Unromantic though power amplifiers may be, they are a vital part of any audio system and should be chosen with care. Paul White takes a look at a practical and sturdy contender from 3G.

Studio monitoring puts heavy demands on speakers, and an under-powered amplifier will place more stress on these vulnerable components than one capable of providing a clean drive signal at all listening levels. Paradoxical though it may seem, you stand more chance of damaging your speakers driving them hard from a 30W hi-fi amplifier than you do driving them from a 100W per channel studio power amp. The reason for this is that the under-powered amplifier is likely to distort the input signal through clipping, and the high percentage of harmonics caused by clipping can cause severe tweeter overload, leading to burnout. For serious home recording applications, a minimum amplifier power of around 75 watts per channel is recommended, and the model under review falls squarely into that category.

Though you may not be entirely familiar with the name, 3G have been building audio components for many years and currently produce a range of low-cost mixers, mainly for PA use. The HP200 amp is a soundly-built workhorse with no pretensions to esoterica. Providing up to 108 Watts per channel into 8 ohms, the amplifier is built into a 1U rack package and requires no cooling fan, ideal for studio applications, where fan noise is an unwelcome intrusion. The frequency response is essentially flat over the entire audio spectrum and has fallen by only 3dB at 70kHz, while the signal-to-noise ratio is typically better than 100dB.

Technically, the design is based on a fairly straightforward MOSFET power amplifier circuit fed from a power supply based around a torroidal transformer. Relay switching is incorporated, so that the speaker output is muted until the amplifier power supply has stabilised after switch-on; this prevents potentially damaging speaker 'thumps'. Though some hi-fi critics claim MOSFETs give an inferior bass sound to conventional bipolar transistors, they have the undeniable advantage of self-preservation. If a bipolar transistor starts to overheat, it can reach a point where it draws more current, resulting in so-called thermal runaway, and eventual destruction of the device. MOSFETs work the other way round, limiting their own current flow when overloaded. The HP200 is also fitted with thermal protection circuitry which automatically shuts down the amplifier if overheating is detected. This automatically restores power once the temperature has returned to normal. Under normal operating conditions, this should never happen, but if any amplifier is severely overloaded or deprived of ventilation, a heat rise is inevitable.

Like most modern power amplifiers, the HP200 is protected against open and short circuits at the output, but a welcome degree of speaker protection is also built in. The HP200 incorporates a relay connected in series with the speaker output; in the event of a DC voltage greater than 5V appearing at the output, the speaker is disconnected from the amplifier.

Layout

Input to the amplifier is via balanced XLR connectors on the rear panel, while the speaker outputs are available on XLRs or standard binding terminals. A ground lift switch is fitted. Both channels are independent, having their own level controls, but a common power supply feeds both amplifiers. It is also possible to use the two amplifiers in bridge mode to produce a single output of up to 185 Watts into 16 ohms — useful when driving, for example, a single, high-powered subwoofer. Constructionally, the amplifier appears quite sound, with well-secured glass-fibre boards holding most of the components and an aluminium heatsink holding the power MOSFETs and temperature sensors.

The front panel is finished in a tasteful metallic grey and houses the level controls, the power switch and the LED status indicators. A single LED indicates whether the amplifier is being used in Bridge mode, and the two channels each have Clip and Protection LEDs. Unusually, the clip LED is a true clip indicator in that it takes account of the speaker impedance and registers actual power clipping.

Power User

The HP200 performed its task with no fuss and no unwelcome excitement. No switch-on thump was evident, so the relay system obviously works, and the amplifier runs quietly, both electronically and physically. It can produce very high listening levels from a typical pair of studio monitors without clipping, and though its subjective performance isn't significantly different to that of other amplifiers in the same price range, it works cleanly and with good transient definition and no obvious bass deficiency.

Given its realistic price and fuss-free performance, see no reason why the 3G HP200 shouldn't hold its own in the competitive small studio and PA market. It is robustly engineered, easy to use and not too ugly — what more could you want from a power amplifier?

Further Information
3G HP200 £499.38 including VAT.

HW International, (Contact Details).