GTELECTRONICS AM40

Apr 1, 2001 12:00 PM, By John Ferenzik

           
 

With the increased reliance on digital recording media, the demand for vacuum-tube condenser microphones, those beloved tools capable of imparting “warmth” to digital tracks, has never been greater. Unfortunately, vintage tube mic prices have soared, thwarting the desires of many personal-studio buyers. Even among the spate of new tube mics, prices rarely fall below $1,500, and typically they're much higher.

The GT Electronics AM40 provides some relief at the relatively reasonable price of $999. The deal is more attractive yet because the mic's design helps it cover a lot of ground. Rather than qualify as a large-diaphragm mic (usually one with a diaphragm an inch or larger in diameter) or a small-diaphragm mic (which typically has a ½-inch or smaller diaphragm), the AM40 is described as a medium-diaphragm condenser, thanks to its ¾-inch diameter diaphragm. This, in addition to its tube circuitry and top-address design, puts the AM40 somewhere between the usual “instrument mic” and “vocal mic” categories. (The GT AM30, which employs Class A FET electronics rather than tube circuitry but is otherwise nearly identical to the AM40, was included in the EM comparison review “To Tell the Truth” in the March 2000 issue.)

I tested a pair of AM40s for this review. Each mic arrived in a foam-filled aluminum flight case, sheathed in a drawstring pouch of silky black fabric. Also packed neatly inside each case were the PSM power supply and AC-power cord, a hard-mount mic clip, and a 25-foot, 6-pin XLR cable.

SOLID DEAL

The AM40 is a solid-feeling mic with a medium-diameter cylindrical body and an attractive burnished silver finish. Two switches are located just below the mic's removable grille cap, one for a 15 dB attenuation pad and the other to activate a 75 Hz highpass filter.

The AM40 ships with the AMC1 cardioid capsule. I also tested the AMC2 supercardioid and AMC3 omnidirectional capsules ($129 each), which can be purchased separately. The capsules are easy to switch out; however, read the manual carefully before changing them. While attempting to unscrew the AMC1, I almost removed the top of the mic — a relatively easy way to mangle the AM40's electronic innards. Fortunately, the instructions are specific and easy to follow on this point.

The AM40's power supply is housed in a compact metal enclosure with a solid heft to it. Unlike some tube mics' large and bulky power supplies, the compact PSM is a cinch to put in a rack or conceal. The PSM's input is a special 6-pin female XLR locking connector and the output is a standard 3-pin male XLR connector. Because the PSM is strictly a power supply and not a preamp, you still need to run the audio output through a mic preamp to get enough signal level for recording. But unlike some tube-mic power-supply boxes that can be damaged if phantom power is inadvertently supplied to the signal chain, the PSM rejects phantom power without damaging either the power supply or the mic — a nice fail-safe feature.

DOWN TO BUSINESS

I put the pair of AM40s to work in my personal studio for a variety of applications, using them to record tracks of my material and on client's projects. I cut most of the tracks on an ADAT XT-20 or direct to hard disk through a Digidesign Digi001. I also auditioned the mics in the analog realm using a Tascam 38 8-track tape recorder. In addition, I ran the AM40s through a variety of mic preamps, including those in my Yamaha 03D console and several outboard units including the dbx 1086 and A.R.T. Pro MPA.

Outside of my studio, I had significant assistance from John Anthony at the Maja Audio Group, a multiroom studio in the heart of Philadelphia's Society Hill Section. Anthony graciously lent a hand with A/B comparisons between the AM40 and comparable mics from Maja's sizable collection. Extreme care was taken to duplicate the signal path and microphone position when the AM40 was pitted against another mic. I also strove to ensure that the timbre and dynamics of performances recorded with different microphones were as close as possible to those of the AM40's.

Anthony gave the AM40s some real-world workouts on recording sessions with various artists booked at Maja. All tracks at Maja were recorded to Pro Tools through an Avalon VT-737sp for mono overdubs and custom-made mic preamps from Mill Creek Audio for stereo applications.

BASEMENT BASH-A-THON

To test the AM40s as drum overheads in my studio, I flew them about two to three feet above a great-sounding old Gretsch kit, positioned on separate boom stands roughly four feet apart with the mic capsules angled slightly away from one another. I routed the signals through the preamps on a Mackie 1202-VLZ mixer and logged the results to 1-inch tape at 15 ips on my Tascam 38.

In this analog application, the AM40 mics sounded, well, smashing. Compared to the Shure SM81s or Crown CM-700s (both are small-diaphragm condensers) that I normally employ, the AM40s exhibited a smoother overall response with warmer mids and plenty of air above 10 kHz. The AM40s also nabbed more of the low ringing tone (around 160 Hz) from the ride and crash cymbals, lending a visceral “body” to the crash cymbal. In addition, the tube mics minimized the toms' tendency to sound muddy in the lower mids from shell resonance — great news for the Keith Moon lurking in all of us.

