Re: Floating local ground?


"Chris Carlen" <crobc@xxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:d73gui02v2i@xxxxxxxxxxxxxxxxxxxx
> Greetings:
>
>
> Can I simply expose the differential input to the outside world of a
> completely floating power system without trouble?

Chris, I think you will run into trouble. Your amplifier has capacitance to
ground which means it is not isolated at AC, but significantly connected.
All that current flowing throught the speaker circuit and who knows what at
the PWM and DC-DC converter frequencies mean your diff amp may have to
reject tens of volts of audio and hash which may easily exceed its input
range. In addition, if it is also not capacitor, who knows what DC level the
various leakages will set up between the input and amplifier circuits. A
differential amp is not magic - it requires the input circuit has some kind
of common connection to the diff amp *other* than the two differential
inputs.

A similar situation exists when you lift the ground of a switched mode power
supply - a gross amount of signal exists from supply output to ground.

I think an audio transformer or an opto isolator, including opto isolated
digital audio are the only genuine no common connection methods.

Roger



.

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