Groove Tubes MD1/MD2/MD3

Paul White turns his critical ear to three Groove Tubes valve mics, and concludes that they are more likely to tell you what you want to hear than the unabridged truth.

Most guitar players will be familiar with Groove Tubes as a source of selected amplifier valves, and a manufacturer of quality guitar amplifiers, but over the past few years, they've broadened their range to encompass valve studio equipment, including compressors, equalisers, and microphones. It's a few years since I first looked at the MD1 and MD2 microphones, and I was impressed by the benignly‑coloured tonal character of these mics, which really flattered vocals. Both mics are still in production, but the main purpose for including them here is to compare their performance against the new MD3 model.

The MD1

The original MD1 is a side‑address cardioid capacitor mic, built into a 2‑inch diameter stainless steel tube, some 8.5 inches long. Ventilation holes in the side of the case keep the circuitry cool, and allow the glow of the valve to shine through. The mic can be mounted directly onto a conventional mic stand, using the threaded socket cut into the bass of the body, and an optional shockmount is available.

As the mic has a valve preamp, it can't be run from phantom power, so you have to use one of three purpose‑built Groove Tubes PSUs. The difference between the PS1, PS2 and PS4 power supplies is simply the number of mics they can power at one time, and any of the mics will run on any of the power supplies. The new model DP1 valve DI preamp will also run off these power supplies.

The power supply connects to the mics via a locking 9‑pin 'D' connector situated on the base of the mic body, and although these are terminally ugly connectors, they are both cheap and reliable. The audio signal leaves the PSU via a conventional balanced XLR connector, and all the mics are transformer balanced.

Valve mics are prized for their interesting tonality, not for their accuracy, and the Groove Tubes mics are no exception. The MD1 features a large‑diaphragm capsule, amplified via a dual triode valve run from an high tension of 120 volts. Looking at the frequency response curve, the overall response is nominally flat (give or take a couple of dBs), although there are a couple of peaks, one at 7kHz and another at 10kHz, as well as a deliberate (but slight) LF rolloff below 500Hz, to help counteract the proximity effect when the mic is used up close. When used at a distance of six inches, which is common in the studio, there's around 4dB of bass boost, centred around 120Hz or so, which adds a nice, intimate warmth to the sound. Being a tube mic, the noise figure isn't quite as low as for a state‑of‑the‑art, solid‑state preamp, but in normal studio miking applications, the mic is more than adequately quiet. Unlike some capacitor mics, the MD1 has no pad switch, and no high‑pass filter.

The MD1 has the bright, yet rich tone associated with valve mics, as well as a liberal dose of what I call the late‑night DJ, throaty character which flatters most vocalists.

The MD2

The MD2 is externally identical to the MD1, except that the body is coated in a suitably vintage black crackle finish. Again, a large‑diaphragm capsule (hand built using a 3‑micron, gold‑sputtered mylar diaphragm) is used. A new valve preamp circuit was designed for the MD2, incorporating a Sensitivity Level control on the base of the mic (in place of the threaded stand insert), which varies the polarisation voltage on the capsule. This provides a 20dB control range, extending the maximum SPL to a massive 150dB.

The dual‑triode, 12AX7 valve stage is designed to maintain a fast transient response, and the main difference between the MD1 and MD2 is that the MD2's response extends right up to 20kHz. Subjectively, the MD2 has all the warmth of the MD1, but has a little more air around the top end, and seems to handle delicate, transient sounds particularly well. It is still very flattering, but at the same time sounds more honest than the MD1. Both the MD1 and MD2 sound great on acoustic guitars and percussion instruments, as well as on vocals, and users also report good results on sax.

The MD3

Like the MD2, the MD3 has a crackled black, tubular body, but the basket is more conventionally shaped, and is fabricated from chromed (or maybe just highly polished?), perforated stainless steel. Inside the basket is a secondary layer of metalised sheer cloth, which provides further capsule protection, as well as RF shielding.

The capsule looks a little different to the ones used in the first two models, but it is still a large‑diaphragm (1.25 inches) design, utilising a gold‑sputtered, 3‑micron mylar diaphragm. Interestingly, the capsule has a rear acoustical port, which may be opened or closed to provide both cardioid and omni response patterns from a single diaphragm. To adjust the pattern, a small screwdriver must be inserted through one of the holes in the basket, and although the job looks pretty straightforward, it is just possible that a real klutz could slip, and trash the capsule!

As with the MD2, a sensitivity control is fitted to the base of the mic, extending the maximum SPL handling from 130dB to 150dB in 2dB steps. Included with the MD3 is an ST1 Shock Therapy shockmount, and a removable pop filter — as with the MD2, there is no standmounting thread, so you have to use a shockmount of some kind. It's worth mentioning that the Shock Therapy is a serious, heavy‑duty mount, and puts some of the competition to shame!

Once you turn it on, it's immediately evident that the MD3 is a no‑holds‑barred vocal mic, that makes no pretensions to tonal honesty. If it could talk, it would probably say something like, "Don't confuse me with the facts, I'm here to sell records!". I have a good collection of large‑diaphragm capacitor mics, most of which were chosen for their larger‑than‑life tonal characteristics, but in a side‑to‑side comparison with the MD3, they all sounded insubstantial, airy, and rather thin. The MD3 has a very solid, rather middly sound, which pushes vocals right to the front of a mix. It's hard to describe, but it's rather like having the best attributes of a good dynamic mic, combined with the warmth and detail of a more conventional large‑diaphragm mic. If anything, the sound is even more flattering to vocals than the other two models in the range (and they do a pretty good job at lying through their teeth), so that in most cases, what you hear is a lot closer to how you'd like to sound, than how you actually sound. I imagine that like other vocal mics, certain characteristics suit some voices better than others, but it's difficult to imagine any rock or pop vocal not sounding good through this beast. This is one mic that definitely sounds as distinctive as it looks — it almost had me believing that I could sing, although more conventionally held wisdom suggests that this is not the case!

Conclusion

All three Groove Tubes mics are wonderfully flattering on vocals, but the new MD3 takes the concept of rose‑coloured glasses to new extremes. Punchy vocals become solid enough to touch, while those with less powerful voices can be beefed up in a way that no equaliser ever seems to manage. The rather clunky packaging is actually quite distinctive once you get used to it, and the only disadvantage is that you have to buy a relatively costly power supply to make the mics work. This is true of all valve mics, but it does put the package price close to the top end of what a semi‑pro studio owner can afford. Even so, if you do a lot of vocal work, you might find that these mics help impress your clients, and if you buy two or more mics, or include a valve DI box in your plans, then the unit cost falls because you can use just one of the multi‑output PSUs to drive up to four mics/DI boxes. If you're serious about recording vocals, and you aren't averse to artificially flattering the end result, you really ought to hear these mics, especially the MD3.