Hum noise from using RCA audio switch

[wolfiesblues]

I am trying to run two turntables (Dual 1237, Harman Kardon hk720) through my Hitachi HTA-5001 amplifier with a passive RCA audio switch. I've run the ground wires to the amplifier's ground post and I can hear a humming noise. I have used the same audio switch with two other turntables on a different receiver without the hum noise. I've also tried substituting a Numark DK 1001 unit, which has its own ground post, and the humming continues. So:
1) I'm not sure if the cause is the ground wire from the harman kardon
2) I'm not sure the Numark unit is the problem

I've read about ground loop noise isolators and balanced RCA interconnects. Never used either. The Numark unit has RCA inputs for unbalanced RCA cables, so I'm not sure if using balanced ones would be a good idea. Any recommendations or tips? Thank you.

Update: I swapped the Harman Kardon hk720 turntable for another one, a Dual CS 503-1. Interestingly enough, I heard no hum coming from anywhere, and I was able to use the audio switch without issues. I suspect the hk720 has some ground issues with the tonearm because a) it has a new stylus and b) I had to pump up the volume compared to the Dual 1237 turntable's audio output. Plus I could hear a faint scratch from one of the channels. I know it couldn't be the stylus (new) and it couldn't be the amplifier or the speakers. Since the hk720 is just a mid-level simple turntable, taking it to an audio shop could be expensive to fix. Any recommendations are welcome.

Wolfie
Glen Burnie, MD

 

[doctor fuse]

I am surprised you have made the audio switch work with the two Duals! It is usually considered impossible to use a typical audio switch with two turntables without adding audible hum or noise.
If the only issue with the HK table is hum using the RCA switch, I doubt there is anything wrong with it.

 

[Butler]

Just a thought is the RCA switch grounded, You have just inspired me to finish my passive switch off, it need a grounding post, suggested by the father-in-law, 1 input (Pioneer PL-12D) 4 out (A60, Trio 4002, Armstrong 521, Bryan 9000). Previously had a hum no matter which amp was selected, added the grounding post, connected all the grounds to the switch box. All good, only get a hum If you have the wrong amp selected, otherwise silent when switched to the correct amp. It goes along my other switch, 4 input (Source's) to 4 out (Amps).
Just don't need to switch the gear round in the rack
Good luck

 

[wolfiesblues]

Just a thought is the RCA switch grounded, You have just inspired me to finish my passive switch off, it need a grounding post, suggested by the father-in-law, 1 input (Pioneer PL-12D) 4 out (A60, Trio 4002, Armstrong 521, Bryan 9000). Previously had a hum no matter which amp was selected, added the grounding post, connected all the grounds to the switch box. All good, only get a hum If you have the wrong amp selected, otherwise silent when switched to the correct amp. It goes along my other switch, 4 input (Source's) to 4 out (Amps).
Just don't need to switch the gear round in the rack
Good luck

View attachment 2942859 View attachment 2942860 View attachment 2942861 View attachment 2942862 View attachment 2942863

Interesting photos. However, my audio switch is nothing like that and it doesn't have a grounding post. I am suspecting that my amp, a Hitachi HTA-5001, has some hum issues with the audio switch connected to it. I applied Deoxit to the RCA outputs in the amp and the hum disappeared temporarily. Maybe the setup is wrong.

 

[Butler]

Yes interesting, a DIY job, simple switch, 3 pole 4 way. The other RCA switch uses 2. Could have maybe bought one but...... more fun to make one.

Is it a DJ 1001? but yes none of the "Numarks" are nothing like mine