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Bottlehead Kits => Mainline => Topic started by: RestoredSparda on December 21, 2021, 03:44:17 PM

Title: 60hz hum
Post by: RestoredSparda on December 21, 2021, 03:44:17 PM
Howdy. Checking in to see if this is an issue or not.

I've recently noticed a quiet 60hz hum through HD800 and HD650 on mainline. It may have always been there but I have just ignored it or thought it was an appliance.

I've removed all inputs, brought it to a different outlet with no source and the hum is still there.  Tightened all screws

It is pretty faint on low gain, but definitely noticeable on high gain. The volume level of hum doesn't change with the attenuator steps. It stays a constant volume. The volume of the hum increases and decreases if single ended or balanced is selected.

Also checking that volume levels are normal. With a 2vrms output from my dac the Mainline is VERY loud if course is on -27 and fine is on -7.5.

I can usually only listen with course on -36 and play around with fine.

Course at -18, -9, and 0 are unlistenable with both HD650 and HD800.

Thanks for any ideas!
Title: Re: 60hz hum
Post by: Paul Birkeland on December 21, 2021, 07:43:59 PM
That seems like a very, very low level setting for the HD800 on the Mainline.  How is the wiring where you're using the Mainline?  Good earthing in the outlets? 

Can you listen to a 120Hz tone and a 60Hz tone to be sure it's 60Hz?
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 03:51:37 AM
Hi Paul. Thanks for the help. Yes, wiring is all good in the house and no issues with any other electronics or amps.

Direct to the wall and through a balanced isolation transformer had the same results.

Just listened to both tones and it is for sure 60 Hz.

Any thoughts on what i may have screwed up for the gain to be so high?
Title: Re: 60hz hum
Post by: Doc B. on December 22, 2021, 05:39:59 AM
Are your voltages all within spec?
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 05:43:02 AM
Let me check again and report back.
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 06:04:58 AM
All voltages checked out.

Kreg a is reading 11.11, and Kreg b is reading 10.7. Only differences I could find. However amp is still warming up and tubes making their way towards the set bias of 145

Title: Re: 60hz hum
Post by: Paul Birkeland on December 22, 2021, 06:42:35 AM
Can you post some build photos?

Do you have access to a tablet or smart phone with a headphone jack? (and an 1/8" to RCA cable?)  My intuition is to start by verifying proper operation of the attenuators, which is easy to do with some AC signal.  I suppose if your DAC is hooked up to a streaming device you can just use it to stream a 60Hz tone too.
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 07:38:16 AM
I'm able to stream or hookup to play any signal. Happy to try if you can explain the next steps.
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 07:57:52 AM
Photos. I also checked all resistors and they are correct on the course and fine attenuator. They only change value when they are selected with the volume knob.
Title: Re: 60hz hum
Post by: Paul Birkeland on December 22, 2021, 08:07:53 AM
I would add some more solder and turn the heat up on your iron all the way on the terminal strip joints.  Many of them look lightly soldered.  An iffy solder joint can definitely make 60Hz noise appear where it shouldn't be, and could also be a symptom of what I perceive to be a likely issue with the attenuator. 

I wouldn't reflow any of the joints on the attenuator switches themselves though. 
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 08:09:28 AM
To be clear, the terminal strips near the attenuators?
Title: Re: 60hz hum
Post by: Paul Birkeland on December 22, 2021, 08:17:09 AM
I would do all of the terminal strips. 
Title: Re: 60hz hum
Post by: Doc B. on December 22, 2021, 08:29:38 AM
Yup, the logic here is if the terminals are questionable because the iron temp was too low that would be the case for all the terminals. I have a new video up on soldering that addresses iron tip temp, how much solder to apply, what to look for in a good joint, etc.

https://youtu.be/EN16Pi7pcfk
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 08:53:36 AM
Reheated and added solder to all terminals. Reheated other questionable spots.   

No change in hum level, and overall volume level is still the same.
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 09:03:26 AM
Tubes? On boot up with headphones in there is a much louder 60hz hum and then it goes to regular operation in a few seconds with very quiet 60hz tone.

I've tried a different 12au7 with no change. I don't have any of the rectifier tubes on hand to try.
Title: Re: 60hz hum
Post by: Doc B. on December 22, 2021, 09:23:17 AM
This falls into the realm of clutching at straws, but are those metal V-Cap cases just floating, i.e., not grounded to the chassis?
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 09:36:12 AM
Beginning to think the amp is fine (sounds wonderful) and it's just my house power. I get a similar very low hum through my emotiva amp to my speakers when my ear is to the driver.

Maybe I'll bbing the amp to a friend's house to see if there's a change. I remember my crack with Speedball also had a very mild hum.
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 09:37:22 AM
That's correct. I was actually wondering about that as they are metal enclosures.  Any quick grounding test I can try without eletrocuting myself?
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 09:42:43 AM
Notes about these caps from the manufacturer...

The short lead indicates the outermost foil, and should be connected to the lowest impedance path to ground. Another way to identify outer foil is the writing on the label flows towards the outer foil.

