I have a Dual CS 505-2 belt-driven turntable, an Ortofon 305 cartridge (soon to purchase an OM 30), RCA AH500 preamplifier and the following problem: intense hum in both channels. So intense that I can barely hear the music. The hum can be heard as soon as the amplifier is turned on, even when the motor is not used and the record is not spinning. I tried swapping the wires connected to the cartridge with no change. My turntable has a grounding wire that is not connected to anything, although I tried connecting it to the back of my computer with no change also. One interesting thing is... when I attached the grounding wire to one of the RCA connections, the hum disappeared completely, although music was playing loud enough only in the right channel; I could barely hear it in the left channel.

Any input is welcome!

Does anyone else have similar equpiment and experience a similar problem?
Any suggestions on how to ground the turntable and/or eliminate the hum?

Thank you very much in advance.

Actually, I did try doing so, but it did not help. My pre-amp has a grounding post, but connecting to it did not solve the problem. See here: http://www.audioannex.com/showthreaded.php?Cat=&Board=4&Number=58318&page=0&view=collapsed&sb=5&o=0.

Thanks again!

Yes, the turntable was made in 1985 and it is a decent one, if not the problem that I am having.

My pre-amp has only two input channels and two output channels, nothing else, and it is specifically a phono (turntable) pre-amp. Unfortunately, I do not have another pre-amp, but this one is fine. I tried running other devices through it and there was no hum.

I did check the continuity of the grounding wire from the RCA to the ground on the chassis and it is fine.

Yes, I am to troubleshooting the problem.

Thanks for helping!

I tried running my computer audio output and my tape player through the preamp, and it worked well. (They do not need that, but I did it for the sake of testing).

Just a few minutes ago I thought about connecting the grounding wire to a power outlet's grounding post, but for that I need to modify the power and the grounding wires of my turntable. I can cut off the original plug, buy a 3-pin plug and safely connect the power wires and the grounding wire to it, after which it will be easy to use. Do you think it will work?

Thanks.

And my response to that: http://www.audioannex.com/showthreaded.php?Cat=&Board=4&Number=58329&page=0&view=collapsed&sb=5&o=0

I do not believe that there is something wrong with the turntable. I strongly believe that the problem is due to improper grounding (I tried a few ways, except the one that you suggest me not to try).