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Burson Audio PI-100 integrated amplifier

Power to the people

[Italian version]

Product: Burson Audio PI-100 integrated amplifier
Manufacturer: BursonAudio - Australia
Cost: * 830 USD (direct from BursonAudio) [*]
Reviewer: Nick Whetstone - TNT UK
Reviewed: May, 2007

BursonAudio have been around for a while now, impressing us with no-nonsense audio products like their HDAM modules, Burson Buffer, and voltage regulators. I've been impressed with the items that I have reviewed so far, so when they told me that they were designing an integrated amplifier, I was keen to see what they would come up with. Some months later, a large package arrived at my front door, and I could tell from the strained look on the courier's face that it was no chip amp!

Burson's aims are simple: take a piece of hi-fi and try and design something better. The integrated amplifier is certainly their largest project to date, and arguably the biggest challenge to come up with something that is significantly better than the opposition. Basically they set out to equal the sound quality of a good valve amplifier but using solid-state electronics. It is true that of recent the valve amplifier has been seen as the archetypal high-end item, with solid-state viewed more as the poorer relation. Burson wanted to show that solid-state amplifiers can be high end too. This was to be a no compromise amplifier, offering power, transparency, speed, and neutrality. Just as importantly, offering good weight in the mid-range, an area where many solid-state amplifiers can fall down.

Realising that there was no need to reinvent the wheel, Burson relied on proven circuitry for their design, but focussed on each and every part of the circuit, fine tuning them until they were happy that they had got each one 'right'. Some sensible 'rules' were laid down. No capacitors were to be used in the signal path. It's true you can get some very good coupling capacitors but none is as good as having no capacitor! The power supply was to use their own discrete voltage regulators, thus avoiding any of the standard three-pin regulators. Likewise, opamps were to play no part in the signal path.

On removing the PI-100 from it's cocoon of packaging, I found a (very) large brushed aluminium box that made me glad that I have substantial equipment racks. Most of the weight is due to the two, large, 500VA toroidal transformers occupying nearly one half of the case. Well if you want power out, you have to put power in, and Burson certainly haven't skimped on that part of the design. I have one gripe about the PI-100 here, and that is the lack of a soft-start system for an amplifier with transformers totalling 1KVA. I have a dedicated mains spur for my hi-fi that has a 10 amp circuit breaker in the consumer unit. Whenever I switched on the PI-100 the circuit-breaker would trip. I eventually got around this by plugging it into the normal ring main. Apart from the circuit-breaker issue, I would be happier to see a soft-start used as I believe it relieves stress on components like the power switch and (expensive audio grade in this case) reservoir capacitors. I did speak with Burson about this and they assure me the PI-100 is OK without a soft-start and they are the designers, but personally I would prefer one!

With the need to house the two large transformers, the case is somewhat larger than most hi-fi components, measuring in at approximately 430 mm (18 inches) square. This means that you will need a deep shelf to accommodate the PI-100. In practise, both my hi-fi racks had no problem accommodating this amplifier but it is something to keep in mind. The custom-wound 500VA transformers from Burson make hardly any hum. With the standard transformers supplied in my review sample, there was a bit of hum, audible when the amplifier was first powered up, but not audible from the listening position. I mention this in case you buy the 'transformer less' version of the PI-100 (see last paragraph).

[BursonAudio PI-100 integrated amplifier - internal]

Despite the size, the outward appearance of the PI-100 is quite appealing. A simple brushed aluminium look, with matching silver knobs is both clean and easy on the eye. The uncluttered fascia has a power switch (and obligatory blue LED) on the left, and the source selector switch and volume control on the right. Once in the rack of course, you don't really notice the size at all!

The PI-100 has three inputs, that can be selected from the front panel via relays at the rear of the case, thus keeping the signal path as short as is practical. Burson don't state the make of the volume control but it has a nice solid feel to it while remaining smooth in operation. On the rear of the case are the various connectors: an IEC socket for mains power, three sets of phono sockets, and some classy looking speaker connectors.

[BursonAudio PI-100 integrated amplifier - rear view]

I couldn't resist a quick peak inside the PI-100 and can confirm that is it beautifully neat and tidy, well laid out, and obviously built to a high quality. Burson have chosen Toshiba 2SA1943 and 2CS5200 transistors (matched of course) for the main output devices and confirm that these are genuine Toshiba devices from a trusted source, and not copies that are unfortunately so widely available. Burson have taken the same care in sourcing the parts for the PI-100 as they have in designing the circuits. In fact they are so confident about the PI-100 that they are offering a 30-day no-risk trial!

