What equipment do you have? Dedicated power lines? Very curious how you have got rid of all turntable hum.
Very little hum on my main MC system, but my bedroom system with a Dual 1009 SK with MM cart has audible hum when there is no music playing, at loud volumes.
Excellent question!
To get a hum free vinyl system, you have to attack the problem from several different angles:
1. Power amplifier(s) need to be located as far as possible away from turntables, phono preamps and line preamps.
2. The phono cartridge needs to be compatible with the turntable. An example of this is running a Grado cartridge in a Rega table (results in hum).
3. Audio interconnects need to be heavily shielded and away from transformers (including wall warts). I use my own DIY cables.
4. Phono preamp and line preamp sheet metal cases should be of a heavy gauge steel (or other materials (i.e. copper, heavy aluminum).
5. Noise drain of turntable (if using a stand alone phono preamp) may benefit from being attached to the line preamp, rather then the phono preamp. In my case, I have 3 turntables, connected to 3 stand alone phono preamps with noise drain attached to the line preamp, not the phono preamp.
6. All lighting should be on a separate branch circuit.
7. Any dimmers for LED lighting should be on a separate circuit and should be the LC type dimmer.
8. No cable TV coax should be part of the system, unless completely isolated. (best to have a separate system for video viewing).
and lastly, turning your volume control on the line stage preamp to full volume to see if you have any hum is not a great idea. Accidents can happen and speaker damage will occur. BTW, as I claimed, I have no hum element (even at full volume), but there is hiss, caused by the incredible amount of gain on the phono stage. If you have hum at 9 o'clock volume position, you have a problem. If you have hum at 12 o'clock volume position, you have a slight problem. If you have hum at a 3 o'clock position, you really don't have a problem and are certainly in the danger zone.
Wayner