Legacy Audio Powerbloc2 Power Amplifier (Amplifier review)

Manufacturer: Legacy Audio, Springfield, IL USA  (800) 283-4644
www.legacyaudio.com

By Karl W. Nehring

Legacy PB2, front

Before commenting on the specifications and performance of the Powerbloc2 power amplifier from Legacy Audio, let me first establish some historical perspective. Back in the late 1970s when I was a graduate student with a growing family, a passion for audio, and a limited budget, Sony released a revolutionary pulse width modulation (“Class D)” power amplifier, the TA-N88B, which was the first such amp to be commercially available. Through a simple twist of fate, I happened to run across a brand-new TA-N88B that an audio store in the area was selling for somewhere around half the standard retail price of $1,200 (which would be more than $4,000 in 2020 dollars). Although at the time I did not have an extra $600 lying around, I just had to have that amp, so I wracked my little brain to come up with a way to get it. (A legal way, that is – breaking into the store in the wee hours of the morning was not a viable option.)

The legally valid plan that I came up with led me to the office of our local bank, where I talked to the manager and explained to him that I had found an incredible deal on this piece of audio equipment. If he would lend me the cash to purchase it, I would be able to pay him back in installments, or else I could sell the thing for more than the purchase price, pay him back with a bit of interest, and we would all be happy. Believe it or not, he bought my story and made out the loan. Small-town (actually, not even a small town – a rural village), old-school (four decades ago, recall) friendliness at its finest. Alas, our local branch shut down long ago, the local bank got swallowed up by a larger one, and I am certain it would be not nearly as easy nor informal today. (Of course, in today’s world, when we want something we can’t afford, we just whip out the old credit card, right?!)

Why was I so desperate to buy this amplifier, besides the fact that it was for sale at such a low price? It might be hard to imagine nowadays, when Class D power amplifiers (and power amp stages in receivers, integrated amps, and powered speakers/subwoofers) are quite common, just how radical the idea seemed when the Sony was introduced. Here was an amp the used then-new V-FET transistors (a term that subsequently disappeared) as switches – the job that transistors are actually best at – amplifying the audio signal. Crossover distortion was no longer a factor, it put out 160 watts per channel, ran cool both at idle and when driven hard, and came in a sleek physical package about the size of a preamplifier. The “B” in the nomenclature indicated a unit with a what Sony called a bronze finish, a kind of light gold or champagne color that was simply gorgeous. Later, most of the units imported to the U.S. were the TA-N88, which featured a more mundane silver color scheme. At about 25 lbs., it was not heavy for a power amp of its output capability, and there were no sharp heat sinks to cut your fingers.

Legacy PB2, rear

The specifications for the Sony amp do not seem very good by today’s standards, but in the late 70s/early 80s, they were nothing to be ashamed of. The amp put out 160 watts per channel into 8 from 5 Hz to 40 kHz with no more than 0.5% THD, damping factor was 20, S/N ratio was 110 dB. Yes, the damping factor was pretty low, and the THD a bit high, but those specs compared well to tubed power amps of the day, and these were the days when tubed power amps were considered the hot setup. But the Sony put out more power, ran much cooler, and weighed much less than any decent tubed power amp. It would fit in your room and not heat it up.

Well, it sounded pretty good in my system back then, driving KEF 105s in the same listening room that I use today, but I did not keep it for long. I soon sold it for $800 or so, paid off my loan, and put some money in my pocket. Why did I keep it for so short a time? Two reasons, really. First, I did not really trust the technology. I always had the sense that the thing was running at the ragged edge of reliability. Second, it was rated for a minimum speaker impedance of 8. At lower impedances, that already narrow treble bandwidth would droop even more as a consequence of the passive output filtering Sony used to keep the high-frequency energy produced by the switching frequency of the amp out of the speakers.

The Sony was on the market for a few years and then disappeared. The failure rate was high and replacement parts became hard to find. But four decades later, there have been significant advances in technology, and the Legacy Audio Powerbloc2  is rated at 325 watts per channel into 8 ohms and 650 into 4, 1.5 Hz to 70 kHz, damping factor of 1,000, S/N of 117 dB, and weight 13 lbs. Compared to the Sony, then, the Legacy amp has twice the power, two orders of magnitude less distortion, nearly twice the bandwidth, a 50X better damping factor, and the ability to drive low-impedance speakers. The amp is a dual mono design, each channel with its own 30-amp power supply. Moreover, the Powerbloc2  at $1,800 costs less than half what the Sony would cost in today’s dollars.

