Back in 2016, I documented the rise of class-D amps using the early TriPath technology. Used in the Bel Canto eVo 200.2, TriPath cracked open the door to the High End but was never admitted due to a dim and opaque treble. The second wave was based on B&O's ICEpower technology, again via a Bel Canto amplifier, the Ref1000M monoblock. ICEpower had more credibility and was accepted by many but, often, only with, ahem, due consideration for size and efficiency. There was an explosion of new class-D amps in 2016 when Stereophile featured glowing reviews of Bel Canto's e.One Ref600M monoblock, Theta's Prometheus monoblock, and NAD's Masters Series M22 stereo amp, all based on Bruno Putzeys's Hypex NCore technology modules. Finally, it seemed that class-D was "in the room," though, even to this day, there remain critics and quibblers who continue to deny them as true high-fidelity products.
Well, time does not stand still and neither did Bruno Putzeys. He, along with Lars Risbo and Peter Lyngdorf, had founded Purifi in 2015, and in 2019 he unveiled the Purifi Eigentakt power amplifier modules. Eigentakt (meaning "self-clocking") is the result of years of research by Purifi into the self-oscillation behavior in class-D amplifiers with algorithms that, when applied in control loops, "improve existing designs by an order of magnitude or more. ... The Eigentakt circuit is expected to outperform any audio amplifier known, regardless of technology or class, with THD and IMD quoted as below 0.00017% at all frequencies and power levels, and the frequency response in the audioband remains within ±0.01 dB under all load conditions."
The 1ET9040BA is currently the most powerful device that Purifi has in its range of Eigentakt modules tailored to different applications. That's great but that's not really why I was attracted to this amplifier. The clue is the word module. I was a committed DIY-er for most of my life, working from scratch or, if I was lucky, working with prebuilt modules where the critical elements were assembled with carefully selected wiring, connectors, and enclosures. All the class-D amplifiers mentioned above are based on factory-built, factory-tested modules supplied as OEM parts to the audio companies (or, in some cases, built by the companies under strict licensing agreements).
This creates opportunities for smaller companies to build amplifiers based on these modules as long as the minimum OEM purchase is reasonable. In this case, the OEM purchase minimum is only 25 pieces, although I am certain better pricing accompanies larger quantities (footnote 1). Of course, there's more to a functioning audio amplifier than the module. First, since the Eigentalkt modules have a relatively low gain (14.4dB for the 1ET9040BA), an input stage is needed to raise it to a more useful level and, in this case, to offer gain options. Second, one must add a power supply to power the amp module and the input stage. Third, of course, is everything else: a chassis; input connectors; output connectors; power switch and indicator; options for signal-sensing; 12V trigger; gain selection; possible heatsinking; internal wiring; and, literally, nuts and bolts. There is nothing daunting to those with relevant expertise and, over the past decades, this has resulted in a new cottage industry that builds amps from these modules or supplies kits for home assembly.
Buckeye Amps is a relative newcomer. After more than a decade of buying and selling to upgrade his system, founder Dylan Launder built a set of Hypex NCore MP amps and never looked back. He was so impressed with the sound quality that he became a North American OEM Hypex builder and sold his first Buckeye Amp in October of 2020. Customer interest, based solely on word of mouth and positive technical reports, has grown his business, and he has gained over 4000 customers in the past two years. His line now includes amplifiers featuring the newest Hypex NCx and Purifi Eigentakt modules, of which the subject of this review is, to date, the most powerful.
Where's the beef?
The 1ET9040BA monoblocks cost $2300/pair, including free shipping in the US. The two amplifiers arrived in a single cardboard carton that weighed less than 15lb! For a pair of power amplifiers, this was surprising, even puzzling. Inside were two smaller plain boxes, each containing an amp and a power cord, and a single-page Purifi Quick Start Guide that also serves for other Buckeye amps. Each amplifier was in a nicely finished black chassis, on the front of which was a single LED to indicate On/Active (blue), clipping (orange), or fault (red), and a painted Buckeye logo. Around back left is sturdy pair of gold-plated, multiway speaker terminals, a balanced (XLR) analog input, and a gain selection switch (25.5dB, 20.5dB, 15.5dB). On the right, there's a 15A IEC AC socket and a power rocker switch. Between these elements, there is a 12V trigger signal socket and a three-position slide switch for power modes (AutoSense On, AutoSense Off, 12V trigger).
I found this feature set entirely logical and suitable, though I did think that the input XLR and the speaker terminals were too close to each other. I was also surprised that Buckeye used a latchless XLR jack for the input over the security of a latched connection but, considering how close the XLR is to the speaker terminals, there really isn't enough room for a latch. I therefore recommend plugging in the input cable before the speaker cable.
