It’s easy to see why integrated amplifiers have made a comeback. Except for very high-end or very high-power amplifiers, there’s not much reason to split the amp and preamp functions. Many integrated amplifiers now are really integrated; they include DACs, and many include phono sections as well, both moving-magnet and moving-coil. So all you need to do is plug in your source equipment.
Designed and manufactured in Warwick, New York, the Rogers EHF-100 Mk2 is a two-channel tube integrated amplifier rated at 65 Class A watts per channel. The EHF-100 Mk2 is a classic integrated: There’s no DAC or phono section. The $8000 hand-wired EHF-100 Mk2 has premium parts throughout. For example, Teflon-insulated wire is used, as are Furutech output jacks, and electronic parts are said to be the same as those used by NASA in the shuttle and space station equipment. I was tickled to see that the EHF-100 Mk2 uses self-biasing circuitry for its four KT88 output tubes. About its self-biasing circuit, Rogers’ website says that the “customer does not need to adjust tube bias. As the tubes age, they adjust for bias changes automatically. The customer can change tubes at any time or replace a single tube rather than the full set of four and the amp will automatically re-bias for the change.” That’s a very useful feature. Biasing tubes is, on a good day, a pain in the posterior.
EF86 pentode tubes are used in the input circuit, described as ultra-low noise and high gain (40dB). Phase splitter tubes are common 12AX7s. The KT88s are Gold Lion-branded, the 12AX7s, Sovteks, and the EF86s, JJs. All these tubes are in current production and not crazy expensive. A rare but welcome feature of the EHF-100 Mk2 is that it comes already burned in for 100 hours. Even rarer but more welcome is its lifetime warranty. Rarer still is the fact that the warranty is transferrable if you sell the amplifier. Tubes are guaranteed for 90 days—pretty much industry standard. Evidently Rogers believes it has a rather special product. Its amplifiers are manufactured using a “statistical process controlled” procedure that is said to offer higher reliability than products made for the airline or hospital industries. No wonder Rogers can offer a lifetime warranty.
The EHF-100 Mk2’s only deviation from a classic integrated amplifier design is its remote control—for volume only. Isn’t that all you really need? Maybe so, although I find a mute button pretty handy when the phone rings. Unlike many tube amplifiers, there’s only one set of speaker terminals, optimized for 4-ohm speakers. I was concerned that my 16-ohm speakers might not be optimal for use with the EHF-100 Mk2, but Rogers assured me they would work fine, and they did. The input impedance for all inputs was 100k ohms, which should not be a problem with any conceivable source. As you would expect from a tube amplifier, the 50-pound chassis is large at 17" by 10" by 14", and of course, you’ll need plenty of room around the chassis for ventilation. Even the four feet are special—constructed of Delrin, conical in shape, but with flattened points so they won’t scratch your equipment rack. The feet are designed to damp vibrations at a center frequency of 1kHz.
Styling for the EHF-100 Mk2 is rather retro, or, if you don’t care for it, plain; the entire chassis is powder-coated in a black finish. I found it appealing, but if you’re looking for audio jewelry à la Rowland or D’Agostino, the EHF-100 Mk2 may not be your cup of tea. Located on the front panel (hooray!) are separate switches labeled “power” and “operate.” The power switch turns on the tubes for warm-up, and 30 seconds later, you flick on the operate switch, which applies high voltage so the tubes will conduct. Front-panel controls are minimal—a volume control and a source selector. There’s no balance control, no mono switch, no phase-inversion switch, no (gasp) tone controls. These would add cost to the amplifier, might degrade the sound, and I suspect most people wouldn’t use them anyhow. There are four inputs, all on RCA jacks; one is on the front panel, a thoughtful feature which allows you to plug in a smartphone or tablet without having to access the rear panel. But you must use a cable—no Bluetooth circuit here. (Bluetooth would have required not only a receiver, but also a DAC.) There is no line-level output, so you can’t easily add a subwoofer—except one that connects to the speaker terminals. A single small meter, centered on the front panel, measures the combined power output of both channels. On the top of the chassis nearest the front panel are the low-level tubes, then the output tubes, then, at the rear of the top of the chassis, a perforated cover over the power and output transformers. All of the transformers appear to be quite sizable for the amplifier’s rated output. The weight of the amplifier was definitely concentrated towards the rear.
On the rear panel, from left to right, you find the left and right speaker terminals, which are carbon-fiber Furutech units, then the three sets of gold-plated RCA input jacks, a fuse holder, and an IEC jack for the power cable. The speaker terminals are spaced far enough apart to allow the use of cables with large spade lugs, in addition to banana plugs or bare wire. Unlike many manufacturers, Rogers offers a special optional power cable for its amplifiers, called the Rogers High Fidelity Quiet Cable, which was included with the review unit. I’m always pleased to see manufacturers recognizing the contribution of power cables to the overall sound. The Quiet Cable sells for $1900 for a 10' length. Like the EHF-100 Mk2 amplifier, the Quiet Cable is also broken in when it arrives, so you’ll be able to enjoy it right away. Also included was Rogers High Fidelity Upgraded Remote Control, a $300 option. Another option, not included with the review unit, is a tube cover, made of transparent Lexan. While essential in environments like homes with small children, tube covers are usually ugly (my view), so making one out of a transparent material seems particularly clever.