60hz hum

[Paul Birkeland]

Man, I am really on the fence about having you send this in for repair.  Let me get my house really quiet and press my HD-800s up against my ears to see if I can hear anything...

[RestoredSparda]

I'd appreciate it.  This is with a balanced cable. More noticeable on high gain, but I only use low. Again,  completely unhearable with any noise on the house.

In a dead silent house it is easy to notice by it's absence. Say, have the amp on, with headphones on, then turn it off.  The dead quiet compared to the (very quiet 60hz hum) is noticeable by it's sudden absence.

Would you mind trying some iems as well? With moondrop Kato the hum is definitely there. 

[RestoredSparda]

Just for some more troubleshooting data, this is how my amp operates when turned on from completely cold with headphones plugged in.

Loud steady 60hz hum for 10ish seconds in both channels, then no hum and 2 seconds or so of white noise in both channels, each goes away to a silent amp with very quiet hum described earlier.

[RestoredSparda]

So, all of my volume levels I shared earlier were using a DAP with line out. Listening to the Bifrost 2 the volume level is almost double, meaning I have much less play in volume on thr Mainline.

-27 coarse and -7.5 fine is very loud on the same pink Floyd album with HD650 single ended. 

-36 coarse and -0db is loud on HD 800 balanced.

All on low gain.

After some research the dap is outputting 1.5vrms and bifrost 2 is 2vrms.

[Doc B.]

If you have been running this amp for some time you might just try different tubes and see if things change.

[RestoredSparda]

Wouldn't hurt to try different tubes. I've only had it completed for a few months.

 Any best place to purchase the 6C45PI?  EDIT: Found some at TubeDepot.

I've tried 3 different 12AU7 and the amp is the same with those.

[RestoredSparda]

Hello again. Chiming back in after some more work. Here's what I've tried.

Different outlets ,different cables.

Moving components...Bifrost 2 was causing a hum, but only when near mainline. I moved it two shelves down from mainline and that issue was solved. Hum solely from mainline remains.

Purchased and tried new tubes, all three. No difference in hum.

Removed vcap odam and and put back in stock caps. No difference, so put back on vcap odam. Resoldered ALL connections in amp.

Set mainline up as preamp to my power amp for speakers and the hum is more noticeable than through headphones. 1/4 inch
to y split rca into power amp. Switching from balanced or nonbalanced on mainline increases and decreases hum.

As a preamp it is very loud.  At minimum volume it's totally listenable. Can only put fine volume, coarse must remain on lowest value.

At this point I'd like to send it in for repair. However before that  I'm going to find some time to go through all the steps in the instructions again to rule out any obvious or stupid mistakes. 

[RestoredSparda]

Well shit. Moving the dac has made a difference for headphones. Bifrost 2 was picking up a lot of transformer hum from mainline when on the shelf below. Some low level hum is still there, but now so quiet with HD650 I really can't notice (even on high gain).

I'll report back if HD800 is still an issue, but this seems to have made a positive difference.
EDIT: HD800 has more noticeable hum with balanced cable but not too bad.

The only reason I discovered this was from picking up bifrost and moving it closer to mainline. Easily could hear transformer hum increases then decreased when moved away. I ended up moving bifrost a few feet away from mainline.

[Paul Birkeland]

That's rather surprising.  The power transformer that goes into the Mainline, Eros, and Reduction is intentionally designed to be abnormally quiet.

[RestoredSparda]

I guess I shouldn't say it was transformer noise, but it was a definite 60 hz hum from the dac when moved within a foot (underneath mainline).

To be clear, when placing an ear near mainline it is absolutely dead silent. No transformer hum or buzz.  My Lyr 3 and Crack both had transformer noise, but not mainline.

[dubiousmike]

Maybe you already found your fix (hope so!), but the fact that you mention transformer hum in multiple different amps makes me wonder if you may have a DC offset issue in the power lines where you live?  (For this to be correct, I imagine your parents would have to have a similar issue since you already indicated you tested your amp at their place too - but the only time my crack ever made noise it shouldn't have was when I tried to run a cheap ebay tube adapter for 6sn7's up front.)  I have never heard any transformer hum from my crack or mainline at all, and the power in my office where the crack lives is dirty enough to make the power transformer in another amp (Firstwatt F3 klone snagged off craiglist), hum like the devil.  Which brings me to my point - this slightly overpriced DC filter from Emotiva totally fixed the hum issue for me, and the F3 klone runs dead silent now.  https://emotiva.com/products/cmx-2  Maybe worth a shot if the issue has persisted?

Since I haven't popped over here for too long, also just wanted to pass my warm greetings and well wishes along to team Bottlehead.  I have been enjoying my mainline with hd800's daily since Nov 2013, from your initial preorder batch, and it is still one of my most cherished possessions.  Much <3 to Doc, Paul, Eileen and their team for this wonderful amp - to say nothing of all their patient help and support so many moons ago, guiding me through the process of finding that one invisible (to me) cold joint, that was throwing off one of the c4s boards.  The profound satisfaction of building the amp and working through the speedbumps truly makes the music that much sweeter for years and years to come.