September 2019

Legacy Audio Powerbloc2 Stereo Power Amplifier
A great value Class D stereo amplifier!
Review By Rick Becker

  When I first discovered high end audio nearly 30 years ago, my economic circumstances and skepticism of the value of products kept me in tortoise mode. The real value of tortoise mode early on was to allow me time to learn how to listen and time to experience of a lot of gear at audio shows to learn what my personal acoustic and aesthetic values were. As the decades have rolled on, my ability to spend larger sums of money has increased but the pace has remained in the tortoise league. Yet, I suspect I may have passed a lot of burned out hares along the way.

As a person whose house is also his home, my dedicated listening room has remained constant for eighteen years, allowing me to refine the system toward my goal, which itself has evolved only slowly. Basically, I'm a tube guy who loves the transparency, tonal color, inner detail and dimensional presentation afforded by relatively low powered single ended triode (SET) tube gear. Along the way, the music has only gotten better.

As a photo journalist covering audio shows, I get to see and hear a lot of gear. My longevity in this field has given me some perspective on technological evolution, dubious fads and trends that offer genuine value. I try to never lose sight of how financially frightening the High-End can be to younger people whose lives are tethered to young families, future obligations to elderly parents, and nowadays, the financial burden of college loans. Even middle age people with solid careers question the value and necessity of our hobby. Still, I come away from shows always dreaming of a handful of products that captured my imagination for one or several reasons, be they logical, emotional, economic or somehow simply intuitive. Legacy's new Powerbloc2 stereo amplifier was one of those products from the recent AXPONA 2019 show.

Class D Amplification?
Didn't I just say I was a low-powered SET tube guy? The Powerbloc2 puts out 325 Watts per channel into 8 Ohms, 650 Wpc into 4 Ohms and is stable into 2 Ohms. What are you thinking, Rick? Well, consider that the invention of the CD was just the kick in the pants that LP playback needed to advance to the pinnacle of performance that is available today. And consider the evolution of CD playback that has occurred since the early 1990's when separate DACs became the hot item. Sometimes technologies take time to develop and Class D is no exception. Bill Dudleston, owner and chief designer at Legacy, tells me it began back in 1955 with a guy name Reed but it didn't really become practical until the mid-1980s. Integrated circuitry for Class D came along in the 1990's with Tripath amps. Semiconductors have led the way to taming the shortcomings of the design and by 2012 Bill says Class D had matched Class AB.

Legacy Audio began as a manufacturer of loudspeakers and is probably best known in audio circles for their speakers. But something happened along the way. In the mid-1990s home theater became a hot category. Back around 1997 they developed their first powered subwoofer with a pair of Texas Instruments' 150 Wpc IC amps giving them 300 Wpc. In 1999 Bill partnered with the Allen Organ Company to gain access to their digital knowledge used to perfect tonal artistry in building electronic organs. This soon translated into the production of Legacy's first active loudspeaker, the Helix, which utilized eight channels of digital processing.

So Legacy is not really a newcomer to the development of electronics. They now offer not only active speakers and the multi-channel amps, but also their Wavelet DAC / Preamp / Crossover and Wavelaunch Processor that perform amazing digital wizardry for their higher end speakers, home theater applications and in the Pro Audio world. The development of a stereo amp seems like it would be comparatively easy, largely limited by the development of Class D modules by outside suppliers, ICE in this instance. My, how time flies.

Today, Class D is making sense as a cool-running, high(er) efficiency amplification technology in an era of rapid climate change, in spite of the massive amounts of CO2 spewed out by the occasional volcano. It has evolved considerably to the point where I'm surprised to learn it is driving numerous very fine sounding speakers at shows. That was the case in the Legacy Audio room at AXPONA this year. What I heard in their room at Axpona, along with the reasonable price, plus the curiosity of what my rig might sound like with a high-powered amp, led me to this review.

