Quiet Hum?
- Thread starter bmkuter
- Start date
Hum that increases with the position of the volume pot tends to be external to the amp and may change depending on where you have it.
If you have nothing plugged into the inputs when you're listening to this hum, then that is making things quite a bit worse.
Having made those two points, it's also possible to have hum problems if the layout isn't reasonably carefully followed.
-PB
If you have nothing plugged into the inputs when you're listening to this hum, then that is making things quite a bit worse.
Having made those two points, it's also possible to have hum problems if the layout isn't reasonably carefully followed.
-PB
The hum is still present when I unplug the RCA inputs. It sounds like general noise.
I'll try and attach a video: https://youtu.be/z2O3VahCFoI
Video is garbage quality, but best I could do with a phone. The noise is from SEX @ 100% volume through Focal Elegia with the mic ~1.5 inches away.
I'll try and attach a video: https://youtu.be/z2O3VahCFoI
Video is garbage quality, but best I could do with a phone. The noise is from SEX @ 100% volume through Focal Elegia with the mic ~1.5 inches away.
What is the noise like with the volume all the way down?
When you have nothing plugged into the SEX amp and you turn the volume all the way up, you're just amplifying whatever ambient noise is available for the input of the amp to receive. This isn't a meaningful measurement.
When you have nothing plugged into the SEX amp and you turn the volume all the way up, you're just amplifying whatever ambient noise is available for the input of the amp to receive. This isn't a meaningful measurement.
You could try tightening the hardware on the power transformer.
There's a file size restriction on the photos. You can just knock them down by about 50% and they should post OK.
Nothing is jumping out at me there, everything looks to be about where it should be.
-PB
-PB
D
Deke609
Guest
Something easy to try: tighten all the mounting bolts/screws of the terminal strips. Many of them are used as contacts to chassis ground and so a loose one could make for an iffy ground connection. I noticed that the terminal strip near the headphone jack has black domed nuts. I'd make sure that the nut closest to the jack that is securing a ground reference is tight. I'd also take a peek at the ground tab closest to the IEC inlet - the one with the bare ground wire running through to the ground lug on the IEC. From the pic, it looks like it could use a bit of solder (but maybe not -- might just be the angle of the pic).
cheers and good luck, Derek
cheers and good luck, Derek
Yes.bmkuter said:
Having spent a lot of time capturing noise measurements of the SEX amp, sometimes it comes down to the environment too. Another issue I have seen happen is that the 8 lug strip in front of the power transformer can touch the nuts securing the power transformer, and if this happens you can get some ground loop hum. All you have to do to fix that is nudge the strip away from the transformer nuts and brush in a little nail polish or clear lacquer to keep them spaced apart.
Any ideas on how to check if its environmental? I checked everything upstream again, including some USB extension I forgot I was running. Something up there is causing the noise, since after resoldering and converting to 4 ohms, the noise is gone when RCAs are disconnected.
The hum sounds exactly like a generator we have near my apartment building, which supplies all the power. Any connection?
The hum sounds exactly like a generator we have near my apartment building, which supplies all the power. Any connection?
Hey, that's great news!bmkuter said:
I would recommend trying this mod since it's inexpensive:
https://forum.bottlehead.com/index.php?topic=11676.0
If your powerline was a problem, then I would expect the noise to just be there, and for it to be independent of the level of the volume pot.bmkuter said:
Thanks! I'll try that and report back once the fix is implemented. Going to take a few days from Mouser.
Are there any other common grounding/shielding mistakes? Its definitely a generator hum with no noise when the RCAs are disconnected that increases with the pot.
EDIT: I actually found some 1n4007s around. Think that'll do? The data sheet I saw says peak of 30A.
Are there any other common grounding/shielding mistakes? Its definitely a generator hum with no noise when the RCAs are disconnected that increases with the pot.
EDIT: I actually found some 1n4007s around. Think that'll do? The data sheet I saw says peak of 30A.
Sure, give them a shot!
This hum is still absent with nothing plugged into the amp? If so, what is the specific component that you plug into the Crack that causes the issue?
Paul Birkeland said:
By nothing plugged in, do you mean including the power cable and headphone? I don't have any speakers connected.
When first starting the amp from off, with headphones plugged in, the hum appears after the tubes have warmed up and are working. Its still around with no RCAs connected. The hum becomes noticeable 1/4 turn in on the volume pot. If I add RCAs, the hum is still present, but I then get some upstream noise added.
