Groove Tubes 5SC & 6TM

Already well known for their valve mics and valve processors, Groove Tubes have introduced two new mics, one a valve model and the other solid‑state. Paul White compares the two newcomers.

Groove Tubes is the brainchild of Aspen Pitman, a self‑confessed tube‑gear addict with a penchant for nice microphones. Over the years, the company have built up a range of distinctive tube microphones that have gained a reputation for their warm, flattering sound, but these new models represent a departure from tradition in two areas. The first is cosmetic — instead of adopting the classic Groove Tubes cylindrical shape of earlier models, these new mics have a very Neumann‑like profile, though the heavy punched grille creates a strong visual distinction. Apparently, the open grille is inspired by early RCA mics, and a further layer of woven material made of nylon and copper forms an inner protective layer that also provides RF shielding. The second big deviation from the norm is that the model 5sc is all solid state — a kind of tubeless Groove Tubes.

To take the enigmatic tubeless mic first, the 5sc is based around a large‑diaphragm (around an inch in diameter), fixed cardioid‑pattern capsule protected by a punched metal grille. This is a true capacitor capsule with an exceedingly thin diaphragm, and requires a 48V phantom power source to operate. To quote the literature, the capsule is reminiscent of, but not an exact copy of, the classic European capsules of the 1960s. Inside the nickel‑plated brass body is a class A FET preamp with a transformer‑coupled output stage, and all the components other than the transformer are mounted on two heavy glass‑fibre circuit boards. Access to the circuitry is achieved by unscrewing the retaining ring around the output XLR connector, which allows the machined body shell to slide off.

Two slide switches are fitted into a machined recess just below the grille section of the mic, one for switching in a 10dB pad, and the other for bringing in a low‑cut filter. The Groove Tubes logo indicates which side of the mic is active. Constructionally, the mic is encouragingly solidly built, with excellent capsule protection and an attractive matt plated‑nickel finish. The recessed switches are virtually impossible to operate by accident, and the mic comes in its own foam‑padded mini flightcase. A simple but effective shockmount is provided.

Tubeless Tone

Tested with vocals, the 5sc delivers 32mV/Pa and is adequately sensitive for most studio work, which generally tends to involve close miking anyway. It has a less obviously flattering sound than the other mics in the range, and gives a greater impression of tonal accuracy. Compared with the new Rode NT1, also tubeless, it didn't sound as warm and delivered a rather less solid sound. Adjectives such as clean and crisp seem appropriate, and the sound exhibits plenty of transient detail, so it would perhaps be suited to someone who already has a rather thick or top‑light voice. This impression is corroborated by the frequency response plot, which shows a nominally flat response with a quite shallow presence hump in the 4kHz region and a more pronounced lift at about 15kHz. Those who need help to thicken their vocal sound will do better to look at the tube models in the range, but for a more straightforward representation of the source sound with a little added top‑end sparkle, this is the model to go for.

Tube Time

Outwardly, the only real difference between the 5sc and the tube‑driven 6TM is that the latter has a black nickel satin finish, and if you look a little more closely, you'll find it has four slide switches rather than two. As for shape and weight, they're identical. Because the 6TM is a tube mic, it requires one of Groove Tubes' external power supplies to provide the HT and heater voltages for the valve, and the model provided for review has two channels, allowing two mics to be used from the same supply. The power supply connects to the mic via a multicore that carries both the audio signal and the power, but as a concession to the number of people who didn't like the 9‑pin D‑connector used on the earlier mics, the company have chosen to fit a 6‑pin XLR connector to the microphone, and the 9‑pin has been retained only at the PSU end. The mic signal emerges from the PSU on a conventional balanced XLR.

Inside, the mic has a similar capsule construction to the 5sc, except that it uses dual diaphragms — again, 5‑micron, gold‑evaporated — to achieve multiple switchable patterns. Both sides of the capsule are matched to within 1dB. Unusually, the pattern switching is handled by two switches, one for selecting omni, cardioid or figure‑of‑eight, and the other for switching from wide cardioid to hypercardioid. The pad and roll‑off switches are the same as on the 5sc. Powering the on‑board preamp is a Groove Tubes‑selected 5718M miniature wire‑ended triode valve soldered directly to the circuit board. Again, the output is transformer coupled using a CineMag Nickel core transformer which is custom wound for low distortion.

In tests against the 5sc, the 6TM has a significantly warmer, more comfortable sound, but it also handles detail well. While some valve mics work well with only specific types of voice, I get the impression that this one will suit most singers. The sensitivity is broadly similar to that of its tubeless counterpart, and in typical studio situations where the mic is used close up, the background noise performance of both mics is more than adequate, the valve model only slightly noisier than its solid‑state counterpart.

Summary

Both these mics are good performers, but in slightly different ways, and the tube‑driven 6TM sounds pretty much as you'd expect from Groove Tubes, with a lively, warm character. The 5sc is the company's first tubeless mic, but it uses the same basic capsule construction and delivers more of a warts‑and‑all, tell‑it‑like‑it‑is kind of a sound. Being ruthlessly honest, I have to say that I prefer the sound of the cheaper Rode NT1 as a large‑diaphragm, solid‑state microphone; if anything, the 5sc errs on the side of sounding just a little lightweight, no doubt due to its presence boost. While lack of coloration is a trait to be admired in certain microphones, large‑diaphragm mics are generally used more for their ability to sound larger than life than for their uncompromising accuracy. Nevertheless, different voices do demand different types of mic, so if you need a mic that can open up the top end of the sound while keeping the low‑mid clean, the 5sc should do a great job.