Groove Tubes MD1b FET

This new mic is a reissue of Groove Tubes' first large-diaphragm condenser, but with solid-state electronics replacing the valve to offer a more affordable package.

The American manufacturer Groove Tubes was founded towards the end of the '70s by Aspen Pittman — a man with a long-standing fascination for valve audio equipment. From its early beginnings in a garage workshop, the company have grown into an international business manufacturing and distributing a wide range of high-quality valves, alongside a range of valve-based guitar amps, speaker systems, and recording equipment including microphones, compressors, preamps, and equalisers. Among an impressive line-up of microphones, the company offer both valve and solid-state medium- and large-diaphragm models, with either fixed, interchangeable, or variable polar patterns. The GT55, GT57, GT66, and flagship GT67 models were reviewed in SOS April 2003, but the subject of this review is an 'enhanced' reissue of the very first Groove Tubes valve mic, the MD1 or Model 1, with solid-state electronics in place of the valve to bestow a significant price reduction.

Hardware Overview

The original Model 1 valve mic has been completely reworked and has been reissued as the MD1b Vacuum Tube. However, its solid-state sibling is the MD1b FET. Both mics share exactly the same capsule, output transformer, and mechanical construction (albeit with different finishes), but the FET version employs a Class-A FET-based impedance converter and preamp in place of the original valve. The review model was supplied as part of a pair (serial numbers 302023 and 302024), each mic shipped in its own cardboard protection case and the two kept together by an overall sleeve. Inside each foam-lined cardboard shipping box is a fabric-covered, foam-lined wooden box which contains the microphone, standmount bracket (complete with an adaptor for converting from 3/8-inch to 5/8-inch threads), warranty card, and handbook. The latter — Choosing & Using Microphones — is well written, with good background technical information and practical mic-placement advice, but offers little specific information on the MD1b FET, and there are no quality-control test plots or even specifications included at all.

The microphone is housed in a cylindrical metal case, measuring 191mm long (7.5 inches) and 50mm (just under 2 inches) in diameter. It weighs roughly 1400g, and the steel case is painted matt black (the valve original is silver), with a dual-layer wire-mesh grille over the top and on the front and rear faces around the capsule. The case is held in place by two screws at the base, and has various holes, cutouts, and etched markings on it.

The forward axis of the cardioid pattern is identified by the etched model name at the bottom and a cardioid graphic at the top of the case front, along with a grid of twelve holes. These were intended to allow the user to view the valve inside the sibling Model 1B tube mic (as well as help to promote a cooling airflow), but serve no real purpose here. The rear side of the mic's case features an inverted cutout Groove Tubes logo designed to look right when the microphone is suspended upside down. The mic's serial number is not visible externally — it is printed on a label glued to the output transformer, and can only be seen after removing the microphone's outer case.

Standmount Confusion

The microphone is supported by (or suspended from) a simple bracket which screws to the base of the mic. A chunky plastic ring cup extends from the mic stand adaptor and a (separate) threaded metal collar passes through this ring to screw into the microphone's base, leaving the mic's XLR output connector accessible through the centre of the construction. Unfortunately the correct method of assembly is not entirely obvious, and the complete lack of any instructions doesn't help, so it is very easy to fit the parts together incorrectly! Fortunately, if the adaptor is assembled incorrectly the microphone will still be held reasonably securely, but it's far harder to tighten and adjust. The difference may appear fairly subtle in the photographs, but the correct form is significantly easier to use. Note that, when fitted correctly, the 'cup' of the collar sits around the microphone's base, and the knurled locking ring ends up slightly proud of the collar. If the plastic collar is fitted the opposite way around, the knurled part of the locking ring sinks into the cup and therefore becomes difficult to adjust. Sadly, the adaptor also has to be removed before the mic can be put away in its case.Correct assembly.

The supplied adaptor incorporates no shock protection at all, although there is an optional basket shockmount design that supports the mic from elasticated loops. However, the microphone capsule is mounted on a pliable rubber internal suspension, and this does offer a degree of protection from mechanical shocks anyway.

No technical specifications are given at all, but an Internet search eventually provided the following figures. The frequency response is claimed to extend between 20Hz and 20kHz, and a response trace I found suggests the mic is fundamentally flat within ±1dB up to about 8kHz, above which there is a peak in the response reaching +4dB at about 12kHz. This high-frequency peak is a common characteristic of most of the Groove Tubes mics, although it would appear to be better controlled here than in some of the other models.The difference between correct and incorrect (shown) assembly of the standmount's plastic cup and knurled metal ring is easily confused, and there's no indication in the handbook as to which is the correct configuration.

Output sensitivity is quoted as a very generous 32mV/Pa, with a maximum SPL of 134dBSPL for one percent distortion. Groove Tubes claim that their quality control is such that every mic is 'matched to the appropriate 'golden microphone' specification within ±1dB across the entire frequency range', and that even more accurately matched stereo pairs are available.