I also tried close-miking the snare drum with the AM40, this time running the signals to the ADAT at 20-bit resolution and to hard disk through the Digi001. For this application, I usually use the ubiquitous Shure SM57, so I was curious to see how the AM40 would fare. I was not disappointed. Overall, the AM40 sounded like a warmer version of an SM57, yet with more sparkle in the high end and cleaner, more detailed presence in the midrange. The mic also captured plenty of snare-wire detail in the 800 Hz to 1.5 kHz range, yet there was none of the tube distortion “fuzz factor” you can get with certain older tube mics. If you need a microphone that handles the ruffs and ghost notes on a busy jazz snare track without being overwhelmed, the AM40 is a formidable ally.

FAIRY DUST

For a song submitted by a client on an ADAT tape, I had to fabricate a world beat arrangement using various hand drums and small percussion instruments. The client's tape provided four tracks: a fretless electric bass, an acoustic guitar, a reference vocal, and a relentless drum-machine-generated sidestick for the click. On those tracks I stacked congas, bongos, a dumbek, an egg shaker, claves, a tambourine, and a triangle, stopping just shy of the proverbial kitchen sink. Most of the tracks were mono, but I miked the bongos and congas in stereo using the AM40s and the SM81s in XY configurations.

It wasn't long before I opted to use the AM40 mics exclusively. With hand drums in particular, the AM40 seemed to sprinkle a bit of “fairy dust” on the tracks. The mics bathed congas and bongos in warm, woody hues and accurately rendered those instruments' unique resonances. The dumbek had the same treatment; a single AM40 caught the clay-bodied instrument's hollow, earthen ring and the sharp patter of finger rolls on the paper head, managing to sound bright and warm at the same time.

All other small percussion overdubs benefited from a touch of the AM40's sorcery. The shaker was appropriately “sandy” yet not scratchy; the clave was bright but not piercing; the tambourine's jangle did not sound uncomfortably metallic; and the triangle's diminutive tinkle seemed less small. Some of the mic's magic seemed traceable to a “warm spot,” a subtle boost between 375 Hz and 600 Hz, that lent a bit of midrange presence to the small percussion instruments. The SM81 also did an accurate job in each of these instances, but it sounded a tad more sterile.

ROOM TO GROOVE

Of the tracks recorded at Maja, the AM40 did its most impressive work when capturing room ambience, especially in the studio's big room. In one setup, I placed one AM40 at a distance behind the drum kit and the other across the room in front of the kit. The resulting tracks provided a terrific bottom-of-the-giant-tank effect and set the bossa nova beat swimming — but not drowning — in woody ambience. A single AM40 also delivered on a track of backbeat hand claps: the claps were warm and realistic sounding and let the room sound “join the band.” The sound quality of the room tracks recorded with the AM40 approached that of similar ambience tracks cut with Maja's vintage Telefunken ELAM 251 — a pretty amazing feat, given that legendary mic's down-payment-on-a-home price.

UNUSUALLY CLOSE

Most engineers use a large-diaphragm condenser mic when recording lead vocals to capture the voice's nuance and subtle quirks. But sometimes a smaller condenser or even a dynamic mic can have just the right sound for a particular song, musical style, or vocalist. To test the AM40 as a vocal mic, I tracked my voice doing a lead part for a folk-rock tune I wrote.

First I cut the lead vocal with the AM40, and then I followed up by doubling the performance with the SM81 and CM-700 on subsequent passes. Compared with the other two mics, the AM40 provided a bit more low-mid detail (around 375 Hz). It also had what sounded like a 3 dB boost around 1.5 kHz, which added a smooth “hi-fi” presence to the track and helped it cut through the wash of guitars. In addition, the AM40 track had a subtle warmth that I could only attribute to “tube voodoo.”

I also used the AM40 to overdub some background harmonies on the same song. The mic again delivered, imparting a warm “tube flair” that helped the harmony lines cohere and made for a nice blend at mixdown.

Typically, small-diaphragm cardioid condenser mics are more prone to bass boosting from the proximity effect than are large-diaphragm cardioid condensers. However, when worked close, the AM40 exhibited less bass boosting than even the large-diaphragm mics I compared it with. I could lean in and work this mic in a way that might have me living in downtown “Boomville” were I using, for example, an AKG C 414 or a Neumann U 87. Of course, this is not to say that the AM40 is better than those studio vocal stalwarts — just that it let me record vocal tracks at very close proximity without building up too much bass.

GUT FEELING

For another client's demo, I used the AM40s on nylon- and steel-stringed guitars. I positioned the microphones as a spaced pair on each instrument, with one AM40 aimed at the fretboard near the nut and the other close to the sound hole, angled slightly off-axis to mitigate any boominess.