Can't tell,if my house is properly grounded

With only the preamp connected to the power amp, TT not connected to the inputs of the preamp, unplug the preamp from the AC power. Turn on power amp and check for the buzz/hum

Did this and no hum.  I'm not clear what that proves or disproves, if the preamp isn't plugged in then the ground isn't plugged in and no ground loop can occure. 

I just unplugged everything but the amp. I didn't notice before the same buzz/hum is there but bearly audible. This make me think that the noise is in the AC line. The phono preamps amplifies small signals so is it possible this bearly audible sounds becomes easily audible once it's boosted?

Just to add to the general dust cloud that the OP is removing hair over...

I had a persistent 60cps 'hmmm' that sent me on a search & destroy mission.  Went through the usual 'disconnect this/eliminate that' routine on my system to no avail.  Moved on to the ac circuit, unplugging or disconnecting everything, including the GFCI 's that were part of that line...

It persisted.  Visions of 'Reddy Kilowatt' giving me the middle finger salute.

Spouse said "Why don't you try a different circuit?"  Since I subscribe to 'the women are smarter' theory (as they've got us pretty much where they want us), I got out the extension cord...3 wire, of course.

*Poof*  Gone.  Beats me as to why.  Only operative reason may be a noisy breaker.  Since the existence of the new extension cord isn't a tragedy nor an issue I'm in no rush to buy a new breaker, BUT...

It could be that simple.  Easy enough to try, can't hurt to do so.

Good luck.  Spouse got thanks, big hug and kiss. ;)  She likes my hobby...she likes how it all sounds as well although the complexity of 'the mains' confounds her.  So the project at hand is to develop a simple 'work-around' for her to enjoy the solution as well. *S*  Marital bliss requires maintenance...;)

last_lemming OP 272 posts 02-20-2017 7:42pm

With only the preamp connected to the power amp, TT not connected to the inputs of the preamp, unplug the preamp from the AC power. Turn on power amp and check for the buzz/hum

Did this and no hum. I’m not clear what that proves or disproves, if the preamp isn’t plugged in then the ground isn’t plugged in and no ground loop can occure.

if the preamp isn’t plugged in then the ground isn’t plugged in and no ground loop can occur.

That is correct. Also if for some reason AC current is leaking from the neutral conductor to the chassis it is not passing through the signal ground wires of the ICs to the power amp chassis and out the safety equipment ground of the power cord to the equipment ground of the mains power grounding system causing the hum problem.

JMHO, it also proves the ICs from the preamp to the power amp are not causing the hum/buzz problem.
I would think it also says nothing is wrong with the power amp.

IF as gs5556 posted,

I second Erik’s suggestion of having a tech look at it. There is the possibility that a safety cap in the receptacle is leaking ac, especially the one from N to ground. If the fuse blew with that extension cord, it’s possible you reversed polarity and ac went to ground through the bad cap, especially if there is an earth line choke between the safety caps.

that could be your problem.

Especially if you did in fact reverse the plug polarity of the preamp when you plugged it into the 2 wire extension cord. Though I am not sure why you cut off the nub of the female cord cap of the extension cord when all you had to do was reverse the plug and the ground pin would not hit the nub. That would reverse the Plug AC polarity for sure though.

By reversing the plug the neutral conductor in the power cord would have become the hot conductor. IF the preamp uses AC line filter caps and the caps are leaking AC voltage through them, then the one on the neutral to ground would be hot to ground through the leaky bad cap.

But wait, you lifted the equipment ground on the 3 wire plug of the preamp. Yes, but the chassis of the preamp was still connected to the AC mains equipment ground by the signal ground wire of the 2 interconnects between the preamp and the amp. The Amp has a 3 wire power cord and plug, correct?

You could spend a few bucks and buy a polarized ground cheater and try lifting the ground pin on the AC plug again. With the polarized ground cheater you will not be able to reverse the plug polarity by accident again. With the ground lifted at the AC plug if it stops the hum then that would prove the hum is caused from an AC ground loop hum. LIFT THE EQUIPMENT GROUND FOR TEST ONLY.

Because you blew the fuse in the preamp the first time you tried to lift the ground on it, that tends to point the finger at the preamp being the problem, jmo.

EDIT
If gs5556 theory is correct lifting the ground at the plug will not stop the hum, imo.
The AC current will pass through the ICs to the power amp. 

By chance do you own a multimeter?
.

@last_lemming ... jea48 was very helpful to me in finding the cause of hum in my system.

I just unplugged everything but the amp. I didn't notice before the same buzz/hum is there but bearly audible. This make me think that the noise is in the AC line. The phono preamps amplifies small signals so is it possible this bearly audible sounds becomes easily audible once it's boosted?

An easy test would be to use a heavy-duty extension cord and run it to a receptacle on a different breaker, (as mentioned above). Then listen to amp only.