August 2007

Burson Audio PI-100 Integrated Amplifier Plus Audio Buffer
A smooth and powerful first step.
Review By Clive Meakins
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  Being a committed fan of tubes I am perhaps not the most obvious person to check out the BursonAudio solid-state integrated amplifier. Burson hail from Australia, they have a strong background in high performance voltage regulators and discrete component OpAmps. More recently Burson have produced their PI-100, a 75 watts into 8 Ohms (150 watts in 4 Ohms) integrated amplifier. My interest was roused by the Burson claims about their competing with the sound of tubes but without compromised tube-amplifier loudspeaker drive capabilities.

Burson don't claim revolutionary design features but they do claim to combine sensible design practices that result in excellent sonics and technical capabilities. The PI-100 does not use coupling capacitors so the signal path is not "voiced" by potentially coloring capacitors. Great fun can be had tweaking amplifiers by substituting different coupling capacitors but the inescapable fact is that the best coupling capacitor is no coupling capacitor. The power supplies are regulated and of course they are implemented with Burson's own super-regulators. All components are discrete; there are no integrated circuits in the amplifier. There are three inputs, a pair of which feed the volume control; the third input is cleverly configured as a power amplifier input.

There are no remote control facilities. The casework is bright aluminum; the faceplate being particularly solid although I feel the rear of the chassis could be made to feel more substantial, securing it to the heatsink might be an option for Burson to consider. Overall the amplifier is attractive, if a little basic, the focus being on performance and value.

The bulk of my listening was done using loudspeakers that I had to hand that are sensible partners for this amplifier, these were Visaton's Topas, quite an easy load but really rather insensitive being at rated at 80dB/W/m. My main comparisons were made using a World Audio Design KaT34 tube push-pull amplifier. The KaT is a power amplifier delivering 32 wpc and it was configured to operate with EL34 or KT88 output tubes. Given Burson's positioning of their PI-100, the KaT34 whilst not currently available, offers a very fair comparison and as I've used the KaT a good deal over the last three years I felt I'd be able to easily work out whether BursonAudio deliver to their promises.

Once a decent period of break-in was out of the way I started listening to the PI-100 configured as an integrated amplifier. I found it very smooth and dreamy with Helene Segara Au nom d'une Femme, this was a great summer sound during the early warm weather we experienced in northern Europe during April 2007. If I stereotype solid-state amplifiers, especially when driven by CD, I would say that I typically hear a mid-range harshness that is rarely emitted by tubes. My initial and enduring view is that the PI-100 is totally bereft of mid-range harshness or "spittyness." Via the in-built volume control there were very smooth sounds that ultimately were just a little laid back.

To be able to make valid comparisons with the tubed Kat34 I brought my transformer volume control (TVC) into play. This was in turn connected to the PI-100 and KaT. Immediately I found the PI-100 came seriously alive, treble was much more evident, mid-range was thrust forward from its previously slight mellowness. No more was this amplifier for background music, it became much harder to ignore the music. Jennifer Warnes' The Hunter exhibited big powerful and well-controlled bass coupled with a big image. There was significantly enhanced detail definition compared with when the PI-100 operated as an integrated amplifier.

Moving on to the KaT34 driven via my TVC I found a similar high definition but now a slightly rounded sound due to the EL34 signature. I felt the sounds of the two amplifiers were much closer matched than I expected would be the case. To tease out a greater difference I substituted KT88 tubes in place of the EL34s. Vocals became more explicit. In fact, quite similar to the Burson with the treble shinning brighter and there was fast bass. Spinning up Mike & The Mechanics All I Need Is A Miracle, the Kat34 with EL34s sounded slightly slow in the bass, vocals were well defined, there was a general smoothness but little less "kick" than I would like. With KT88s the sound bore more similarity to the Burson but in the end the KaT34 equipped with KT88s was a little wearing on this high-energy track whereas the Burson trod a fast and explicit but more listenable path.

My conclusion is that the BursonAudio PI-100 when operated as a power amplifier outperforms the KaT34 tube amplifier whether equipped with EL34 or KT88 tubes. Bear in mind my preference for tubes and that the KaT34 cost me around double the purchase price of the Burson. You may now appreciate that my conclusion took me somewhat by surprise. Clearly BursonAudio have achieved their goals.

