Peachtree Audio nova125 integrated amplifier

With Peachtree Audio's new nova125 integrated amplifier, most decisions are made for you.

Need a DAC with three S/PDIF inputs (two coax, one optical)? An asynchronous USB DAC? A line stage? A tubed output buffer? A power amp that should be able to drive even difficult speaker loads? Remote control? You've got them all for $1499. Just add speakers. (I assume you have a laptop computer and several disc spinners.) You may want a separate phono stage, because there is none onboard.

While well furnished with digital inputs, the nova125 has only one pair of RCA line-level analog inputs. Thus, if you connect an outboard phono stage, you'll have no extra inputs for an SACD player, an FM tuner, etc. (What's an FM tuner?)

By the way, there is only one pair of speaker outputs—very high-quality binding posts, not the cheap crap often found on budget gear—and, accordingly, no speaker-selector switch. There is a pair of RCA preamp outputs, good for a subwoofer or two, or maybe another amp. The nova125's single pair of RCA line-level inputs could be a major inconvenience for some, like me. There is no mono switch. There are no tone controls. The result is a refreshing lack of clutter.

The nova125 is resolutely two-channel. You know how you look at the back of a home-theater amplifier and see 52 pair of inputs? There's none of that here. Money is not spent and sound is not spoiled by crappy connectors, too much circuitry, etc. The Peachtree nova125 is not a pile of consumer shit.

The nova125's ESS Sabre 903 DAC chip is sometimes found in far more expensive models. The USB DAC is asynchronous up to 24-bit/192kHz, if you're into high-resolution downloads, or might be in the near future.

Setup and System
Alas, I was not able to use the nova125's USB input. It would not recognize the original Mac mini in my office, which runs OS 10.3.9. I should have a more up-to-date computer, but I really can't decide whether to get another Mini or a laptop or an iPad, or all three, or even whether to stay with Apple. My original Mini works fine. So does my 1958 Underwood office typewriter, which I still use at least once a day. Every day I keep my Mini, I have outfoxed Apple. My wife more than makes up for it, with all the newest 'pods, 'phones, and 'pads.

I plugged my Sony XA-777ES SACD/CD player into one of the nova125's coaxial S/PDIF inputs, so that I could use the Sony as a disc transport. For SACDs, I ran the player's two-channel output into the pair of RCA analog inputs. This put me in a fix for my EAR 834 phono stage, not to mention my XDR-F1HD digital FM tuner, a product so good that Sony stopped making it.

I would have welcomed a convenient way to connect my iPhone 4, which Marina bought for me when I wouldn't. Some kind of dock would have been nice. But maybe Peachtree Audio is prescient: The new iPhone 5 dock is different from earlier docks and requires an adapter. For me, the only way to listen to the BBC through my iPhone was to use the phone's headphone output into the nova125's single pair of analog inputs. Of course, I had to disconnect my phono stage, SACD player, or FM tuner.

Speakers were my Harbeth 30.1 monitors. They made a peach of a pair with the nova125, especially in terms of dynamic drive. Resolution and transparency were other matters, but what do you expect for $1499? Everything? Compare the nova125 with some of your dealer's more expensive integrated amplifiers—the ones that don't have an asynchronous USB DAC, a tubed output buffer, etc.

Speaking of which: The nova125's line stage is followed by that buffer—a single Russian 6N1P dual-triode tube—which the user can switch in or out from the remote control, though not from the front panel. The tube looks hard to access, and the manual doesn't tell you how. When the buffer stage is engaged, a blue LED illuminates the tube to let you (and everyone else) know it's on. Showmanship!

The headphone output is a proper ¼" jack that takes its signal directly from the line stage, with the tubed buffer in or out of circuit, depending on the user's preference. You decide. The remote is a great convenience with headphones—I needn't jump up and spill my glass of Bas Armagnac. Plugging in a set of headphones mutes the power-amp section.

The cabinet is beautiful: real-wood veneer over MDF. When the cabinet is made, a machine squashes the MDF and wraps the veneer at the same time. This results in rounded sides—no edges. A "tool" inside the cabinet prevents it from getting crushed in the process, which I think involves steam. Sexual innuendos invited . . .

