Weird ground loop issue.

[IPunchCholla]

I’ve been running into a weird ground loop issue and was hoping someone might be able to help find a solution.

Equipment: (connections in parenthesis)

Technics SL-QD33 connects to Cambridge Audio Alva Solo (ground and rca) connects to Focusrite Scarlet 4i4 (long RCA with RCA to TRS adapters) connects to Mac Mini M1 (USB-C).

Output is Mac mini to 4i4 to Presones Eris 66s (via TRS).

All equipment is plugged into same circuit.

Symptoms:

After playing a record and only after playing a record, I get ground loop buzzing, but very faintly. The buzzing gets much louder after turning off the phone preamp. The buzzing will persist after disconnecting all incoming and outgoing connections (except usb) from the 4i4. Buzzing will get much quieter if the phono pre is turned on and connected.

The buzzing can be stopped entirely by unplugging the usb from the Scarlett 4i4. It returns once playing a record.

Things I’ve tried:

Using an adapter to remove the ground on the phono pre.
Plugging the 4i4 into ports on hubs vs ports on mini.
Resoldering the grounding wire on the turntable.
Cleaning the TT grounding wire connection at the phono pre end.
Plugging everything in to a single power strip.

Any ideas on how to resolve? Thanks!

 

[somebodyelse]

USB isolator for the Scarlett.

 

[Blumlein 88]

So you have no buzz, play a record and you get buzz which will only stop if you unplug and then replug the USB cable. I wonder if something about playing a record sets off an oscillation. The oscillation continues until you stop it by unplugging the USB cable. Have you tried using a different sample rate on the Scarlett? Just a guess it might change something going on.

Ran into something slightly similar using a Mac mini once. The power supply of the Mini would cause motor-boating in the phono. The solution was to move the phono a few feet away from the Mini. It sounds like you already have the phono away from the Mini since you said you had long RCA cable with an adapter on the end.

Just a shot in the dark, can you use a TRS cable with a short RCA connecting to the adapter closer to the TT? Or perhaps the unbalanced RCA is picking up something from the Mini. Maybe move the Mini a little further away from the Scarlett and the RCA cable that comes toward it.

 

[IPunchCholla]

USB isolator for the Scarlett.

Thanks! Never knew those existed. Can you recommend one?

 

[Doodski]

Thanks! Never knew those existed. Can you recommend one?

Topping makes 2 models.

HS01 - TOPPING AUDIO

www.toppingaudio.com

HS02 - TOPPING AUDIO

www.toppingaudio.com

 

[sam_adams]

long RCA with RCA to TRS adapters

And there's your problem. As with XLR adapters and unshielded cable, use the right adapter cable:

 

[IPunchCholla]

So you have no buzz, play a record and you get buzz which will only stop if you unplug and then replug the USB cable. I wonder if something about playing a record sets off an oscillation. The oscillation continues until you stop it by unplugging the USB cable. Have you tried using a different sample rate on the Scarlett? Just a guess it might change something going on.

Ran into something slightly similar using a Mac mini once. The power supply of the Mini would cause motor-boating in the phono. The solution was to move the phono a few feet away from the Mini. It sounds like you already have the phono away from the Mini since you said you had long RCA cable with an adapter on the end.

Just a shot in the dark, can you use a TRS cable with a short RCA connecting to the adapter closer to the TT? Or perhaps the unbalanced RCA is picking up something from the Mini. Maybe move the Mini a little further away from the Scarlett and the RCA cable that comes toward it.

Yes to the situation. Except that the buzzing is loud when the pre-phono is off and quiet when the pre-phono is on.

I’ll give the sample rate a shot. I might have enough TRS to RCA adapters to see if that helps. The Scarlett and the mini are already a couple feet apart, but if the first two don’t work, I’ll see about moving them further.

The

 

[IPunchCholla]

And there's your problem. As with XLR adapters and unshielded cable, use the right adapter cable:

View attachment 387266

You had my hopes up for a minute! I went and looked and realized it was store bought adaptors plugged into the Scarlett. I switched them out for two I had built myself using the green labeled diagram above. Unfortunately they still have the same issue. Everything is fine until after the phono amp is turned on then off again. After that the Scarlett needs to be unplugged and plugged back in to the Mac. Practically, the only issue is the phono amp has an auto off.