Papa's Got A Brand New Bag
The amp arrived promptly as it was light enough to be shipped by UPS at 17 pounds for the boxed unit, and 13 pounds for stereo amplifier inside. What impressed me was the use of what I call "cardboard angle iron" on the four long outer edges of the box. This packaging material is widely used in the furniture industry where imported products have to survive oceanic container transporting. It is really strong and Legacy's use of the material on the four long edges of the outside of the cardboard box was not only novel, but extremely successful in maintaining the configuration of the box and protecting the sides from being scraped up. No doubt that the amp could be shipped to many new owners over the coming decades in perfect condition if the packing material is retained. Other manufacturers should take note. Nobody likes to receive a damaged product.

The Powerbloc2 is easy to set up. The only trick is to activate both power switches. The master switch is on the back near the IEC connection. The rocker switch on the faceplate beneath the plastic oval with "Power BLOC2" illuminates in a medium/dark blue to indicate the amp is active. The color is unobtrusive, the function is useful and the presentation between the routed "\ /" channels on the 3/8" thick faceplate is very tasteful. A second oval with a brass tint and the Legacy name is elegant, but seems a bit superfluous and visually competes with backlighted blue oval. The blue oval reads well when the unit is powered up and the brass oval reads well in a lit room. It's one of those tough branding decisions but I wish the two could be combined on the blue oval, particularly since I chose to leave the amp powered up continuously. (I'll come back to this last point later.)

With the amp up and running I took an initial listen just to make sure everything was connected properly and running smoothly. It was a huge disappointment; I really wanted this to be a very positive review. But I've been around long enough to know that most equipment needs to be burned in so I didn't give up hope. This amp, especially. I let it run 24/7 for a week with a variety of CDs thanks to the "repeat" function of the Sony ES player I use as a transport. At one week out, the music was listenable, but not great. Two weeks out, say a couple of hundred hours, plus, it was ready for some critical listening.

The Listening: Bass
It is not unusual to have expectations for what a new component might contribute to a system. But it is important to be cognizant of those expectations to be sure of what I'm actually hearing (versus what I might want to hear.) This was especially true in the bass region in my case. I normally drive my Kharma speakers with 18 Wpc SET amps that employ seven transformers and utilize parallel 300B tubes for power. The speakers are rated down to about 33Hz and with my Eddie Wong monoblocks, they get soft and a little plump in the lower bass. They also lack the tight leading edge and physical impact I hear with solid state amps at shows. Tube amps typically have a low damping factor that mitigates against controlling large drivers.

This is a trade-off that I've chosen in favor of the glorious midrange for which 300B tubes are known. With a damping factor of 1000< 1kHz and more than 500 below 1kHz on the Powerbloc2, I was interested in what I might be missing. The amp also puts out peak current of 30 amps, which is the amount of current my JPS Labs dedicated line delivers, so the amp was never likely starved for current.

With the Powerbloc2 the base did become more controlled (better focus) as expected, but it also didn't seem to go as deep. The depth I was hearing with my monoblocks seemed to be more harmonic distortion that made the bass seem deeper as well as louder than what I heard with the Powerbloc2. This was a mixed blessing at first, as I was hoping for a stronger (louder) bass presentation, especially given the enormous power of the Legacy amp. Instead of louder, I got more accurate bass with a sharper attack and a quicker decay. Missing was the thumping in the chest that audiophiles sometimes dream of.

But I'm not a head banger; typically I play music with peaks in the 88 to 92 dB range. This allows for long term listening pleasure, but doesn't supply the chest-pounding experience you get from attending live concerts — rock or classical. It is also true that different recordings (of different kinds of music) have different optimal playback levels to achieve the most rewarding listening experience. With that in mind, I increased the volume on numerous tracks of my compilation test CD and behold — I could feel the drums in my chest! (e.g. Diamonds On The Souls Of Her Shoes by Paul Simon.) I'm not talking 100dB at the listening position, but maybe 3dB louder than I normally listen. I did dabble with 100dB momentarily and the Powerbloc2 maintained its control and poise, but I don't get pleasure at that consistent volume.