So, after all that, how does the amp perform? Very well indeed. Over the years I have owned and auditioned many power amplifiers by virtue of my decades as a reviewer and editor of an audio magazine. Most of these I have auditioned in my own listening room, but I have also auditioned my amps in the systems of friends and audio dealers (remember those?). At the time I obtained the Powerbloc2 for audition, my reference amplifier was the Audio by Van Alstine (AVA) FET Valve 550HC, a 275 wpc Class A/B design with a hybrid tube/FET input stage driving a MOSFET output stage. Of all the amps I had ever employed in my system, it offered the best sonic performance.

When I compared the AVA with the Legacy, I preferred the sound of the latter, which just seemed to be slightly cleaner in the trebles and slightly tighter in the bass without giving up any of the glorious midrange provided by the AVA  What the Powerbloc2 did for beautiful choral recordings such as The Suspended Harp of Babel by Cyrillus Kreek or Translations by Eriks Esenvalds was simply breathtaking, revealing the nuances of voices in space better than I had ever heard. No, I am not talking about “night and day” differences, I am talking about subtle shadings of difference. I am not one to claim that all amplifiers sound the same; however, I do believe, a belief bolstered by many years of direct experience, that the differences between competently designed amplifiers of similar power ratings are largely indiscernible and subtle at best. If you hear a big difference between two such amplifiers, chances are you are in fact hearing differences in volume level between the two amplifiers, an amplifier with some sort of problem, or your own prejudices or imaginings.

Still, listening to the Powerbloc2 driving my Focus SEs has been a truly rewarding experience, especially on the large orchestral music that I love by composers such as Mahler, Bruckner, Shostakovich, Vaughan Williams, Sibelius, Elgar, Arnold, Ravel, etc. An especially revealing and rewarding musical experience for me recently was listening to the SACD version of the Mahler Symphony No. 2 (“Resurrection”) with the St. Louis Symphony Orchestra on Telarc. Not only were the big sounds rendered cleanly and powerfully, but the near-silent moments such as when vocalists and/or chorus would enter after a pause were simply sublime. The Powerbloc2 excelled at both ends of the volume scale of this excellent recording. On completely different sorts of music, such as the acoustic guitar shadings of Ralph Towner, the modal jazz on Miles’s Kind of Blue, and Vikingur Olafsson’s expressive piano stylings on Debussy-Rameau, the Poswerbloc2 made the music come alive without fail.

Incidentally, after spending a good amount of time enjoying music with the Powerbloc2 in my system, I decided I would like to try the Goldpoint SA-4 “passive preamp,” which has been recommended in Classical Candor by both John Puccio and Bryan Geyer. Having been perfectly satisfied with my Legacy Audio StreamLine preamp (no longer available) for quite some time (again based upon auditioning many units over the years, including solid-state, tube, and hybrid units of great repute), I was not expecting any sort of noticeable – much less “revelatory” – sonic improvement. To be honest, I was motivated primarily by the idea that a passive unit would never present any problems caused by capacitors or other parts in an active unit eventually falling off in performance or, worse yet, failing, and secondarily by my knowing a music lover/audiophile friend who had expressed an interest in acquiring my preamp should I ever be inclined to part with it. With these factors in mind, I auditioned the Goldpoint, found that it performed just fine in my system, possibly even offering a slight bit more transparency and clarity overall.  Once convinced of the impeccable performance of the Goldpoint, I sold the StreamLine and am perfectly content with the way my system sounds. For those with turntables, of course, the passive controller route is not a viable option, but for those whose source material is exclusively digital, the Goldpoint is certainly an attractive alternative to a high-quality, big-buck preamplifier.

Back to the Powerbloc2. What a wonderful amplifier and what a solid value! No, $1,800 is not inexpensive, but if you are a classical music lover (especially of large-scale orchestral works, opera, or organ music) with audiophile leanings who is looking for a terrific sounding amplifier with this kind of power and an  ability to drive difficult speaker loads, the choices available to you are not many, and if you want an amp that can do so while running relatively cool, taking up little space, and weighing so little while still being solidly built (e.g., premium input and output connectors, a rugged metal case, and a confidence-inspiring on/off switch), I know of no real competition for this amplifier at anywhere near this price.

KWN