Burson Audio’s Cable+ Pro interconnects are designed to match impedance differences between your source output and amplifier input. The Cable+ Pro is an interesting proposition and one that I was keen to test against my existing, high quality Tara Labs RCA cables – is it snake oil or is it the real deal? Let’s find out…

(Note: this review is for the Cable+ Pro. I might be lazy and write “Cable+” only sometimes, but I am always referring to the Pro version with the impedance matching circuit)

A Bit About Impedance Matching

Impedance matching is an interesting topic for conversation and something that can stir up all kinds of debate (hopefully this post will only stir up helpful and constructive discussion) and I first discussed it in my posts about the PC audio setup I use to maximise my sound quality via BNC audio (which is more closely impedance matched than RCA-style coaxial connections.

The theory behind impedance matching is two-fold. Firstly, different impedances between your source, amplifier, and the cables connecting them can lead to unwanted alterations in the power delivery as the music signal varies. Secondly, some theories suggest that each different impedance in a signal chain can create reflections which degrade the audio quality. This second theory is debatable in the world of analogue audio due to the generally short cable lengths so I’m going to focus more on the possible implications of the variations in power delivery.

Before I go any further, please keep in mind that I am not an audio engineer, or a physics expert so I will not try to explain this in depth and will be sharing my understanding as a layman audio enthusiast. I welcome constructive comments to help readers further understand the phenomena at play if you have deeper expertise and experience in this field.

Power Variations Due to Impedance Differences

Note: my explanation of the theory here may contain errors (I told you I’m not an engineer!) Please refer to the comments for more detail on this topic.

If you remember your high-school physics, you might remember the formula, V=IR, which means “voltage equals current multiplied by resistance”. What this means is that changes to voltage, resistance and current can each affect one another. Let’s put this into a basic audio example…

When you listen to a recording, the sound is made up of constantly varying frequencies and amplitudes (volume). This means that the voltage and current in your system is never fixed – it’s always changing. Now, if there are also multiple impedances along the signal path these will all respond differently to the variations in the audio signal. Based on this theory, the sound quality of the system will be inconsistent. It may not be obvious without a fixed-impedance comparison, but the theory suggests that the sound will be affected to some degree.

About the Cable+ Pro

Based on some of the questions and differing opinions around the web on this topic, I had limited expectations of the Cable+. I expected subtle differences, but not necessarily anything too significant. On top of that, I am always a little cautious about anything that adds complications to the audio chain and, as you’ll see in the images, the Cable+ includes a fairly complex little circuit board right in the middle of the cable – simple this is not. So, I immediately wondered, “Is it messing with my audio or just keeping the signal pure?”

Before I tell you what I am hearing, let’s introduce the cable itself. This test is for the Cable+ Pro RCA-to-RCA interconnect and the specs are as follows:

• Input impedance:  250,000 ohms
• Frequency response:  0 – 55,000 Hz (+/- 1 dB)
• Total harmonic distortion:  <0.005%
• Output impedance:  3 ohms
• Signal to noise ratio:  >118dB at 6dB gain
• Cable length:  120 cm / 47.2 inches

This is the first time I have ever even considered the input and output impedance or harmonic distortion of a cable, but it’s due to the active circuit (audio buffer) built into the cable and speaks to my earlier concerns that the cable is adding complexity to the signal path so I am keen to see if the benefits outweigh the drawbacks.

Because of the active circuitry, the Cable+ also needs power (it consumes 5W according to the specs) and is powered via a micro-USB cable and a small power brick supplied with the Cable+. This adds extra cabling which is not always ideal, but once setup you don’t really need to see any of it.

Something else that’s of interest is the 6dB gain added to the signal (see signal to noise ratio above). This means that the sound seems to be instantly more dynamic if compared like-for-like with passive interconnects and it may also cause issues if your system is already quite loud so keep that in mind. For all my comparisons I used the Bottlehead Mainline’s stepped volume control to play the signal from my existing interconnects exactly 6dB higher than the Cable+ signal.

Design & Aesthetic

The Cable+ is a fairly basic looking cable which some will like and others might not. Personally, I like the fact that Burson themselves are not making any grand claims about their cables. They are using simple Canare two-core cables for each channel and basic, but quality Canare connectors. The result is a fairly ordinary cable, despite its red colour, that doesn’t scream “expensive” or “fancy” so much as looking utilitarian and professional (except perhaps for the little black box with the USB cable hanging out of it…) I don’t care much for cable aesthetics so for me the Cable+ is perfectly fine, but I can see some people not liking the basic design – to each their own.

One thing I very much appreciate about the Cable+ design is the long, spring-style strain relievers at each plug. With an amp like the Mainline that has top-entry cables, these strain-relievers are very important to prevent long term damage to the cable from the constant sharp bend of the cable. More traditional rear-entry designs may not need these quite as much, but more strain relief is always better than less.

One thing I don’t appreciate, however, is the little coloured o-rings on the plugs to delineate the left and right channels. These look fine, but can easily become displaced when connecting and disconnecting the cables. It’s not a big deal, but it’s slightly annoying having to refit them when they move.

