60hz hum

[Paul Birkeland]

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)

 

[RestoredSparda]

I'll try that and get back to you. Thanks!

 

[RestoredSparda]

.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.

 

[Paul Birkeland]

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.

 

[Paul Birkeland]

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.

 

[RestoredSparda]

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.

 

[Paul Birkeland]

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.

 

[RestoredSparda]

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.

 

[RestoredSparda]

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.

 

[RestoredSparda]

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.

 

[Paul Birkeland]

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?

 

[RestoredSparda]

Measuring terminal 16u to each lug, both read .525vac with the same 60hz tone.

 

[RestoredSparda]

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.

 

[Paul Birkeland]

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?

 

[RestoredSparda]

Reading .627vac

 

[Paul Birkeland]

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!)

 

[RestoredSparda]

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.

 

[Paul Birkeland]

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? 

 

[RestoredSparda]

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.

 

[Paul Birkeland]

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!