Interference in left channel

[Nignoog]

Bad news, I added the two diodes as directed but the sound still persists. As far as I can tell, the modification made no discernable difference. I reflowed the joints twice after the initial installation to make sure it wasn't a cold/flaky joint. I am attaching pictures for reference. Assuming the pictures look good, any other ideas?

[Deke609]

When you took the Crack to work, did anything change in the signal chain from source to amp to headphones to your ears?  I.e., was it identical to the setup that gives you interference in your room at home?

Do you have LED lights near the Crack? Perhaps a desk lamp? They can have weird effects on nearby electronics.

cheers, Derek

[Paul Birkeland]

I forgot to ask if this noise is attenuated by turning down the volume control to 0.

[Deluk]

The black brick switching type power supplies can produce strong electronic noise into their local area. Make sure there are none of those plugged in near the Crack. They can be supplying power to all sorts of devices and it's easy to forget about them if they are plugged into a power strip behind a desk for example. The power to your crack might be coming from the same power strip.

[Nignoog]

@Deke609 Sort of. I just brought the amp in with the my HD650s so I didn't plug it into a DAC. However, I have tested the amp like that at my apartment as well, so in regards to the test being the same, it was. There are no LEDs or lamps nearby, I have tried turning off all electronics in surrounding area to no avail.

@Paul The noise is completely unaffected by the volume.

@Deluk I have tried unplugging literally everything in my room and in addition, turned off the the Wi-Fi router and HVAC, even though they are in another room; no dice.

In contrast to what I said on the 10th, the diodes now do seem to make a slight difference (which makes me think burning in might have done something), but the interference is still present. Any other ideas or thoughts? I have 3 extra diodes available, is it worth it to slap another one or two on? I am assuming that's a no go though...

[Deke609]

Maybe post some pics, including one of the entire underside.

cheers, Derek

[Nignoog]

I am wondering how helpful pics will be for two reasons:
1. I sent my Crack in to be repaired a few years ago and I haven't touched it since.
2. If the interference goes away when I relocate the amp, shouldn't that imply that the issue lies outside of the amp, not within?

I am happy to post some pictures if you and others think it might help, I am just weary about the prospect of having to do an soldering.

[Deke609]

Dunno. But what's the harm in posting some pics?

I'm curious as to why the interference only shows up in the left channel. That suggests to me that there is something about the wiring of that channel that makes it more susceptible to picking up noise. Maybe that's something worth exploring. Pics might help with that.

cheers, Derek

[Paul Birkeland]

2. If the interference goes away when I relocate the amp, shouldn't that imply that the issue lies outside of the amp, not within?

Yes, this is quite true.  It's somewhat possible that picking up a cheap pair of used tubes on eBay might mitigate this issue a little bit.  It's certainly an inexpensive experiment to try!

[Nignoog]

I have a few other tubes here already that I will try.

In the meantime, I am wondering if the picture I am attaching shows what is negatively impact the Crack's performance. I noticed that the building across from mine has a lot of satellite dishes and antennas on the building. And the area in my apartment where there is no interference is in the opposite direction. If you think the antennas are the culprit, is there anything I can do short of relocating the amp?

https://imgur.com/a/2qwDmmi

[Paul Birkeland]

Yeah, that would do it!  It's probably particularly bad because you are up above the ground and those are aiming right at you. 

One thing you could try is to buy a 0.1uF Z5U capacitor (voltage doesn't matter) and solder one end to the right RCA jack shell and the other end to terminal 22 (be sure terminal 22 has continuity to the chassis plate).  That may give the noise an alternate path to travel that isn't through the circuit itself.