OTL Asylum: If the ground is truly ground then 'no' by Ralph OTL, Output Transformerless Amplifier User Group.

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Posted by Ralph (M ) on October 1, 2014 at 09:56:23

In Reply to: What if I'm using a 'Balanced Power Supply'? posted by Cousin Billy on October 1, 2014 at 08:18:51:

One thing about balanced power- equipment is not designed for it. Here is an example:

If you are to meet UL or EU directives (CE mark), the fuse has to be able to blow to protect the user. The tricky area is what if the power switch, which is mounted to the chassis, gets shorted to the chassis and allows it to become 'hot'? The fuse will blow, because it is in series with the chassis. Now the same thing is true of balanced power.

But what if something happens such that the other side of the line shorts to the chassis? What then? There is no fuse for that. As best I can make out, in this situation there will be 60VRMS on the chassis- IOW it will be 'live', as in a balanced situation there is no 'hot' and 'cold'; both side are 'hot'.

As long as everything is working, balanced power offers lower noise if you have bugs in your equipment's grounding scheme. This is because if there is a grounding bug, there will be current in the ground connection. This can cause ground loops and in a really bad situation even damage something. Balanced power offers a solution for this. But ideally, there will be no appreciable current in the ground, because in a properly grounded audio system, the circuit ground floats at chassis potential, but they are not the same circuit- IOW its bad design practice to use the chassis for a ground!

A lot of audio manufacturers have not sorted this out, and it does not matter what field (pro audio, broadcast, high end audio) they are operating in. For this reason you will see some pretty respected names extolling the virtues of balanced power.

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