Sound

Enough of the design and specs. Let’s find out how this $200 (USD) cable actually sounds. I am going to use my old, faithful Tara Labs interconnects as a reference. I can’t tell you how much these cost when they were new because they’re probably 15-20 years old, but they have stood the test of time and haven’t yet been bettered by anything soundly enough (no pun intended) to be superseded. Let’s see if today is the day…

As I already mentioned, when you first switch from traditional interconnects to the Cable+ you might think they have transformed your system, but it’s because of the 6dB boost they apply in the active circuit. A boost like that (no matter the cable) creates an instant sense of greater dynamics and excitement. This isn’t to suggest trickery by Burson – they aren’t hiding the gain increase – it’s just the way the circuit works.

Switching between the 2 pairs of cables (precisely matching the volume each time) there is a noticeable difference in the presentation of both cables. The Tara Labs’ sound is a little brighter or perhaps that should be thinner. The Cable+ lends the sound greater weight and depth in the mids and bass while tidying up the treble slightly. There is no loss of treble energy or quality with the Cable+ so when I say it’s tidied up it is a case of the slight sibilance I hear from the Tara Labs cables being removed by the Cable+ and replaced with crystalline, sharp treble. It’s subtle, but there’s no doubt in my mind that the Cable+ treble is more enjoyable. As to why I am hearing this? I can’t say. Perhaps it is an artifact of the active circuitry or perhaps it is the benefit of the impedance matching – I am not going to hazard a guess. All I can say for certain is that the Cable+ is a more enjoyable cable for me despite the Tara Labs being a very good cable in their own right.

In that last sentence I deliberately said “the Cable+ is a more enjoyable cable for me” because it’s important to distinguish the role of personal taste in this comparison. I don’t doubt that some people would prefer the presentation of my old Tara Labs cables because their thinner tone leads to a greater sense of texture in the upper-midrange. In time, that texture becomes fatiguing for me and I will gladly trade it away for the better balance between treble / upper-mids and lower-mids / bass that the Cable+ provides. Regular readers will know that I prefer a warmer sound and some components that add warmth can be troublesome for me, but the Cable+ just adds weight, not warmth and this added weight adds to the realism of the music with marvellous results.

Second Opinion

Having read a review on 6moons Audio (http://www.6moons.com/audioreviews/burson/buffer.html) about the Burson Audio Buffer (same concept as the circuit in the Cable+ Pro, I was keen to try another amp. The 6moons review talked about the differences they found between different device combinations so I hooked up the Burson Audio FUN amp (running the V6C op-amps, review coming soon) to see how the Cable+ Pro performed with that combination compared to the Tara Labs cables.

Without the precise volume control, the matching of the signals was more difficult and there was more delay between each cable because there is only one RCA input on the FUN (the Mainline has two inputs so I could change cables with the flick of a switch), but the results were very similar. Once again the Cable+ brought greater weight and depth to the sound while tidying up the slightly reedy treble (in comparison) from the Tara Labs. What I found with the FUN amp though was how much more transparent the sound became. With the Tara Labs cables, the sound was very good, but a little congested. Swapping to the Cable+ Pro was like lifting a veil when using the FUN. Suddenly I could hear details that were obscured in the Tara Labs setup (even with the Tara Labs setup slightly louder). Transients were sharper and cleaner with the Cable+ and mid-range details were easier to hear, but not pronounced.

I switched cables a few times on different tracks to ensure that it wasn’t one of those track-specific things where a certain synergy occurs between the recording of the music and the signature of the setup, but every track sounded significantly better with the Cable+ Pro. The Tara Labs setup sounded distinctly flat and far less enjoyable.

This all tells me that some systems will benefit more than others with the Cable+, but I am confident that all systems will experience some benefit, the question is just “how much?”

Summary

At $200 USD, the Cable+ Pro is not a cheap interconnect cable, but it’s also not that expensive (there are $1,500 interconnects on the market!!) I see the Cable+ as an affordable audiophile upgrade without getting crazy. If you’re looking for a better interconnect for your system I would highly recommend adding the Cable+ Pro to your shortlist. If nothing else, it is a very well-made, sturdy interconnect that is likely to last for a very long time. To my ears it also adds noticeable audible improvements and no audible degradation of the sound quality. Some systems will show significant improvements while others will be more subtle, but my time with it suggests that the Cable+ will always lend some degree of improvement, just the degree of improvement will vary. Do keep in mind that you will need to have a power source available for the little brick and cable to drive the Cable+ circuitry, but as long as you can hide this (or deal with seeing it) there are no real drawbacks.

I am certainly going to enjoy having the Cable+ Pro in my signal path for many years to come and have finally demoted the much-loved Tara Labs cables to secondary amp duties thanks to the wonderful weight and clarity offered by the Cable+ Pro.

If you’re interested in picking up a Cable+ Pro for yourself (and I definitely recommend it) and you’d like to help support this blog, please use the link below. It costs you nothing, but provides a small amount of income to help me keep the reviews coming along…