Help Troubleshooting a Ground Loop Issue

[Connor1a]

Hey Guys -

I could use a bit of your expertise. I’m having a helluva time troubleshooting what I believe is a ground loop issue.

My power path is grounded wall receptacle —> Panamax M5400 —> Pro-ject Tube Box S2 / Technics SL-100C.

There’s a ground wire running from the lug on the Pro-ject phono preamp to the lug on the Technics.

The the music path is:

Technics SL-100C (RCA Out) —> (RCA In) Project Tube Box S2 (RCA Out) —> (RCA In) WiiM Ultra ADC/DAC (RAC Out)—> NCx500 Amps —> Warfendale Speakers + SVS Pro 1000s

The symptoms are:

1) I’m hearing a hum whenever I place the stylus in down position on an album.
2) The hum occurs both when the turntable is plugged in as well as when its unplugged.
3) It seems to be coming from the subs vs the mains (which I currently have filtered at 80hz).
4) If I tap on the plinth while the needle is up I receive nothing; no taps through the speakers.

What I’ve tried so far:

1) I mounted the turntable on a shelf on the wall to remove floor vibrations. Improved the overall sound, but did not correct the hum. So no joy.
2) I tried connecting both the turntable and the preamp directly to a grounded power powerstrip and via plugs directly on the Panamax. No difference so no joy.
3) I moved my speakers around to get the subs away from the turntable. No joy.
4) I purchased a fluid dampener upgrade for my tonearm to reduce resonance. Some improvement, but overall, no joy.
5) I’ve tested the receptacles with a Klein tester. They’re confirmed as grounded and correctly poled. So no joy.

I seriously doubt it’s the turntable. It’s new whereas my home was built in the 1940s. I’d guess electrical issues before I guessed that I received a lemon from Technics. What can you guys recommend? I’m starting to pull my hair out.

Thanks so much.

 

[DVDdoug]

Does everything have 3-prong grounded AC plugs? That's the most common way to get ground loop. (Otherwise there's usually only one ground path.)

You can try one of these adapters to TEMPORARILY break the power ground. It's a safety ground and those things are INTENDED so you can plug a grounded device into an old-ungrounded outlet and the tab is supposed to be attached to the screw on the outlet. You're not supposed to use them to break the ground but it can be useful for troubleshooting.

1) I’m hearing a hum whenever I place the stylus in down position on an album.
2) The hum occurs both when the turntable is plugged in as well as when its unplugged.

That seems to imply mechanical vibration... It's not the location of the pickup, right? As soon as the stylus is slightly above the record it stops?

But since moving it to a shelf didn't help that seems like the whole house is vibrating. That's possible, but it seems unlikely.

If you think it's vibration maybe you can get some little springs from the hardware store and try some isolation experiments...

There are different approaches to turntable design. My old Tehcnics is "solid" with little or no isolation/suspension. My 1st turntable was a "floaty-springy" AR.

 

[Connor1a]

First, thank you for the reply.

I’ve taken your thinking and tried a different approach.

I think you’re right about the whole house shaking. I live in a small 1940s cottage. I have 3 in window AC units. One in a window on the other side of the wall from the turntable. Different wall, but same corner. I turned off all the A/C units and … … the hum stopped. So I don’t think this is a power issue after all. I think its the vibration from the A/C units (not just the one on the other side of the wall from the turntable shelf).

Possible solutions…

1) I could place some sort of foam material between the mounting plate of the shelf and the wall. Perhaps something like Sorbothane. Basically build a “decoupled” membrane between the shelf and the wall. I don’t place a lot of confidence in this approach. I’ve tried foam in the past with limited success, but there seem to be a lot of others who’ve had more success.

2) I could purchase 3rd party vibration dampening “feet” for the SL-100C. They’re expensive. Something like these:

Technics SL-100C Turntable Isolation Feet (Set Of Four)

These custom isolation feet for the Technics SL-100C turntables are "Made to Order" so expect 1 - 5 business days before shipment. Each Technics SL-100C upgrade foot 2.75" (69.8mm) diameter x 1.77" (45mm) tall when the Sorbothane is under compression. Mnpctech's Technics SL-100C Turntable...

www.mnpctech.com

3) This is a vibration reducing platform on Amazon:

Amazon.com

4) Another approach on the feet:

https://www.amazon.com/dp/B076DGD3X2?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1&th=1

5) Or these:

Amazon.com

With so many options, I’m clearly not the only guy dealing with sneaky vibrations affecting my turntable. Really appreciate your help…

Thanks greatly for the assist….

 

[Connor1a]

I tracked down the source of the issue. I’m posting it here only to help out the next poor soul who may run into something like this.

It wasn’t a ground loop issue. It was vibration.

To find the source, I had to unplug everything from all the surrounding rooms. Literally everything. Once I had an electrically silent home, I slowly began plugging things back in, one at a time, listening for the turntable to restart its feedback. I started around the turntable and worked out. I had to go slowly as it took the turntable a bit of time to pick back up on the vibration as I restarted devices. I live in a 1940s bungalow style home. I don’t have central air conditioning so have several in window A/C units running. I tracked the vibration down to a A/C unit in the room opposite to my lounge where my turntable is setup. It’s a fair distance away from the turntable / not an obvious source of vibration when you’re standing there looking at everything in the other room. Lesson being that if you’ve removed all the possible sources of a problem, it’s time to start looking at the impossible. I didn't think the A/C unit was close enough to cause an issue, but I was wrong. Now the question is whether vibration dampening feet on my turntable will be able to deal with the issue or whether I’ll just need to wait out the hot weather (until I put the A/C unit back in the basement)…

I thought it worth sharing what ended up being the cause of my ills… YMMV.