Bottlehead Kits > S.E.X. Kit

Hum (60hz) only with Headphones

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EnsgnofIndustry:
S.E.X. 3.0 just built. Amp set up to run at 4ohms. Passed all tests as best as I can tell. Listening through 8ohm (15 watt) bookshelf speakers and the amp sounds insane! Dead silent in both channels! No pops, crackles, hum, or other aberrancies from 0-10 on the volume dial. 

My issue is with headphones. Regardless the headphone model or headphone cable, I get the same low level hum, which I believe to be 60hz.
A couple observations with headphones:
I can kind of drown the hum out when playing music loud.
I get the hum with nothing plugged in but the phones.
The hum is present with the volume knob at zero but changes in tone (kind of like a wah pedal) when I roll up the volume knob.
The hum remains present but very gradually goes away when I power down the amp.
As mentioned in a previous post, I had to buy a CAT5e cable online but the specs seem to match the one included with the kit.
Oh, and I slightly melted the sleeves of a brown wire and brown and white wire together near the sleeve and ring connection area of the headphone jack (side closest to the volume knob). I couldn't tell whether the copper actually touched and it's a pain to get to with the green wires obscuring them. Also, didn't want to investigate and make things worse, but if that's the likely culprit, I'll address it.

Thoughts? And as always, I appreciate the support.


 

Paul Birkeland:
Are terminals 29 or 36 touching the #8 nuts next to them that hold the power transformer on? This kind of issue generally happens when terminal 36 is in contact with that nut, which creates a ground loop.

EnsgnofIndustry:
Thanks Paul. I was worried about the potential T36 and PT nut contact when building. It's a tight fit. I just double checked T29 and T36 and they aren't touching the nuts. 36 is close but I put a piece of electrical tape between the nut and T36 and still get the hum with headphones. Again, speakers are whisper quiet. Pics attached and I'm happy to take more.

 

Paul Birkeland:
You can also try running a jumper wire between the two lowest lugs on the headphone jack, which some have reported as helpful.   It could also help to know which headphones you're using, as some slight modifications may not be a bad idea depending on what you're running.

EnsgnofIndustry:
I’ll give that a go. I’ve also read elsewhere that the speaker jack soldering in particular needs to be on point, so if the jumper thing doesn’t work, I may just resolver the speaker jack connections. As for headphones I’ve tried, I’ve used Meze 109 Pro, B&W I forget the model, Audio Technica ath50, and VModa something-or-others that are like 10 years old. All have different cables and the frequency and loudness of the hum doesn’t change regardless of the headphones. Does the quality of the hum changing as the volume knob is adjusted offer any additional insights?
Speaker jack soldering pic attached just in case something obvious sticks out.

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