Dynacord L1300FD DSP amplifier

Transcription

1 Added value Dynacord L1300FD DSP amplifier By Stefan Kosmalla I find it hard to believe that the tools4music laboratory has received an amplifier for review that does not contain a switching power supply. When carrying the sturdy packaging carton containing the new Dynacord L1300FD DSP amplifier, I had the impression I was actually carrying one of the standard Class D "pulse width modulation models" due to the low weight, together with a low-budget switching power supply maximized for profit. Weighing in at 12.9 kilograms, the two height units combine to form an impressive amplifier. Although the amplifier has a generous installation depth of 46.2 centimeters, the mini display makes it a genuine eye-catcher. But enough talk time to get out the screwdriver. Somehow the design of the new Dynacord amplifier reminds me of a combination of the revered classic, namely the d&b D12, and the Crown Macrotech. Ready to go: a brief activation of the two rear fans and the appearance of a Dynacord logo on the display indicate that the unit is ready for operation. After 4 seconds, a click inside the device indicates that it is ready. A central tactile rotary knob allows you to start experimenting. Turn to the left, turn to the right, push in, turn again I navigate intuitively through the clearly presented, logical menu 38 structure. It is worth mentioning that I am already able to operate the onboard DSP without a tablet or PC software after being connected to the mains for less than a minute. I am interested to know why the amplifier is so deep. The lightweight aluminum cover is held in place by four screws on the back of the unit. A toroidal transformer with four electrolytic capacitors and a rectifier dominate the front section of the housing, while the actual audio channels and heatsinks can be seen on the right and left exterior of the rear section. Fig. 1 shows the complete unit: solid design, robust power unit technology twinned with a class AB amplifier that incorporates a digital sound processor board give the nod of approval. It takes four minutes to arrive at this point from unpacking the unit. First of all, I would like to mention that the Dynacord L1300FD amplifier is one of a series of new amplifiers manufactured by Dynacord (editor s note: part of the Bosch group for several years). The series includes three additional perfor-

2 mance variants as well as other available installation versions. The amplifier has a uniform design, two channels and comes with free Multi Amplifier Remote Control Software (MARC). Equipment The amplifier only requires two controls, namely the power switch and the editor knob. The display mentioned not only provides information about the adjustable input level attenuation (maximum 0 and minimum -80 decibels as well as mute the setting is adjusted in 0.5 decibel increments) but also a large number of variable parameters. The amplifier can be configured as a stereo amp or bridge circuit and the input can be routed flexibly from channel B to the input of channel A, for example. Needless to say, crossover frequencies can be set for each channel and essential frequency response corrections can be made using five equalizer bands. Each channel also has a separately adjustable delay which can be set to a maximum of 650 milliseconds (207 meters). This article does not aim to describe the full range of DSP functions and is the main reason why the ten programmed manufacturer presets and a total of 50 free memory slots for customized set-ups are only mentioned briefly in the following. One interesting extension is the automatic measurement of the impedance of connected speakers and indication of the actual value on the display. The display also provides information on the firmware version, number of operating hours and temperature inside the amplifier. A USB port on the back allows communication with the PC software. The Dynacord L1300FD amplifier is equipped with looped-through XLR sockets and Speakon fittings, while an IEC inlet supplies power to the unit. The two internal cooling fans blow towards the rear of the device. Detachable and therefore replaceable filters are not provided. Finally, there is a ground lift switch that can eliminate unexpected ground loops. Lab time The manufacturer specifies that the Dynacord L1300FD amplifier is Fig. 1: The Dynacord L1300FD incorporates proven technology: A centrally positioned power transformer with separate condensers for symmetrically arranged audio channels on an epoxy board; option of installing extra power transistors with larger heatsinks and additional condensers for more powerful models Fig. 2: The separate DSP board is fitted with high-quality Burr Brown converters and a "Symphony DSP56725" suitable for load impedances of 2 ohms or more without limitation. This is surprising, especially considering that the 600 VA toroidal transformer does not appear particularly large. The transformer generates two separate output voltages of 57 volts which are rectified and filtered by four ELNA condensers, each with 4,700 microfarad, to produce an amplifier operating voltage of 2 x 80 volts. Why 2 x 80 volts when the transformer only generates 2 x 57 volts? The answer is that the power unit condensers are charged with the peak value of the rectified alternating voltage half waves, the factor of which is Multiplying the transformer voltage by this factor produces exactly 80.6 volts. One disadvantage of condenser charging is that it discharges under load. When the amplifier circuit draws current from the power supply, the operating voltage decreases because the condensers are no longer fully charged when the power unit load exceeds a certain value. This also leads to an increase in hum on the operating voltage, which influence the THD+N measurements slightly as a 100 hertz interfering compo- 39

