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Product Review
 

Burson Audio PI-100 Integrated Stereo Amplifier

August, 2007

Chris Groppi

 

Specifications:

● Design: Integrated; 75 Watts RMS x 2
   into 8 Ohms, 150 Watts RMS x 2 into 4
   Ohms
● Connections: Three Sets of RCA Inputs;
   One Set of Speaker Binding Post
   Outputs
● MFR: 10 Hz - 120 kHz
± 3 dB
● THD+N: 0.01%; 20 Hz - 20 kHz
● S/N: 96 dB
● Dimensions: 4" H x 17" W x 14.3" D
● Weight: 28.6 Pounds
● MSRP: $1,040 USA

Burson Audio

Introduction

Burson audio began 10 years ago in Melbourne, Australia, as a DIY cooperative producing components for their members. Just two years ago, they introduced their first commercial product.

Most of their product line is aimed at the DIY market, with op-amp replacement modules made entirely of discrete components, all discrete voltage regulators, and a low jitter clock module upgrade. In addition, they make interconnect cables and three complete products, the Burson Audio Buffer (a unity gain buffer with discrete op-amps), the new P-100 preamplifier, and the PI-100 integrated amplifier reviewed here.

The PI-100 is available as a complete component, or in bare-bones version where the user supplies the power transformer.

Burson's philosophy is based on circuits built entirely of discrete components. No integrated circuits are used in the signal path, and special care is paid to the design of discrete voltage regulators and discrete op-amps. These parts, built from individual transistors, have the same function as an IC voltage regulator or op-amp, but take hours of hand soldering dozens of components. The advantage is the ability to tailor the design to the application, with performance exceeding that of generic IC designs. All transistors can be carefully matched for the best performance.

When replacing dual or quad IC op-amps, discrete fabrication also reduces crosstalk (if done correctly). The disadvantage is a vast increase in parts count and complexity. Usually, only the most expensive components offer fully discrete construction, as is found in the PI-100. For a thousand bucks USA, this is very unusual.

The small size of the company and DIY heritage make ordering a bit more difficult for US customers. Burson sells their products directly from their website, and on E-Bay. They have organized service locations in many countries, including two in the USA.

As far as I know, no warranty is offered. Shipping costs are a bit steep, but that is more than made up for in the low cost of the amplifier itself. The packaging of the review unit was also a bit strange, with hand cut pieces of Styrofoam that left crumbs all over the amp, and no manual (or paperwork of any kind for that matter) included.

The review unit came with "120V" written in permanent marker on the top panel of the amp, which I cleaned off with some adhesive remover. While these are small issues, they are also easy to fix for Burson, and will make the first impression of their products much better. While the $1,040 purchase price is quite low for an amp of this quality, it's still a thousand dollars. The PI-100 deserves better quality packaging, a well-written users manual, and a pristine component upon unpacking. The DIY background of the company still shows through.

Design and Construction

The PI-100 uses a minimalist design, with as few bells and whistles as necessary to maintain function. The amp has three single-ended inputs, one of which is a unity gain input that bypasses the volume control for use as a power amplifier with a separate preamp, or with a surround sound processor. The front panel has a source selector switch and volume pot (unlabeled), and a power switch. The rear panel offers two sets of five-way binding posts for speaker connection, 3 pairs of RCA inputs, and an IEC jack for AC power. No extras like line level pre-outs, an extra set of binding posts, a tape loop, muting, a remote etc. are offered. This is a conscious decision that rings true with the Burson philosophy: no unnecessary features should be included. Extra toys will only decrease the performance of the amp and increase its cost.

Unusually, the case of the PI-100 is custom made. Most manufacturers purchase the chassis from another manufacturer. The PI-100 case is made by hand, out of five pieces of aluminum plate and a thick, machined aluminum front panel, all secured with four corner blocks. The result is a nice looking case, but with a little more flexibility than I would like. Also, the case seems to be made of raw, un-anodized aluminum that could require periodic cleaning to maintain an attractive appearance.

