Speaker hiss and the ground-lift switches on an EMU-0404

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JohnnyCosmo

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Hi, I'm using an EMU-0404, Mac and Tannoy Reveal 501a's, and have a couple of questions...

1. I have a very quiet hum or hiss coming from the Tannoys. I'm not sure if it's normal or not, but it doesn't change with the volume, and it isn't anything to do with any other gear (it happens when they're not connected, just switched on).

2. I've never really been sure where the ground-lift switches should be on the EMU-0404 - left or right? I normally use a Rode NT1A and an SM57, from time to time I plug an electric guitar straight in. Not sure what matters.
 
From my experience, if the ground-lift switch is going to do any good, you will know it, right away- reversing it either does nothing (which indicates the problem is not ground-related) or it makes a DRAMATIC difference, either good or bad depending on which is needed. There may be more precise ways of using the GL switch, but I just flip it back and forth and listen to what happens. If things get better, that's where it stays! 95%- maybe 99.9%- of the time, I am setting a live sound system, so time is of the essence- I don't have the luxury of delving into the theory, at the moment.
 
Thanks, I guess I don't need to worry because I can't really hear any difference. About the speaker hum though - is it normal to have a little bit? It is pretty quiet, only really audible if there is either no sound playing or if I boost the volume on the speakers.

Just out of curiosity, is it preferable to have my soundcard output level full (labelled +0dB on the Emu 0404), or to have it lower, and boost the speakers? It might seem silly, considering I just said I get some noise from boosting the speakers, but I'm not sure if that's normal or not yet.

Another question, I have crackling when i turn the output level on my soundcard. I assume it's dust in the pot, but I don't really know how I can clean it. I've sat turning it up and down, which is supposed to work, but there is still some there. It's only in the right channel though (and it's not the cable, or speakers, I've tested that). Ideas? The dial doesn't seem to come off.
 
No. Hum shouldn't be normal. At high gain levels the amp in the reveals might have a bit of hiss (noise) but hum is generally an indication of an ground/earth (depending which version of English you speak!) problem somewhere or, just occasionally, a problem in the amp power supply.

Normally I'd suggest isolating bits of equipment but if it's there with nothing connected, either the mains supply is faulty or there's a problem with your Tannoys.
 
Hmm. It probably is more hiss than hum... a mixture - but I've just tried pushing the power cables further in (that came with the speakers), and the hum was reduced... so I'm guessing I do have a problem there.

About the possibility of a ground problem, I can't seem to understand how I'd remedy that? What do I need to do to test that?

Thanks for the response.
 
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