Power Amplifiers

Jones Audio PA-M300 Series 2 Monoblock Power Amplifier

ARTICLE INDEX

Introduction

Imagine my surprise when Secrets' Editor-in-Chief, John Johnson, asked me if I would review a pair of Jones Audio's 300W solid-state monoblock power amplifiers. "Now that would be quite a switch," was the first thought that popped into my head.

My last three amplifiers – the Bruce Moore 100W Dual Mono power amp, Jadis 100W DA-7 Luxe amplifier, and VTL 450W monoblock Signature 2 prototypes – have all been tube-based. In fact, the only solid-state amplifier I've spent much time with at home in many years was a Class D baby that was not to my liking. The last thing I expected was to be asked to review powerful solid-state monoblocks.

All of which made me relish the prospect of reviewing these babies even more. Given that so many music lovers whose taste I value prefer solid-state to tubes, I was eager to discover how the Jones Audio monoblocks would sound. And with 300 watts, I expected dynamic swings, especially on high-resolution computer files, that would sound great in my large space.

I had actually taken a brief listen to these amps once before, at one of the shows I was blogging for Stereophile. On that occasion, they were displayed in a molto sub-optimal hotel room. Here was an opportunity to revisit them in my own home, in a room whose sound I understand quite well.

Another thing that excited me was the potential of the PA-M300 Series 2 monoblocks to control the woofers on what were then my reference loudspeakers, the Talon Khorus X Mk. 2.5. (I'm not sure there was a 2.5, but there were so many upgrades to the speakers, performed over some many years, that it's impossible to state with certainty where my four times upgraded pair stood in the grand scheme of things.) All Khorus models have two 8" woofers, one hidden within the cabinet, arrayed back-to-back in isobaric configuration. They demand a lot of power, and are a bitch for a tube amp to drive. So when John asked, I paused but 30 seconds before I replied with an enthusiastic yes.

Jason Jones, son of co-amplifier designer and company Sam Jones, was able to deliver the amps personally to Casa Bellecci-Serinus. As fate would have it, by that time, the Talons had been moved to the side, and replaced by Eficion F300 loudspeakers. Jason came over just when Nordost Odin jumpers arrived to connect their upper and lower modules. Together we set them back up on Stillpoints, and inserted the jumpers. We also placed the amps on Stillpoints amp stands, and made sure everything was running smoothly.

A month later, Jason returned for an amp demo that I staged for the Bay Area Audiophile Society that also included a preview of the Auraliti L-1000 music server. At the close of the demo, the amps were packed up and carted back to Jones Audio's home in Black Diamond, WA. I hated to see them go.

Specifications

  • Design: Solid State Monoblock Power Amplifier
  • Power Output: 300 Watts RMS into 8 Ohms, 560 Watts RMS into 4 Ohms, Class A/AB
  • MFR: 10 Hz - 200 kHz, - 1 dB
  • THD+N: <0.003%
  • SNR: -119 dB (A-Weighted)
  • Transformer: Toroidal 1,000 VA
  • Power Consumption: 775 watts
  • Dimensions: 8.2" H x 16.2" W x 16.3" D
  • Weight: 80 Pounds/each
  • Price: $24,000/pair
  • Jones Audio

PA-M300 REVIEW
NEXT SECTION: DESIGN


Design

In a recent phone interview with Jason Jones, I learned that his father Sam, who considers himself a lifelong audiophile, was building Heathkit amplifiers at a young age. An autodidact who started a computer software company 28 years ago, he shifted to part-time consulting seven years ago, and let others in the family run the computer business. This liberated Sam to befin working full-time on developing the amplifiers of his dreams.

Jones Audio began showing their Series 1 amps at audio shows as early as 2008. At that point, they were more interested in receiving feedback, doing much more listening, and perfecting the design. The company began to promote the amps seriously at CES 2011. A fledgling distribution network now exists in Canada, Hong Kong, and the Northeast.

One distinctive feature of the PA-M300 Series 2 monoblock is that it uses lateral MOFSET output devices. "What's great about these is that they're much faster than the bi-polar transistors you usually find," Jones explained. "That creates a much cleaner and more natural sounding high end. We encountered tube lovers at the Rocky Mountain Audio Fest who expected to hate the sound of solid-state, and couldn't believe that they liked it. This is because of these output devices.

