Smaller & Lighter & Digital
By Jeff Kuells

Powersoft digital amplifiers in the field and on the bench

How small can power amplifiers get before they become ergonomically difficult to use? I believe Powersoft might have found the limit.

The Q4002 at rest, but its four channels are capable of producing 950 watts each.

The model Q4002 is only one rack space (1U) in height and weights just 21 pounds, but it packs four independent channels, 950 watts per channel. RMS, plus XLR combo and Neutrik Speakon connectors. Now that’s a compact package!

It wasn’t long ago that 3U and 4U amps were standard in the pro touring world. Then came along 2U amps, and everyone thought that was unbelievable. At the time, weight wasn’t even a primary concern - all we were concerned about was reducing the number of racks in a truck pack. The late ‘90s saw amps that were dramatically lighter, and then we moved to switching power technology, which has changed forever the perception of pro amplifiers.

Powersoft is one of the latest technology companies to get into the amplifier business. Founded in 1995 in Florence, Italy, the company is known in Europe for its advanced technology in electronic and software development. Powersoft believes one of the reasons it’s emerging as a leader in amplifier technology is close work with the local university, ensuring fresh ideas from younger (and presumably non-opinionated) emerging engineers.

Powersoft amplifiers are based on PWM (Pulse Width Modulation) technology, also known as Class D (digital) amplification. This type of technology, used for decades in non-audio related fields such as computer power supplies, brings to high-efficiency to amplifiers design. Benefits include minimization of heat, lower weight and smaller size.

Until recently, this technology could not be used in the majority of audio applications, primarily due to bandwidth limitations, poor signal-tonoise ratio and high total harmonic distortion (THD). However PWM amplifiers were ideal for low-frequency audio applications because the LF domain does not require such tight specifications. Good LF requires high power and a high damping factor, hallmarks of Class D.

TIMING IS RIGHT

Faster components have allowed the switching process to become more precise and fast enough to overcome the inherent problems of PWM amplification. Powersoft took advantage of these new high-speed components and combined them with new design approaches to develop one of the first high power full bandwidth Class D professional amplifiers. In 1998 they introduced (in Europe) the first generation of DIGAM amplifiers, ranging in power from 450 watts per channel at 8 ohms to 3,500 watts per channel at 2 ohms. (Keep in mind these models are only 1U high and weigh only 21 pounds.)

The DIGAM amplifiers are 95 percent efficient, reducing the need for large heat sinks. They also incorporate a PFC (Power Factor Corrected) power supply, allowing them to operate line voltage around the world, from 95 volts to 265 volts. The power supply remains stable under any AC line condition while maintaining a consistent power output from the amplifier. To insure good audio performance, DIGAM amplifiers utilize switching frequencies up to 50 MHz with a sampling frequency of 250 kHz.

I was recently supplied with a newer Powersoft Q Series amplifier, the model Q3204 four-channel unit, and immediately took it to a gig for evaluation. My first impression after opening the box is how good looking the blue and black color scheme is, and how nicely the front panel is laid out. The amplifier is a bit deep at 18 inches, although it certainly has a superb power to weight ratio.

This was a small live gig, requiring coverage for 300 people. I was using Tannoy V18 active subs along with four Tannoy V12 passive tops that were all to be powered by the Q3204. On paper, this was a perfect match delivering 500 watts at 8 ohms to each cabinet. The only problem I ran into was the power cord, supplied as an IEC removable type with a European plug.

THD plus noise versus power, measured at 4 Ohms, 1 kHz, for the Q3204.

Oops - lucky I had a spare U.S. cord to swap out. (Note that there is less current draw with amplifiers that utilize power-factor correct power supplies, because they are using more of the AC waveform.) The amp performed comfortably in this environment. I’m very familiar with the V12 speaker and can notice just about any form of audible distortion. I was concerned about using a Class D amplifier for mid- and high frequency applications, due to the traditionally poor THD levels and inherent “non-musical” characteristics, but this system was both very loud and clean. Driven at low levels up to its limit, there was no audible distortion or popping. It performed continuously for hours and due to its efficiency and whisper-cooling fan, remained cool to the touch. Sonic quality was pleasing.