For all of its up-to-date features, I find something retro about the look of nova125—and about its sound. With its silver faceplate, it reminds me of classic Yamaha gear from the early 1970s. The nova125 does not look primitive, excessively macho, or gaudy. It is tasteful, not tacky.

Class-D isn't digital, even if it sometimes sounds that way
The D in class-D does not stand for digital, although early class-D amplifiers made me think that it did.

With a class-D amplifier, almost all the electricity you draw from the mains is turned into power that actually drives your speakers. I was once told that 45W from the mains would produce something like 42W of amplifier output. At idle, a class-D amplifier uses practically no power at all. Some day, the Green Police may decree that all amplifiers be class-D—just as they're trying to ban old-fashioned light bulbs, and take away real Christmas-tree lights.

Class-D amps are sometimes called switching amplifiers because the output devices are either completely on or completely off. A class-D amp delivers either all the current available from its power supply or none at all. Its voltage output doesn't vary, except for the few microseconds it takes to switch from on to off. This is called pulse-width modulation (PWM). The longer the pulse, the louder the sound. In quiet passages, the pulses barely peep. The pulses are produced by modulating a carrier frequency way above the audioband. The carrier frequency is filtered out. AM radio works much the same way, but its carrier frequency is much lower. The first switching-amplifier designs date back to the early 1930s. So, no, class-D does not mean digital.

With class-D modules, an amplifier designer can reduce the size of the power supply, cutting the amplifier's size and cost. I'm told that the modules are almost plug-and-play for a designer. There's another advantage for manufacturers: There seem to be fewer ways an amplifier manufacturer can muck up a product because so much of each amplifier has already been made, in the form of those modules.

Alas, there have been some problems with class-D amplification that have tended to outweigh its advantages for serious audio listening.

Ah, yes, noise: the PWM process generates high-frequency noise akin to digital audio quantization noise. (Maybe this is why some listeners have found that class-D amplifiers sound "digital" even when they're not.) And that pesky carrier frequency, which requires a sharp-slope brick-wall filter, can in turn mess with phase and cause high-frequency ripple in the audioband: the so-called "in-band artifacts." This is probably why one British critic (I can't recall who) likened the sound of class-D amps to the sound of shattering glass.

Manufacturers of class-D amplifiers have tended not to talk about these things, just as manufacturers of traditional class-A/B designs would rather not mention notch distortion: that moment when the waveform passes from positive to negative or back again, push and pull. Push/pull is always audible. That's the joy of single-ended triodes.

Did I mention that many audiophiles and most hi-fi critics hear what they want to hear and disregard the rest? The problem is, we are not born with notch filters.

In home-theater amplifiers and car audio, where class-D has long ruled, these niceties need not matter.

The Dead Zone: The truth comes out
In class-D there is a form of notch distortion, too: what engineers secretly call "dead time." That's the interval, however short, when neither the positive nor the negative stage is conducting current. In other words, switching amplifiers don't just turn on and off; there's a dead zone between: silent gaps in the audio output. How does that show up in the sound? Maybe as timing errors that mess with the music's harmonic structure. For me, class-D amplifiers have tended to sound threadbare—like my worn, thin trousers from Walmart.

Why not solve the dead-zone problem by allowing both devices, positive and negative, to be simultaneously on—but ever so briefly? That, unfortunately, can blow up the amp, either immediately or over time. In other words, if a switching amp doesn't switch quickly enough, it can fail. Ever had a powered subwoofer blow up? I have. Boom, then bust.

Now the good news.

Manufacturers of class-D modules and amplifiers have not been standing still. There is too much riding on making class-D work: labor savings, reliability, customer acceptance (smaller size, less heat), and, just maybe, the Green Police. If you wake up tomorrow morning and find that Australia or New Zealand has mandated class-D amplifiers, don't be surprised.

Peachtree Audio
2045 120th Avenue NE
Bellevue, WA 98005
(704) 391-9337

anjeza1987's picture

Cute amp,nice review.Thanks.

Dr.Kamiya's picture

An interesting thing is that SACDs and DSD work exactly the same way as Class-D amps, just with line-level output voltage/current.

So food for thought: Either Class-D is digital, or SACDs/DSD are actually analog.

FWIW, I do find SACD/DSD the most analog sounding out of all disc formats.