.

Enter the Cambridge Audio 651P. Yet again, Cambridge Audio comes to the rescue  of the budget conscious audiophile. Their range features 2 phono stages – the 551P, a basic moving magnet stage, and the 651P, an MM/MC phono stage with subsonic filter and low noise, audiophile circuitry designed to get the best from your vinyl.

Just What Is A Phono Stage, Anyway?

At this point, you may be wondering exactly what a ‘phono stage’ actually is. Modern, hi-fi turntables typically use 2 types of cartridge – MM (moving magnet), or MC (moving coil). These cartridges have a very low output – roughly 5MV for MM and even less for MC), and therefore the signal coming from the cartridge must be amplified before it reaches the line level input of your amplifier.

A phono preamplifier must also perform equalisation on the sound, due to the way records are cut. This is known as RIAA equalisation. If you attempt to play record without RIAA equalisation, the sound will be thin and lacking in bass. Some phono stages (such as the 651P) also offer filters, such as a subsonic filter. Some phono stages also feature high pass filters and stereo/mono switches. These filters aid in reducing vinyl rumble (which can damage sub woofers), and can also reduce the crackle and surface noise of older recordings.

The 651P

With the 651P, Cambridge Audio’s goal was to design an audiophile phono stage, without the high end price tag. Outside, there’s not much going on – a single power button adorns the thick, brushed aluminium front panel. Around back, you’ll find RCA input jacks both for MM and MC cartridges, as well as a switch to switch between the 2. There’s a switch to toggle the subsonic filter, jacks for line out and DC power, and a ground.

However, there’s a lot going on inside that acoustically damped, full metal chassis. Low-noise input stages, built with discrete components feed Single ended class A gain stages with passive RIAA equalisation. Multi-parallel capacitors help to achieve exceptional RIAA accuracy, multiple transistors wired in parallel guarantee low noise and low distortion, and copper shielding protects the delicate input circuitry from external interference – which is especially important when using MC cartridges, as the required gain is much higher.

Finally, an external power supply reduces noise and interference offering a path for  later upgrades, and a power switch cuts standby power to 0 when not in use.

Packaging And Setup

Packaged in a  deceivingly large box, held in place by 2 cardboard inserts, the 651P itself comes wrapped in Cambridge Audio’s traditional cloth bag designed to protect the aluminium finish. A plastic bag contains some documentation, and a small box contains the DC power supply. No interconnect cables are provided, which is not surprising and is actually a good thing – at this level, you should be providing your own.

Setup couldn’t be simpler. 2 switches on the rear allow you to set the subsonic filter and choose between MM and MC cartridges. Then it’s simply a matter of hooking up your turntable to the appropriate input, making a connection to one of your amplifier’s line level inputs, and connecting the power.

The 651P lacks adjustments for cartridge loading or input capacitance – this is something I’d like to see on a phono stage claiming to be ‘audiophile’. The fixed 47 KOhm (MM), 100Ohm (MC), 220PF settings should be good for most setups, but it would be nice to have the ability to more appropriately match the 651P to a wider range of cartridges. It would also be nice to have the ability to switch between MM and MC on the front panel, enabling you to easily switch between 2 connected turntables.

The 651P features an output muting relay which will activate after 15 seconds of being powered on. This allows the electronic components to stabilise, and prevents thumps or pops being heard through your speakers.

Sound

After powering on the 651P I immediately noticed the low noise floor – in fact, with no signal, the 651P added little if anything to the already exceptionally low noise of the Cambridge Audio 851E/W system to which it was connected. This is a good thing, as it means less background noise getting in the way of the sound of your vinyl.

So, to some tracks. All vinyl was spun on Rega’s RP3/Elys2 combination. The 651P was allowed 2 weeks to run in, which should be enough to insure the best sound possible. Cambridge Audio interconnects were used to connect the 651P to the 851E/W pre/power combination. The subsonic filter was enabled at all times – during testing, I found it had little, if any, impact on the sound – and what impact it did have can only have been positive.

First to Queen’s ‘Millionaire Waltz’ from A Day At The Races. The simple bass/piano introduction is rendered beautifully. The reverb on Freddie’s voice displaying the 651Ps excellent sound staging and ability to convey the sound of a 3-dimensional recording. Instrument separation is excellent when things get busy, and the 651P displays an impeccable sense of rhythm during that infectious guitar/bass solo.

AC/DC’s ‘Shot Down In Flames’ displayed the 651P’s ability to uncover subtle details, such as reverb and room acoustics. The sound stage was somewhat narrow, and crisp highs were lacking compared with other phono stages.

Finally, to ‘Whisper’ from Evanescence’s ‘Fallen’ album. The 651P put in a faultless performance from beginning to end – beautifully uncovering the layers of detail in this track, particularly during the classical outro. Bass was weighty and precise, the sound stage was broad and expansive, and Amy Lee’s voice was delivered with passion. Great job.

Summary

If you own an amplifier that lacks a phono stage, or fancy an upgrade and don’t have a turntable to justify a higher end phono stage, the 651P may just be the stage for you. It’s small, simple and does its job well. It supports the 2 most common cartridge types, so it’ll get you by when you upgrade your turntable or cartridge.

Those fixed cartridge load and capacitance settings mean you’ll have to take care choosing a suitable cartridge – I found other phono stages were better able to support the Elys2 on my Rega RP3. That said, match it well, and you’ll have a phono stage that, for the price, is tough to beat.