SPL Gold Mike

Paul White tries the hybrid sound of SPL's new dual‑channel precision microphone preamplifier.

I can't help but get the impression that most of us employ a dual standard when it comes to deciding what we're prepared to pay for studio equipment: if something makes an interesting noise, we'll dig deep to be able to afford it, but at the same time we seem to resent paying a penny more than we have to for gear like microphones, mic preamps, patchbays, cabling or even computers. Even so, just about anyone who's had any experience at all in recording will concede that good mics and good mic preamps can make a significant qualitative difference to the way a recording sounds — the trouble is that the esoteric models tend to come with esoteric prices.

SPL used to have a reputation for being both esoteric and expensive, but as the company has grown, they've looked into ways of delivering high‑quality audio processors at more affordable prices. The SPL Gold Mike preamp reviewed here is designed to compete with some of the best mic preamps around, yet it has a distinctly mid‑market price tag, well within the reach of any serious project studio owner.

What You Get

Viewed simplistically, the Gold Mike comprises a pair of independent mic preamps sharing the same 2U case. Convex mesh grilles on the front panel show two selected ECC 83 (dual‑triode) valves glowing away inside the unit, but as with other SPL tube products, this one uses hybrid circuitry in an endeavour to combine the best attributes of both valve and solid‑state technology.

SPL first came to fame with their Vitalizer, a sort of enhancer‑cum‑equalizer based on psychoacoustic principles. Since then, little psychoacoustic twists have popped up in many of their designs, and the Gold Mike is no exception. This time they've developed something called FLAIR that can be switched in to gently enhance the presence of vocals and other sounds. Unlike so‑called 'Air' EQ that relies entirely on high‑frequency EQ boost, FLAIR combines a broad‑band boost centred at 6kHz with phase‑shifting effects to accentuate upper harmonics without making the sound rough or aggressive. The circuit employs an inductor/capacitor filter and mixes directly in with the valve's source signal via a front panel switch. There's no user adjustment — you either use it or you don't. I read the manual twice to try to find out what FLAIR actually stands for, but if it's in there, I couldn't find it!

Layout

The Gold Mike features two identical but electrically independent channels, each with a balanced XLR mic input plus both balanced XLR and unbalanced jack outputs. Mains power comes in via a central IEC socket and there's a ground‑lift switch nearby. I imagine the unbalanced outputs are a concession to those many users who have high‑resolution computer soundcards with unbalanced inputs, though the XLR outs may also be wired for unbalanced operation if required.

A large and suitably retro knob sets the mic gain, up to a generous maximum of 72dB, though the bulk of the gain comes from the solid‑state (class A Analogue Devices SS2017 chip) front end. Laser‑trimmed input resistors are used to achieve a high degree of common‑mode rejection, which means less interference when using long balanced mic lines. The valve stage comes next, and contributes just 6dB to the overall gain along with whatever magic it is that valves bestow. Using a hybrid approach like this is not a new idea by any means, but SPL have been fastidious in their choice of components and circuit board layout to enable them to achieve a dynamic range in excess of 110dB along with very low distortion. In effect, they've achieved the paper spec of a well‑designed, all‑solid‑state preamp while still including a valve stage. A star grounding system is used to minimise hum, while each channel has a separately regulated phantom power supply.

A small moving‑coil VU meter monitors the signal level, and setting a nominal 0VU peak level delivers the optimum conditions for valve drive and minimum noise. Other than the gain controls, there are just five other buttons per channel, each with its own indicator LED. First is the 48V phantom power, followed by Phase Reverse, a 30dB pad, 12dB/octave 50Hz high‑pass filter, and of course the enigmatic FLAIR button.

Checking the specifications reveals a frequency response that's flat to within half a dB from 10Hz to 100kHz, as well as dynamic range of 111dB — better than that achieved by some 24‑bit converters. The maximum output level is a healthy +25.7dB, so there's plenty of signal to feed those level‑hungry digital recorders, and the equivalent input noise is down at 135.4dBu (a typical console mic preamp manages only around 128dBu).

Going For Gold

When the Gold Mike is switched on, a warm‑up circuit mutes the audio for a few seconds until the valves' anode and heater voltages have settled, then the unit springs to life. Nevertheless, as most valve circuits take a few minutes to warm up completely, it may be best to switch on the Gold Mike a short while before you need to do any serious recording. After that, using it is absolutely straightforward — all you need do is adjust the gain to get a nominal 0VU on signal peaks, which also optimises the signal level fed into the valve stage.

Normally, the phase switch is only useful when recording with two or more microphones when there may be phase differences to compensate for, though there is at least one situation where it can be useful with a single mic. I don't know if you've noticed this before, but switching the phase of a vocal mic when you're monitoring your own performance via headphones causes a very significant timbral change. This is due to the interaction of the sound of your voice inside your head and the sound from the headphones. Often you'll find one position better for monitoring than the other — you can try this on any mixer or mic preamp that has a phase switch.

...the FLAIR button is interesting. According to the manual, there's something like 2.5dB of boost centred at 6kHz, but the subjective effect seems much more subtle. The sound remains perfectly smooth but articulation improves and details stand out more.

The pad and LF rolloff switches also do exactly as you'd expect, but the FLAIR button is interesting. According to the manual, there's something like 2.5dB of boost centred at 6kHz, but the subjective effect seems much more subtle. The sound remains perfectly smooth but articulation improves and details stand out more. It's as though the sound gets closer and becomes better focused but without any blatant signs of enhancement. Furthermore, FLAIR doesn't seem to have a significantly adverse effect on sibilance.

Conclusions

Overall, the sound of this preamp is exceptionally clean and open without the hint of muddiness that some valve processors introduce. It's difficult to evaluate the valve's contribution to the proceedings, but it does seem to help the various components of the sound knit together more naturally. A lot of care has gone into the technical design of the Gold Mike, not only in the audio circuitry, but also in circuit board layout and in the crucial area of the power supply. The result is a classy sound that's both detailed and very smooth.

The addition of the FLAIR enhancement is tasteful and effective, and though it isn't adjustable, the amount of gloss added is subtle enough and musical enough that further adjustment would probably be quite unnecessary.

These days we're spoilt for choice with mic preamps and voice channels, but if you need a really nice‑sounding mic pre without EQ, compression or all the other frills, and if you want high‑end performance at a mid‑market price, then the Gold Mike is a very attractive proposition. It also looks as attractive as it sounds.