Technical Aspekts atacama:
On the bottom rear of the bass-corpus a modified behold power amplifier UPA192 is incorporated. The features of this approach are describe here after:
• Tri-Amping with active crossover
The three different ways of power amplifiers driving the chassis are fed from non-compromised phase-linear filters. This can only be done in digital domain by a signal processor. The DSP used is from Analog Devices, the ADSP-21369. It offers three band passes for the low-, mid- and high-range totally independent from each other, which never will be true with a passive crossover. The resolution of the filter process works at a frequency step size of 23Hz.
• Two double D/A converters
Of course, a digitally based amplifier containing two analog power amplifiers needs to convert the digital audio signals from the digital to the analog domain to feed those both amplifiers. This is performed by two dedicated stereo monolithic D-to-A-converters (CS4392). Both work with fully balanced outputs.
• Two different analog power amplifiers
The atacama has two different analog power amplifiers, one for the mid frequency range and one for the tweeter. The mid range amplifier is serving up to 80W @ 4Ω out of a fully balanced design, it consists of two half bridges. Since the high range never needs that much power therefore one half bridge against ground is serving 20W @ 4Ω for the tweeter. The large upright passive cooler on the rear of the atacama is decent in its shape and serves the both analog amplifiers with adequate heat sink.
• One DSP each analog power amplifier
Both analog stages are controlled by DSP taking fully control of the power feeding MOS-FET making possible to serve A-class audio performance at an AB-class power consumption. This technical approach is common to all the behold power amplifiers, the BPA768 and the behold Gentle G192 and is unique in the High End Audio World. The result is the most clean sound as you expect from a conventional high power consuming A-class amplifier.
• Digital D/S-Modulator at the switched mode amplifier
The third amplifier contained is operating in switched mode offering 160W @ 4Ω. It is dedicated to drive the low frequency range of a speaker. The plus 3dB is very useful since, to get an excellent bass performance, additional power is needed. The final switching stages are driven by a digital D/S-modulator converting the PCM-format coming from the DSP to PWM-format (Pulse-Width-Modulated) operating at 192kHz sampling rate the full 24Bit audio bit word. So there is absolutely no D/A-converter present compared to other “class-D” designs since they are still analog. Besides other advantages the technology used in the atacama allows the operation with an open loop output circuit, totally insensitive against the feed back power of a low frequency speaker driver, which is very important, much more than a high value damping factor for this stage. Same as the analog power amplifiers for the mid-range the switched mode amplifier has a balanced output, for the identical reasons.
• Analog and switched amplifiers have their own separate switch mode power supply
This ensures not only a power conditioning just in front of the power feeding system of the amplifier but offers best way possible isolation of all the analog power amplifier channels against the switched mode amplifier. This is to be compared like using separate mono blocks. Besides that a third switch mode power supply feeds the low level analog section as well as the microcontroller and DSP.
• Multi functional input sockets
Due to the fact that the atacama accepts almost all common audio signals, regardless if they are analog or digital domain, many different input sockets would be necessary. To reduce the total number to an absolute minimum, the present sockets have to be multi functional. The only single function is the optical input which is a Toslink. The XLR socket takes a fully balanced high level analog audio signal as well as the digital AES/EBU. The three Cinch take three different analog inputs to feed all three amplifiers separately with high level analog audio as well as a single mono analog as well as digital domain. The functionality, input or output, and the impedances are set automatically to the values according to the applicable needs.
• Wiring in analog domain
Since the atacama functions as a mono block it has to be fed accordingly. This means that one left or right channels analog signal must be applied to each UPA192 block. A high level signal, balanced or un-balanced, will be accepted. Besides that mains power supply is necessary, but nothing else. The volume scaling of the music must be done in the used pre-amplifier as usual. The UPA192 runs always on full scale (0dB gain). There is no volume control available on the device.
• Wiring in digital domain
Since the atacama functions as a mono block and the digital audio signal comes always with two channels a selection has to take place. The separation of the channels is done in the DSP. With the help of the DIP-switch on the rear of the atacama you can select for left or right channel. The pre-amplifier serves in most cases only one digital output. To feed the second atacama involved all the UPA192 have a repeating capability. In digital domain mode one of the Cinch sockets works as an output to forward the digital domain audio signal. The data rate at this output is always the same as on the digital input signal. No A-to-D conversion takes place this mode. No analog fed input signal will be forwarded digitally. The input can be driven balanced or un-balanced.
• 50Ω and/or 75Ω wiring in digital domain
Unbalanced digital audio signal come in most cases on 75Ω transmission cables. So the atacama is designed to accept this. But not to be limited to this world the UPA192 is also capable to run 50Ω or both. Both means that you can enter with 75Ω and cascade with 50Ω or vice versa.
• USB connection
The USB connection allows to transfer the room correction filter data from a WinXP or WinVista based PC to one of the atacama at a time to be processed in the DSP in stereo applications. Besides that the control centre “myALS” communicates with the atacama via the USB connectivity.
• “myALS” control center
This PC based tool serves to show the actual status of the unit as well as the installed options. If a software option should be added, the software key entry takes place here too.
• Firmware update
In case a later firmware for the atacama is available an update can be performed out of the “myALS” control centre by having the atacama connected through USB and pushing the “Update Audio Proc.” Button on the menu screen.
• Auto-Power-Off function
The atacama has the capability to turn off its power amplifiers automatically. This takes place when set active and the entering audio level is lower then the given threshold value. This value can be entered in steps of “dB”. Besides the level a time needs to be selected too. This time determinates in which period an audio signal is able to set back the switch off process. When this period is over and no signal higher then the threshold occurred the atacama will switch its power amplifiers off. This lasts until audio occurs again, wake up begins and the full process starts from its beginning. This functionality applies for both input domains, analog and digital.
• Active room correction option
The atacama can process an active room correction for stereo as the behold APU768 with its ADP192 can do or the behold Gentle G192. Room correction manipulation can take place every 23Hz from DC to 24kHz. The generation of the applicable data can be done with the Ascendo Room-Tools. The data transfer takes place through the PC to atacama USB connection. The atacama must be fed one after the other. The corresponding channel, left or right, is selected automatically by the atacama. This software option can be added at the customers site by entering once a dedicated software licence key.
• Mains Supply
Supply runs from any AC power source at voltages from 100V to 240V 50Hz or 60Hz. The unit incorporates a power conditioner and should be connected to the mains supply directly. No special power cord is necessary.