Is this risky?

[cbutterworth]

Upon Sy's recommendation, I replaced the signal wiring for one of my inputs with a shielded cable, the shield connected to the Aikido PCB GND pad. All remaining traces of hum were instantly banished from my Aikido.

That works great for my CD-player - a Rega. However, when I hook up my DVD-player to the same input, I get a ground-loop hum. The CD-player is a Sony and has only a two-pronged plug. As it happens, I have not yet rewired the remaining inputs with shielded cable, so on these other inputs, the signal is connected, but the signal ground isn't. Anyway, I thought that maybe a gnd-loop couldn't occur if I used one of these inputs for my DVD-player. When I connect to one of these inputs, I get great sound and no hum.

So my question is:

In order to break a ground-loop with another piece of equipment (that only has a two-prong plug) is it safe to disconnect the RCA ground in the Aikido???? I get great sound, no hum, but are there any pitfalls about doing this, such as maybe greater risk of external noise, etc.

Thanks,
Charlie

[cbutterworth]

Sorry, I meant to add, that I would end-up with a bunch of RCA's that have the GND bussed to the shielded cable, and the RCA for the DVD hook-up being left totally unconnected, save for the signal +.

Charlie

[jarthel]

according to rod elliot, you only need 1 ground-loop breaker in your system.

[SY]

This is why I'm such a fan of input transformers.

As long as the chassis is firmly connected to safety ground and everything is hooked up in the system, you're fine. If there were a shielding/noise issue, you'd hear it.

[cbutterworth]

Good. I thought that there shouldn't be a problem, but you never know. The DVD-player is obviously double insulated (I guess) as there's no earth pin; and my Aikido and AKSA are all securely earthed via their own earth-pins. I expect that the TV will also cause hum, as may the video player, although we rarely use it. It is easy simply to disconnect the ground buss at the Aikido end for these devices.

I know Rod Elliot's website. He has the neat ground-lift schematic that I am using in my Aikido. It uses a resistor/cap network across a dioide rectifier. He reckons that it gives a very safe ground lift that pretty failsafe.

What puzzles me though is that according to the schematics, I have a ground loop between Aikido and AKSA, although both are lifted. However, when I floated ground in either, I couldn't get rid of the 60Hz hum, which disappeared when I went to DC heaters.

Thanks for the replies,

Charlie

[astouffer]

My apex DVD player gave similar hum problems but running a wire from chassis ground to an earth ground stopped it. Floating filaments can also cause hum. Bypass one side to ground with a .1uf cap.