Audio Systems: Speaker hum when connecting small amp, definitive technology speakers, ground loop isolator

Question
I recently purchased an inexpensive turntable to try and listen to my old LP's through my home audio system. I discovered I couldn't get sound once I hooked it up to my Denon AVR5800 receiver with Definitive Technology speakers. I did a little homework and found out I needed a small amplifier to generate more power to the turntable. My problem-I hooked one up and as soon as I did, the turntable works and I hear the music but I get a hum so loud you can hardly hear the music. How can I fix this? Thanks in advance for your help.

Mel

Answer
Hi Mel,

 Yes, you do indeed need a "pre-amplifier" to use a turntable.  If you bought a phono pre-amp then you're all set.  If you went out and bought a "small amp" and hooked that into your receiver then you've got the wrong equipment - return it or exchange it for a Phono pre.

  Your hum problem is not uncommon.  It can usually be fixed as long as you figure out what's causing it.

  First, you need to make sure that the gain on your pre-amp is set correctly.  If you have a volume knob on your pre, it's bad practice to leave it turned all the way down and then turn your stereo amp all the way up.  When that happens, you're sending a very weak signal to the amplifier, which you then have to boost WAY UP - thereby also amplifying all the electrical noise that's in the system (but usually too low to hear).

The other common problem is a ground loop.  The hi-fi solution is to go around putting all equipment onto one phase, grounding all chassis to one bus ("star-point" grounds) etc. - I do that frequently but BOY is it a headache.
If you have an inexpensive turntable and just want to listen to some old tunes, try adding a ground loop isolator inline first:
http://www.epanorama.net/documents/groundloop/
http://www.audioholics.com/techtips/setup/avhardware/groundloopcableTV.php
http://www.radioshack.com/sm-see-all-needs-and-wants--pi-2062214.html
http://www.crutchfield.com/S-VfBltYSH2XU/cgi-bin/ProdView.asp?search=ground+loop...

You might also want to check your cabling and re-wire to avoid "induction".  
When audio, speaker, and power cables run together in parrallel often noise can be electromagnetically transferred to the audio cables.  Again, this noise can then be amplified and reamplified to develop into quite an annoying buz.   Try seperating your cables - especially the audio from the power - by at least 2 feet.  Where they have to cross, they should do so perpendicularly (90-degrees, like a cross) from eachother.
-whatever isn't cleaned up by one method should be resolved by the other.