AudioValve Baldur 70 monoblock power amplifier
By Michael Fremer   •   April, 2006 In this hobby, nothing's for nothing. To get that gorgeous midrange, with its harmonic depth and inner detail, tube-amp enthusiasts are willing to give up some things in the bass. Tube folks put up with heat and occasional maintenance—routine or otherwise. To get the ideal middle, fans of single-ended triodes are even willing to shave off considerable dynamic range and settle for ultra-efficient speakers that often have limited response at the frequency extremes. Those who say nothing is lost by preferring tubes are in denial.

Walk into a room at a hi-fi show touting low-powered SET amplifiers and you'll likely hear recordings of flute, shakuhachi, or a cappella music, not symphony orchestras or Nirvana—although, within the constraints of the system, even those recordings will probably sound good. It all depends on what you're listening for and what you're able to ignore.

Solid-staters are willing to lose some warmth and lushness to get, among other things, the benefits of rock-solid bass extension, transient speed, and zero maintenance. To tube enthusiasts, such systems sound grayed-out, harmonically bleached, and all leading edges with their harmonic envelopes licked shut, despite their frequency extension, overall speed, and increased dynamic range.

These traditional sonic characteristics of tube and transistor designs are clichés, but clichés are often grounded in truth. In my long experience of both types of amplifier, the clichés hold more or less true.

I don't think anyone argues that solid-state amplifiers can match the midrange soul, body, and rich harmonic structure of tubes, but the full musical picture is made up of many other elements, some of which solid-state does deliver more effectively. To actually argue over which is better and more musical is, in my opinion, the province of wankers. What we're left with is a series of personal value judgments and justifications for preferring one form of amplification over the other. I don't think superior measurements prove the superiority of solid-state amplification. As a vinyl enthusiast, how could I? I don't measure music, whether live or recorded. I listen to it.

The Baldur 70...
...is a 70W, fully class-A, push-pull triode-tube monoblock amplifier from Germany. It's compact, beautifully built, and pleasing to look at, and, thanks to its Automatic Bias Regulator (ABR) "smart-bias" circuitry, promises essentially maintenance-free performance. AudioValve claims that the ABR automatically adjusts and distributes the bias current flow, thus maintaining ideal tube performance at all times, and allowing you to replace a single burned-out output tube in a push-pull pair without worrying about having to match the characteristics of the surviving tube. They say you can use different tube brands, even mix and match new and used tubes, and the sound will remain "balanced and coherent." No meter or screwdriver is ever needed. As the tubes age (often at different rates), the ABR circuit will adjust itself to maintain the proper bias. Six LEDs mounted on the circuit board associated with each output tube alert you to when a tube needs replacement.

The Baldur 70 uses two 12AX7, two 12AU7, and two 6N6P tubes in the input stage, and two pairs of 6AS7G dual-triode tubes in its output section. These are relatively inexpensive tubes—new Sovtek versions of them go for less than $20 apiece. Given AudioValve's mix'n'match claim, maintaining a pair of Baldur 70s should be easy and relatively inexpensive.

There are two front-panel switches, Power and Operate. The rear panel contains RCA and XLR jacks; the instructions say the latter is to be used for "balanced operation," and that running the Baldur via its XLR input offers the best performance, but the circuitry is not true dual-differential balanced. There are also 4 and 8 ohm speaker terminals and an IEC AC jack. The speaker terminals are of a particularly awkward variety on our review sample, encapsulated in clear plastic. Your choice is to use banana plugs, or to thread bare wires through the small holes in the plastic. However, Audio Valve says that terminals without the plastic shrouds are offered as an alternative and these will accept spades.

Components and tube sockets are mounted on a single dual-sided, mil-spec-copper circuit board laid out using CAD/CAM software. The laser-cut steel chassis is, variously, 4mm and 5mm thick and is available in black or silver finish. The tubes protrude through a PCB protector of tinted acrylic, and the black-enameled tube cage has tasteful chromed accents. The overall construction quality appears to be high. In fact, the Baldur 70 exudes a jewel-like precision and an aura of luxury commensurate with its price of $7200/pair. (Importer Elite Audio says that price may soon rise.)

To operate the Baldur 70, you throw the Power switch and wait 15 minutes for the tube filaments to warm up. Then you flip the Operate switch. If you listen to music daily, AudioValve recommends you leave the power on and the Baldur in Standby when it's not in use. If you're not going to listen for a few days, shut it off completely.

How many watts are enough?
I once wrote that reviewing tube amps for Stereophile is like appearing on stage with your pants down. You can like what you hear and rave about it, only to then read John Atkinson's measurements and find that the amp's power output is far lower than claimed, and its distortion specs far higher. Some tube amps measure so poorly, especially in terms of linearity, that the magazine's "measuring entity" is moved to call them "expensive tone controls"—and not without justification.

Tube amps tend to sound louder than solid-state for a given power output, but going from +1500Wpc down to 70Wpc does take some getting used to. Fortunately, I keep on hand a reasonably priced ($3450), 100Wpc tube amp I bought a while back—a Music Reference RM-200—as a more comparable point of reference for tube designs.

Driving a pair of Wilson Audio Specialties WATT/Puppy 7 loudspeakers, the Baldur 70s produced a somewhat compact soundstage that was usually well focused for a tube amp, and on which images appeared tightly sprung, featuring more defined leading edges and sharper transients than I'm used to hearing through tubes.