Hovland Sapphire power amplifier
But looks alone don't sell hi-fi equipment in the specialty audio market—especially when you're asking $7800 for a 40Wpc two-channel amplifier. Hovland knows this, so they've fortified the 82-lb Sapphire with innards to match its fancy skin, as well as some interesting design twists. They insist that, for the most part, form follows function in the design, even when it looks as if it doesn't. For instance, the chassis is said to act as a heatsink. The glass column around each output tube is not there just as a visual accent—it's a convection chimney designed to more efficiently draw heat away from the tube. (The instructions caution you to never run the amplifier without the chimneys.)
What's Going On?
What sort of small high-end audio company has the audacity to make its first amplifier a 40Wpc job selling for almost $8000?
Hovland Company has been around for more than 20 years. Chief designer and CEO Bob Hovland worked as a designer for Marantz before that, so even though this is the company's first commercially marketed power amplifier, there's a great deal of history and design experience behind it. The company, best known for its cables and MusiCap capacitors—and, lately, for its HP-100 preamp—first exhibited a power amp back in 1993, but never put it in production. The Sapphire grew out of that prototype, the most intensive design work on it taking place over the past two or three years, according to Bob Hovland. When I asked him why he chose EL34s for the output, he said that they were on the "top of the list, musically."
He also told me that while the two pairs of tubes are working in push-pull, the Sapphire is not your classic Dynaco or Williamson circuit. The amp has no global-feedback network. Rather, the feedback used is "nested" in a small portion of the amp around the gain structure, with each output and driver tube having its own separate and entirely independent feedback network. In more conventional, "global" designs, feedback is applied from the speaker terminals back to the front of the amp.
Hovland says that since the point of feedback is to compare the output and input and reconcile the two, there is always uncertainty when the feedback is being handled by more than one device, especially at lower power. The Sapphire's design allows feedback to be applied independently to each tube. Therefore, Hovland contends, the amp operates more linearly than had been believed possible. It won't "test" differently, he said, but functionally, it behaves as a more linear circuit.
As well as a pair of EL34s for each channel, the hybrid Sapphire uses a 12AU7 vacuum tube and small bipolar and FET transistors at each channel's input and driver stages. The design is essentially dual-mono; the "overbuilt"—nearly 25 lbs—custom power transformer has separate windings for each channel, and is capable of delivering more current than a 40Wpc amplifier would ever require.
"Sounds better that way," said Hovland, who added that custom filter chokes were developed for the Sapphire, and that the design of the high-voltage power supply was "critical" to the amp's claimed high performance. I asked if he'd also used high-speed diodes; Hovland said no, they can make the music sound "stressed."
Construction includes a combination of point-to-point wiring and printed circuit boards in a very neat, even elegant layout. Resistors, power-supply capacitors, and other components are chosen through careful auditioning (including, according to Hovland, different lot runs from the same manufacturer). Of course, all caps are Hovland MusiCaps and internal wiring is Hovland, including Generation 3 shielded, silver-plated interconnect.
All components—circuit boards, ceramic tube sockets, input and output facilities, transformers—are attached to the main chassis, a 1"-thick plate of tempered aluminum alloy supported by three tapped aluminum cylinders that protrude through holes machined in the bottom chassis cover. Conical feet can be screwed into the cylinders for better mechanical coupling to the support. (This is one amplifier you don't want to isolate via its bottom plate, so devices like Symposium Acoustics Rollerblocks, which need a chassis bottom for support, are out.) Tubes and transformers protrude through chassis cutouts, the transformers neatly encased in aluminum.
The aluminum back plate features a pair of RCA input jacks and side-by-side five-way binding-post sets, with 4, 8, and 16 ohm impedance posts for each channel. In a departure from most tube amps that feature output transformer taps of multiple impedances, Hovland fixes the positive terminal and varies the negative, claiming it sounds better that way. Also on the back is a bridging switch for converting the Sapphire to an 80W monoblock.
Each of the six tubes comes labeled for its intended socket; the Russian-made Electro-Harmonix output tubes are matched pairs. After you apply stick-on felt protectors to the walls of the circular chassis cutouts, you insert the four glass convection cylinders, polished ends down.