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Smartlight SL600S

Studio Power Amplifier By Martin Walker
Published February 2000

Smartlight SL600S

Martin Walker tries out a good‑value, British‑built studio power amp.

Smart Sound Direct will already be fairly well known to SOS readers for the SoundTech range of amplifiers, mixers, and speakers, and have now introduced their own range of power amplifiers that are both designed and built in the UK. The SmartLight range currently includes four models, all of which utilise the same compact 1U rackmounting case. The SL600 and SL1200 are primarily intended for live use, and provide 300 and 600 Watts per channel respectively into 4Ω, while the SL600S and SL1200S have been heavily re‑engineered for optimum sound quality in the studio. As with all other Smart Sound products, the range is sold direct to the end user from the factory, the benefit of this approach being a competitive price.

Guided Tour

For studio use, the SL600S reviewed here provides 300 Watts per channel into 4Ω, or 200 into 8Ω, and is powerful enough for nearly all nearfield or midfield studio monitoring duties. The 1U rack case is quite heavy at 8kg, and if bolted into a rack should also be supported at the rear (using the slots provided and a suitable bracket). It has a grey, powder‑coated finish, with a solid 2mm steel fascia and heavy‑duty carrying handles on the front.

The front panel has an illuminated rocker power switch, twin replaceable air filters, and a separate rotary level control for each amp channel, with green signal LED and red Peak/Protection LED. On the back panel are an XLR and quarter‑inch TRS jack socket for each input and a Neutrik Speakon connector for each output, along with an earth link switch (in case you get hum problems — I didn't) and an IEC mains socket.

Using bipolar A‑B class output stages on amplifiers of this power does tend to generate a fair amount of heat, so forced cooling is almost inevitable. However, this is the only fan‑cooled design I've heard to date that I'd be happy to have in my studio. Only at sustained high output levels does the fan come on at all, and even when it does, the variable‑speed design is barely louder than a whisper.

The Acid Test

The most important aspect of any power amp is, of course, what it sounds like, and here the SL600S most definitely didn't disappoint. The high frequencies sounded smooth but extended with plenty of detail and transparency, but I have never heard my ATC speakers sound so tight and well controlled at the bass end. This is no doubt due to the high damping factor (which effectively brakes the speaker cones), as well as having plenty of output power available — I even spotted a problem at the bass end of one of my mixes that had previously been submerged. The overall sound compared well with that of the highly respected Hafler range (I reviewed their P1000 in SOS September '99), and my ATCs were happier with the much greater 200 Watts per channel power output of the SL600S.

I also had occasion to test out the extensive protection circuitry when another review item sent an unexpected DC surge through my system. My speaker cones leapt forward alarmingly, but the amp output was immediately muted and both Peak LEDs on the amp stayed on until the fault condition was removed, no doubt saving an expensive repair bill.

The SL600S is an amplifier designed by engineers rather than stylists, with audio quality taking precedence over fancy features. At £599 it may be expensive, but it's still considerably cheaper than any other amp of comparable power and quality that I've auditioned to date. If you need several hundred Watts of excellent sound quality for your studio, you really should audition the SL600S.


  • Excellent audio quality.
  • Fits in a single rack space.
  • Extremely quiet variable‑speed fan cooling.


  • None.


A clean, powerful amplifier design with sound quality to rival much more expensive models.