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發表於 2012-11-15 22:13:04
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Secondly,the iUSBPower plugs into the USB connection between the PC/Mac and any USB Audio Device. Some of the more extreme High End gear does not draw power from the USB, the vast majority of USB Audio Devices, including USB to SPDIF Converters do.
In recent times we have seen some attempts to for example split up USB Cables and Lithium Polymer batteries to substitute the power supply, however most batteries when actually supplying are quite noisy (see our AP2 measurement which includes a 9V Dry Cell, rechargables are worse).
The iUSBPower contains noise filtering using multiple LCR filters and a so-called super regulator (as opposed to a simple cheap 3-pin regulator) which is similar but not identical to the one described by Walt Jung under this name.
As a result you isolate the USB Audio Device (including USB to SPDIF converters) from the computers power supply and you give a power supply much cleaner than that from the Computer.
Additionally we have also build in some ground impedance management and the option to break the USB ground connection entirely. This can help a lot with noise loops.
Third, you ask is it powered by an SMPS, plugtop type which we supply, however any source of around 9V DC may be applied (at your own risk, mind you). As we wanted a simple way of being able to sell and use the iFi worldwide and we wanted to avoid wasting power, we had to use a custom low noise SMPS.
In basic principle an SMPS is a much better choice power supply than using 50/60Hz rectified. The high frequency at which they produce their AC means transformers can be small and thus minimise noise leakage from the mains, they always use choke input filtering and the high frequency means relatively small components are required to filter any noise.
Another factor, such a supply may be made universal (runs on any mains voltage/frequency current, even DC) and if well designed efficiency will be very high, well over 90%.
However, many common inexpensive examples are build so badly they barely pass FCC requirements. This means they radiate a lot of noise back into the mains and often have very large levels of noise on the output.
The first examples we bought straight in shops like Radio-shack were horrendous. The noise on both the mains input side and the output side was sufficiently high to be visible easily on cheap oscilloscopes. output ripple went from 10's to 100's of millivolt.
Opening them up revealed that the RF filtering was not fitted, that the chokes and capacitors where of insufficient value and that several parts that would have produced low noise where missing, even though there where spaces provisioned on the PCB to fit them.
So we worked with a factory to produce our own plug-top power supply, which not only has all the extra parts fitted but goes beyond this. The result is a power supply that leaks very little noise into the mains (you can measure it, but it needs an expensive analyser, scope traces are clean).
Overall, a common linear supply using a transformer, common rectifiers and a 3-Pin regulator will produce more noise (including noise radiated into the mains) than our SMPS. Do not expect most SMPS's to perform similarly.
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樓主: DigitalMana
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發表於 2012-11-10 18:27:29
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