Can't tell,if my house is properly grounded

last_lemming OP 277 posts                                               02-21-2017 5:47pm

Ok here is the results with power of preamp and amp on:

hot + neutral = 120.5V+/-

hot + ground = 120.5V +/-

neutral + ground = .05V steady

The voltage measurements look great.
Neutral to ground AC voltage of 50 millivolts is ok.
With that said though IF there is an internal problem with the preamp and the neutral conductor is bleeding off somehow to the equipment ground conductor would a 50mv difference of potential, voltage, cause the hum you are hearing?

Per NEC code the safety equipment ground and service entrance neutral conductor is intentionally bonded, connected, together at the main electrical service panel and not at point there after.

If a difference of potential is present, (50mv), and a closed circuit exists, will current travel through the circuit? Yes, imo.

Someone like Al, ( almarg ), could answer that question. Hopefully maybe Al is following this thread and will chime in.

Curious what scale on the multimeter did you use when you checked the neutral to equipment ground voltage? The lower the scale the more accurate the reading.

//

How about the other test?

With the preamp plugged into the AC outlet but powered off, not in standby if it has a standby feature, do you get hum/buzz through the amp/speakers?
I believe if the preamp has AC line filtering it is done near the IEC inlet connector ahead of the main power on/off switch. I am not 100% sure of that though.

Check to see if you get the hum with the main power switch turned off on the preamp.
.

GOOD NEWS!!!

So I found a proper cheater plug and tried putting it on the tube amp only - buzz completely gone whether the phono pre was on or off. So it appears the amp was to blame and the phono preamp just amplified the problem.

The cheater plug on the amp did break the ground loop circuit, but that does not prove the amp is at fault. It could still be the preamp causing the problem.

So now, hopefully, when my new Decware integrated tube amp comes in it wont exhibit this buzz/hum, if it does at least I know its not the AC line.

Time will tell.

Good luck,
Jim

Jea48,

i did get the hum with the preamp turned completely off - though barely audible, it
was there, just not as loud. 

It's a good idea to have the amp and preamp on the same circuit to eliminate too many paths to ground. A cheater plug is usually safe as long as you have the interconnects plugged in though.
This is also the reason most of us use balanced cables now.