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Safe to bypass ground (on AD9200a) in a digital Genelec setup?

tedkron, modified 5 Months ago.

Safe to bypass ground (on AD9200a) in a digital Genelec setup?

Youngling Posts: 4 Join Date: 10/28/15 Recent Posts

Hi! 

I have an issue with hum and noise when using unbalanced floating (no safety ground = 2 pin internal psu) sources in my digital signal Genelec system.

Question:

Is there any risk of malfunction or harm to my system or myself if I connect an RCA sleeve directly to the chassis of my Genelec AD9200 AD-converter?

 

The signals in my system runs like this: 

AV preamp (Canton Smart Connect 5.1 RCA) -> [optional ] Art T8 Transformer Isolator -> Genelec AD9200a converter -> Genelec 7260 Digital Sub -> Genelec 83x0 monitors  

i.e., from the AD9200a and down the signal is digital and balanced. 

The problem is that the unbalanced return channel needs to be firmly connected to ground/earth at the monitor end, otherwise I get an audible hum at -30dB gain and louder on my Genelec monitors. I preferably wish to run the Genelec system at around -10 to -15 dB for the preamp volume control to be useful. 

If I connect/attach a cable between any RCA sleeve (or the HDMI sleeve) on my preamp and the rack screws on the AD9200, the hum completely goes away. 

Can I do this safely?

 

Some observations for completeness’ sake:

1) Using a multimeter on disconnected gear; the resistance between pin 1 at the analog end and pin 1 and the digital end in the AD9200a is 100 Ohms. Bypassing the ground would of course give zero (or negligible) resistance. The resistance between RCA pin and sleeve on my preamp is 50 Ohms. The preamp output voltage is spec’d at 2 Vrms. 

2) Using the Art T8 transformer above (isolation between signal grounds) makes the hum MUCH worse. Connecting the ground lug on the transformer to the rack screws on the AD9200a removes the hum completely. Is this safe to do?

3) Connecting via analog without the Sub works perfectly:

Preamp -> Genelec 82x0/83x0 monitor via analog RCA-XLR cable (pin 1 and 3 tied together).

4) Connecting (for example) my RME Babyface Pro interface (floating balanced) to the AD9200a and Genelec system works perfectly.