Barely audible hum

[pofofo]

Hi,

I`m been using my SEX 3.0 with C4S for a while now with Audeze LCD-3.
A while ago, hard to say exactly when, I started to hear some very low humming noise. It is very low and I really need to concentrate to hear it, most times. Sometimes the hum is a bit louder, but mostly it is very low and almost inaudible. It`s audible with all my headphones: DCA Aeon Flow closed, Sennheiser HD600 and Audeze LCD-3.

My setup is: Raspberry PI > Schiit Modi 3 > SEX.

- The hum does not change with volume (although the amp hums a bit with no input/music playing and the volume at max, don`t know if it`s the same hum).

- It`s still there with no input connected.

- Terminal 36 isn't touching the nut on the adjacent power transformer screw.

- The amp is wired at 4 ohms.

- It`s connected in a basic power strip along with other things, but the hum is still there when the amp is plugged directly to the wall.

- I`ve added some diodes to the ground at the power connector (as seen in the Crack portion of this forum). The hum is present with or without these.

- The voltage in my apartment is 240v and the amp is wired as in the manual page 34.


I had problems with noise and I reflowed the whole thing (it turned out to be the tubes picking up wifi/4G signals), so I think every connection is pretty solid.

At this point I think the problem could be the power in my apartment, if so, could a power conditioner solve my issues? Or a DC-blocker maybe?

 

[Paul Birkeland]

If you listen to a 60Hz tone and a 120Hz tone, which does it sound like?  Is this hum on both channels?

 

[pofofo]

Sounds like it`s at 60hz. Yes, both channels. The amp is usually in my bedroom and I moved it to my living room. I`m having a hard time hearing it in my living room, but there`s more ambient noise there.

 

[Paul Birkeland]

Some have had a bit of luck with wiring a jumper in between the lower inner and lower outer lugs of the headphone jack.

 

[Doc B]

60 is usually picked up from nearby equipment. We had this situation at my son's house a couple weeks ago. He had a Sonos Port next to his phono preamp. Moved the Port away and the hum was gone. Your mention that the hum is harder to pick out in the living room makes me wonder if there was something emitting a field near the amp in the bedroom.

 

[2wo]

Have you tried, disconnecting the source and shortening the inputs of the SEX?

O.T.  How do you run your Pi? I use Pi core player, Allo hat to a Bottlehead DAC but I am always  curious as to what others are doing...

 

[pofofo]

Some have had a bit of luck with wiring a jumper in between the lower inner and lower outer lugs of the headphone jack.

What does that do? Is it the ground points? Do you have any pictures of it?

Doc B.: I thought it might be some other equipment, so I disconnected everything other than the amp in the bedroom to no avail. I do have the wifi router just behind the wall (in the living room), but it`s been there since I moved in and I didn`t have a humming problem earlier. I also have a computer, dac, turntable, bluetooth transmitter, cd-player, pre amp and power amp there, but that`s turned off when I`m using the SEX.

2wo: Can I safely shorten the inputs of the amp? Just using one RCA to RCA cable betweeen left and right input?
A friend of mine set the Raspberry pi up for me, so I don`t know much about it, but it`s got Volumio and I`m running Spotify and Qobuz on it with my phone.

I switched out the SEX for another headamp in the bedroom (Atrox v2), which is a power house (2x20w into 8 ohms). When I set the gain to max (24x) and turn the volume knob all the way up (not music playing of course) I can hear humming and noise that kinda sounds like rapid machine gun fire, without the bass.

Thank you so much for the help, as you understand I`m a bit of a novice when i comes to this.

 

[Paul Birkeland]

What does that do? Is it the ground points? Do you have any pictures of it?

It means connect a wire between the lower inner and lower outer lugs of the headphone jack.

 

[pofofo]

It means connect a wire between the lower inner and lower outer lugs of the headphone jack.

Didn’t help.

 

[Paul Birkeland]

Didn’t help.

There are six lugs on the headphone jack.  Connect the two closest to the chassis plate with a piece of wire.

 

[pofofo]

Yes, I did, but the hum is still there.

 

[Paul Birkeland]

I would continue the debugging my moving the SEX around and possibly taking it with you to work to try a difference source of power.  It's possible that what you're hearing is interference from another device or from grunge on your powerline.

 

[Mucker]

My S3X and Crack can hum exactly as you describe depending what kind of foundation it is on. I believe it could be vibration you are experiencing.

Try pressing the plate against the wood base or picking the amp up in the air while it's on with your headphones on. Just separate it slightly from the table and be careful not to get your fingers up underneath and inside. When I do this the hum goes away. Possibly figure out a way of dampening the feet.

 

[pofofo]

60 is usually picked up from nearby equipment. We had this situation at my son's house a couple weeks ago. He had a Sonos Port next to his phono preamp. Moved the Port away and the hum was gone. Your mention that the hum is harder to pick out in the living room makes me wonder if there was something emitting a field near the amp in the bedroom.

I tried it again in the living room early in the morning when it was dead quiet and unfortunately I hear it there as well.

My S3X and Crack can hum exactly as you describe depending what kind of foundation it is on. I believe it could be vibration you are experiencing.

Try pressing the plate against the wood base or picking the amp up in the air while it's on with your headphones on. Just separate it slightly from the table and be careful not to get your fingers up underneath and inside. When I do this the hum goes away. Possibly figure out a way of dampening the feet.

I also hear the hum when I`m holding the amp, so no luck there either.

 

[pofofo]

Is it a way to lower the output power of the amp? It is pretty overkill for my phones anyways and I was thinking that may help lowering the noise floor as well (if thats what I`m hearing).

 

[Paul Birkeland]

See Reply #5 here:
https://forum.bottlehead.com/index.php?topic=13832.0

 

[pofofo]

Would these do?

https://no.mouser.com/ProductDetail/Vishay-Dale/CPF38R2000JKB14?qs=d4jCo194jjrI1mBX%252B%252BRScQ%3D%3D

The 8ohm 3w resistor mentioned in the other thread are not in stock.

 

[Paul Birkeland]

Yes, those will work.

 

[pofofo]

Thank you

 

[pofofo]

I was finally able to do the modification, and it worked!

It`s now dead silent, and it sounds like it didn`t have a negative impact on the sound quality.

Thanks for the help!