"The MOFSETs can also take a higher range of bias and a higher total amount of bias. This helps get rid of crossover distortion, which looks like a notch in the waveform. If you increase the bias using bipolar transistors, you can create a notch in the other direction. The MOSFETS, on the other hand, can create much more bias without creating artifacts. This allows us to have a high bias amplifier that runs Class A up to 38 watts, then switches to A/B. With most music except the peak transients, the amp plays in Class A."

The Jones Audio monoblock also features a fully complementary input and voltage stage. The company claims this dual-differential design helps to cancel out some noise from the power supply, and some artifacts from differences in part tolerances. It also produces symmetrical clipping, which makes the amp operate and sound more like a tube amplifier because the positive and negative clipped waveforms look the same.

Jason stresses that the company pays particular attention to detail. (What company is going to tell you that they don't?) I wasn't sent a picture of the amp's inside, but it contains a 38 lb., ultra low-noise torroidal transformer as well as extensive heat-sinking. That's one pound for each watt of pure Class A sound. The amp's resistors, capacitors, and other parts are chosen, not according to price, but rather because they work together synergistically and sound the best (at least to the company's ears).

PA-M300 REVIEW
NEXT SECTION: SETUP


Setup

As you will see from the equipment list posted at the end of this review, my system now uses Stillpoints amplifier stands. The difference in sonic control between these stands and what I was using previously is immense. Placed on the stands, the amps received maximum isolation from external vibrations.

Given that Jones Audio monoblocks sport 20-amp power receptacles, I counted myself extremely fortunate to have on hand 20-amp Nordost Odin power cables. I've tried using adapters to convert 15-amp cords to 20 and vice versa, and I'm convinced that they compromise bass extension, slam, and midrange fullness. Interconnects between my Theta Gen. VIII Series 3 DAC/preamp and the monoblocks were a 1.5meter pair of balanced Nordost Odin. Though I do use audiophile grade fuses in my own equipment, I did not upgrade fuses in the amps.

The amps accept both single-ended and balanced interconnects, and spade as well as banana-terminated speaker cables. Perfect.

The amps had already been broken in prior to arrival. With the rear toggle switch set in "balanced" interconnect position, I first turned on the main power switch on the back of the amps to put them in standby mode. To prevent any possibility of turn-on transients blowing out my loudspeakers, I paused to turn on all my other components (which were already in standby mode). Finally, I turned on the amp's front power switch, located beneath the front of the unit.

Although the amps were capable of playing music immediately, I let them warm up an hour so they would produce optimal sound. Before serious reviewing, I also ran either the Ayre demagnetizing / break-in CD or the more elaborate break-in sequence from Isotek. Finally, I also made sure that all power cables and interconnects were well over an inch apart, as in 2-3" or more.

PA-M300 REVIEW
NEXT SECTION: IN USE


In Use

The first thing that jumped out at me was the sound of the bass. Boom! Wham! Slam! Big, powerful, tight, focused, and viscerally thrilling bass. Not since I reviewed the Parasound JC-1 Halo monoblock amplifiers in August, 2004 have a heard such jaw-dropping bass from my system. The timpani thwacks at the start of Ivan Fischer's recordings of Mahler's Symphony No. 2, "Resurrection" (Channel Classics) were floor-shaking.

But that head-turning bass was only from the CD layer of a hybrid SACD, whose ultimate dynamic range is limited. A far bigger surprise was in store when Ray Burnham of Auraliti brought over the prototype L-1000 music player to prepare for the BAAS demonstration, and put on a not-yet-available hi-resolution file of Reference Recordings' fabled version of Copland's Symphony No. 3. This is the symphony from which the ubiquitous Fanfare for the Common Man originates. I wonder, when the Republican Party chose it as their election year theme song a campaign or two back, if any of the decision makers were aware that the composer was a liberal who narrowly escaped total vilification and career destruction by Sen. Joe McCarthy's House Un-American Activities Committee.

Well, if Joe had ever gotten the chance to hear what the Jones Audio amps could do with the big bass drum thwacks on this ultra-dynamic, hi-resolution file of Copland's symphony, he might have stopped pointing the finger outward and run for cover. The bass was like nothing I'd ever heard before in my room, or just about any room I can think of.

