Feb28

Written by:Rip Rowan
Wednesday, February 28, 2001 6:00 PM

Anyone who follows my articles and newsgroup posts knows that I'm a big fan of Groove Tubes equipment, particularly their condenser microphones and preamps. The MD1a, MD2a, and others are all excellent microphones that represent the best confluence of modern engineering and art.

So you can imagine that I was quite interested in the products to emerge from the acquisition of Groove Tubes by Alesis. Frankly, I was very skeptical of this alliance. Alesis is known for producing average quality pro-sumer digital gear. Groove Tubes is a boutique tube company focused on esoterica and which offers products with a real handmade approach. So when I got the opportunity to review two of Alesis' new GT tube mics, I jumped at the chance to see if these products live up to the Groove Tubes tradition.

AM62 Multipattern Large-Diaphragm Tube Mic

The AM62 is a large-diaphragm multipattern tube mic designed for instrument and vocal use. The mic is housed in a large machined brass body giving it a nice feel and weight. The mic features four polar patterns: cardioid, omni, figure-8, and supercardioid. A –15 dB pad and 75 Hz bass rolloff are provided.

The AM62 utilizes a miniature military-spec tube (GT5840M) in its preamplifier. The capsule includes oversized (> 1") diaphragms made from gold-sputtered 3 micron Mylar film and a special center-mounted gold disc which is said to extend high-frequency response and improve transient response. Unlike the original Groove Tubes mic, the AM62 uses a different kind of preamplifier. Whereas the MD1a and MD2a utilize a standard mic preamp tube (a kin to the 12AX7) and large, heavy-duty electronics, the interior of the AM62 reveals a low-voltage subminiature tube, Groove Tubes GT-5840M, and miniaturized electronics.

The AM62 sports respectable but not amazing specifications. The manufacturer claims a 20 – 20 KHz frequency response, fairly poor self-noise of 23 dB SPL yet high sensitivity of 35 mV/Pa, maximum SPL of 129 dB (without the pad), dynamic range of 107 dB, and S/N ratio of 71 dB.

For stand mounting, the mic ships with a simple clip that screws into the base of the mic body. I would have preferred a shockmount or other mount that seemed less likely to break. Also included in the package is the PSM tube power supply. All of the components are included in a sturdy but unflattering aluminum lunchbox flight case.

Real-World Use

I spent several months with the AM62 and discovered some of the AM62's strengths and weaknesses. Over time, I came to dislike the weaknesses more than I liked the strengths.

On male vocals, the AM62 is capable of providing a warm, rich, inviting sound with more "hair" than "air" on the treble. High frequency content is somewhat harsh, and the AM62 is fairly sensitive to sibilants. S's and T's can take on a nasty, distorted quality with the wrong singer. You will want to pay close attention to mic placement when working with a sibilant singer. The vocal has a good presence in the mix with a forward, slightly edgy sound, and a round, thick bottom end.

As I worked with other male singers and compared the AM62 to other mics in my collection (especially the MD1a and MD2a) I found that I never found a voice where I preferred the AM62 to the MD1a or MD2a. By comparison, the MD1a is more distorted and compressed sounding, much warmer, and has a similar sibilance. The MD2a offers low distortion and that magic glassy sheen with more treble and less sibilance. Between the MD1a and MD2a I could always achieve either a warmer, rougher, prettier, glassier, or edgier sound than the AM62.

Of course the AM62 offers several patterns while the MD1a and MD2a are cardioid only. I had several opportunities to try out the AM62 on drums, guitars, percussion, and group vocals. In all cases I found it to be a competent mic, but not especially "pretty" sounding. I did not like the AM62 on female vocals, preferring instead the MD2a or more neutral AT 4050. And I did not find any application where the AM62 was "the" mic to use.

AM62: Conclusions

So, the question. Does the AM62 carry on the tradition of the MD1a or MD2a?

The answer is No. It is a good mic, but suffers by comparison to the classic Groove Tubes models.

The MD1a is a very tubey-sounding mic: gobs of harmonic distortion, a slightly compressed sound, a very warm midrange, and a slightly diminished deep bass and treble. Sing into an MD1a and you'll immediately hear the tube. The MD2a is a beautiful-sounding mic that is warm but not distorted and offers magnificent transient response and a delicious, glassy treble that makes vowels sparkle yet doesn't seem to accentuate consonants. Both have that handmade look and feel, and both offer real sonic mojo.

