Dual Mic Preamp
Given a big enough budget, analogue electronics designers could deliver virtual audio perfection decades ago. Today, the same level of performance can be achieved for a mere fraction of the price and technical specifications become increasingly meaningless as everything boasts near-identical (and almost always exemplary) figu
Trident Audio S20 £1169
Variable high-pass filter.
Solid technical performance.
Both balanced and unbalanced outputs.
Gimmicky glow behind front-panel grille.
A dual mic preamp in a retro-styled package. The solid technical performance and hint of vintage sound quality almost play second fiddle to the visual presentation.
One company taking advantage of this popular trend is Oram, or more particularly its subsidiary Trident Audio. Following on from the fastidiously accurate replica of the Series 80 console channel in the S80 Producer Box (which I reviewed back in SOS December 2000), Trident Audio have now released a simple, no-frills, two-channel mic preamp called the S20. The company claims the raison d'être of the S20 is to provide the 'warm sound quality' typical of vintage, or at least veteran, audio equipment, and which they claim to be missing from modern products. I'm not sure I'd agree with that as a generalisation -- there are plenty of good-sounding modern mic preamps around -- although I can accept that many budget designs frequently sound a little bland and cold.
First Impressions & Second Thoughts
Cutting straight to the chase, as they say, the Trident S20 is as much about appearance as it is sound. This is not a product which claims to redefine the state of the art, or even to provide an accurate replica of a historic product. It is designed, basically, to appeal to anyone who requires a competent mic preamp which has great visual appeal.
The plain 1U rackmounting black case has clear legends and simple, coloured aluminium knobs which shout 'retro styling'. Yet in contrast, its bar-graph meters employ rows of bright blue LEDs which give a very modern appearance. However, the most unusual aspect is a grille to the right of each channel's controls, which hints at the inclusion of internal valves... Indeed, a warm glow can be observed through the white dust filters behind these grilles, and the brightness increases with the audio signal level -- particularly when it is in the top half of the meter scale. As if to continue this ruse, the publicity material for the product even claims it to be 'truly tube-like'.
Unfortunately, this is really just a clever visual gimmick -- the S20 is entirely solid-state and the glow is provided by a series of orange LEDs mounted behind the grilles. So now you know -- if you enjoy the effect, fine, but I wouldn't want you to be misled.
The front-panel facilities are very simple. Both channels are identical and start on the left with a rotary switch offering A or B input selection from the two rear-panel XLR sockets (the audio signal is actually switched via a sealed relay). Next is a white button to impose a polarity inversion on the selected input, followed by the input Gain control. This is calibrated from 0 to 60dB and has a soft detented feel as it rotates. In fact, if the balanced output is being used, the true output gain is 6dB higher -- so 66dB is available overall. A red phantom power switch comes next, followed by a fully calibrated 6dB/octave high-pass filter which can be adjusted between 5Hz and 200Hz. This is the only part of the S20's circuitry which shares any direct heritage with the original Trident console products. When activated, phantom power is applied to both rear-panel sockets simultaneously.
The bar-graph meters span -20dB to +8dB with an amazingly bright white LED at zero (corresponding to +4dBu at the rear-panel output), and a red LED at +8dB. The only other front-panel facility is a black rocker switch on the right to power the unit. There is no indicator to show when the unit is powered other than the hint of an orange glow from the grilles, although this is hard to see unless the ambient light is fairly low.
The rear panel groups all four XLR inputs together on the right-hand side (as viewed from the rear). These connectors are identified as Source A and Source B within areas marked Channel A and Channel B. The two channel outputs are provided, with both balanced XLRs and unbalanced quarter-inch jack sockets. To the left are mains inlet, voltage selector, and fuse holder.
Internally, the electronics are housed on a main PCB, with a smaller separate board for the linear power supply which, unusually, carries two encapsulated toroidal transformers. The two audio channels are completely independent of each other, with circuitry appearing to occupy both sides of the board -- some surface-mount components are located on the underside with a couple of ICs per channel on the top surface in sockets. The familiar SSM2017 op amp seems to be handling the input stage, while an NE5532 is used to drive the output with a +28dBu capability -- both pretty conventional and a typically modern solution. Apparently, this mic input design, which is entirely transformerless, is John Oram's quietest to date.
The S20 is certainly a competent mic preamp and worked well enough with a variety of capacitor and dynamic mics across a wide range of budgetary levels. Its sound character has, if anything, a tendency towards a mild richness or warmth -- although this is not immediately obvious in the manner of, say, a genuine valve-based preamp. This subtle character seemed to be revealed most with percussive material or anything with complex transients, which seemed to be rounded and smoothed slightly in a musically flattering way.
The variable high-pass filter is very handy -- I wish more preamps would provide a similar facility to permit conscious control of unwanted subsonic noises. And with half the control's rotation covering the range from 5Hz to 35Hz, it is easy to fine-tune the optimum turnover point.
The input selection facilities are less impressive, and I would question their worth. It is suggested that the two inputs -- Source A and Source B -- can be used to compare two mics or to switch between mic and line sources. Unfortunately, since this switch is right at the front end of the preamp, with a hefty lump of gain following immediately, there is an inevitable and very loud 'splat' each time the source is changed. The worst case is with typical mic gains and phantom power switched on -- the splat frequently illuminated the +3dB LED in the meter bar-graph and could potentially destroy monitor speakers! The problem is not quite as bad if phantom power is switched off, or if the gain is lower, but it is still unpleasant. Of course, if you are prepared to dip the gain manually when switching you can minimise the problem, but why should you? This is not a budget product, nor is it trying to replicate a vintage circuit design, so there is no practical reason I can see why the output could not be automatically muted for a brief instant when the source switch is operated.
With regard to using the two inputs to accommodate mic and line sources simultaneously, I would also be concerned about the fact that phantom power is applied to both. There doesn't appear to be an obvious means of isolating one input from the phantom supply switch -- an internal link would be a simple and inexpensive solution. I have experience of some electronic line output stages which get very upset (sometimes terminally) if they see phantom power coming down the cable.
The S20 has been designed to appeal primarily to those who place fashion and image above pure audio quality. That is not to say this unit is in any way technically inferior, but at this UK price point the competition is very hot. Indeed, the Amek System 9098 Dual Mic Amp, DACS Micamp, Dbx 586, and TL Audio PA1 all share virtually the same list price and make very challenging competitors. For example, the Amek unit provides adjustable stereo-width facilities, the DACS is stunningly quiet, and both the DBX and TL Audio products offer valve circuitry.
The S20 makes a stylistic statement and will certainly draw attention to itself in the rack. It also performs well and has the very useful variable high-pass filter facility. However, if you have a thousand pounds to spend on a mic preamp, there is a lot of choice available and you really should try to compare your short-listed products side by side.
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Test plots to accompany the article.
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