Quiet Hum?

[bmkuter]

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.

[Paul Birkeland]

Sure, give them a shot!

[bmkuter]

The diodes reduced a lot of the noise! Now its only noticeable at max volume.

The generator hum is still there though.

[Paul Birkeland]

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?

[bmkuter]

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?

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.

[Paul Birkeland]

By nothing plugged in, do you mean including the power cable and headphone? I don't have any speakers connected.

Nothing plugged into the inputs. 

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.

How old is the wiring where you live?  Do you have grounded outlets?  You may want to try attaching a wire to the chassis of the SEX and the chassis of your source.

[bmkuter]

Hum exists regardless of inputs.

I would say the wiring is maybe 15 years old at most. The apartment building is relatively new, but at least a decade old. The hum is most noticeable with low impedance headphones, especially my IEMs. The power should be grounded, and I'm plugged into a Furman Power Conditioner (got it very cheap and I needed another power extension in my house).

[Paul Birkeland]

And just to confirm, with the amp on and the volume control all the way down, is it detectable with IEMs?  (and is the amp wired for 4 ohms?)

[bmkuter]

And just to confirm, with the amp on and the volume control all the way down, is it detectable with IEMs?  (and is the amp wired for 4 ohms?)

Its very detectable with the IEMs all the way down, and the amp is wired for 4 ohms. Not sure if it matters, but I can also hear the tubes crackling/warming up (?) with the IEMs on volume off.

[Paul Birkeland]

Could I see a side photo of the terminal strip with 23-28?

[bmkuter]

I bent one of the caps out of the way for the pic. Orientation normally matches the instructions.

[Paul Birkeland]

I just wanted to make sure the shoulder washers were in place.  If a shoulder washer is missing from one of the terminal strip terminals with a plastic acorn nut, you could end up with some hum.

[bmkuter]

Ah okay. I checked and they're both there.

Does it sound like a grounding issue? I've gone through and looked at all the solder joints, but there could be ones for grounding that need to be reinforced.

[Paul Birkeland]

It could be loose hardware, it could be a power line problem (still seems unlikely in your case), or external interference.  You're certain 36L isn't touching the power transformer mounting nut right?

Even for me to get a proper noise floor measurement when testing the prototype SEX 3, I had to wait for a day when everything was super duper quiet. 

[bmkuter]

Can you expand on loose hardware? I just went around tightening all the screws, but is there more than just that?

Why would the power line hum not be affected by the pot? I looked at 36L and the transformer nut, and they were separated by several millimetres of space.