By comparison, the AM62 is sort of "watered down." It lacks the richness of the MD1a, and lacks the clarity of the MD2a. And, it lacks the vibe of these unique mics. The AM62 doesn't match the workmanship or sound of the original Groove Tubes mics.

If you go looking around at web sites that sell the new Alesis GT mics, you'll see inviting text like "Alesis restyled the bodies of the microphones, but the quality remains the same." Don't believe it. This is not the same microphone at all. This is an Alesis mic with a Groove Tubes tube.

AM40 Medium-Diaphragm Tube Condenser

The mic that really got my attention was the AM40. This fun, funky mic is a medium-sized diaphragm (.75") condenser mic with a hybrid FET/tube gain stage. Three interchangeable capsules are included: cardioid, omni, and hypercardioid. The mic features a 75 Hz bass rolloff and 15 dB pad. Like the AM62, the AM40 is housed in a machined-brass body and uses a subminiature Nuvistor-type GT tube. Unlike the AM62, the AM40 utilizes relatively thick 6 micron gold evaporated Mylar diaphragms.


The AM40 offers an average self-noise rating of 20 dB, and fairly strong sensitivity, coming in at 28mV/Pa. This combination makes the AM40 an acceptable mic for recording quiet sounds. Additionally, the AM40's maximum SPL rating of 138 dB makes it useful for recording very loud sounds. All of these numbers crunch together into a highly-respectable 110 dB S/N ratio. This ought to be a versatile mic indeed.

My first thought when I saw the AM40 was "cool – it looks like a KM56". And it does. Which may partially explain my positive reaction to it.

AM40: Real World Use

I immediately wanted to hear what this mic did for acoustic guitar. And that's when I fell in love with it. The combination of tube electronics and the open sound of the omni capsule instantly created that warm, open sound I hoped the mic would be able to provide. This mic instantly became a precious commodity for rich, lush acoustic guitar sounds with just a little tube character. I can easily imagine that the AM40 would be an excellent choice for many kinds of acoustic string instruments.

I also had a lot of fun with the AM40 as a room mic for drums. Placed in an adjoining hallway (again, with the omni capsule), and pumped up with a heavy dose of compression, this mono mic created a great big fat wall of Bonham-like drums.

The AM40 is also a good mic to choose for electric guitar amps. It's a little brighter and crisper than an SM57, and if you want to get close-miked sounds without the proximity effect of a cardioid, just drop in the omni capsule.

The AM40 has the useful characteristic of not revealing its true tube nature until either driven hard or presented with a heavy bass content. So you can mic quiet, detailed sounds with clarity, yet get a little extra " oomph" from loud sounds by slightly overdriving the tube stage. Unfortunately, the use of a low-voltage miniature tube also means that the AM40 (and the AM62) do not generate the same kind of harmonic distortion produced by microphones that use larger, 12AX7-family tubes running at higher voltages. However, since the AM40 uses a hybrid FET/tube topology, I found that it really isn't capable of producing all that much harmonic distortion anyway.

I also used the AM40 to mic an acoustic bass. The combination of the cardioid proximity effect, and the generally warm bass response of the mic proved again to be a winning combination. All of the detail on the strings was present, and the bass was round and full.

Drawbacks? There are a few. Because the AM40's diaphragm is larger and thicker than the typical small-diaphgram condenser, and perhaps also partly because of its hybrid amplifier design, the AM40 does not respond to transients with quite the grace of mics like the Earthworks or Schoeps mics. Also, after only a few weeks use, the head assembly of the mic became a little loose, causing a somewhat dicey connection between the capsule and the mic. This is not a "tough" microphone. Keep it in the studio.

Alesis really has hit a home run with the AM40. The AM40 exemplifies the importance of uniqueness of design. Adding an AM40 (or a pair of them) to your mic collection will add an entirely new range of colors and capabilities to your sonic palette. If you're in the market to add some character to your mic cabinet, look no further than the AM40. It's a winner.

It's a shame that with the acquisition of Groove Tubes by Alesis, the best part of the Groove Tubes studio lineup - the MD1a and MD2a mics and MP1 mic preamp - are now relegated to Tone History. My unfounded suspicion is that the complexity (and excellence) of the design of these microphones would have required a list price well over $2000 in order to generate a sufficient profit margin - a price point that would be considered unacceptable to a budget-conscious company like Alesis. Too bad for us. Needless to say, I think I'll hang on to my MD1a and MD2a for a little while longer.

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