Yamaha H3000

Power amps may not be as exciting as synths, but they can make a big difference to your sound. Paul White checks out Yamaha's latest power tool.

The Series power amplifiers are not simply old ideas packaged in new boxes — Yamaha have gone to great lengths to improve the electrical efficiency of these amplifiers without compromising their audio performance. Greater efficiency means you can get more power in a smaller box and, more importantly, that there isn't so much heat to dissipate. In normal use traditional class A/B power amplifiers tend to be only around 30% efficient, so you might say that the circuitry is really a heater which amplifies music as a bi‑product! In recent years, several strategies have been employed to make amplifiers more efficient, but most have weaknesses and may be costly or technically difficult to implement.

One increasingly popular trend is to use a system of power supply voltage switching, so that the amplifier's power supply only produces enough voltage for high power operation during signal peaks or high level average signals. Such systems work well enough, but because of the constantly changing dynamics of real‑life programme material, the power savings are not as significant as you might imagine.

Another approach, which has been around for at least a couple of decades, is PWM (Pulse Width Modulation). Here, the audio signal amplitude is used to modulate the width of a steady stream of pulses. A low‑pass filter in the output stage converts the PWM waveform back to recognisable audio, but because of problems in designing effective filter circuitry, the frequency response and transient response of such devices is difficult to maintain.

More recently, Switched Series Regulation systems have been devised in which the amplifier's power supply effectively tracks the signal level. At any instant, the amplifier is working near its maximum power limit, regardless of the input signal level — thus, the power rating of the amplifier is constantly changing to meet the demand. Because an amplifier working flat out is at its most efficient, this system is very effective in reducing the amount of wasted power. However, the drawback is that the power supply circuitry can't always respond to fast transients, which means that some signal peaks may be clipped.

Yamaha appear to have adopted this latter approach, refining the concept by adding an auxiliary power supply that delivers the necessary short‑term power to allow transients to be reproduced cleanly during the period in which the main power supply is jacking up its voltage. They call this system HED, or High Efficiency Drive, and according to the published graphs, it claims to be around twice as efficient as conventional amplifiers.

HD3000

The HD3000 is the smallest model in the Series and is rated at 350 Watts per channel into 8 Ohms, 450 Watts per channel into 4 Ohms, or 900 Watts bridged mono into 8 Ohms. This kind of power makes it suitable for medium‑sized studio monitoring systems as well as smaller PA and installation applications, and though the amplifier is fan‑cooled, the fan speed is fairly low which means there isn't a lot of fan noise. The frequency response of the Series range extends from 10Hz to 50kHz within 1dB, and the distortion levels, while not quite in the 'two noughts something' category, are respectably low.

The H3000 is a 2U rackmount package, making it the same size as my trusty old Yamaha 2075 (which delivers only 75 Watts per channel). Air is drawn in through vents at either end of the front panel and vented through the rear of the box, which means that suitable ventilation space needs to be left behind the unit. Because the unit is quite deep and heavy, integral rear rack fixing brackets are provided.

Two large rotary controls are used to set the left and right channel gains and a comprehensive array of warning LEDs, four for each channel, provide information relating to clipping, the presence of an output signal in excess of 2 Volts, the presence of an input signal in excess of ‑40dBm, and operation of the protection circuitry. When the clip LED lights, a limiter comes into operation, and push‑on knob caps are provided for applications where the amplifier's gain setting needs to be made tamper‑proof.

Balanced inputs are provided on both jack and XLR connectors, and further XLRs allow the input signal to be daisy‑chained to a second amplifier. A slide switch allows for Stereo or Bridge operation with a further position providing a parallel input feed, whereby channel A's input feeds both sides of the amplifier. A ground lift switch is also fitted.

The speaker outputs are on conventional binding posts, but in acknowledgement of the new EEC regulations (which may be interpreted as: 'a frail old granny, soaked in sea water and fitted with a dicky pacemaker, should be able to poke about in any piece of electrical equipment with a two‑inch steel hatpin, without being able to come into contact with any source of electrical power greater than that required to produce a mild tingle'), a plastic cover is thoughtfully provided, which the majority of users are likely to omit to replace once they've removed it to connect the speakers.

A 15‑pin D connector is fitted so that a suitable remote/monitor may be connected, but this is purely for the benefit of installers who can provide such a device, since Yamaha don't manufacture one themselves. The pin‑outs provide tallies for the warning LEDs and provide for remote power‑up and muting.

As you'd expect from a modern power amp design, the speakers are disconnected at switch‑on and switch‑off to prevent thumps, and the protection circuit steps in if the heatsinks exceed 95 degrees Centigrade. In real life, this isn't going to happen unless you're either running flat out in Death Valley in the middle of summer, or if you've buried the amp beneath a pile of duffle coats!

Opinion

Until you switch it on, a power amp is just a boring black brick (and if you're really lucky, it will remain just as boring once you've switched it on). While I didn't take the H3000 on a gig, I did connect it to a rather nice pair of ATC SCM20 monitors, and it performed flawlessly. Having plenty of clean power in hand really allowed these speakers to work effectively, resulting in a much tighter, more confident bass sound than I obtain using my older (and less powerful) Yamaha 2075 amp. The high end comes over as well defined but not in any way shrill or harsh, and the overall impression is one of extreme competency. During periods of silence, the H3000's fan noise is audible, but not obtrusively so.

It's clear that Yamaha's Series amplifiers are well designed and well specified. They perform properly in a real life environment, they're built to a very high standard, and in subjective terms they sound extremely good.