HIDDEN FEATURES

The manual was not as informative in comparison to those of most premium amplifier manufacturers. Without as much guidance as I would prefer, however, I did find some features that can be useful.

Q3204 frequency response at 8 Ohms (10 watts).

Each channel has user settable high-pass and low-pass filter settings at 65 Hz, 100 Hz and 130 Hz. Filters can also be cascaded to achieve a band pass filer. Each channel has a gate select option. If signal levels drop below -50 dBu, the input will be muted, preventing low noise from passing through. These features however, are pretty well hidden inside the unit, making them more practical for installs only. To access them, the front panel and sub plate must be removed to get to the 40-pin shunt array. The settings are listed in the manual, but the filter pin assignment can be a bit confusing.

The Q3204 is quite versatile. It can be used in a number of configurations, such as four channels independently; two channels of high power by bridging; two channels of bi-amping; or one high power channel bridged with two stereo channels.

ITS BENCH TIME

I usually just run a series of basic audio tests unless asked to do more when bench testing.

Noise measurement of the Q3204.

My job is to determine if the manufacturer is telling the truth in power output, THD, noise and bandwidth. When testing output power on switching power supply type amplifiers, one must be very quick at recording power measurements because due to the current sensors and limiters in the power supply. A note to bench hobbyists: when testing any newer amplifier, never remove the cover during thermal or power testing. In order to reduce the size and weight of these amplifiers, the chassis has been made an integrated part of the cooling system. Failure to comply will result in amplifier damage. (I know because I’ve had a few go up in smoke!)

And based upon hearing several discussions regarding power measurements and thermal limits of switching amplifiers, I’d like to clarify some misunderstandings. Most new switching amplifiers are designed to amplify a signal at maximum output for no more than five to 10 seconds Does this mean they are not as good as the old conventional power supply models? Nope - they’re as good as, if not better.

This time, data on the model Q4002: power sweep, measured 2 ohms at 1 kHz (four channels driven)

Many believe an amplifier must be able to run at full power over long time periods to be any good. However, the reality is that peak or burst power is more important that continuous power for audio applications. I found the Q3204 power output to be close to the Powersoft specified rating, particularly with all channels driven. Any measured power differences were clarified by Powersoft as RMS limiter interaction. As a side note, I also measured a model Q4002 amplifier and the power specification was met, including at two ohms. THD and noise met the specs of the unit as well.

Note that the spec sheet and manual do leave out common useful information, such as input sensitivity and the parameters by which the stated measurements were actually made.

A look under the hood: here's how it all fits together.

Powersoft offers remote control hardware and diagnosis software for both the D and Q lines of amplifiers, allowing a network of 100 amplifiers can be controlled and monitored from a maximum distance of 1,600 feet. A rack mount control hub as well as an optional amplifier network card is required for operation. And for those interested, Powersoft also supports a full line of OEM powered loudspeaker modules. As one might expect, these are small and light, with power levels ranging from 30 watts to 1,800 watts.

FUTURE TREND?

The Q3204 is a fine amplifier, sounding good and performing to professional- level expectations. In addition to a more comprehensive manual, I’d also suggest that Powersoft add features such as front panel channel identification, locking power cord and a gain selection switch.

However, if “compact” and “light” are requirements for your next amplifier application, the Q3204 is worthy of consideration. It is fun to think about the possibilities of a single amp rack with 20 individual channels, delivering 20 kW of power, using only five amps and five rack spaces. And weighing just 100 points!

I can’t help but think we’re seeing the future of professional amplifiers with this type of technology, and what a bright future that is. Anything smaller and lighter with this output and capability might even seem counterproductive!

For more info on Powersoft amplifiers, go to www.powersoft.it. In the U.S., Powersoft is distributed by Martin Professional, www.martinpro.com.

Jeff Kuells is an audio engineer and audio manufacturing consultant and was previously director of engineering for a major amplifier manufacturer. He is Live Sound’s amplifier technical editor. Reach him at proamps@foothill.net