Isolation Transformer - Use with Cheater Plug

02-22-09: Hhawk
Forgot to say that I do have Directv and audio is connected to the preamp via RCA jacks. So maybe a RCA ground isolation device is what I really need.

Could very well be the source of the ground loop hum....
For lightning protection the SAT system has a lightning protection arrestor. The cable/s from the SAT dish connects to the arrestor then exits the arrestor and runs on into your home.

Some SAT installers use an outside driven ground rod to connect the lightning arrestor to earth. This will cause ground loop hum.

Temporarily disconnect the Directv ics from the preamp! Check for hum.....

Still have hum?
Just to make sure you are isolating the SAT 100% from your audio system disconnect the RG6 coax/s, (at the receiver), that comes from the dish to the SAT receiver. You may have two RG6 coaxes if you have a DVR.

Post back the results.

Forgot to say that I do have Directv and audio is connected to the preamp via RCA jacks. So maybe a RCA ground isolation device is what I really need.

Thx again. And the humor went over my head - I have no idea what you are talking about :)
Jea48 - Yes, without the cheater plugs and even inserted into the same outlet I get the hum. I replaced a Parasound with a McCormack power amp and that started my having this problem. Cheater plugs do solve the problem but I had read where an isolation transformer might solve it as well and there would be no possibility of a nasty shock using that method.
It appears from what you guys are telling me, it that I am still better off to have the pair plugged into the Tripp-lite using the cheater plugs than to go back to having the pair plugged directly into the outlet. It reduces the chance of a lethal shock.

A balanced power system is still a grounded AC power system, (60/120Vac). True both 120V legs are ungrounded with a reference from each leg to the grounded neutral of 60V.
The neutral is still connected to earth ground per NEC Article 647.
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I originally had the pair plugged into the same outlet with the cheater plugs. (I did not have this problem until I replaced my previous power amp.) Without the cheater plugs, the hum is very loud.
02-21-09: Hhawk

Hhawk,

Are you saying with all the associated equipment, that is connected together by ics, plugged into the same outlet without using ground cheaters you get a loud hum?

By Chance do you have a CATV system hooked up to the audio system in any way?

HHawk: I guess you missed Jea48's humour. Yes, you can still get a minor shock. The iso will reduce common mode noise in the AC line and reduce voltage spikes. Sizing is important. For both a preamp and amp, 1 KVA is minimal.

You might want to do some search and research into "ground loop"

Rives: You guessed right. Shhh.

But NGjockey--you are probably using a balanced center pole grounding scheme I'm guessing--in which case there is no neutral--it really is negative.

Thanks for the responses. I originally had the pair plugged into the same outlet with the cheater plugs. (I did not have this problem until I replaced my previous power amp.) Without the cheater plugs, the hum is very loud.
Sorry to still be confused - I didn't word my original question very well. Since the Tripp-lite did not solve my ground hum problem, is it at least giving me some protection from shock since I have to use the cheater plugs one way or the other? Or should I just go back to plugging the pair straight into the wall outlet and try something else? (I might try isolating the RCA cords next.) Thx again.

Forgot about that. That explains a lot about why iso's have gone out of fashion. My wiring has been more creative and with larger transformers. Yes, I should have said neutral instead of negative.

02-21-09: Ngjockey
According to code, the ground is not isolated by the iso and is continuous. The positive and negative are isolated.

And just to add....
For isolation transformers less than 2 KVA, if memory serves me right on the size, the safety equipment grounding conductor from the wall outlet can be used to connect one of secondary winding legs to ground. This grounded conductor, known as the neutral conductor. This connection also becomes the connection for the receptacle/s equipment grounds. A separately derived power system, (an iso transformer), shall have its secondary wired as an AC grounded power system.

In other words the secondary of the transformer can not float. It must have a direct reference to ground.

According to code, the ground is not isolated by the iso and is continuous. The positive and negative are isolated.

If you plug equipment into a isolation transformer like a Tripp-lite using cheater plugs, do you still get the shock benefit?

You bet! You could receive an electrical shock if a ground fault condition were to exist under the right conditions.

(The only way I can prevent loud hum is by using cheater plugs on both my preamp and amp. Plugging them into the Tripp-lite without the cheater plugs did not work.)

What happens if you do not use the Tripp-lite and plug the audio equipment directly into the wall outlet? Still have ground loop hum?