Inside the chassis all is neat and clean. Towards the front is a Hypex SMPS1200A180 1200VA, high-efficiency, switch-mode power supply which provides 2×46VDC (footnote 2) for the 1ET9040BA module and also powers the input board. The latter is a proprietary Buckeye design mounted to the rear panel. Wiring among the elements is by plug-in cables, making for easy replacement:
AC input to power supply.
Power supply to input board and 1ET9040BA module.
Input board to 1ET9040BA module.
1ET9040BA module to speaker outputs.
Installation was as easy as can be imagined (since you can hold the amp in one hand) as I just transferred the XLR input cables and speaker cables from my bridged Benchmark AHB2 amps to the 1ET9040BA monoblocks. The Buckeyes were set to medium gain (20.5dB) and, after I flipped the power switches, internal relays clicked once and the LEDs on the front panels glowed blue. In operation, there was no mechanical noise nor any perceptible noise whatsoever, even when I applied my ear to each of the drivers in each of the speakers. I do not recall what track I played first because my intent was not to listen but simply to find out if everything was connected, operating, and quiet. It was.
Footnote 1: The price of a sample 1ET9040BA module from Purifi is $660 or, with a very simple mono front-end board, about $760 plus relevant taxes, fees, and shipping. Footnote 2: This power supply limits the ultimate output of the amp to 1200W into 2 ohms. Buckeye offers an optional Micro Audio SMPS1K-SN power supply that offers Active Power Factor Correction, higher power output (a 0.67dB increase from 1200W to 1400W into 2 ohms), and standby control, which allows for under 1W power draw when the amp is not in use.
The 1ET9040BA is currently the most powerful device that Purifi has in its range of Eigentakt modules tailored to different applications. That's great but that's not really why I was attracted to this amplifier. The clue is the word module. I was a committed DIY-er for most of my life, working from scratch or, if I was lucky, working with prebuilt modules where the critical elements were assembled with carefully selected wiring, connectors, and enclosures. All the class-D amplifiers mentioned above are based on factory-built, factory-tested modules supplied as OEM parts to the audio companies (or, in some cases, built by the companies under strict licensing agreements).
Where's the beef?The 1ET9040BA monoblocks cost $2300/pair, including free shipping in the US. The two amplifiers arrived in a single cardboard carton that weighed less than 15lb! For a pair of power amplifiers, this was surprising, even puzzling. Inside were two smaller plain boxes, each containing an amp and a power cord, and a single-page Purifi Quick Start Guide that also serves for other Buckeye amps. Each amplifier was in a nicely finished black chassis, on the front of which was a single LED to indicate On/Active (blue), clipping (orange), or fault (red), and a painted Buckeye logo. Around back left is sturdy pair of gold-plated, multiway speaker terminals, a balanced (XLR) analog input, and a gain selection switch (25.5dB, 20.5dB, 15.5dB). On the right, there's a 15A IEC AC socket and a power rocker switch. Between these elements, there is a 12V trigger signal socket and a three-position slide switch for power modes (AutoSense On, AutoSense Off, 12V trigger).
Inside the chassis all is neat and clean. Towards the front is a Hypex SMPS1200A180 1200VA, high-efficiency, switch-mode power supply which provides 2×46VDC (footnote 2) for the 1ET9040BA module and also powers the input board. The latter is a proprietary Buckeye design mounted to the rear panel. Wiring among the elements is by plug-in cables, making for easy replacement:
AC input to power supply.
Power supply to input board and 1ET9040BA module.
Input board to 1ET9040BA module.
1ET9040BA module to speaker outputs.
Installation was as easy as can be imagined (since you can hold the amp in one hand) as I just transferred the XLR input cables and speaker cables from my bridged Benchmark AHB2 amps to the 1ET9040BA monoblocks. The Buckeyes were set to medium gain (20.5dB) and, after I flipped the power switches, internal relays clicked once and the LEDs on the front panels glowed blue. In operation, there was no mechanical noise nor any perceptible noise whatsoever, even when I applied my ear to each of the drivers in each of the speakers. I do not recall what track I played first because my intent was not to listen but simply to find out if everything was connected, operating, and quiet. It was.
Footnote 1: The price of a sample 1ET9040BA module from Purifi is $660 or, with a very simple mono front-end board, about $760 plus relevant taxes, fees, and shipping. Footnote 2: This power supply limits the ultimate output of the amp to 1200W into 2 ohms. Buckeye offers an optional Micro Audio SMPS1K-SN power supply that offers Active Power Factor Correction, higher power output (a 0.67dB increase from 1200W to 1400W into 2 ohms), and standby control, which allows for under 1W power draw when the amp is not in use.
