Power Amplifiers - AudioTechnology
AT sits down with Dynacord’s Australian design head to hear what makes the new TGX series of high-output multi-channel power amps different.
TGX represents a bold assault on the touring markets by Bosch. There’s plenty of headline features, and is an impressive demonstration of a huge engineering-based multi-national like Bosch flexing its R&D muscles.
This is the first point to make: the Dynacord marque is to be a thoroughbred manufacturer of power amps and DSPs. It will no longer be a European step brother to the ‘all-American’ Electro-Voice. That extra degree of separation will help the market differentiate and distinguish the offerings. No one will assume that here is a range of companion amps for Electro-Voice loudspeakers. Dynacord isn’t owned by EV, it’s owned by Bosch.
Helming the design of the new range of amplifiers is an Australian. These amps are Jonathan ‘Jono’ Bailey’s babies, and it was with considerable pride that AT witnessed him reveal TGX to the marketplace at the ISE tradeshow earlier in 2018.
AudioTechnology sat with Jono to find out what’s under the bonnet. We’ll let Jono do the talking from here:
ROLE OF DSP
Jono Bailey: We set very high goals with these amps, and were able to achieve the industry’s highest audio quality and highest output power ever produced in a multi-channel amplifier. However, this means nothing unless you are able to do it reliably year after year under the most extreme conditions. Meeting those criteria requires huge amounts of processing power to ensure the amplifier is performing optimally under any mains condition or thermal situation. Features like JTM and Cycle by Cycle filtering [more later] would not be possible without processing like this. So the processing power of modern amplifiers is not only so signal processing can make things sound better, but now also plays a critical role in output reliability. DSP is here to stay.
The problem with DSP is that under poor mains conditions, where there could be a drop in mains power for even a second, DSP amplifiers are essentially fragile because they’re a computer that requires time to reboot, establish network connections, and only then produce audio.
This is one reason why many system designers have compromised their designs with the use of old analogue amps and centralising DSP or using lower-powered DSP amplifiers that can be backed up via UPS. This becomes extremely expensive and increases rack space. But they don’t want to take the risk of being exposed to mains power-related audio disaster.
The challenge for me was to build a high performance DSP amplifier that’s able to restart its audio instantly — just like an analogue amplifier. With TGX we achieved this. So during a short term power outage the amplifier never drops its network or DSP connectivity, as a result, there’s no long reboot times. This has been extremely well received in parts of the world where mains hand-off to a generator backup supply often requires many seconds of no power at the rack side.
FULL POWER COME WHAT MAY
Jono Bailey: JTM (Junction Temperature Modeling) provides the ability for the amplifier to operate under any operating — thermal or power — conditions.
Traditionally, power amps shut down or reduce the output voltage when the temperature at the heat sink exceeds a certain temperature. The idea is you have to play it safe to safeguard the electronics.
What we do is model, in real-time, the actual junction temperature inside the semiconductor components, based on the operating parameters, such as operating voltage, housing temperature, output current and output voltage. Parameters such as current and voltage are continuously measured. This approach means you get the most out of your semiconductor components — more output; more reliability.
We also use Mains Circuit Breaker Protection (MCBP); algorithms to ensure a steady and safe operation range of the amplifier’s circuit breaker and prevent a false overload alert under normal operation. The circuit breaker’s primary protective role won’t be affected. With this process, Dynacord’s power amplifiers offer maximum power at highest operational safety and optimum availability.
BELOW 2 OHMS
Jono Bailey: ‘Cycle by cycle current limiting’ allows the amplifier to safely operate below two Ohms — it actually goes down well below that. In fact, we stop the amplifier from going too much below one ohm — 0.7Ω to be precise. Beyond that we tell the amplifier to pulse the power, as it’s quite likely that whatever’s connected to the amp is on fire at that point!
96K SWITCHING FREQUENCY
Jono Bailey: We fixed and stabilised the switching frequency at double the normal Class D frequency. That way, there’s not as many intermodulations down into the audible frequency spectrum. We’ve done blind tests with golden-eared acoustic consultants and speaker designers, they can’t believe they’re listening to a Class D amp.
Class D and switch mode power supplies have known issues with reproducing really high or low frequencies and we have both those areas covered. I believe TGX represents a new era of amplification. Class D, until now, has hit a performance ceiling and we’ve broken through that.
HIGH CHANNEL COUNT
Jono Bailey: People now expect multi-channel amps. Four channels was a minimum for us.
Of course, at the top end, immersive audio and a cellular approach to powering loudspeakers is driving the push for more channels. In the mid market, and in the install market especially, people want to drive more speakers with fewer channels — the market wants lower cost but a higher output.
Features like the cycle-by-cycle current limiting (allowing the amplifier to drive down to 1Ω), while still utilising the full dynamic range of the amplifier… that’s attractive to installers. It allows somebody to run their PA into 2Ω or below and have four speaker boxes off one channel and really reduce the total system cost. So that mid-market is the opposite of the prevailing winds of the upper market, but I’d argue it’s a larger, more important market. Which is why we’ve produced technology that meets the mid-market while still providing no-holds-barred, eight-channel systems via Dante, 96kHz, full granularity, full resolution audio for the top end. So we do both.
BOSCH BEAST MODE
Jono Bailey: I’m confident in saying this: you won’t see another amplifier like this anytime soon, because I know the engineering effort and investment required to get it to market. You need a large privately-owned multinational to underwrite a platform and technology development like this. Fortunately, we’re fully owned by Bosch which happens to also be an engineering company — Bosch understands the level of commitment required and has the thermal labs and the aerodynamic design facilities that helped us map the airflow through the amplifier. We’ve made the most of those facilities that other companies just don’t have access to. They have to guess, for us it’s all science.