SoundTech PL200

Power Amplifier

Published in SOS May 1997
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Reviews : Power Amplifier

Power amps certainly can't be classed as particularly exciting, but they're a necessary part of the project studio, and if you've got to have one, you might as well make sure it's powerful and quiet. MARTIN WALKER checks out one of the strong silent types...

 

SoundTech will be a new name to most SOS readers -- they're an American manufacturer of professional audio products, and these are distributed in the UK by a company called Smart Sound Direct, who make use of a rather unusual approach. Rather than go through normal retail outlets, with all of the associated mark-ups, Smart Sound Direct deal directly through mail order. This has the advantage of keeping prices down, but of course you don't get the opportunity to see the equipment before you purchase. However, Smart Sound Direct offer a 10-day money back guarantee, so you have that long to try the gear out with the rest of your equipment, and change your mind if necessary -- a novel idea.

MEET THE PL200

The SoundTech PL200 power amplifier under review here offers 100 Watts per stereo channel (into 4(omega) speakers) or 65W (into 8(omega)). It is housed in a 1U rackmounting case, and since it is convection-cooled (rather than using a fan, with all the noise that implies), it is aimed primarily at monitoring applications in small studios, where low ambient noise is important. If you need sheer power, the two stereo outputs can be bridged to provide 200W into an 8(omega) load, by connecting the loudspeakers between the two positive terminals and adjusting a switch on the bottom of the case. If the amp is rackmounted, this switch is inaccessible, but fortunately, it isn't something that you're likely to want to reach on more than rare occasions. The PL200's casing is rugged, and there are plenty of convection holes top and bottom to provide a throughflow of air. Inside, there are two large heatsinks with plenty of metal 'fingers' to further aid the cooling process (the fingers have a large surface area from which heat can escape). The circuit board is neatly laid out, and sits next to a large mains transformer.

The front panel features twin-channel level controls, each with an associated peak LED which comes on at 10dB below clip point. These should never flash more than momentarily on peaks -- if they do, you need to turn the level controls down a bit. Bridge mode is indicated by another LED, and there is a further LED, labelled Protect. This (as shown on the useful block diagram printed on the top of the case) monitors any DC or overload present on either output, and shuts the amp down if any error is found. Not only should this protect your speakers in the event of amp problems, but it also prevents the amp from doing itself a mischief if you accidentally short-circuit its outputs, or attempt to run it into loads of less than 4(omega). Although hi-fi purists maintain that any extra circuitry of this sort in the signal path can affect the sound marginally, it's far better to be safe than sorry! The front panel is completed by an on/off rocker switch and a green Power LED.

Around the back, the PL200's captive mains lead may lose the support of those who like the removable IEC type, but a reliable connection is important, particularly for a power amp, and in my experience, not all IEC mains plug/socket combinations give a firm grip. Inputs are provided on both unbalanced quarter-inch jacks and electronically balanced XLRs. The outputs on the review model were on four banana sockets (two red/two black), but to comply with the latest regulations, production models will have a pair of Speakon connectors instead. Overall, build quality was good, although I did notice that the labelling of the output sockets was partly obscured by a flange from the top cover, and the level controls were a little wobbly -- but these are both minor points.

LISTENING TEST

I replaced my normal power amp with the PL200, switched it on, and left it to warm up for a bit. As Paul White is fond of mentioning in SOS, most amps benefit from reaching their normal operating conditions, so it's better to wait a while rather than start listening from cold. It is always encouraging when you stick your head into the speaker and hear little or no noise from the power amp itself (unless you find that you've gone deaf!). When I sat back to listen, the top end seemed marginally tame at first, but this was soon cured by cleaning the pins of the mains plug with wire wool. Everyone who has tried this on my recommendation has found an improvement in low-level detail. Opinions vary as to why this works, but it will lower the impedance of the mains supply if the contacts are really clean -- try it for yourself! Once the top end had opened out, the PL200 produced a very detailed soundstage, with good stereo imagery and depth -- each instrument could be located accurately not only between the speakers, but also from front (near) to back (distant). The bass end was firm, and overall, the sound seemed very 'natural', which is intended as a compliment -- for studio monitoring you need a natural sound, not one that is hyped to the eyeballs.

