Reference Probe Question

[ch83575]

This one is pretty basic. When using a potential divider reference probe for SPL measurements is it better to have a probe that attaches to the hot and ground of the amp, or to "float" the probe by attaching it only to the hot and connecting the ground leg of the potential divider to the soundcard ground only? This is of course assuming the amp doesn't have an elevated ground voltage. Is there a benefit one way or the other? I have only ever done the latter, which seems to work, but perhaps I am risking my soundcard or something 8O

Sorry if it is a stupid question, but "grounding" is one of those concepts I have just never been able to quite wrap my mind around totally.

-Chad

[cjd]

Well, there's ground and there's earth in these circuits, and they're often tied together too.

Theoretically it should all be the same ground. Sound card ground or the "ground" speaker output. But that can depend very much on the amplifier.

C

[Dennis H]

It should work either way with a 'normal' amp where the (+) speaker terminal is hot and the (-) terminal is ground. Most hookup diagrams show using the amp (-) as the reference ground for the probe. However, with a bridged amp, like the T-amp discussed in another thread, the speaker terminals are both hot but with opposite polarity. In that case, grounding to the soundcard or the input side of the amp is the only way that will work.

[ch83575]

So, if using a compatable amp which is best:

1. Grounding probe to speaker (-) only. No ground conection at soundcard.

2. Grounding probe to soundcard (rca sleeve) only. No ground conection to amp.

3. Connecting probe ground to both (-) of amp/speaker AND ground of soundcard input.

Or are there no best ways... each should work the same?

Thanks,
-Chad