The ODAM, TONE, and OIMP series capacitors have metal bodies that are electrically conductive. Ensure that the body doesn't make electrical contact with any other portion of the circuit other components or electrically LIVE circuit traces. Heatshrink, 3M foam tape, or silicone tape around the body may be used to help insulate, and protect from electrical short. The TONE Cap series with values from .01 uF to .047 uF have a clear insulating sleeve over the brass canister and provides some isolation, but you should still safeguard against any laceration or puncture of this 'skin' to prevent any short...
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 09:44:02 AM
I'd be willing to reinstall the original caps to rule that out if you think it's worth while.
Title: Re: 60hz hum
Post by: Paul Birkeland on December 22, 2021, 09:56:08 AM
Can you play a 60Hz AC tone into the amp and measure the AC voltage across the RCA jacks?  Then turn coarse and fine switches all the way up, then measure the AC voltage between the ground buss wire at the front of the amp and each of the lower lugs on the coarse attenuator?  (you can/should do this with the amp off)
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 10:36:30 AM
I'll try that and get back to you. Thanks!
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 12:03:24 PM
.005 vac on rca jacks playing 60hz 10db file

.400 vac on front lower lug on coarse

.398 vac on back lower lug on coarse

This was with both coarse and fine on max volume.
Title: Re: 60hz hum
Post by: Paul Birkeland on December 22, 2021, 02:02:12 PM
The volume shouldn't go up between the RCA jacks and the output of the attenuator.  Are you sure it's not 0.5V at the RCA jacks? If anything you could play a 2V signal at -0dB to bring the levels up.  No harm will come to the Mainline feeding lots of voltage into it.  I wouldn't feed the 120V available at the wall into the RCA jacks, but 2-10V of signal is totally OK.
Title: Re: 60hz hum
Post by: Paul Birkeland on December 22, 2021, 02:03:26 PM
I should also mention that *if* the AC voltage does go up, that kind of nonsense is what I would expect from a ground that's not solidly connected.  We see this sometimes in Crack kits where a builder will somehow measure 400V of B+ in a kit designed to put out around 200V, and that's generally resolved by tracking down a bad ground connection.
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 02:36:58 PM
My mistake. I did not have the power cable plugged in.

Now I get a reading of 1.1vac at the jacks, and .50 at both lower lugs, with a 0db signal playing. So, about half the voltage at the lower lugs compared to at the jacks.  Does this seem about right?

Turned all the way down i read .001vac at the lower lugs.
Title: Re: 60hz hum
Post by: Paul Birkeland on December 22, 2021, 02:39:50 PM
Does this change with no power cable plugged into the Mainline?  That in and of itself would be rather significant as it shouldn't make any difference.
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 02:44:47 PM
Ok, using the same test signal the power cable now removed, the result is the same as my last post. About half reduction in signal at jack compared to lower lug.  1.1vac to .5vac with volume all the way up.

This is a 0db white noise signal if that matters.

My first readings must have had the multimeter auto adjusting.
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 02:49:51 PM
Ok, stranger and stranger.  With the 60hz signal instead, I am indeed reading .005vac at the jacks, but 1.255vac at the lugs.

This is without a power cable into the amp.

With 0db white noise it was the opposite.
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 02:54:08 PM
I may be testing incorrectly.

Placing the black probe on the ground lug of either of the jacks, and the other on the solder point where the signal wire goes, I read 1.99vac at the jack, and 1.25vac at the lower lug with volume max on course. This is with a 60hz tone.



Prior, I was testing jack voltage by placing red probe on RI-1 signal wire/solder point, and black probe on LI-1 signal wire/solder point.
Title: Re: 60hz hum
Post by: Paul Birkeland on December 22, 2021, 02:56:46 PM
Placing the black probe on the ground lug of either of the jacks, and the other on the solder point where the signal wire goes, I read 1.99vac at the jack, and 1.25vac at the lower lug with volume max on course. This is with a 60hz tone.
The 1.99VAC to 1.25VAC is exactly what's expected. 

Can you measure the AC voltage between terminal 16 and each of those output lugs of the coarse attenuator?
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 03:06:12 PM
Measuring terminal 16u to each lug, both read .525vac with the same 60hz tone.
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 03:16:38 PM
Apologies, they read 1.255vac.  I had not put the fine attenuator on max.

One click down from max on coarse reads .445vac on both lower attenuator lugs.
Title: Re: 60hz hum
Post by: Paul Birkeland on December 22, 2021, 03:36:00 PM
That is all as expected.  Can you turn the coarse switch up all the way and turn the fine down to -6dB and report what comes out of those coarse switch output terminals?
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 03:39:58 PM
Reading .627vac
Title: Re: 60hz hum
Post by: Paul Birkeland on December 22, 2021, 03:44:39 PM
That all seems to be reading properly, which is surprising.  My DAC (and others) also puts out around 2V AC and I have to have my Mainline turned up pretty far for reasonable listening, and this is a shared experience with others. 

What DC resistance do you get between terminal 7 and E on the IEC power entry module?  (Also best measured with no power cord plugged in!)
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 03:52:07 PM
Interesting.  What coarse setting do you usually have for a modern album with HD800, at a comfortably loud level?

