60hz hum

RestoredSparda · 4420

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Offline Paul Birkeland

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Reply #30 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?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline RestoredSparda

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Reply #31 on: December 22, 2021, 03:06:12 PM
Measuring terminal 16u to each lug, both read .525vac with the same 60hz tone.



Offline RestoredSparda

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Reply #32 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.



Offline Paul Birkeland

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Reply #33 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?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline RestoredSparda

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Reply #34 on: December 22, 2021, 03:39:58 PM
Reading .627vac



Offline Paul Birkeland

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Reply #35 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!)

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline RestoredSparda

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Reply #36 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.
« Last Edit: December 22, 2021, 03:55:34 PM by RestoredSparda »



Offline Paul Birkeland

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Reply #37 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? 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline RestoredSparda

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Reply #38 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.


« Last Edit: December 22, 2021, 04:00:20 PM by RestoredSparda »



Offline Paul Birkeland

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Reply #39 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!

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline RestoredSparda

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Reply #40 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.  :)
« Last Edit: December 22, 2021, 04:50:46 PM by RestoredSparda »



Offline Paul Birkeland

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Reply #41 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. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline RestoredSparda

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Reply #42 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. 







Offline Paul Birkeland

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Reply #43 on: December 23, 2021, 07:22:42 AM
How is it set to low impedance?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline RestoredSparda

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Reply #44 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.
« Last Edit: December 23, 2021, 07:35:02 AM by RestoredSparda »