The microphone's self-noise figure is a little disappointing by modern standards, at 22dBA — a full 15dB noisier than the Neumann TLM103, for example. Having said that, the Neumann produces almost 4dB less output level, which mitigates the situation slightly. The mic has a transformer-balanced output with a nominal 200Ω output impedance, and requires 48V phantom power.

The capsule itself is a traditional 1.1-inch design constructed from brass, with a three-micron evaporated-gold diaphragm. The capsule is mounted on a metal post supported by a flexible rubber cone to provide some mechanical isolation from the microphone body. The electronics are carried on two printed circuit boards mounted either side of the microphone's internal frame, and conventional components are used throughout. PCB markings suggest the same boards are used for the GT55 and GT77 mics as well.

The front board appears to carry mainly the Class-A audio circuitry, with a metal-canned FET at the top handling the capsule's signal and a second transistor evident further down the board. The rear PCB appears to carry the power-supply components, and a compact output transformer sits at the base of the microphone. A nice feature is that the phantom supply circuitry has been designed to ramp up and down slowly (over about twenty seconds) to minimise the risk of loud pops and bangs on the mic's output when connecting things up.

Listening Tests

As would be expected, the MD1b FET benefits from the use of a decent pop shield — the internal gauze grille offers little protection from plosives when used for close vocals. The mic seemed slightly more resilient to stand-borne vibrations when suspended from above (rather than below) using the supplied standmount adaptor. However, I found mechanical noise remained a problem on occasions, and with no integral high-pass filter a decent elastic shockmount would certainly be a very useful purchase. A suitable device is available as a cost option, but I really think Groove Tubes or their distributors should consider including one with the MD1b FET as standard. After all, most of the Chinese microphone manufacturers seem able to include free shockmounts with even their least expensive mics these days.

My first impression of the MD1b FET was of a very nice and versatile mic for the money, and I have been using the supplied pair alongside the rest of my permanent mic collection for some time. I was particularly interested in how the mic fared against my most comparable mics: the AKG C414B ULS, the CAD M179, the Neumann TLM103, and the Audio-Technica AT4040. All of these are large-diaphragm, true-condenser mics with solid-state electronics, but all of them are more expensive — between 1.5 and five times the UK price of the MD1b FET. Interestingly, they all exhibit a high-frequency presence peak — although with varying degrees of peakiness and bandwidth — and similar variations in polar response with frequency.

The MD1b FET had by far the highest output level of the collection, and needed almost 10dB less gain than the quietest of its review rivals, the AKG C414B ULS, but it was also clearly the noisiest too. However, its self noise wasn't an issue when used for close-miking applications, and only became an irritation when I tried to use a pair of MD1b FETs as a distant stereo pair to cover a small string group.

The AKG and Neumann mics sounded the smoothest and most refined of the collection, the AKG seeming to have a better bass response when used at a respectable distance too, but these two mics are significantly more expensive that the MD1b FET. The obvious presence peaks of the CAD and Groove Tubes mics sounded particularly similar to each other, while the Audio-Technica's presence hump seemed to start a lot lower — around 6kHz — and was broader than the Groove Tubes and CAD mics, which appeared to have narrower peaks starting around 10-12kHz. This characteristic tended to give more a sense of 'air' instead of the sharper presence 'edge' typical of the Audio-Technica mic. The AKG's peak was the most subtle, followed closely by the Neumann's — although neither were as flat as my reference Sennheiser MKH40s. However, I should stress that these are all relatively minor differences when heard in isolation, and which will tend to favour different mics for different sources.

Overall, I found the MD1b FET to have a typical large-diaphragm character with a well-behaved polar response and a reasonably balanced off-axis response, which means that spill from off-axis sounds won't become too badly coloured. The general sound quality is fairly rich and full — tending towards the 'larger than life' sound typical of good valve mics, but not quite reaching that lofty goal. The mic is suitable for a broad range of close-miking applications, but it wouldn't be my first choice for more distant mic techniques because of the relatively high noise floor.

The airy top end and rich mid-range suited most vocals well — although not all, especially sibilant female singers — but male voices in particular were portrayed with a nice, full bodied character and good articulation. The high maximum SPL figure also allowed the mic to be used for miking up guitar cabinets, percussion, and brass sections. For the latter I found I often had to tilt the mic down to help reduce the effect of that high presence peak, but the same peak proved beneficial in drum overhead applications, where transients were delivered with clean, crisp attacks.

Overall then, I'd put the MD1b FET in a similar category as mics like the CAD M177 and Audio Technica AT4040 in terms of the general performance and sonic abilities. Its price is not too dissimilar to the quieter CAD M177 mic, and it is worth noting that the CAD M177 VP version at £188 is supplied with a suspension shockmount and pop shield as standard.

Unsurprisingly, the MD1b FET is not quite as smooth and detailed as the Neumann TLM103 or AKG C414B ULS — although they both have their own idiosyncrasies anyway — and not as rich and involving as Groove Tubes' more expensive valve mics. However, it does provide a very good and usable sound quality at a very attractive price which competes closely with many of the better Chinese offerings, and its vintage styling and sound character will have strong appeal for many. It's certainly well worth auditioning, particularly for anyone considering a new condenser vocal mic.