AKG Solidtube, January 1998

CARDIOID TUBE MICROPHONE 5/13/2004 8:00 AM Eastern

At last fall’s AES convention in New York, AKG unveiled Solidtube, a large-diaphragm vacuum tube microphone at a retail list price of $1,500. Although Solidtube’s pricing is attractive, and it sounded good during a quick demo at the show, how does this mic perform in real studio conditions? Mix decided to find out.

Outwardly, Solidtube is hardly a “no-frills” model; the mic package includes an aluminum flight case, power supply, shock-mount and windscreen. But to meet its affordable pricing, some concessions were made. Solidtube is a single-pattern (cardioid) mic. The mic body itself is cast-pot metal rather than the brass housing featured on AKG’s top-of-the-line tube C12VR, and the -20dB pad switch (for an impressive SPL handling of 145 dB!) is plastic and has an inexpensive feel. But Solidtube’s A-weighted self-noise is rated at 20 dB, which is better than most tube mics.

Under the grille is a newly designed condenser capsule with a 1-inch diameter, 6-micron-thin, gold-sputtered Mylar diaphragm. When powered up, the mic’s transparent-red AKG logo is illuminated by the faint glow of the 12AX7a tube inside. The 12AX7a provides impressive performance (it surprised me!); it is also readily available and reasonably priced. The mic body also stays cool, even after long sessions.

Solidtube comes with a slightly too-bright lemon-yellow foam pop filter, which you shouldn’t need anyway, as the fine mesh grille offers excellent protection from plosive syllables. The six-conductor cable that connects the mic and power supply is an ample 30 feet long, but the 3/16-inch-diameter cable is too thin, is highly susceptible to kinking and has generic, no-name XLR connectors. Anyone buying this mic should eventually plan on replacing the stock cable with a larger-gauge, more durable cable, which will not only be more reliable, but will also offer improved audio performance and increased protection from outside electrical interference.

The mic snaps securely into place, and in a rare example of form and function in harmony, the raised Solidtube logo locks the mic into the mount, which is elegantly simple and highly effective against shocks, bumps and thuds. Interestingly, there are two channels in the mount for keeping cables in place: One fits the stock cable exactly, and the other is designed for a larger-diameter cable. Hmmm—the base of the mic body also offers standard 5/8-inch threads for direct stand-mounting, but the shock-mount is so nice why bother?

The power supply features a -12dB/octave bass-cut filter, ground lift switch and an LED power-on indicator. It’s shipped with the voltage set for 230 VAC, but I recommend setting it for your local standard before use. AKG thoughtfully includes two removable IEC power cables (U.S. and Euro standard) so you jet-setting engineers won’t have to use your shaver adapter if your next tracking session is at Capri Digital.

In my first session with the Solidtube, I used it on acoustic bass for a jazz trio (piano/bass/brush drums) recording. I set the mic on a short stand, about 15 inches from the “f” hole and aimed slightly toward the bridge. The results were full, rich and creamy, with even reproduction throughout the instrument’s range—no bumps, peaks or dips. Oooh!

On my next date, I was tracking male and female vocals, and I had a chance to compare Solidtube with a C12VR. A couple of things became clear. In the cardioid setting, the C12VR has tight pattern control, while Solidtube’s cardioid pattern gets progressively wider in the upper midrange, becoming nearly omnidirectional above 4 kHz. In this case, we were overdubbing, so rejection/bleed wasn’t an issue, but it’s something to keep in mind for multi-mic situations. Both mics have a nice warm low end with just enough—but not too much—proximity effect. But Solidtube’s upper response was smoother than the cardioid C12VR, and it was perfectly suited for female vocals where too much top end can be edgy. Male vocals had a natural, full bottom end with Solidtube, but in this case, I preferred the C12VR’s extra 5 to 10kHz top-end sizzle over Solidtube. Of course, for the $3,000 or so price difference between the two mics, you could buy a really nice equalizer and add a couple dB here or there.

Anyone looking for an affordable, versatile studio mic may want to consider adding one—or a couple—AKG Solidtubes to their mic locker. Just budget in a couple extra bucks for a better cable and you’ll have a solid performer for years to come.


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