Dynacord IPX10:8 Review
“Our test candidate, an eight-channel power amplifier with DSP system and OMNEO interface, promises high performance and provides interfaces for signal transmission and remote control”
With currently four models, Dynacord’s IPX amplifier series represents the traditional Straubing manufacturer’s highest performance class for the installation market. The three four-channel and one eightchannel amplifiers are equipped with everything that modern amplifier and DSP technology have to offer. The flexible output configuration should be interesting especially for fixed installa-tions, as – additionally to the common 70 and 100 V direct drive and Low-Z operating modes – the series also allows users to operate two or four amplifier channels in bridge, parallel and also in a combined parallel-bridge mode.
This means that especially powerhungry loudspeakers and systems can also be powered in 140 V or 200 V systems. In its various operating modes, amplifier channels can be configured from 1,250 W up to 10 kW. IPX power amplifiers are therefore particularly suitable for mixed requirements, for example if some larger loudspeakers need to be controlled with low impedance while, at the same time, 100 V lines are required to power peripheral zones. Further typical applications include line arrays, where many ways have to be supplied and additional, highpower subwoofer amplifier channels are required.
For this article, we tested the IPX series’ 10:8 model. The model’s name refers to the fact that a total output of 10 kW is distributed over a maximum of eight channels. The other three IPX series models feature four channels and have a total output of 5, 10 or 20 kW. Externally, all amplifiers are identical and are integrated in a solid 2 RU housing with 463 mm rack mounting depth. The device can be operated directly via an OLED display with 256x64 pixels and three buttons or – for the complete range of functions – using IRIS-Net software. As is common for equipment designated for fixed installations, all amplifiers feature Euroblock (or Phoenix) connectors. Due to the required power, the loudspeaker connectors are relatively large and allow users to connect cables with a crosssection of up to 6 mm².
On the technical side, IPX amplifiers offer a whole range of modern features on all levels. Eco Rail technology ensures that the amplifier requires particularly little power in idle mode or in light load operation ; with its Smart PFC circuit, the power supply unit monitors the amplifier’s power supply thanks to its own DSP and adjusts the amplifier’s behaviour to the power supply available; and the modern SHARC audio DSP provides almost unlimited possibilities for signal processing and monitoring at a continuous sample rate of 96 kHz.
The universal amplifier: eight channels and loads of power
To ensure a better understanding of the IPX’s concept, let us begin with some simple basics regarding amplifier design. An amplifier’s capabilities are determined by the maximum output voltage and the maximum output current. Both are primarily determined by the semiconductors used – which in turn are defined by a SOA (safe operation area). While the maximum allowable voltage is a fixed value, the maximum allowable current also depends on the temperature of the semiconductor. The warmer this component gets, the less power it can cope with. This relation can be accounted for by using a simple hard current limiter with a fixed value in the protection circuit or – as is the case for the IPX amplifiers – by integrating an “intelligent” circuit, the socalled Junction Temperature Modelling (JTM). The JTM always optimally adjusts the current limitation in relation to the currently measured temperature so that the entire SOA can be optimally used. Another limiting factor in an amplifier is the power supply unit, which needs to provide sufficient voltage and current. If several amplifiers share one power supply unit, the power can be distributed cleverly: when one channel requires only a small amount of power, then more is available for a different channel.
The question now is how much current and voltage are needed. According to Ohm’s law, speakers with low impedance, such as 4 Ω or 2 Ω, need a lot of current. If, on the other hand, the loudspeaker has a rather high impedance of 8 Ω or 16 Ω, then high voltage is required. It would therefore be desirable if an amplifier could adapt as well as possible to these different requirements. The precondition for this is a high maximum output voltage in combination with safe current limitation and flexible power supply.
In addition to the socalled Low-Z loads (2, 4, 8 or 16 Ω), 70 V (US) or 100 V lines are also widely used in fixed installations, especially when a lot of loudspeakers are installed in extensive premises. Here, all sources (amplifiers) and sinks (loudspeakers) are defined in such a way that they reach their nominal power at 70 or 100 V (effective value). On the loudspeaker side as well as with amplifiers with low and medium power, this is usually ensured with the help of transformers.