 

[sam_adams]

Everything is fine until after the phono amp is turned on then off again.

Have you tried shorting the inputs to ground (Might want try using an RCA connector with a low value resistor—4.7Ω to 10Ω—between center and ground instead of a direct short to ground.) of the Cambridge while it is connected to the Scarlett while the Cambridge is powered off to see if there is still an issue?

 

[Blumlein 88]

You had my hopes up for a minute! I went and looked and realized it was store bought adaptors plugged into the Scarlett. I switched them out for two I had built myself using the green labeled diagram above. Unfortunately they still have the same issue. Everything is fine until after the phono amp is turned on then off again. After that the Scarlett needs to be unplugged and plugged back in to the Mac. Practically, the only issue is the phono amp has an auto off.

The point is whether you are running a long RCA to those adapters or do you have the adapter either at the RCA output jack or with a short piece close to it. Optimum is a long 3 conductor TRS cable from the Scarlett back to an adapter right at the Phono or with the end of a properly made cable having an RCA plug on the end with the 3rd conductor only being grounded at that RCA end.

It still is weird that once you get the buzz it stays even if the Phono is off or disconnected. So something a little weird with that.

Just thought of something else to try. Disconnect from the phono, and short the RCA pin to the shell and see if it makes the buzz go away.

I see Sam Adams posted seconds before I did. Similar idea.

 

[somebodyelse]

Thanks! Never knew those existed. Can you recommend one?

This thread covers a few, including people's experiences with them. Beware changing Amazon listings though - high speed devices sometimes get changed for slower ones.
https://www.audiosciencereview.com/forum/index.php?threads/cesy’s-usb-3-0-isolator.55215/

 

[IPunchCholla]

The point is whether you are running a long RCA to those adapters or do you have the adapter either at the RCA output jack or with a short piece close to it. Optimum is a long 3 conductor TRS cable from the Scarlett back to an adapter right at the Phono or with the end of a properly made cable having an RCA plug on the end with the 3rd conductor only being grounded at that RCA end.

It still is weird that once you get the buzz it stays even if the Phono is off or disconnected. So something a little weird with that.

Just thought of something else to try. Disconnect from the phono, and short the RCA pin to the shell and see if it makes the buzz go away.

I see Sam Adams posted seconds before I did. Similar idea.

With the correctly built adapters, disconnecting the cables from the phono does kill the buzzing, now. If I touch the pin of the rcd cable to the shield of the jack on the phono it also kills the buzzing, but not if I touch the pin of the cable to the chassis of the phono (which strikes me as odd).

I think my plan at this point is to build balanced shielded cables that terminates as per above to RCA/TRS.

 

[Timcognito]

Check the phono cartridge pin connections and wire integrity at both ends

 

[IPunchCholla]

Check the phono cartridge pin connections and wire integrity at both ends

I did that recently, when I took apart the TT to make sure the ground was properly done. There was an issue with the pin connector so I soldered a new grounding wire. I also resoldered the pickup wires where necessary and checked what wiring condition I could. It all looked good.

If I have time tonight, I’m going to open up the solo and make sure the connects are good inside that.

 

[IPunchCholla]

They really don't want you to open the solo. It is designed such that metal tabs on the case were bent around the back and held there by screws such that it is impossible to slide the case off without unbending the metal.

 

[Ken Tajalli]

My guess is, that when you switch off the phono stage, a relay or something, lifts the output connections. So the rest of the system, just sees the interconnect with no connections (open loop). The interconnect picks up hum and buzz from a nearby device.
The USB, can have noise on the ground wire. That's why the buzzing comes back once you plug it in. The noise pollutes the ground plane of the rest of the system.
The afore mentioned Topping isolators both, will remedy the situation and more!
The HS01 is cheaper and just as good. The HS02, I believe manages USB-3 speeds, hence the increased cost.
If you don't require USB-3 speeds (audio is USB-1/2 only), then just get the cheaper one.
My Topping DX7-pro also floats its output when switched off, so I can get a buzz out of my poweramps. As soon as I switch the DAC on, and the relay clicks, the buzz is gone.
HS01 also filters RFI, as well complete isolation. Some amps, can sound hard, if RFI is present! after HS01, they can sound mellower and cleaner.