I'm reading from the terminal 7U (between thr attenuators) and E on the power inlet .000vdc.       I am reading 00.1 ohm


From everything we checked, I'm thinking it's fine and not an issue. Hmmm...could just have sensitive ears? Lol.
Title: Re: 60hz hum
Post by: Paul Birkeland on December 22, 2021, 03:54:42 PM
I believe I'm usually at -9 on coarse and using the fine attenuator from there. 

Can I get an overall overhead shot of the amp? 
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 03:58:04 PM
Oh wow. Yes, -27 is incredibly loud and if I switch up any further I would fear breaking a driver.

I tried a DAP with line out and it gives the same volume levels as from Bifrost 2.

I'm willing to switch back to the original caps, however I do not recall any difference in my volume habits before the cap swap. It was still very loud at -27 on coarse and minimum level for fine.


Title: Re: 60hz hum
Post by: Paul Birkeland on December 22, 2021, 04:07:41 PM
How about the soldering products used? 

This may end up as a repair on my bench, but I'm always iffy about something like this where it may be environmental or related to home wiring, so being thorough is a good idea!
Title: Re: 60hz hum
Post by: RestoredSparda on December 22, 2021, 04:12:14 PM
I'm stumped.  I used Cardas Soldering Wire Quad Eutectic Silver Solder with rosin flux on 90 percent of the amp, ran out, and finished it with Kester rosin core.

Worth trying at a friend's house to see if the volume level changes / rule out bad power?

Possible the higher voltage rating of the vcap ODAM caps are the cause?

I'd hate to be without this wonderful amp for the time it is being repaired, however I'd rather not keep using if it isn't operating properly. Just let me know what your thinking. I very much appreciate the late night responses.  :)
Title: Re: 60hz hum
Post by: Paul Birkeland on December 22, 2021, 05:41:15 PM
Yeah if you have used repair flux or plumbing flux, that could cause some strange noises, but that also leaves a residue that's somewhat easily recognized.   I do not believe the ODAM caps would cause any problems.  Trying the amp in a different building is a very good idea. 
Title: Re: 60hz hum
Post by: RestoredSparda on December 23, 2021, 07:04:48 AM
Ok, so with the amp st my parents house it is acting the same.

Starting to think it is operating just fine. The hum at both houses is very quiet, can only hear it if in a room with no other noises (air, fridge, fan). Just to let you know the volume.  It's very hard to hear with HD650, slightly more noticeable with HD800.  I plugged in an IEM and it definitely a more noticeable hum, but it's a sensitive iem. 

For volume,  on a modern hot recorded rock album I am getting -27 on coarse and -6 on fine is as loud as i can comfortably go in a quiet house. This is with a balanced cable to the HD800.

-27 on coarse and -0 on fine gets me to this same volume level on the same song from same source on HD650, but with a single ended cable.

However, on Pink Floyd's Dark Side of the Moon, 24/96 remaster, I can go to -18 coarse and -1.5 fine on HD650 with single ended.

If this all sounds about correct I think I'll let this go and assume the amp is functioning correctly. Unless you think this is out of the norm. 




Title: Re: 60hz hum
Post by: Paul Birkeland on December 23, 2021, 07:22:42 AM
How is it set to low impedance?
Title: Re: 60hz hum
Post by: RestoredSparda on December 23, 2021, 07:25:56 AM
This is all on low impedance.  High is only about 2 or 3 dB higher sounding to me? Not a huge difference.
High impedance I go about 2 clicks down on fine compared to low.

Side point, My dad has terrible ears and needed the amp on negative 9, and half way or more on fine for his liking.
Title: Re: 60hz hum
Post by: Paul Birkeland on December 23, 2021, 08:03:58 AM
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...
Title: Re: 60hz hum
Post by: RestoredSparda on December 23, 2021, 08:14:39 AM
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. 
Title: Re: 60hz hum
Post by: RestoredSparda on December 23, 2021, 08:37:27 AM
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.
Title: Re: 60hz hum
Post by: RestoredSparda on December 23, 2021, 11:06:54 AM
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.
Title: Re: 60hz hum
Post by: Doc B. on December 23, 2021, 11:29:54 AM
If you have been running this amp for some time you might just try different tubes and see if things change.
Title: Re: 60hz hum
Post by: RestoredSparda on December 23, 2021, 11:36:34 AM
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.
Title: Re: 60hz hum
Post by: RestoredSparda on January 08, 2022, 10:18:01 AM
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. 

Title: Re: 60hz hum
Post by: RestoredSparda on January 08, 2022, 05:36:18 PM
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.
Title: Re: 60hz hum
Post by: Paul Birkeland on January 09, 2022, 06:11:45 AM
That's rather surprising.  The power transformer that goes into the Mainline, Eros, and Reduction is intentionally designed to be abnormally quiet.
Title: Re: 60hz hum
Post by: RestoredSparda on January 09, 2022, 06:57:38 AM
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.
Title: Re: 60hz hum
Post by: dubiousmike on March 18, 2022, 06:56:08 PM
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.