The simplicity of design continues on the inside of the PI-100. The power supply, including the power transformer, are in a separately shielded box placed on the left side of the amplifier chassis, connected to a single PC board on the right side of the amp. An aluminum heat spreader runs down the center of the chassis, to which the output transistors are bolted. The PC board is laid out in a dual-mono fashion, with relay switched inputs, at the rear of the board. A fully discrete voltage regulation stage (one each for the right and left channels), based on the design of the Burson Super Regulator DIY upgrade module, is on the center of the board. This regulation stage includes 40,000 µF of capacitance ("B" in the photo below). The voltage gain stage, which is normally based on an IC op-amp in most audio circuits, uses a fully discrete topology (blue area surrounding "D" in the photo), similar to that used in the Burson Discrete Op-amp. The output of this gain stage is then routed through a relay for speaker short circuit protection, before heading to the final current gain stage ("E").

The quality of the electronics in the PI-100 is beyond reproach. The board, layout and assembly quality are exceptional. A wire caused my only quibble with the internal assembly. The wire from the volume pot was trapped between the front panel and bottom panel. This was easily fixed by removing some of the screws holding the case together to free the wire.

Both the flexibility of the chassis and the trapped wire still were a somewhat annoying reminder of the PI-100's DIY heritage. As with the packaging and lack of manual, these are easy problems for Burson to fix, and would go a long way towards eliminating the "almost done" impression of the product. Other than the few packaging and quality control issues I found with the PI-100, I was very impressed with the design, and hoped upon listening that the minimalist design of the PI-100 resulted in spectacular sound.

The Sound

I broke in the PI-100 with casual home theater listening for several weeks before doing any critical listening. I left the amplifier on all the time. As there were no pre-outs, I did not use the Gallo Reference SA subwoofer amplifier, and drove only the primary voice coil of the Reference 3.1s with the PI-100. I was immediately struck by what wasn't missing from the presentation. My new Emotiva separates I bought after my last review are spectacular components, that offered vast improvements in almost every way compared to the Plinius 8150i integrated they replaced. There was nothing about the PI-100 that struck me immediately as negative compared to the Emotivas.

As I listened to the PI-100 more, I found several areas where the PI-100 excelled. Even though I was not using the Gallo subwoofer amplifier, the bass performance was still very good, with great impact, weight, and extension. Only the last octave at the low end suffered, as you would expect. Without the Reference SA, the bass power and agility of the PI-100 was superior to that of the Emotiva RSP-1/RPA-1 combo. I could imagine that with the Gallo amp, the bass might be too much, though. Take this into account of your system already suffers from bass bloat.

The most impressive area of the PI-100's performance was in the accurate and detailed presentation of timbre. Each of the PI-100's images had a three-dimensional size, shape, and texture that were particularly compelling. Whether it was Connie Kay's brushes on a snare, or acoustic guitar on the Mexican rock band Café Tacuba's Vale Callampa, the PI-100 not only reproduced the sound accurately, but the space around the sound. The tonal texture allowed me to hear each wire of the brush on the snare head, or the fingers moving along the neck of the guitar in a very real and visceral way. While the Emotivas offered a cleaner, more precise presentation of images, with fantastic tonal separation outlining every sound, they were not able to offer the holographic 3D presentation of the PI-100. By comparison, the Emotiva pair produced images that were precisely located and delineated, but were a bit flat. Note that in the Emotiva review, I praised the RSP-1/RPA-1 for this same trait, compared to my previous Plinius 8150. The PI-100 moves this reproduction of texture to a new level, with even more texture extracted out of every image. This is one of the advantages of a design with very few components in the signal path.

In the soundstaging and imaging department, the PI-100 produced larger, more realistically sized images, at the expense of pinpoint imaging accuracy. Combined with the timbral presentation mentioned above, this resulted in extremely realistic presentations, especially when the source material was small in scale, like solo voices or instrumentals and small combos. With larger scale recordings, the large image sizes could cause some spatial confusion. Presentation of soundstage depth was excellent, and superior to the Emotiva pair.