The Listening: Treble
I wasn't expecting a more extended treble, given that the 300B tubes of my reference amp roll off a bit on top and my ancient ear/brain mechanism is not what it used to be. (Unfortunately, acquired wisdom in the brain doesn't compensate for abuse of the ears.) So I was quite surprised to experience the more extended treble. Extending the bandwidth of the Class D modules has been one of the developmental challenges of this technology. The Powerbloc2 is said to have an ultra-wide 1.5 Hz to 70 kHz bandwidth so apparently great progress has been made. At first it seemed like the frequency response had an upward tilting tonal balance, but after a while I recognized that not only was it simply an extended frequency response, but it was also very well focused. Cymbals were more resolved, revealing a shimmering sheen when well recorded. Violins could be sweet or raw, depending on how they were played. In the early stages, the resolution and extension of the treble was more mesmerizing than the tightening of the bass. But as familiarity with the amp grew, tonal balance seemed perfectly flat and there was continuity of focus from top to bottom.

The Listening: Midrange
With my reference loom (sourced from a variety of cable manufacturers) the midrange, early on, provided superior cognitive recognition of obscure or difficult lyrics, yet there was an edginess to the words that provided a "cognitive grip" with which the brain could sort out the words. I was understanding more words and hearing more distinct musical notes, but a certain analog smoothness was missing from both the words and the music. Pace, rhythm and timing were more clearly documented with the Powerbloc2. The performers were clearly anchored in space, but the depth of the soundscape was not as great as with the SET amps. The front of the stage was about the same slight distance behind the plane of the speakers and the width and height of the stage was as great as with the SET amps.

This surprised me in that I usually expect monoblocks to have greater stage width and more pinpoint imaging than stereo amps. The Powerbloc2 was not as pinpoint with imaging as some of the "best" amps I've heard, but it was certainly the equal of my monoblocks, which is to say pretty damn good. To clarify, the singers and musicians occupied space on the soundstage giving them physical size and presence, like you would expect. They were not thin like Giacometti's sculptured people and the music emanated from full-size instruments, not something as thin as a ribbon tweeter.

Pinpoint imaging is not a high priority for me. Live music, be it in concert or at the local bar, does not have pinpoint imaging. It is merely a construct of the two-speaker stereo paradigm that adds interest in the music for many folks and I can certainly respect that preference. Yet even with the pinpoint imaging dialed back a bit in the Powerbloc2 I was easily able to follow the dance of the music as the musicians interacted with one another. Credit here goes to excellent dual mono circuitry. I never once felt the need for a monoblock version of this amp. On the other hand, this can easily be accomplished along with bi-amp'ing your speakers by adding a second Powerbloc2. (My speakers do not permit this opportunity.)

Where the Powerbloc2 fell short for me (with my reference cables) was in the presentation of tonal color — an area in which tube amps (and SET amps, in particular) excel. This was to be expected, but it is not as bad as it might sound. If all you had ever listened to was solid state amps, the Powerbloc2 would likely sound pretty good to you, even with regard to tonal color. Adjusting the playback volume to the sweet spot of each recording certainly helps optimize the presentation of tonal color, but when the volume is too low the tonal color and micro-dynamics of the music do not come through as well. The same can be said for tube gear, but in my experience, it is less affected by volume. And maybe this is more a factor of the ear/brain connection than the amp/speaker connection — which brings me around to Game 2.

Game 2
You weren't expecting a double header, were you?

A complete loom of Synergistic Research's new Foundation cables (one series above their entry level Core UEF series) finally arrived and I burned them in, giving the Powerbloc2 another two weeks of exercise. This was something of a game-changer for the rig and the amplifier in particular. Of course, everything matters in music reproduction, but the amp/speaker connection is very important in the way the amp and speaker see each other, electronically. This is a critical junction where the electrical signal is converted to physical motion. At $649 for an 8' pair of speaker cables, the Foundation cables are still in the ball park for an amp in the $2000 range, or thereabouts. And they are far less expensive than the vintage cables I have been using for the past decade and a half. Times have changed in the cable industry, too.

