Hi!
I bought a Teac TN-300 turntable about six months ago and I've been having problems with feedback sound. This only occurs while the turntable is playing at a high volume, and the problem increases on songs with a lot of bass. This doesn't happen with other devices and I've tried different cables. The amplifier is a K-12G that I put together over the weekend

and I'm using the preamplified output from the TT.
The speakers are on the floor (concrete floor) and the TT is on a desk (not a heavy or robust desk, almost everything on it vibrates when the volume is up). The TT is also close to one of the speakers (two or three foots distance). I've also reset the settings of counterweight and antiskate, but it doesn't make a lot of difference.
As far as I've read, this could be a mechanical vibration issue and I should try isolating the turntable.
I'm thinking on building a wall shelf for the TT. My questions are:
Would putting the TT on the floor get the same results as putting it on a wall shelf? Not to leave it on the floor for the eternity

, but to see if building the shelf would help.
And how far away from the speakers should the TT be?
PS: The speakers highlight a lot the bass (these are from a Sony mini-component) and I don't think I like that. What characteristics should I look for when buying a replacement?
Thanks in advanced guys!