Superline-552: right channel hum

As the days are less busy towards the end of the year, I find more time to listen to music and also to ask for advice here:

So my Superline is connected to 552 powered Aux2 and there is audible hum on the right channel, loud enough to disturb music through quiet passages.

The turntable cable is ok, my dealer tested it and when I flip left and right channel, the hum is still on the right channel.

When listening to other sources, there is no hum.

Directly after switching on the 552, there is no hum.
It´s only after several hours or sometimes several days, that there is an audible hum on the right channel.

Before I bought the 2nd hand 552 (DR and service in April 2019) I ran the Superline via dedicated HiCap into 282-HiCap for some years without any hum.
After a few months connected to 552 Aux2, the hum appeared.

I feel that further inspection by my dealer might be necessary, yet I wonder if there is a way to narrow down the fault either to the Superline or the 552 or the 552PS or the SNAIC?
Then I would not need to bring everything to my dealer but only the faulty device.

Any advice appreciated.
Happy holidays and of course a happy new year!

Is the turntable connected via RCA Phonos or BNCs?

If RCA Phonos, make sure any locking collars are tightened up as much as possible. The Next Gen sockets can make contact of the outer part of the RCA Phono plug tricky (unless you are using the matching Next Gen RCA plug, in which case you need to make sure it’s accurately orientated otherwsie you have no contact at all!) and thus may be marginal hence why it gets worse over hours or days.

Does it occur with other sources?

Got the same issue few weeks back (RP10/Superline/Supercap/NAC 282 )and after deep investigation found that was cause by Superline 53x crypto plug …remove it and put it back again …problem solved. (issue was not found with Superline standard plug)

Give it a try , hope helps


I unplugged and checked the RCA connectors, they are both tight as much as possible.

Still there is humming in the right channel

Only with the Superline, other inputs are fine, no humming there

Those may not make a good contact withe the WBT Next Gens as you can’t tighten the outside of the plug. What if you swap them around Left to right?

Otherwise, do you have any RCA to BNC adaptors? If so, try connecting via the BNCs and let me know the result.

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Thanks so much for this hint!

When I remove the capacitance plugs the hum is gone!
The cap plugs (1, 4,7, 10nF) each induce hum in the right channel, the resistor plug has no effect on the hum.

Thanks very much Richard! It seems the cap plugs are responsible for the humming.

Try cleaning their contacts…re-inserting…etc?

How does it sound just leaving off the 1 nF plug? With my Rega, it’s quite listenable without it. A bit dry.

I prefer the sound with the 1nF plug.
So I changed the cable dressing of the SNAIC and tt cables in a way that I could use the plugs again without humming.
The cables did not touch any power cord or burndy before nor after rearranging them, yet it seems to make a difference, don’t know why. Hope the humming will not return in the next days…

They look like Moonglo plugs?

The plugs are Neutrik Profi, most likely the OEM base for Nordost.

So rearranging the cables had no effect:
With cap plugs humming started a day after powering up the 552.

Without cap plugs no humming, it stops immediately after the plug is removed.

Any idea how humming with caps plugs can be avoided?

By first visual inspection the contacts seem fine. How would you clean the contacts?

Correct! :slight_smile:

do you have any RCA to BNC adaptors? If so, try connecting via the BNCs and let me know the result.

These are the original OEM Nordost - and they unscrew so you can check the innards.

I have one, which is used for the digital cable for the nDac.

When I use this one RCA-BNC adapter on the Superline, there is no effect on the hum:
With capacitance plug there is hum on the right channel, without capacitance plug no humming.

I‘ve tried the BNC adapter on the left and right channel, each time with the left and right tt cable.