The principle of a single chassis

The combination of the unique properties of transformers with effective shielding and protection allowed to refuse completely pointless and only high cost the product of two or more structure-options.

Transmission line of the clock signal at IC DAC is made in the form of a closed microstrip line harmonized in the structure of the multilayer printed circuit Board. This allows you to virtually eliminate the influence of external noise on the clock signal and to bring to the tact converters with jitter less than 50 - 60 femtoseconds.

Apollo DAC implemented in a common housing (chassis) as functionally finished product. Still in the design phase discussed options for separating the device into two or more blocks, but a study of all factors affecting the final result, we came to the conclusion about the meaninglessness of such a topology. Usually additional blocks or power supplies, or clock generators. A separate power supply is primarily designed to physically spread in space transformers, creating a relatively high external field, and a signal circuit, and to eliminate the effects of vibration of the transformers on the elements of the signal circuits. Such a solution makes sense only when you use standard power transformers, which are designed and manufactured on the basis of maximum economy.

For the DAC, the Apollo was designed, developed and custom special power transformers with extremely low external stray fields (50-100 times lower than that of standard industrial products), a sinusoidal form of magnetizing current and low inherent vibration. To further reduce interference and vibration transformers placed in a special closed screen made of magnetic steel with a thickness of 2 mm, and the transformers do not have a rigid mechanical connection with the housing, and bathed in a freely-suspended state elastic silicon-organic compound having a high anti-vibration properties.

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The combination of the unique properties of transformers with effective shielding and protection allowed to refuse completely pointless and only high cost the product of two or more structure-options.

The imposition of a separate unit of the clock generator consider it highly detrimental step. As the use of rubidium, hydrogen, and other types of generators with higher long-term stability, having absolutely no values for the devices DAC. The accuracy of the d/A conversion depends not only on the parameters of the Converter in the gain region, but also on the accuracy of the timeline conversion. In other words, the intervals in time between the moments of conversion, determined by the sampling frequency should be equal or as close as possible. If one interval is a bit shorter and the other is slightly longer, the code conversion to analog will not happen in those moments that originally intended, and a little earlier or a little later that, in the end, the equivalent nonlinear distortion of the converted signal. The accuracy of the clocking pulses in time is determined by the low frequency phase noise (short-term instability, jitter). The smaller it is, the better the points conversion located in time. The jitter is mainly determined by the properties of the clock generator and the interference induced on a transmission line of the clock signal. The lowest phase noise at small delays have crystal oscillators with high q-factor crystals, the largest of the various system PLL and frequency synthesis. All generators with ultra-high long term stability built on the basis of the system PLL, or heterogenerous. Actually the frequency of the rubidium lamps - GHz, and not a multiple of the audio 44.1 and 48 kHz, that is, to bring them to the desired DAC clock frequencies around 30 MHz will require a system phase-locked loop - PLL. And short term stability of the signals at the output of such systems will be significantly worse than even the usual crystal oscillators average precision. That is, the use of such generators in the DAC devices is not even just useless, and leads to the degradation of sound compared to high quality quartz oscillators and exclusively for two purposes - to entertain the conceit another winner of a rubidium atomic oscillator (so cool!) and try to justify the ultra-high retail price for such a product.

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The removal of the clock generator away from the point where d/a conversion is just as detrimental as mentioned above. Any line induced noise, which together with a clock signal fed to the input of logic element in IC DAC. Here, the result of amplitude-phase conversion (due to the finiteness of aperture time of logic elements and a limited rate of change of the state of the active elements) is the additive interference induced on the line will be converted to multiplicative, that is, the current on the phase parameters of the signal. In other words, significantly increases the jitter. This is what's happening in any circuit, and the longer transmission line and the more sections, the higher the induced jitter. The clock signal from the external generator will be a lot of sites and quite a long line. As a result, the jitter of the measured clock input IC DAC will be much higher than the actual jitter of the generator. For this reason, in precision measuring equipment (spectroanalyzer analyzers, phase characteristics, high-speed digital oscilloscopes) clock oscillators features directly at points, which is the primary signal conversion. Otherwise, such devices simply won't work.

The DAC in the Apollo, we used normalisatie quartz oscillators with high-q crystals, placed in close proximity to the DAC chips.

Transmission line of the clock signal at IC DAC is made in the form of a closed microstrip line harmonized in the structure of the multilayer printed circuit Board. This allows you to virtually eliminate the influence of external noise on the clock signal and to bring to the tact converters with jitter less than 50 - 60 femtoseconds.