Intermittend high pitch noise

[bergurbrag]

Hi !
I am loving my Mainline amp, but there is a intermittend high pitch noise on the right channel. It comes and goes. It is no a high sound even with the volume turned all up but it is annoying specially when listening to some types of music.

Please help me troubleshoot this issue.

With regards, Bergur Bragason

[Paul Birkeland]

Can you describe what the noise sounds like?  If you move the amp to a different room, is it still present?

[bergurbrag]

Hi !

Thank you for your most helpful answer. I tried it in another room with another DAC, 300$, and no sound... funny... and again in my listening room connected to my NAD M33, which is an 5000$ unit, I got a little bit more low hum but no high pitch noise. This time I eliminated an extra extension cord.

So mains noise is a real thing, not snake oil

[Paul Birkeland]

You could also give this mod a try:
https://forum.bottlehead.com/index.php?topic=11676.0

[bergurbrag]

Is this a possible sollution for my Mainline issues ?
See attached photo

[Paul Birkeland]

Yes, that's what's in the link that I posted.

[bergurbrag]

Hi !

I have done some tests.
Moved the Mainline to another room and connected it to another DAC (Audioquest Dragonfly Cobalt). And no low pitch hum and no intermittent high pitch noise. Then moved it back to my listening room and connected it to my preamp and the hum was back. The high pitch noise seem to be almost gone after eliminating a powerstrip.
Then still in my listening room I connected it to the DAC, the Audioquest Dragonfly Cobalt connected to a Mac. I used the same power connection as when I heard the hum. The hum was gone.

Is this what is called a ground loop noise ? Can it be fixed with a Rca to Rca filter or are there any other solutions ?
Does this mean that adding diodes to the ICE of the Mainline is unnecessary ?

With regards,

Bergur

[Paul Birkeland]

I would try the diode modification.

[bergurbrag]

Hi!

I am sad to say that the intermittent high pitch noise is back. I tried to run my preamp and Mainline of the same power strip so that they would share the same ground, as someone suggested, but to no avail.

Something new I noticed is that when the Mainline is connected to my preamp through input 1, and playing music and I moved the input switch to nr. 2 I got more high pitch noise and I could hear the music very faintly.

Does this indicate any issues ?

P.s. I have ordered the diodes you suggested.

With regards,

Bergur

[Paul Birkeland]

Have you tried the diode modification?

[bergurbrag]

Hi !

Here is a photo of the input switch. It seams to me that the connections are ok apart from the fact that I have spilled some solder on one of the pins. The solder reaches one of the metal side plates of the switch. Does this mean that this pin has continuity to ground and should I remove this solder ?

[Paul Birkeland]

If that solder touches the metal, you will lose the audio from that channel.

[bergurbrag]

Ok, thank you for your reply. I will remove this solder.
But what about that I got more noise and signal bleed?

[bergurbrag]

Checked this soldering issue under a magnifying glass.
It is nowhere near the side plate. The angle of the photo doesn’t show it.

Please respond to my earlier question.

With regards,

Bergur

[Paul Birkeland]

A little bit of signal bleed isn't necessarily abnormal and isn't a useful piece of information for debugging.  If you put a pair of shorting plugs into the unused pair of RCA jacks or if you hook up a second source that's powered on, the signal bleed will reduce substantially (likely to inaudible levels).