With the new Foundation cables in the rig, all of the good things I've said about the Powerbloc2 either remained or improved. Most noticeable was the cognitive recognition of lyrics. Whereas earlier I said "there was an edginess to the words that provided a 'cognitive grip' with which the brain could sort out the words", now there was a more analog-like smoothness. The degree of cognition was about the same, but the texture of the music was smoother. Imagine a motorcycle hand grip with a knurled metal surface and another version with a smooth but grippy synthetic material. Both allow a firm grip that facilitates twisting the throttle, but they feel quite different from one another. I suspect most people would choose the Foundation cable over my vintage one.

Micro-dynamics and tonal color also improved a bit, too. Overall, the music was easier to listen to — the brain seemed to have less work to do. While this was particularly true at reasonable volumes, the benefit carried upward to the 100 to 105dB range (measured at the listening chair, about 9' from each speaker.) The Powerboc2 never whimped out on me, even at volumes that crossed the threshold of pain. This, of course, is great news for head-bangers and home theater enthusiasts, alike. While I choose not to test this, I expect with 650 wpc into 4 Ohms, no explosion will sound too small.

With the very positive experience with the new Synergistic Research cable, it occurred to me to pull out a more affordable speaker cable featured in my 2014 Entry Level Project where I put together a very fine sounding system for $5000. The Audio Sensibility Testament speaker cable (~$339 for two meter length) is a cryo'd cable with PCOCC copper. This cable, too, performed very well with the Powerbloc2 — maybe not quite as good focus as the Foundation, but a little brighter in the presence region (something that worked especially well with tube amps.) Nonetheless, it is an easy recommendation with this amp if your budget is tight. The take away here is the Powerbloc2 is revealing of the equipment and cables both before and after it in the reproduction chain.

I should also point out that it has been fed some very fine power coming from my breaker box along a JPS Labs 30 Ampere In-Wall dedicated line shared with the entire system. Power conditioning was with a Synergistic Research PowerCell 8 UEF SE and I used a Synergistic Research UEF Level 2 power cord. Admittedly, using a $2000 power cord on an $1800 amp may not be likely to happen in the real world. But the question is not "Why do I need to spend so much on a power cord?", rather, "Why do I need to spend any more on an amplifier?"

Game 3
It's a home stand? Let's make it a home theater stand... sort of.

I'm not into home theater, but I normally run the headphone output of my Sony TV into a Coincident Dynamo 34SE MK II amplifier ($1499) driving a pair of vintage Coincident Partial Eclipse Mk. II floorstanding speakers ($3299, back in the day.) The interconnect between the TV and the amp is an Audio Sensibility Impact SE with stereo 3.5mm mini plug to RCA connectors. This is their entry level cable and it cost about $129 Canadian. The speaker cables are Mil-Spec silver plated copper 12 awg twisted pairs with bare ends. Cost? Maybe $15, and that's a guess — it was bought so long ago. The power cord for the amp is also from Coincident and cost about $600 at the time. So the rig is a cobbled together mixture of some respectable products along with some entry level and home-brew cables. And here again, we don't listen at World War volumes.

I swapped out the Coincident amp for the Powerbloc2, a procedure that took only a few minutes — not enough time to let it cool down. Linda set the volume at only 27 (of 100) using the variable output of the TV. After a few minutes of straining to comprehend the heavily affected lyrics that struggled to come out of the mouth of a female singer on SNL (You know the type.) I cranked it up to about 40. With the 92dB/W/m sensitivity of the Coincident speakers, it was clear the headphone output of the Sony TV was insufficient to drive the Powerbloc2 to full output power. At maximum output the show was loud with peaks at 98dB, but not painfully so, nor would it cause the neighbors to visit with a complaint. That was a bit disappointing in that once in a while we enjoy a good explosion on TV.

A proper pre/processor in a home theater setup would not have this problem. The good news, however, was that the sound was really clean and the focus was excellent — in spite of the entry level and home-brew cables. Here, as well as in my audio rig, I appreciated the tight focus from top to bottom and the extended frequency response in the treble. With the speakers not very far out from the wall and not much further apart than the 55" screen I wasn't expecting great sound staging (and I didn't get it.) Nonetheless, I was very impressed with what I heard coming through the TV audio pathway.

