Putting a choke on the output of an existing supply does not do anywhere near the effect it does when it put in the right location, between the rectifiers and the regulator.
And you can't just put a choke into any existing linear supply, the whole system has to be tuned to work properly. The value of the choke, caps and parameters of the transformer all have to be right to get the best results. If the values are wrong you could very easily make things worse. The choke does two primary things: It loads the transformer properly so no high frequency harmonics are injected back into the mains and there are no high frequency harmonics sent on to the regulator. With a common cap only filter current only flows out of the transformer/rectifiers when the voltage is greater than the voltage on the cap. This means current flows through the transformer in short high current spikes. For example I've measured a simple cap only design, for the Touch and it has over 20 amp current spikes, even though the Touch is only drawing 1 amp! The high current spikes inject a lot of noise back into the mains, which get into your other components. The output waveform from a cap only supply is a sawtooth, the transformer charges the cap up quickly (those 20 amp spikes), then the load discharges it slowly, this results in a sawtooth. This waveform contains lots of high frequency components which are fed to the regulator. Most regulators work very well at dealing with low frequencies, but do less well as the frequencies increase. This is one of the reasons why a lot of the "audiophile" supplies use high quality discrete voltage regulators, they do a MUCH better job of dealing with high frequencies. But with a properly designed choke supply there are no high frequencies being sent to the regulator, just a pure 120Hz sine wave which just about anything can deal with. There are other advantages but these are the two main ones. John S. -- JohnSwenson ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=91383 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
