Langevin Dual Vocal Combo

Judging by the ever-increasing number of valve-based designs on the market these days, you could be forgiven for believing the valve is some kind of recently discovered, magical cure-it-all device. Of course, if you did come to this conclusion, then you would have fallen – hook, line and sinker – for a truly global marketing conspiracy. At the core of this global master plan is our latent desire to ‘warm up’ all those nasty digital signals we all have to contend with these days. Conveniently, valves are associated both with audio’s analogue heritage, where warmth was the only option, and also with generating heat. So, basically a marketing manager’s dream, then.

But back here in the real world, of course, things are not always quite that simple. If manufacturers are returning to valve-based designs for amplifying signals, then it is because they’re actually rather good at it, albeit a tad more cumbersome and fragile than their solid-state counterparts. However, to believe valves are the only option would also be foolish. Take a quick look at history’s most revered designs – Focusrite, API, Langevin, Neve, GML, to name but a few – and there’s not a valve in sight.

So where’s this all leading? Langevin – pronounced with a soft ‘g’, by the way – was one of the first pro audio companies back in the ’50s and ’60s. First they produced valve-based equipment, then transistor-based gear, and their transistor mic preamps gained them quite a in reputation the recording industry. In 1992 Manley Labs bought the rights to the Langevin name and designs. Manley’s reputation up to this point was as a manufacturer of high quality valve gear for audio and hi-fi. So, over the last few years, they’ve developed the Langevin name to cover their solid-state products. These include updated versions of classic Langevin designs and the Pultec EQP1A equaliser. The latest in the Langevin range combines two existing units, the dual mic pre with EQ and the dual opto-limiter – hence the ‘Dual Vocal Combo’ tag.

Overview

As you have probably gathered, the Dual Vocal Combo is a twin-channel unit, offering a mic pre-stage with EQ, in this case passive, and then an opto-limiter, with stereo link option. The electronics are discrete transistor, so there are no op-amps in the signal path – although there are a couple driving the meter circuits. As the name suggests, the Langevin is designed with vocal recording in mind, and could seem a little basic compared to other channel strip designs. But the philosophy here is one of simplicity. The EQ is shelving, and at only two selectable frequencies for each band.

The opto-limiter is also a very simple design, with only gain reduction and gain make-up controls. To allow connection of high impedance sources, the Langevin does feature a front panel jack connection, which is a nice feature. So, in essence, this unit is all about getting the cleanest signal to your recorder of choice at the right level with the minimum of fuss. With the rights to the old Langevin designs, as mentioned above, Manley have been able to modify some of the characteristics, and improve upon, some of the components used in the ’60s. The mic pre is therefore a modified version of the original Langevin AM-4 channel strip.

It incorporates Manley’s own ‘6469’ transformer mic amp stage and is a Class A discrete amplifier design, which uses a minimum level of negative feedback. It offers up to 53dB of gain, if you modify the internal trimmer, although it is factory set to a maximum 45dB. There are two shelving EQ bands, offering 10dB of cut/boost at selectable frequencies – 40Hz and 80Hz for the low band, and 8kHz and 12kHz for the high band. As you would expect, the EQ can be completely bypassed, if so desired.

Phantom power (48V) can be selected individually for each channel, and switches are of the ‘pull-to-latch’ type, which avoids any accidental loss of mic power. Unfortunately, there’s no phase reverse switch, which is a bit of a pain.

The opto-limiter is also based on the old Langevin designs, but incorporates some elements of the Universal Audio LA limiter designs. Manley have already put this type of design into use in their valve units. So, this is essentially a solid-state version of the Manley opto-limiter. The opto circuit makes use of a Vactrol cell (a component incorporating a light-dependent resistor and a light source). This has certain inherent response characteristics that dictate the behaviour of the limiter. As with the classic opto limiters – Universal Audio’s LA series, for example, the controls are pretty straightforward: reduction and gain make-up. However, this simplicity hides quite complex response characteristics. In essence, the unit has a pretty fast attack, but tends to be faster if the transient is faster. The gain reduction is again dependent on the level of the signal – the higher the level, the higher the ratio, up to a maximum reduction of around 20dB.

Similarly, the release characteristics are signal-dependent, but are between 10 and 20 times slower than the attack rates. Thankfully, the VU meter can be switched to gain reduction, as well as output level, so you can see what’s going on. The gain make-up control itself offers an additional 15dB of gain, which brings all but the most heavily compressed signals back up to a reasonable level. A quick look under the Langevin’s lid reveals an extremely tidy and well-constructed unit. The mic transformer and mains transformer are both custom-made Manley devices, and the wiring and circuit board quality are exemplary.