Another observation in this video application was that the amp performed as well as it did without being on any sort of footer or vibration absorbing shelf. It was simply on a short riser made from a pressboard end table top. In my audio rig I had been using a Svelte Shelf from Symposium Acoustics in order to stack the Legacy amp on top of my monoblocks to facilitate the swapping of cables. As I wrote these words, the light bulb came on in my head and I flashed back to my earlier conversation with Bill Dudleston. I realized I might be short-changing both him and the readers.

Game 4
Unlike some people in the industry, I'm a big fan of tweaks. Some people have the means to throw around cash in large sums in pursuit of perfection that never comes in a lasting way. That's not me. I've found that the cumulative small improvements of tweaks can be more cost effective and allow more flexibility in dialing in a preferred sound than throwing major money at core components. (Just today I received another press release for an over $200k loudspeaker premiering at RMAF — and it will not likely be the only one.)

One of the important bits of data typically left off the spec sheet is the type and value of the fuse used to protect the component. In this age of designer fuses that information becomes important. Even Bill Dudleston expressed his amazement about the seemingly insignificant importance of the fuse as a gateway to all the expensive parts and intricate engineering within components. (In the new multi-channel amp they are introducing at CEDIA in September there will be a circuit breaker rather than a fuse.) Bill told me they supply the Powerbloc2 with a small size slow-blow 6A @ 250V generic fuse, but advise people who have trouble with them that it is OK to use an 8A fuse.

In most of my components that use fuses I've preferred the Synergistic Research Blue fuse and as luck would have it, I had an 8A Blue in my monoblocks. But before swapping that in, I tried the Powerbloc2 with a set of Synergistic Research MiG small dome footers, first with two facing up and one down which produced a very pleasing, more diffuse sound, and then with two facing down and one up for a more focused sound — just as advertised. I can imagine some people preferring one orientation while others prefer the opposite. Both orientations also provided a small increase in the sense of space of the recorded venue.

Then I added the Blue fuse and the music got really good with increased holographic soundscape, greater focus and more tonal color. Sustained notes became smoother, the sheen of cymbals more shimmery, and the decay of notes seemed longer. The music became more involving. It was very good before adding the fuse and the footers and it was a lot better afterward. So good, in fact, that I slipped into head-banger territory for a couple of minutes with the needle bouncing up to 104dB with regularity. The music was clean and listenable with no apparent pain, but nonetheless, I knew damage was being done.

Class D Efficiency
Two of the things frequently heard about Class D is their cool running and high power efficiency. The graphic here comes from the Legacy website and raises some questions. I found the Powerbloc2 runs warm to the touch, but I can easily keep my hand on it. It seems like it would be an inviting place for your cat to nap in the winter. Since I found it takes about a half hour to warm up from room temperature before sounding its best, I left it powered up all the time. If you wish to keep it off when not listening, the protocol becomes a lot like tube gear — it has to warm up before sounding its best. For TV watching this didn't matter much, but critical listening was a different story.

The other factor concerns the efficiency. In the graph above, if you run a vertical line just to the right of the vertical axis, you can estimate that the power consumption at an output of a watt or two is really 20 Watts for a Class AB amp vs. 8 or 9 Watts for the Powerbloc. While this is a savings of more than 50%, it is a lot less than the savings at 50 to 100 Watts suggested by the graphic... or the 86.5% stated on the back of the amp. Since most of my listening requires just a few watts with speakers having 89dB/W/m efficiency, the savings are not that great. In fact, they are wiped out if you choose to leave the amp fired up all the time, as I did. Power draw at idle is 13 Watts.

This brings me back to the two power switches. The one of the back of the unit is the Master power switch. The rocker switch on the front panel turns the amp "on" when pushed to the right, and when pushed to the left, turns the amp "off" and leaves it controlled by the 12V DC input when tethered to another component such as your preamp or processor (providing it has that capability.) The fuse holder is in the IEC input/Master power switch module on the back of the amp, making it relatively easy to pop in the aftermarket high end fuse of your choosing.