When we first played the track, I was experimenting with midrange port loading, and had loosely stuffing the rear ports on my speakers' upper modules with white anklet socks. The first time we turned the volume way up to realistic symphonic levels – not ear-deafening levels, but definitely loud – and the bass drum pounded in 24-bit, 88.2 kHz sound, one of the socks shot straight out the rear port and hit the wall behind the speaker!

Even more dramatic, the huge current draw required to reproduce such realistic thwacks soon tripped the internal protection circuit on the amps. The sequence sounded something like this: Boom, Pop (as the first sock shot out one of the rear ports), Boom-Boom, Pop (as the other sock shot out), Boom-Boom-Boom, Click (as the amps shut off).

This was accompanied by a huge emotional swing on my part that went from "What?" to "Wow!" to "Are you kidding!" to "Oh no!" in the space of a few measures. Right after Ray quipped, "How's that for a case of sock it to me," our elation crashed.

As we retrieved the socks, both Ray and I saw that the amps looked dead to the world. Then we realized that the BAAS demo was but two days away. We had no idea if we had burned them out, if they contained esoteric value fuses that we would never be able to replace in time, or what.

An emergency call to Jason Jones, who bless his heart was available, produced reassurance that the amp's internal circuit breaker had tripped to avoid damage, and would reset once the babies cooled. We able to turn the amps back on in a few minutes.

As a result of this quasi-hilarious mishap, the amps' headroom has been bumped up a bit to avoid similar unnecessary simulated meltdowns in the future. Glad to serve.

Bass, of course, was only one aspect of the sound. The rest of the range was also as tight as could be. Midrange was strong, and highs were brightly illumined, extended, but never piercing. (This is not a dark sounding amp by any means). In addition, as mentioned above, the dynamic range was far greater than I was accustomed to, especially from CD. The huge chorus at the end of Mahler No. 2 was astounding, as hundreds of singers, two soloists, gongs, bells, timpani and everything else in the huge Mahler orchestra joined together in one huge, clearly articulated outpouring of resurrectional release.

One of the reasons I wish I had been able to spend more time with the PA-M300 Series 2 monoblocks is that I've since learned far more about optimal positioning of the Eficion F300 loudspeakers. They are now considerably closer together, with less toe-in. I've also established that, at least in my room, the more the toe-in, the more the tonal balance shifts from midrange-full and top just right to midrange lean and top over-pronounced. I can even white out the sound by not toeing in enough. There is a delicate balance where top to bottom sounds in correct proportion both tonally and in volume, but it takes time and patience to dial it in.

While the Jones Audio monoblocks were at my home, I experimented with the exact degree of speaker toe-in by using a protractor. Please join me in a chorus of "the best laid plans of mice and men…" As it turned out, the protractor I was using was inaccurate, and whose 90º middle setting was more like 88.8º. As a result, when I tried to toe-in both speakers 2.5º, one speaker was actually angled closer to 3.7º, and the other 1.3º. This produced an uneven tonal balance between the two speakers, and skewed the certainty of my evaluation..

Hence, when I say that, if pushed to characterize the sound of these monoblocks, I would describe them as having just a touch of the muted silver, gunpowder gray patina that I recall from the Parasound Halo JC 1 monoblocks, I would also say with certainty that I cannot trust that call. Had the amps remained through the time when I finally found a Taiwan-sourced protractor that gave accurate readings, and was able to position the speakers properly, I'd feel far more comfortable describing their tonal balance.

Let us instead say this . . .

PA-M300 REVIEW
NEXT SECTION: CONCLUSION


Conclusions

The Jones Audio PA-M300 Series 2 monoblock amplifiers rank alongside the Parasound Halo JC 1 monoblocks as the most impressive solid-state amplifiers to ever reside in my system. The dynamics are wide and stunning, the bass tight and awesome on every level, and the top as extended as the bottom.

In the month I spent with these monoblocks, I heard nothing but smooth, effortless, and transparent full-range sound. Symphonic music, jazz with bass, and of course rock became more exciting than ever. Hi-resolution material was at times jaw dropping. I only wish I could have spent more time exploring PA-M300 Series 2's many strengths.