Primare A35.8 8-channel power amplifier

Back in 1999, while reviewing the Wazoo integrated amplifier from Bow Technologies, I learned that its designer and company founder, Bo Christensen, had previously founded another audio company. That’s how I discovered Primare. Over the years, various products from Primare have appeared at audio shows but never grabbed my attention. In a recent EISA press presentation, however, Primare showcased an eight-channel amplifier that did, given my interest in multichannel audio. I was glad to be able to attend.

Expectations were high for the new A35.8 power amplifier. Its stablemate, the A35.2, which Herb Reichert reviewed very favorably in the April 2022 issue, earned Class A status. Stylistically similar to the A35.2, the A35.8 offers more than just additional channels: It supports flexible channel bridging. This allows it to drive anything from a high-powered stereo setup to various multichannel configurations. (Together, these two amplifiers can realize practically every imaginable speaker arrangement.)

Cool power
The A35.2 stereo amplifier is based on Primare’s proprietary class-D amplifier module, the UFPD2. Fitting eight of these modules, without major redesign, into a reasonable chassis for the A35.8 and operating them consistently within thermal limits was impracticable. Primare, therefore, opted to use the reliable and powerful Hypex NC500 amplifier module, with some modification. The NC500 has an aluminum plate for thermal coupling with a heatsink, but to maximize thermal transfer and optimize shielding, Primare replaces this plate with a heatsink of its own design. Four of these heatsinks, each carrying two modules, are mounted vertically into cutouts in the main circuit board. They cool by convection as air flows up through the top- and bottom-perforated chassis. The A35.8 is elevated by three large, damped feet that aid this airflow.

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Is the move from the UFPD2 to the modified Hypex a step backward? Primare maintains that “it is not possible to gauge the sound quality of any Primare model based on a single part or circuit component” and notes the company’s long experience optimizing class-D power amplifiers based on a variety of modules. “It should not be inferred that the A35.8 is compromised or inferior in any way by using the Ncore output modules.” Rather, comparisons of the UFPD2-based A35.2 and Ncore-based A35.8 showed that although the new amp “did not sound better,” it was “close.”

The A35.8 is powered by a dual-output, switch-mode power supply with power-factor correction, which is said to be about 5% more efficient than passive, linear power supplies. It is rated at 1500W and has soft-clipping circuitry, and each output is wired to one bank of four NC500 modules. Thus, the four channels on the right are supplied independently of those on the left—something to keep in mind when bridging channels.

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Unpacking and configuration
The packaging of the A35.8 was adequate for an amp of this size and weight. Included with the amplifier were a safety-and-warnings booklet, an AC power cord, an AC polarity pen (footnote 1), and a 3.5mm trigger cable. No user manual or quick-start guide is included, but a note tells where to find the user guide on Primare’s website; it can also be accessed through the QR code on the box. The guide consists of a few short sections, presented as webpages of different lengths. Saving these pages to PDF and printing them out is tedious and wasteful—I ended up printing two illustrations and kept going back to my computer to look up information I needed, though others would likely read it on a smartphone or tablet.

The A35.8 is sleek, but it’s surprisingly heavy. The only front-panel features are Primare’s logo and an LED indicator that doubles as a power button. The rear panel is crowded with connectors and switches. On the right is an in/out pair of 12V trigger jacks, an RS232 port to connect the A35.8 to a controller system, a master power switch, and an IEC power socket (footnote 2). The rest of the panel bears the inputs, outputs, and controls for the eight amplifier modules, grouped into four pairs. Each module has an RCA (unbalanced) input and an XLR (balanced) input at the top. Between the XLRs of each pair are two toggle switches: one to choose between the balanced and unbalanced inputs, the other to select among two-channel operation, bridged operation, and bridged operation with 6dB gain.

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What’s that about? Normally, bridging two channels yields a 6dB output gain. Combining bridged and unbridged channels, as I did—three bridged pairs to run my Left-Center-Right speakers and the remaining two channels to run my two surround-channel speakers—results therefore in an output-power imbalance. When the user selects the A35.8’s first bridged mode, 6dB of attenuation is applied to avoid this imbalance. But if only bridged outputs are used, the user can select the 6dB bridged mode to avoid attenuation.

The ubiquity of a center channel explains why it’s rare to find multichannel amplifiers with an even number of channels. Primare’s choice of eight channels in the A35.8 makes perfect sense, as it increases the bridging options.

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It’s an eight-channel amp!
I connected the A35.8 to my multichannel system using the balanced inputs and turned it on. Two banks of red LEDs inside the amp flashed briefly as the eight Ncore modules activated and a relay clicked. The front-panel LED blinked a few times and then steadied to indicate that the amplifier was ready. I first played Ferdinand Ries’s Sextet for harp, piano, clarinet, bassoon, horn, and double bass, with the Franz Ensemble (DSF rip from MDG Scene MDG 903 2136-6), one of my 2022 R2D4 choices. This five-channel recording presented each of the instruments with equal prominence and clarity, summing into a colorful sonic bouquet. The soundstage was broad and deep and was endowed with excellent detail.

Footnote 1: Reversed AC polarity is possible where symmetrical two-prong plugs (or a “cheater plug”) are used and can increase noise. This device is used to test whether the polarity is correct.

Footnote 2: Primare advised that “due to the high current draw, the A35.8 features a C20 IEC socket on the back panel, rather than the usual C13/14 IEC socket, so a replacement power cord should be terminated in a C19 IEC plug.”

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