Design Considerations
I've always commented on the visual design of components and I found the Powerbloc2 to be an attractive design in the traditional sense of what I expect a power amp to look like. The build quality looks superb and it feels extremely well built when held in the hands, in spite of its relatively light weight. The disconnect for me comes when I factor in the excellent audio output. The Powerbloc2 sounds and feels like it should cost a lot more, yet its appearance is relatively basic and straight forward. With Legacy's expertise in woodworking, a couple of side panels to match their speakers would raise the beauty of this amp to the point where audiophiles (perhaps more than home theater buffs) would be proud to display it on an amp stand between their loudspeakers. A small upcharge could very well result in a lot more sales, even if were just an option. With my life-long roots in the furniture business, Legacy's expertise in woodworking is easy to acknowledge and this would be an easy upgrade.

That said I popped the top off the amp to examine the layout and mentally blurted out that iconic advertising line, "Where's the beef?"

A large slab of anodized aluminum hides almost everything but the wires inside. Bill told me Class D modules come with a heat sink, but in order to provide even more cooling to provide stability and improve longevity, they have added the thick plate. This plate also serves to keep dust and cat hair from dropping onto the circuit boards. I don't have a cat — but trust me. I know. It is also obvious there is a lot of free space in this chassis. The four-channel Powerbloc4 uses the same chassis, so that space is filled with two additional channels.

While I never felt the need for monoblocks while listening, it is obvious from looking inside that small monoblocks could easily be designed that would sit on the floor behind or beside floorstanding speakers. This would allow for speaker cables of only a foot or two, which would be beneficial from both a cost and engineering standpoint. Long interconnects and short speaker cables are generally preferable to the opposite when the source/preamp is located far from the loudspeakers.

While I think of it, the input impedance is 40kOhm on both of these amps and they have high sensitivity making them an easy load for a tube amp such as the Coincident Statement Line Stage in my rig.

After testing the amp with the MiG footers and Blue fuse, I restored my monoblocks and had another spin through my compilation CD. As good as the Powerbloc2 is, I fell back in love with the superior tonal color, larger holographic spatial presentation and inner detail presented by my much more expensive 300B amps. I know their limitations and shortcomings well and I can live with them. An apt comparison might be to say my tube amps are to the Powerbloc2 like Kodachome is to Ektachrome film. They were both excellent films, but with different strengths. If you're old enough to know these films, you know what I mean. If you don't... well, have a listen to Paul Simon's Kodachome.

Summary
Inviting the Legacy Powerbloc2 into my home was an educational and rewarding experience for this lover of tube gear. It is light weight, solid, well-built and very powerful. Frequency response is flat and tight across the entire audible spectrum. It is also very revealing of interconnects and power cords coming into it as well as speaker cables going out. It responded favorably to aftermarket footers and fuses. Its reasonable price will attract many who are looking for something above entry level to the high end and it will grow with you as you invest in better cables and a few tweaks.

It is a worthy teammate to very fine sources, preamps and speakers, not to overlook obvious applications in home theater where its relative cool running and high power are prime attributes. The Powerbloc2 is an amp you can put into your system and enjoy as you upgrade everything upstream and down. That's a great value added proposition to an amp that's a great value right out of the box. Strongly recommended!

Specifications
Type: Class D solid-state stereo amplifier
Power Output: 325 Watts per channel @ 8 Ohms (650 Watts @ @ 4 Ohms)
Inputs: Two balanced XLR and two unbalanced RCA
Outputs: Two pairs of gold plated safety approved five-way binding posts
Damping Factor: 1,000< 1kHz
Voltage Gain: 27.4 dB
Dynamic Range: 117 dB
Peak Current: 30 Amps per channel
THD: 0.005% at rated output
TIM: 0.0045% at rated output
Input Sensitivity: 2.1 Volts to rated power
Dimensions: 3" x 17" x 14" (HxWxD)
Unit Weight: 13 lbs.
Price: $1800

Company Information
Legacy Audio
3023 E Sangamon Ave.
Springfield, IL 62702

Voice: (217) 544-3178
E-mail: info@legacyaudio.com 
Website: www.LegacyAudio.com