That hifisonix document has some other very useful tips for reducing outer noise sources.
The hum breaking resistor described on pages 37 and 38 is a trick I have used in several amplifiers to reduce magnetically induced noise in the signal paths.
The hum breaking resistor described on pages 37 and 38 is a trick I have used in several amplifiers to reduce magnetically induced noise in the signal paths.
lhquam - Yes it has a lot of info. What do you think about his statement to NOT use a bridge rectifier ground lift if you don't have GFCI in your house?
My belief is that the fuse in the amplifier before the power supply should be adequate. In the event of "leakage" currents from the signal ground through the bridge rectifier to chassis ground that do not cause the fuse to blow, the voltage on the between the chassis and signal will remain below about 1.5V-2.0V, assuming that the bridge rectifier current limits are not exceeded.
Consider a typical FirstWatt amplifier with +/-24VDC power supplies and fused at 3A. The transformer secondaries are 18VAC, resulting a voltage ratio of 120V/18V = 6.67. A 3A fuse should blow if the secondary current is more than 3A*6.67=20A, well below the 35A rating of the bridge rectifier.
Consider a typical FirstWatt amplifier with +/-24VDC power supplies and fused at 3A. The transformer secondaries are 18VAC, resulting a voltage ratio of 120V/18V = 6.67. A 3A fuse should blow if the secondary current is more than 3A*6.67=20A, well below the 35A rating of the bridge rectifier.
The problem here comes from how to protect against a gross fault where the chassis becomes live and there's no safety ground connection or an improper connection. With a GFI backstop, if the consumer touched the chassis, it would trip because there would be a hot-to-neutral current imbalance back at the service panel (they call it a 'consumer unit' in the UK). If you don't have a GFI, it won't trip and the user is exposed to mains.
I am not up to the US electrical wiring code, but certainly, here in the UK, a ground lifter would be frowned upon. If there was an electrical accident or a fire, you would not be covered by insurance. It really should only be used if you don't have any other easy avenues open to breaking a ground loop.
I don't want to scare the bejesus out of anyone, but try to avoid ground lifters if you can. Usually, good wiring practice (minimal loops, no cross-channel ground loops, no common impedance coupling etc) solves the problems - as evidenced by the thousands of consumer audio products that are dead quiet and don't use ground lifters.
Hands in the air disclosure: I have used ground lifters in the past, and a phono preamp of mine has one built in so if builders have a loop they cannot break, they can float the signal ground +-0.6V.
Always adhere strictly to the wiring regulations in your country 🙂