Puzzling hum issues with turntable and new audio interface

[vinylvirgin]

I am working on a system which includes a Technics SP-15 turntable with an Audio-Technica ATP-12T tonearm and an Ortofon DJ cartridge. The tonearm is connected to a RANE PS 1 phono stage, which has balanced outputs.

This setup was once connected to a computer with an Echo Gina 3G audio interface. The Gina has balanced inputs. The setup worked with no issues (well, maybe a smidgen of residual hum, audible only with the monitoring headphones cranked way up).

The old computer and interface has since been replaced with a Windows 10 machine, and a Focusrite Scarlett 2i2 interface (First generation).

After connecting the balanced outputs from the phono stage to the Scarlett, the first thing I noticed on powering up the turntable and its phono stage was a nasty, buzzy hum. The hum is present even when the phono stage is on but the turntable is disconnected from the wall socket.

I checked online to make sure that the 2i2 has balanced inputs as the old Gina 3G did, and according to Focusrite, it does.

The separate ground wires from the turntable and the tonearm are joined and then terminated in a single wire that connects to the ground thumbscrew on the phono stage.

The hum does increase noticeably if the tonearm headshell is removed.

I tried disconnecting the grounding wire from the phono stage (with the headshell reconnected). I was expecting a marked increase in the level of hum, but strangely enough, the level and tone of the hum did not change noticeably.

Furthermore, the level and tone of the hum varies slightly if the phono stage is moved.

I checked the continuity of the grounding connections to the turntable and the tonearm. They appear to be okay. The turntable and phono stage are located a good 4 feet or so away from the computer.

I’d be most thankful if someone here could help shed some light on what might be going on.

 

[bimasta]

Too complicated for me to suss out. But this stuck out —

"The separate ground wires from the turntable and the tonearm are joined and then terminated in a single wire that connects to the ground thumbscrew on the phono stage."

I've had hum problems (deafening) with such rigs before. One system needs both table and arm grounded, while another only wants the arm, and grounding the TT too causes hum. And joining the two ground-wires into one may have worked with the old set-up, but not the new.

That's all I can offer, I just don't have knowledge.

 

[lini]

vv: Which sort of cables from the Rane phono stage to the Forcusrite USB sound interface do you use - or more specifically, is the shield of these cables connected at both ends or at one end only?

Greetings from Munich!

Manfred / lini

 

[vinylvirgin]

vv: Which sort of cables from the Rane phono stage to the Forcusrite USB sound interface do you use - or more specifically, is the shield of these cables connected at both ends or at one end only?

Greetings from Munich!

Manfred / lini

Greetings from upstate New York to you as well! Thank you for your reply!

The cables from the RANE phono stage are shielded TRS cables which I presume have shields at both ends. They go to a patchbay, where they are connected by short lengths of TRS cables to the sound interface, which is connected to the patchbay via shielded TRS cables.

Now, the RANE doesn't have TRS connections on it, only screw terminals. I've connected the shield wires from the TRS jacks that I've added to the RANE to ground, the positive leg of each channel to the red wire in each TRS jack and the negative one to the white wire in each jack.

I've checked all wires and they all appear to be seated and connected correctly.

 

[vinylvirgin]

Too complicated for me to suss out. But this stuck out —

"The separate ground wires from the turntable and the tonearm are joined and then terminated in a single wire that connects to the ground thumbscrew on the phono stage."

I've had hum problems (deafening) with such rigs before. One system needs both table and arm grounded, while another only wants the arm, and grounding the TT too causes hum. And joining the two ground-wires into one may have worked with the old set-up, but not the new.

That's all I can offer, I just don't have knowledge.

Thank you for your reply. Perhaps I'll look into that.

 

[lini]

Greetings from upstate New York to you as well! Thank you for your reply! (...)

You're welcome. Then for a try, I'd suggest to check, whether removing the shield ground connections at the output terminals of the Rane changes anything. And it might be a good idea to try that both with and without the patchbay in between. And apropos patchbay, I suppose you already tried it with the shield ground connections connected at the Rane, but without the patchbay in between, did you?

Greetings from Munich!

Manfred / lini

 

[vinylvirgin]

You know, suspecting a ground loop, I got an isolation transformer. Connected it between the Rane and the patchbay. Didn't help. Bypassed the patchbay with a direct stereo TRS cable. Again, didn't help.

Then I tested the connection of the turntable/tonearm grounding wire to the Rane's ground screw. Secure. Then I got the idea into my head to touch that grounding wire to the outside (ground) connection of the input RCA jacks.

Gone. No more buzz.

I disconnected the grounding wire (from the turntable/tonearm) from the nominal "ground" terminal on the Rane and connected it to the ground connection at the balanced outputs.

Apparently, end of problem. Seems there's an issue with the so-called grounding thumbscrew on the Rane. Don't know how that could have happened, but at least I appear to have my phono back in working order.

Thank you once again.