3 additional transistors are required to simulate a sinusoidal current draw. This technology is called active PFC (Power Factor Correction) and is neither affordable nor durable. Fig. 3: At a test frequency of 1 kilohertz, the output voltage into 4 ohms is 2x48 volts during a measurement period of 30 milliseconds amounting to 2x576 watts of power Fig. 4: The power frequency response into 4 ohms shows a constant power output until the transmission is restricted by the DSP at 24 kilohertz facts Manufacturer/model: Dynacord L1300FD DSP amplifier Sales price: 649 euro Sales: Bosch Sicherheitssysteme GmbH/Dynacord 40 nent (see Fig. 7) at double the mains frequency. In spite of the disadvantage of the somewhat unregulated power unit and the fact that controlled power supply units are commonplace, Dynacord still uses classic power unit technology in this amplifier series. One obvious advantage of concepts based on classic power unit technology is the degree of reliability as well as the efficient attenuation of voltage peaks from the power supply. A transformer always acts as a kind of inert low-pass filter that prevents momentary peaks in the power supply from affecting the secondary voltage in any meaningful way. This characteristic also protects downstream electronics from sudden voltage surges, thereby making a significant contribution to maximizing the service life of the unit. In terms of repairs, I can only welcome the return of the 50-Hz power supply because no other power unit technology is quite as durable as this puristic combination of transformer, rectifier and filtering condensers. The fact that the power factor does not need correcting is another new feature of the transformer technology. In contrast, switching power units generate huge electrical impulses that must be isolated from power grids through the use of passive filters. From a certain power class upwards, active power factor correction circuits that incorporate The two audio output stages consist of a total of four insulated heatsinks, each with eight TO-3P transistors per channel. When the cover is removed, it must be noted for health reasons that the heatsinks conduct the full operating voltage to the housing. This installation variant is not uncommon and is designed to prevent essential insulation washers between the transistor and heatsink from causing thermal issues. The well-known type NJW1302G and NJW3281G output transistors can be loaded with a dielectric strength of 250 volts and a power capacity of 15 amperes up to 200 watt per transistor. A large motherboard forms the centerpiece of the amplifier and the majority of the analog electronics in SMD design are concealed on the underside. The heart of the digital audio processor is the Symphony DSP56725, a 24-bit multi-core processor that is installed on many A/V receivers in the Home Entertainment industry due to its special design. Burr Brown PCM-1802 stereo A/D converters in 24-bit delta sigma converters establish communication with the analog circuit technology. Fig. 2 shows the separately configured DSP board. The amplifier is designed for a mains voltage of 240 V; we have conducted the following tests at 232 volts in our test laboratory. This must be taken into consideration when making the following power measurements because a conventional power unit with transformer has a linear relationship between the input and output voltage. If the mains voltage is a few volts lower, this has an immediate effect on the output power, which can be confirmed by making comparisons with the manufacturer's specifications. There are many different methods and theories for measuring the output power. The simple fact is that there is only ever one maximum output voltage at a defined load impedance.

4 As a result, multiple measurements of the maximum amplitudes are taken using burst packets. Dynacord has applied a specification with a burst ratio of 20 milliseconds "Signal on" compared to 480 milliseconds "Signal -20 decibels at a test frequency of 1,000 hertz. Measurements are always taken within the 20 millisecond signal phase, while the 480 millisecond break phase is sufficient to recharge the amplifier operating voltage that decreases during the signal phase. I also use burst signals to take measurements in the tools 4 music laboratory, but the activation phases last 100 milliseconds and the deactivation phases last 500 milliseconds. I use the measurement software to determine the effective values of the output voltage in parallel to the current load impedance during a measurement cycle of 30 milliseconds, in other words, the average value during this measurement period. Fig. 3 shows a measurement at 1,000 hertz with a load of 4 ohms. The vertical lines indicate the measurement period of 30 milliseconds, while the average output voltage appears underneath in the measured value window. It is clear to see that the amplitude level is higher before the 30 milliseconds have elapsed due to the decrease in the operating voltage at the smoothing capacitors. It is no reason for concern or criticism. A slight overload is visible at the very start of the amplitudes, which indicates that the test amplifier is modulated with a sufficiently high input signal. In brief: I carry out the tools tests at 1,000 Hz and 60 Hz (with extended time frames) the table below shows the output powers achieved. As already mentioned, the output powers we measured vary slightly from the manufacturer's specifications. One reason is the low mains voltage in our laboratory while the other is the long value measurement period and resulting average voltage. All things considered, the Dynacord L1300FD generates considerable output power, while the stable operation and corresponding increase in performance at 2 ohms deserve a special mention. This is especially important given that the temperature-monitored 600VA power transformer would not actually be capable of tolerating these kinds of measurements with sinus signals at full modulation. Due to the operating voltage level, the amplifier is suitable for producing an output power of 2 x watts with a load of 2 ohms. This corresponds to a total of watts, which a 600 watt transformer cannot generate in the long term. Nowadays, music is not a series of permanent sinus signals, but a Manufacturer: Dynacord Model: L1300FD Impedance in ohms Power in watt*** per channel at frequency Hz Voltage in volts at amplifier output Load 60 Hz* Hz 60 Hz* Hz** 2 760, * Burst signal at 60 hertz, 1,000 milliseconds on / 500 milliseconds off, measurement period: 100 milliseconds ** Burst signal at 1 kilohertz, 100 milliseconds on / 500 milliseconds off, measurement period: 30 milliseconds *** measured simultaneously on all channels Fig. 5: At 1 watt into 8 ohms, the total THD is only per cent Fig. 6: This measurement identifies the influence of an increasing power unit load on the development of hum components at 100 hertz the output power is 220 watts into 8 ohms, while the distortion values are low 41