Mixing Burson's Audio Buffer With The PI-100

A few years ago Musical Fidelity introduced the tube-based X10D buffer. The X10D was to be connected between CD player and amplifier. Along with some inherent sonic warmth the buffer was there to provide optimal loading between source and amplifier. The X10D succeeded in bringing some relief in systems where harshness was attributed to the CD player.  However, the X10D wasn't the last word in transparency so whilst what it did was often welcome it would also slightly veil an otherwise transparent source. BursonAudio designed their Audio buffer to offer an easy load to source components and to be able to drive amplifiers with ease. Burson's discrete power supply regulators are used and the circuit is fully discrete, there being no ICs in use. Unlike the X10D the Audio Buffer delivers gain of two times (6dB). There is a power button on the front panel while the rear panel has an IEC power socket and RCA phono sockets for input/output.

My first running of the buffer saw me use it between my phono stage and transformer volume control which was feeding a type 45 SE tube amplifier (built by David Counter in the UK) driving open baffle Bastanis Alas speakers. If the buffer did anything unpleasant this setup would highlight. I found a little more bite to strings and no nasties. Otherwise there was little difference, which was a very good indicator that the buffer is doing something right. I then tried the buffer downstream of the transformer volume control, the effect was much the same with the added bonus that bass timed better than when the TVC was used on its own. The effect is not too surprising given that the TVC had just become an active preamp with 6dB of gain. Bass is an area where active preamplifiers often beat passives. Passives normally win out on transparency but I could not detect any loss of transparency when using the buffer. This is one good buffer from Burson.

Using my Merdian 588 CD player into the BursonAudio Buffer feeding the PI-100, I found more detail in the upper-mid than when the PI-100 was operated "bufferless." There were more powerful dynamics listening to the acoustic guitars of Rodrigo y Gabriela. Music with the buffer in the systems was more controlled and faster sounding. This bodes well for the new BursonAudio preamplifier, which is based around the discrete buffer circuit. Playing the White Stripes track "Blue Orchid" brought home even more strongly the benefit of the buffer, bass was better defined, treble was stronger and clearer, indeed there was greater clarity overall from a track that could easily turn into uncontrolled mush when using lesser equipment. Moving to Alison Krauss "Stay" from Forget About It exhibited all the previously heard benefits when using the buffer; Alison's sweet vocals now touched me all the more. Even when using high quality equipment the buffer provides performance improvement with no tradeoffs such as the X10D used to suffer.

Conclusion

As an integrated amplifier the PI-100 offers little in the way of frills, the focus being on sound quality. Sound quality is above what I would have expected for the price, I would simplistically describe the sound as smooth and powerful. The clever PI-100 input arrangements mean it's a doodle to turn it into a power amplifier or you can use it with the Audio Buffer in front of it. My advice would be to consider purchasing a PI-100 as the first step, you really should consider using the Audio Buffer or a quality preamplifier with the PI-100. I should add that the buffer is not expensive and is worth trying in most systems to check if its effect is beneficial.

BursonAudio have recently introduced their preamplifier that matches the PI-100, this is based on the Audio Buffer but with more gain. I fully expect this to be the perfect partner to the PI-100. Take the PI-100 to the max with a good preamplifier as you may be well rewarded.

Scores

Please understand that I am scoring where five notes is the best there is, irrelevant of price. The price of the PI-100 sets an expectation of scoring around two to three notes in most categories.

Specifications

PI-100
Type: Stereo integrated amplifier
Frequency Response 10Hz to 120kHz (+/- 3dB)
Output Power: 75 wpc @ 8 Ohms (150 wpc @ 4 Ohms)
Operation: Class AB
S/N Ratio 96dB (CD, Line) 
Input Sensitivity: 240mV
Input Impedance: 20kOhms 
Color: Silver
Dimensions: 430 x 100 x 360 (WxHxD in mm)
Weight: 13 kg
Price: $840 for barebones, $1010 complete (price in Australian dollars)

Audio Buffer
Frequency Response: 0Hz to 220kHz (-3dB) 
Output Noise Level: 0.015MV (nil input) 
Maximum Output Voltage: 12VRMS 
Maximum Input Voltage: 6VRMS 
SNR: 118dB
Gain: 6dB
Net Weight: 2 kg 
Dimensions: 210 x 145 x 60 (W x H x D in mm)
Price: Approximately $375 (check their website for current pricing)

Company Information

BursonAudio
E-mail: bursonaudio@yahoo.com.au
Website: www.bursonaudio.com