Actually you CAN get some magnetic shielding with aluminum. A 1/4 inch thick piece of aluminum will drop a 60Hz magnetic field by 5-10db. So putting a linear supply in a thick walled aluminum enclosure is not just cosmetic. If I remember correctly the thickness is directly proportional to the attenuation, so don't skimp, use massive thick heavy stuff.
Even with a linear supply you can get a significant amount of radiated noise caused by the secondary of the transformer ringing at high frequencies when hit with the current spike from the recifiers. This effect is worse the "higher" the quality of the transofrmer. Its very easy to damp this ringing with a resistor and capacitor (the two inseries) placed across the secondary of the transformer. Almost no commercial supplies have this. I tried it on mine and it made a significant difference. Jim Haggerman has a paper on this on his web site if anyone wants to look at it. Its a bit complicated to find the exact values to use, but it turns out that damping too much doesn't hurt anything. So I came up with a set of values that worked for every one of the transformers in all my equipment, 330 ohms and .022uf. I put these on everything and the results were startling, the acoustical space of the original recording is now much more a part of the listening experience. Its probably the largest improvement in sound for any one thing I've done. And this one IS measurable. With my scope set to its highest gain setting I could always see some high frequency "hash" on the supply rails and the audio outputs of pretty much anything in the system. After this change the hash was gone. The scope trace is just a thin line now (with no signal). The SB linear supply was one of the biggest offenders, since it runs at a fairly high current it has large caps, which result in very large current spikes. I also used a high quality transformer which had very low losses, unfortunately that means it rings like a bell at 200KHz! Cheap crud transformers actually don't ring as much beause their internal losses tend to damp the resonances. I would definately recommend this simple "tweak" if you are using a large high current supply, it will almost certainly have this problem. John S. -- JohnSwenson ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=34291 _______________________________________________ audiophiles mailing list [EMAIL PROTECTED] http://lists.slimdevices.com/lists/listinfo/audiophiles