With IPX amplifiers, as is the case for various other models of this power class, the transformer can be dispensed with, as every individual channel is already capable of feeding a 100 V system in the socalled direct drive mode with a maximum output voltage of 150 Vpk. The maximum output current of the IPX10:8 model we tested is 41 Apk. Even with a 4-Ω load, the power amplifier would not reach its limit. If current Ω und/or voltage are still not enough, two channels can be bridged (double voltage) or connected in parallel (double current). This way, even rather rare 200 V systems could be powered directly. Such a 200 V system could be found for example in the Moscow Luzhniki stadium before its reconstruction in 2018 – where cables from the amplifier control room to the loudspeakers had a length of over 300 m.
If an amplifier operates in bridge mode, then theoretically it can achieve double the output voltage – an operation, which also results in a correspondingly high current. In bridge mode, the IPX10:8 can deliver an output voltage of up to 300 Vpk. With a load of 4 Ω, this would mean a peak current of 75 Apk – something a single channel could no longer deliver. This rather rare case is a case of the parallel bridge mode.
Here, two amplifiers each operate in parallel are then bridged – delivering a peak current of 82 Apk. What sounds simple at first is in fact a major challenge in terms of circuitry. Lowimpedance sources operated in parallel can lead to equalisation currents, which can strongly load or even destroy the amplifiers. Parallel bridge operation is therefore only mastered by few devices and manufacturers.
OMNEO, Dante, OCA, AES70, …
IPX power amplifiers are equipped with two OMNEO network interfaces, which not only transmit the audio signal in a Dante audio network format and but additionally also transmit the parameters for remote control and device monitoring. OMNEO was jointly developed by Bosch and Australian manufacturer Audinate and presented in 2012. The objective was to transmit both the media channel in the Dante format and the system control component in OCA (Open Control Architecture) format using a standard Ethernet connection. Dante is an audio network that is widely used throughout the world. It uses normal network technology, is easy to configure and can be easily integrated into existing network architectures. Almost all manufacturers of digital audio devices today have either already integrated native Dante interfaces into their devices or offer them as an optional supplement. OCA might not be quite as well known, however the standard for control parameters is now also defined in the AES70 standard. It can be operated in parallel to various media channels in a given network, such as Dante, AVB, Cobranet and more, and the OMNEO ports can be used redundantly as primary and secondary ports or as switches for daisy chaining. Users can configure their Dante network either by using Audinate’s Dante controller software or by relying on a Dante controller, which is integrated in the IRIS-Net software. With their OMNEO interfaces, devices from Bosch can exchange both media signals and peripheral control parameters with devices from other manufacturers using standard IPbased Ethernet connections. As the necessary infrastructure already exists in a lot of buildings, the OMNEO network can build on this – a fact, which in turn can contribute to a considerable reduction in costs. The network load caused by audio data is comparatively low, considering that 64 audio channels with 48 kHz sample rate and 24-bit resolution only produce an 8% load on a 1 GBit network. Separate networks are not necessary for this. For security reasons, IT experts are even increasingly recommending that audio devices be integrated into existing networks, as everything then happens under IT control and the devices are monitored and protected accordingly. Currently, OMNEO devices do not yet support encrypted transmission and do not check the authenticity of the accessing Dante or OCA controller software.
Frequency response and damping factor
Additionally to an amplifier’s power, which we will discuss later, values for the frequency response, damping factor and signal-to-noise ratio as well as the distortion values are also important.
Due to a Class-D amplifier’s circuit concept with passive lowpass filters in the outputs, the frequency response at the upper end of the transmission range fluctuates to a greater or lesser extent depending on the load. FIG. 06 shows the measurements on the IPX10:8 for purely resistive loads of 2, 4, 8 and 16 Ω as well as with loudspeaker dummies for 4 and 8 Ω nominal impedance and with open output. Apart from the extreme case of 2 Ω, the resulting fluctuations up to 10 kHz lie within a range of ±0.3 dB maximum. With a 4-Ω load, the level at 20 kHz has dropped by just 0.5 dB. Results of this magnitude are entirely unproblematic. If, for comparison, one takes a look at the curves measured with the loudspeaker dummies, the drop in treble is completely compensated for anyway by the impedance, which typically rises to high frequencies with loudspeakers.