Removal of the grille-style lid is very easy, requiring removal of only two screws. This is useful as the lid needs removing to access the various trim pots that line up the meters, adjust the stereo linking, and tweak the mic amp gain range (which can be changed from 38dB to 53dB maximum). The back panel is also very well laid-out. The IEC mains socket is dead-centre, with accompanying slow-blow fuse access. As seems common with pro gear, there are also two earthing posts, one connected to the circuit earth, the other to the case and mains earth. This is very useful for removing that unwanted ground loop that sometimes appears for no apparent reason.

Audio connections are pretty straightforward and mirrored for both channels – the mic input and channel output are both on XLRs. However, there is also a balanced input to the limiter circuit on a TRS jack socket. This actually cuts the mic channel signal, so unfortunately it’s not possible to use the mic pre and limiter on separate signals. In addition to the balanced output, there is also an unbalanced one on a TS jack socket. The reason for this is that the output is transformerless, so connecting the balanced output to an unbalanced input will result in a 6dB loss in level and a little distortion, probably.

In use

The first thing you’ll notice with the Langevin is that it’s actually quite heavy, even though there’s plenty of room for air to circulate. This must in part be due to the many traditional components (capacitors, resistors and transistors rather than ICs). Also rather striking is the red brushed steel front panel and traditional black knobs. All in all, the unit feels very solidly constructed and combines traditional and contemporary styling to good effect.

On powering up, the meters take a couple of seconds to settle down and come to rest either at zero or below –20dB – depending on whether they’re set to output or gain reduction. It’s probably worth explaining at this point that the Dual Vocal Combo has a number of trim pots to align the meters, set the gain ranges of the inputs and even trim the 36V DC supply to the circuit board (14 trim pots in total).

Thankfully, in the normal course of events you won’t have to go near more than a few of these, and then only to tweak the stereo link and meter zeroing. However, Manley do warn that the unit could take 15 minutes to settle down after power on, and also that the meters may drift by half a dB over the course of the day. In fact, the review unit seemed quite good in this respect, with only a little tweaking needed to fine-tune stereo limiting.

Although aimed at vocal recording, the Langevin test kicked off using a classical guitar. This proved quite interesting, as it felt as if we were using a lot of gain, with the attenuator knob at well over a quarter past, but, in fact, this is what you might expect – 40dB of gain for miking a quietly-played classical guitar is about right. However, because you are essentially attenuating the mic amp circuit, it’s stunningly quiet.

Switching in the EQ proves very encouraging with the 12kHz band adding some useful ‘air’ to the sound. For this application, the limiter also produces good results. One thing that is worth checking is that the limiter gain make-up is at unity. As this isn’t marked, it’s a case of trial and error, but basically it’s at about one o’clock. Of course, also worth bearing in mind is that the limiter circuit incorporates a further 15dB of gain, should the mic amp really not prove to be enough. This may prove quite useful if the 25dB of gain you get at the instrument jack input on the front is not enough.

Moving on to some vocal recording, the Langevin really came into its own. Even if you have a favoured compressor for recording vocals, you may find yourself trying the opto-limiter out, anyway. Of course, if you’re trying to get the cleanest signal to tape, there really is no need going anywhere near any other bit of gear, apart from the tape machine.

The opto-limiter is ideal for vocals – it’s as simple as that. As far as the sound of the unit is concerned, strange as it may seem, ‘warm’ is a term that springs to mind, but also natural and real-sounding.

Finally, linking the two channels for stereo limiting was very straightforward. Both sets of controls remain active, with the control voltages generated by each channel being combined to achieve stereo limiting.

Verdict

The Dual Vocal Combo is not a ‘do-everything’, bells-and-whistles-style channel strip – neither does it have bags of gain, so it’s probably not a first choice for ambient location recording. What it does have is a character of its own, both as a mic pre and as a limiter. A few pieces of gear have been hard to part with over the past year, and, strangely, they always seem to be mic preamps – Focusrite’s Producer Pack immediately springs to mind here. The reason quite simply is that when you get your hands on gear like the Langevin, you tend to rediscover just how good things can sound without resorting to EQ’ing and other corrective procedures. Do we really have to give it back? Oh, alright, then…