5 Fig. 7: At dbu(a), the Dynacord L1300FD is an extremely low-noise unit only minimal influences from the 50 hertz power transformer can be identified. spectrum of pulses and only the sum of these many individual pulses places a strain on the power transformer. As a consequence, it is never a problem to generate high pulse powers at low load impedances using a compact power transformer while simultaneously using intelligent power and temperature management systems to process signals digitally and monitor the load limits of all the components involved. The added value of such measures is demonstrated in lightweight transformer power units that offer the advantages already mentioned, such as reliability and the avoidance of active power factor correction circuits. Multi Amplifier Remote Control (MARC) software: intuitive system control: design, operation and monitoring of a maximum of eight amplifiers; control groups can be freely configured with GEQ, PEQ and Delay, System Scene Manager for saving and retrieving system presets, comprehensive offline editing for processing projects independently IN DEMAND Josef Plager, Dynacord: A very positive and convincing test report! We made a conscious decision to select the combination of a proven toroidal transformer power unit and Class AB/H amplifier technology together with digital signal processing. As already described in the test report, the toroidal transformer offers greater resilience against the mains supply, which can only be achieved on switching power units at considerable effort and expense. The amplifier and DSP system offer maximum concert sound quality which was only previously available in the top price segment. The accompanying Multi Amplifier Remote Control (MARC) software can be used to elegantly configure, control and monitor small to medium-sized systems. Altogether, this is an extremely attractive overall package, which is also confirmed by our users. 42 Measurement of the frequency response in Fig. 4 shows the maximum upper limit frequency with 24 kilohertz because the DSP reaches its maximum bandwidth due to the sample rate of 48 kilohertz. The distortion pattern in Fig. 5 at 1 kilohertz and 1 watt into 8 ohms illustrates low per cent K2 distortions and is already moving into the high-end hi-fi areas with a total THD of only per cent. Fig. 6 is also interesting. Here I have measured the amplifier with an input level of 3.5 dbu at an output power of 220 watts into 8 ohms. The distortion values are still within an excellent range, but the higher power unit load has given rise to a low 100 hertz hum component. The overall THD is only 0.09 per cent. In line with these outstanding values, the interfering noise generated by the Dynacord L1300FD DSP in Fig. 7 is only -70 dbu(a). The voltage gain of the amplifier is 32 decibels, while the overall dynamics in conjunction with the maximum possible output amplitude is approximately 105 decibels. The Dynacord amplifier easily passed the load test in the laboratory at load resistance with full modulation and music program from the library. The fans accelerate up to maximum speed in three stages even with a load of 2 x 2 ohms, the amplifier does not shut down. Our test specimen acknowledges the short circuit test with a short display message "short" in the faulty channel so that the unit can continue playing undisturbed after the short-circuit is eliminated. Summary The engineers at Dynacord who developed the Dynacord L1300FD have raised the bar extremely high. The test sample we have available presents itself at its very best. Some benefits include genuine manufacturer's specifications in terms of technical data, an accompanying manual and a comprehensive range of DSP functions. Furthermore, the sophisticated concept, outstanding measured values and attractive design have proven that even modern power amplifier concepts can be competitive despite the conventional circuit technology used. In line with the motto "save the best 'til last", we shall now have the obligatory look at the price of the product. The price matches the positive overall impression of the product as the amplifier is currently available in retail outlets at prices starting from just under 650 euro. My tip: whether used for touring, fixed installations or powerful hi-fi systems this series of amplifiers offers all the qualities required for reliable longlife operation as well as an extremely competitive price-performance ratio. n