In other words, the level loss at high frequencies could also be defined by the amplifier’s frequency-dependent internal resistance. If the source’s internal resistance is then related to the load impedance, this becomes the wellknown damping factor. FIG. 07 shows how the IPX10:8’s damping factor relates to the frequency at 4 Ω. Very high values are achieved at low frequencies; below 200 Hz, rising from approximately 200 at the beginning to over 600. In the mid-frequency range, this results in approximately 100. The curve then drops towards the high frequencies, so that a damping factor of 25 is achieved at 10 kHz. A high damping factor is especially important at low frequencies, where the loudspeaker needs good control by the amplifier to ensure that it does not oscillate too long. In practice, however, values of 100 for the power amplifier are already more than sufficient, as cable and contact resistances usually result in even greater resistances on the signal path anyway. These in turn make it possible to effectively measure a damping factor of more than 25 at the loudspeaker only with short cables and ideal connectors.
Let us now have a look at the next important measured value of an amplifier, the dynamic range. For the calculation, we first need to determine the maximum output voltage. In the case of the IPX10:8, this is around 44 dBu. On the other hand, there is the noise level to be measured at the outputs, which we measured once using the analogue inputs and once using Dante. For this purpose, the analogue inputs were connected to a 200-Ω resistor. The noise level measured in this way was –68 dBu unweighted and –71 dBu Aweighted. After switching to a digital signal feed, the results improved by 3 dB. Based on the Aweighted noise level, a signal-to-noise ratio of 115 dB is achieved with an analogue feed or 118 dB with a signal feed via the Dante network. The corresponding interference spectra from FIG. 08 show an evenly distributed white noise without any monofrequency components.
Which distortion measurements are meaningful for amplifiers and which results should be achieved? And, are they relevant at all, since the following loudspeakers usually produce distortions many times over? These questions have been an issue to audiophile circles for quite some time. If one takes a closer look, one notices that loudspeakers primarily produce 2nd and 3rd order harmonic distortions. However, distortions caused by amplifiers often also contain distortion components of a higher order, which are less well concealed in the audio impression and can therefore be noticed more easily. Classical Class-AB amplifiers already come quite close to the ideal of rapidly decreasing distortion components towards a higher order. Class-D circuits, however, are rather unfavourable in their behaviour and often generate a lot of higher-order distortion components. There are therefore several aspects that need to be considered: the absolute distortion value, their spectral composition and the curve depending on the frequency.
FIG. 09 shows a first series of measurements with THD+N values as a function of the output voltage for a load of 8 Ω and 4 Ω, exemplarily shown for two of the IPX10:8’s eight channels. The results lie between –70 and –80 dB (0.01%) and are thus already in regions that actually do not require any further discussion and can compete with many Class AB or Class H amplifiers. A recently measured, very popular studio technology amplifier also lies within this range. The small jump at 3 V occurs when switching from normal operating mode to eco mode. This series of measurements was carried out in steps from a high level to lower values. If the measurement is reversed, the jump takes place at a higher output voltage, namely where the switch from eco mode to normal operation takes place.
If one has a look at the distortion spectrum in FIG. 10, all harmonics – when looked at individually – are at or below the –80 dB line. The even-numbered harmonics (k2, k4, ...) also show the desired falling tendency. The odd-numbered harmonics present themselves in a little less favourable way. However, it is questionable, to what extent this can still be relevant here. It should also be mentioned that the distortion spectrum is completely free of hum components thanks to the switched-mode power supply.
The further THD curves from FIG. 11 were measured with a constant level depending on the frequency. The total of four curves show the two IPX10:8’s exemplary channels at 4 Ω and at 8 Ω loads. At 1 kHz, we can find the familiar values from FIG. 09 again. The distortion values fall towards lower frequencies, while rising evenly towards higher frequencies. In principle, this behaviour can be observed with all amplifiers and is caused by the loop gain or negative feedback, which decreases at high frequencies. With Class-D amplifiers, this effect is somewhat more pronounced than with conventional Class-AB amplifiers.
