Electronics > Beginners
Why wounldn't big "modern" stereo amp have main's Earthing ?
(1/1)
lordvader88:
I'm just wondering, it has a big linear trans, bolted to the case, made + 2001 by Kenwood, and I'm sure meets all safety requirements to be sold here, yet has no mains earthing ?
ebastler:
It must be double-insulated, or "class II", then. You should find the "two concentric squares" symbol on its type label:
https://en.wikipedia.org/wiki/Appliance_classes#Class_II
madires:
Some amps with 2-prong plugs have a ground terminal for optional earthing. Since ground loops are a common problem with audio setups an enforced ground via the amp's mains plug might be not the best idea.
mariush:
There are ways to make transformers with enough insulation between primary and secondary that earthing is not required.
For example, there are R core transformers where each winding is in a separate spool, on opposite sides of the core material : http://jamestransformer.com/en/transformer/R_core_transformer.html
Or you can use double insulated wire, or plastic frames with plastic wall between the two windings...


floobydust:
Historically consumer audio gear is not grounded, instead double-isolated because of the ground-loops that occur.
Power amp, tape player, turntable, TV, DVD player etc. would be connected together and lots of mains hum results.
You would have to use balanced audio connections instead of single-ended RCA jacks, so added cost there they avoid.

Really old audio gear from the 1950's or so, there was no earth ground in North American outlets. So they manufacturers used the "death cap" to stop RF and noise from being a problem.
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