Having checked the DC offset on the outputs (there isn't any) I connected up some speakers and a CDP for a quick test. There is no nasty noise when you power up the PI-100 because the outputs are relay-controlled and don't 'open' until the amp has fully powered up and 'settled down'. Likewise, if any DC is detected in the event of a fault, the outputs are shut down immediately. Burson recommend that the amp is allowed to warm up for an hour so I left it playing. Returning with a cup of tea, and a handful of my favourite auditioning CDs, I sat down to have a good listen. At lower volume levels, the PI-100 reminded me much of the sound of my Gainclones. But it was clear that it did a lot of things better, more so as the volume level increased. First off it is an easy amplifier to listen to. There is nothing nasty about the sound, you could listen to it all day and not get tired. Satisfied that it was working OK, I moved it into my main system. It was here, fed by a modified SB3 (Squeezebox), NOS DAC, and Burson Buffer, and playing into the Hawthorne Audio Duets, that the PI-100 really made me take notice!

Burson recommended using the Burson Buffer in front of the PI-100 stating that the two had been designed to work together. Whether it was the addition of the buffer, or the rest of the system I don't know, but I was hardly ready for what I heard next! This was not an audition where I had to listen very hard for an improvement! I won't say that the PI-100 dug out extra detail, rather it took all the small detail that was there and boosted it, making it more palpable. For instance, all the little Q sound effects on Roger Waters 'Amused to Death' album were more tangible, firmed up, more solid.

The sound stage was large and particularly deep with the various elements clearly portrayed at increasing distance from the front to the back. Each element was also clearly separated from the others with plenty of air around it. Imaging was sharp with no apparent sign of moving about in the sound stage. On live recordings there was an excellent sense of ambience.

[BursonAudio PI-100 integrated amplifier - internal view]

The PI-100 has effortless power. There is no sense of straining, even on heavy and complicated passages with the volume wound up loud enough to worry about the neighbours. On the Dadawa album 'Sister Drum', the final track includes what can be a cacophony of Tibetan horns, drums and chanting. With the PI-100 I was picking out individual details right through this loud passage that I haven't noticed before and it was altogether a more pleasant listening experience. Bass is tightly controlled, but where tighter bass sometimes gives the impression of less bass, the PI-100 manages to keep both bass accuracy, and level, high enough to provide a highly satisfying low end.

Timing is spot on, the PI-100 gets the toes tapping alright. Rhythm and pace make some recordings like Paul Simon's 'Gracelands' addictive. There's impact, the combination of this amplifier with the open-baffle bass made for life-like percussion that on some recordings could be felt as well as heard.

Mid-range is natural and silky smooth without even a hint of thinness; violins surely never sounded sweeter! The top end is clear and detailed without giving the ears a hard time. In fact the PI-100 is one of those amplifiers that you can listen to all evening without any fatigue. I was going to say that it doesn't excel at any one type of music because everything I played through it was very good. But I am going to say that I have never enjoyed classical music quite so much through any hi-fi that I have listened to before. The PI-100 also seemed to bring to life some of the older recordings that I listened to. From solo guitar or piano to full orchestral pieces, from light jazz to techno, from folk to rock, the PI-100 just plays it all well without adding or taking anything away. Does it sound like a valve amplifier? Well, if the Gainclone is meant to have a 'valve sound', I guess the sound signature of the PI-100 is very similar. I would prefer not to make comparisons though because quite simply, the sound of this amplifier is good enough not to need comparisons.

To me, no piece of hi-fi is any good if it cannot convey the emotion of the music but once again the PI-100 scores top marks. Classical music particularly was both enthralling and moving.

Although Burson are correct, and the PI-100 does sound its best after a good warm up period, it says a lot for its sound quality that if you come in and turn it on to listen straight away, it still sounds better than most other amplifiers that I have heard!

No need to tell you now that I like the PI-100! If I had heard this amplifier a few years ago and been told that it cost several thousand dollars, I would have wept at the thought of it being out of my financial grasp, but not been surprised. That it offers the performance it does for the price of a mid-range commercial amplifier makes me smile even more. My only real gripe about this amplifier is the lack of a soft-start but I also understand that Burson have tried hard to keep the price within the range of what they call the 'wage-earning audiophile'. And it is such an enjoyable experience listening to the PI-100 that I feel a little guilty about making any criticism!

I predicted a rush for the Burson Buffer and was proved right. While I would always advise an audition before buying any piece of hi-fi, in this case, I would say take my word for it and order one of these quick! Yes, it is that good! Oh, and I should add that Burson are working on a pre-amp, and have a power amplifier on the drawing board!

[*] Finally, if you want to save your postman, and your bank balance, some strain, BursonAudio will supply the PI-100 in what they call 'bare bone form'. Basically this is a finished PI-100 but without those large transformers. As an example, somebody buying a bare bones PI-100 in Europe will save 80 euros on shipping and 120 euros on the price of a complete amplifier. That 200 euros will more than cover the cost of the two transformers bought 'locally'. Obviously fitting transformers and connecting them to the mains supply is a job for an expert!

Update July 2007
I recently tried the PI-100 without the Burson buffer in front of it and found that it lost a lot of its magic. Burson tell me that the PI-100 is specifically designed to work with either the Burson Buffer, or their own pre amp so please keep that in mind when deciding to buy (or audition) one.

© Copyright 2007 Nick Whetstone - www.tnt-audio.com

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