Many people think that all power amps do is create a version of the input signal at a higher output level, but in fact, with good equipment, different power amps will give slightly different sounds. One of the complicating factors is that the final sound is dependent on the connection between the amp and speaker. Yes, we're talking about cables affecting the sound. The fact is that any cable connected between amp and speaker will at the very least compromise the damping factor (the ratio of amp output impedance to that of the speaker), leaving the speakers less controlled, particularly at the bass end. Active speakers (with built-in amplifiers) remove this uncertainty, but with a separate power amplifier, you should at least use a heavy-duty speaker cable to minimise the contribution to the sound.

 

"The best test equipment is ultimately your ears, and subjectively, I found the PL200's audio quality excellent..."

 

With my speakers (nominally 8(omega), lowering to about 6(omega) minimum) the peak LEDs started to illuminate at levels approaching 100dBA SPL at a listening position one metre from the speakers, but this sort of test is entirely dependent on the efficiency of your own speakers. All I can say is that it was louder than I ever monitor on a regular basis! With 8(omega) speakers, the output power of the PL200 is rated at 65W per channel (EIA rating at 1.0% total harmonic distortion). With speakers of a 4(omega) nominal impedance, the output power will increase to 100W per channel.

Throughout the listening tests (and I carried on listening while I wrote this review) the sound was sweet and detailed -- indeed, there was such a good sense of the position of sounds in the stereo image that I ended up swapping back and forth to my previous amp (a well respected £300 hi-fi power amp with a very similar spec to this one) to check that my ears weren't being deceived. Each time I returned to the SoundTech PL200, things sounded slightly more focused. The only strange thing occurred when I finally switched off -- a loud (but not damaging) click came from the speakers and the Protect LED came on, staying on for about 10 seconds until the PSU ran down. I contacted SoundTech about this, and they answered my query within 24 hours. Apparently, the way the PL200 operates is intentional -- any brownout (drop in mains voltage) or power cut (including switching the amp off!) brings protection circuitry into play to protect your speakers. After a certain time, the protection gives up waiting for the power to return, and releases the speakers. SoundTech also mentioned that they were already looking into improving the PL200's wobbly knobs. With this sort of response to user feedback, they deserve to do well.

CONCLUSIONS

Power amps are not exciting beasts -- if they work, and work well, you rarely notice their presence, unless something goes wrong. The SoundTech PL200 falls into this category. Its electronic and physical design is good, and the audio is clean, quiet and hum-free, apart from a tiny mechanical buzz from the transformer in the review model, that you wouldn't notice from more than a couple of feet away in a quiet room. Although its specifications are not state-of-the-art, many people have found to their cost that amps with superb specs don't always perform as the numbers suggest they should. The best test equipment is ultimately your ears, and subjectively, I found the PL200's audio quality excellent; I would happily leave the review model connected to my gear if it didn't have to be returned. If you have 8(omega) speakers that are inefficient, and you like monitoring at high levels, you might find that you need a higher-powered amp, but this one is aimed fair and square at small studios, and most nearfield monitors should be efficient enough to give you plenty of level before amp clipping. Although the sound of a power amp in a complete system does depend on the rest of the equipment, all I can say is that in my system it sounded better than the aforementioned, well respected amp it replaced.

I also like the concept of direct mail sales -- at £169, this amp is an absolute bargain, and if you don't like it in your own system, you can send it back! The only cheaper way to buy an amp with these specs is to look in the clearance bins for superseded hi-fi models, and I know which I'd prefer. Highly recommended.

 

BRIEF SPECIFICATIONS

• Power Output: 2 x 100W into 4(omega)/2 x 65W into 8(omega)

• Bridged Output: 200W into 8(omega)

• Frequency Response: 20-20kHz +/- 1dB Input

• Impedance (balanced or unbalanced): 10k(omega)

• Input sensitivity: 1.23V (+4dBu)

• Signal to Noise Ratio: 90dB

• Total Harmonic Distortion: < 0.1%

 

pros & cons

SOUNDTECH PL200 £169

pros
• Excellent sound.
• Low noise levels.
• No fan!

cons
• Wobbly level controls on review model.
• Bridging mode switch inaccessible if rackmounted.

summary
At this price, and with this performance,
the postman's going to be very busy!

 

 

info

£ £169 inc VAT.

A Smart Sound Direct, PO Box 1098, Caterham, Surrey CR3 5ZS, UK.

T 0990 134464.

F 01883 343894.

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