Our final distortion measurement is the DIM (Dynamic Intermodulation Distortion) measurement from FIG. 12, for which a 15 kHz sinusoidal wave with a steep-edged 3.15 kHz square wave was superimposed. The resulting intermodulation products are evaluated as this measurement reveals weaknesses in fast transient signals. The rectangular share’s steep flanks are a lot more demanding for the amplifier than the THD measurement’s sinusoidal signal. The DIM measurement is therefore more important for an amplifier’s audio qualities. The IPX10:8’s DIM values lie between –50 and –80 dB and thus in a range which is – in any case – sufficient and can also be described as good for a Class-D amplifier.
For high-power amplifiers, the load on the electricity grid is an important issue. Directly or indirectly related to this are installation costs, operating costs and ultimately also operational safety. Three aspects play a role here:
Efficiency is all about providing as much power for the loudspeakers as possible without generating a great deal of heat loss. High efficiency reduces direct electricity consumption from the grid and indirectly saves electricity when external cooling is used, as this then has to absorb less waste heat. FIG. 16 shows the amplifier’s efficiency using two curves. The blue curve sets the output power in relation to the total active power consumed from the power grid. Together with the base load, this results in rather low efficiency values at low output power. For the red curve, therefore, the output power is only set in relation to the power consumed in addition to the base load. The IPX10:8 demonstrates a good efficiency of slightly more than 80%.
2. The course of the mains current
The current drawn from the grid should follow the voltage in its course as far as possible and the amplifier should thus behave in a manner comparable to a real resistance as a load for the grid. Deviations are caused by displacement reactive currents (capacitive or inductive) and by distortion reactive currents (upper wave component). How well the current curve approaches the voltage curve is expressed using the power factor (PF). FIG. 17 shows the IPX10:8’s measurement at full load. Apart from a slight offset and some distortion of the curve shape, the current curve (blue) follows the voltage curve (red) very well. The power factor is 0.99. Such a value is achieved by an active processor-controlled PFC circuit (Power Factor Correction). In addition to the almost ideal current consumption curve, another advantage of Dynacord’s Smart PFC circuit is the precise monitoring and control of the current consumption, which reliably prevents an overloading of the power grid and thus triggering of the circuit breaker
3. The base load
The third relevant benchmark value when it comes to the subject of grid load is the already mentioned base load or idle power consumption. This value is always important when devices are permanently operated, as is the case in many fixed installations. The IPX10:8’s mains power consumption in idle mode is approximately 100 W, which is reduced to 18 W in standby mode. The standby mode can be activated or deactivated either on the device itself or remotely via IRIS-Net software.
With the IPX series, Dynacord presents four installation amplifiers that set standards in many respects. The four- and eight-channel models feature all conceivable operating modes including bridge, parallel and even parallel-bridge operation and are therefore suitable for all applications with outputs from 1.25 kW to 10 kW. Additionally, even loudspeaker lines with 70, 100, 140 V and 200 V can be amplified without any problems. More flexibility is hardly possible. Another impressive aspect is the amplifiers’ absolute stability, which – almost no matter what you do to them – always offer the maximum of what is possible and are stable in operation. With Smart PFC, fuse simulation and Eco mode, the power grid is also optimally used. In addition to their actual function as amplifiers, the IPX models also feature DSP with OMNEO interfaces. Their range of functions is impressive and includes everything one needs for the safe operation of speakers. However, a multitude of DSP functions is only one side of the story. The other is: The developers have also succeeded in designing the ampliers’ operation within the framework of the proven and wellknown IRIS-Net software in such a way that setting and operation are intuitive and safe. The corresponding IRIS-Net manual is needed only in rare cases and for some special functions, whereby the manual itself can also be described as exemplary in its scope completeness and depth of explanation.
To sum up, the IPX amplifiers are genuine hightech installation devices of the upper performance class, which fully meet all requirements in terms of flexibility, stability and functional scope.