Depth presentation depends very much on the accurate presentation of tonal cues, so I would expect that the PI-100 would do well here, and it did. On many recordings that sounded relatively planar with the Emotivas, the PI-100 was able to extract plenty of depth information. The Emotivas did win on soundstage width and height, with a significantly wider and taller presentation.

The midrange and treble smoothness of the PI-100 were excellent. I never was reminded that I was listening to a sub-$1000 solid-state component. The tonal purity was unaffected by any sort of grain or hardness that wasn't already there from upstream sources. Both the midrange and treble were perfectly liquid and smooth, without being TOO liquid or smooth. Some components (not all tube, by the way) take the smoothness thing too far, and end up killing the excitement and attack of the music where some harshness should be there. I tested this with one of my favorite big band recordings, Telarc's Dedicated to Diz. As a longtime bass trombone player in big bands in secondary school and college, I know what a big band brass section should sound like. Many times, the point is to sound the opposite of "liquid and smooth." A stereo component needs to accurately convey this brass bite when called for, without diluting it in candy-coated sweetness. The PI-100 does the job, bringing out the power of Slide Hampton's all-star big band in this album.

The macro-dynamics produced by the PI-100 were particularly impressive for an amplifier with only 75W per channel. There was some loss in slam and attack in the low range, with no detectible loss of impact in the midrange and treble when compared to the Emotivas. The Emotivas did produce a bit more life and excitement in the music, leading me to conclude that the PI-100 was bested in the area of micro-dynamics. This is not to say the PI-100 sounded unexciting, but it did give up a little in this area compared to the best amplifiers I have heard. Of course, the best amplifiers I have ever heard are, shall we say, just a bit more expensive to say the least.

Conclusions

With all the characteristics taken into account, I can safely state that the PI-100 is an excellent integrated amplifier, equaling and besting amplifiers costing 3-5 times more. It has essentially no sonic shortcomings. The description I give above reveals some details of the presentation that I might prefer to be otherwise, but there are no clear flaws of any kind.

The real question is if the minimalist design of the PI-100 meets your needs in a system context. For me, it does not. There just aren't enough inputs, or any line level outputs to properly drive my subwoofer amplifier. There is also the issue that the PI-100 cannot really be auditioned in advance, nor can it be easily returned.

Some might be bothered by the DIY image of the amp as well. But, for me, sound quality ALWAYS trumps appearance. If I had a simpler, two-channel-only system as I had in the past, the PI-100 would have been perfect. If you have the luxury to have a second two-channel-only system, or would like to build one at a reasonable cost, the PI-100 is a great, no frills component that can be the core of a fine system.

It would also be the perfect integrated for someone's first real Hi-Fi setup. A PI-100 combined with a quality universal disc player, and monitor-class speakers could make a fabulous $2000-$3000 stereo system. I eagerly await future components from Burson, like the new P-100 preamp. This hobby needs more performance for less cost, and Burson is helping to deliver.
 

- Chris Groppi -

Associated Equipment:

Source Components:
Oppo Digital DV-981HD Universal disc player
Bel Canto DAC-1.1 Digital to Analog Converter
Linn LP-12 Valhalla, Ittok LV-II, Grado Reference Platinum

Amplification:
Acurus 3x100 3-channel power amplifier (center, rears)
Anthony Gallo Acoustics Reference SA subwoofer amplifier

Video Components:
Rotel RTC-965 Surround Sound Processor
Directv HR-20 HD-DVR
Westinghouse LVM-37W1 1080p LCD panel

Loudspeakers:
Anthony Gallo Acoustics Reference 3.1 (left, right)
Anthony Gallo Acoustics Reference AV center (center)
Anthony Gallo Acoustics A’Diva (rear)

Power Conditioning:
OneAC 1920VA Isolation transformer

Cables:
Nordost Red Dawn speaker cables
Nordost Flatline Gold MK-II speaker cables (2nd voice coil for Reference 3.1s)
Audioquest 4+ speaker cable (center channel)
Audioquest F-16 speaker cable (rear channels)
Nordost Blue Heaven & Kimber PBJ interconnect
Best Deal Cables DVI & HDMI cables

© Copyright 2007 Secrets of Home Theater & High Fidelity

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