Ground Loop(?) leads to blow speaker


Aloha 'goners!
          I'm going to do my best to get the details down here as I am a bit stumped on this one.

I have a Wadia 121 DAC that was recently repaired.  The issue was the RCA/XLR outputs produced mostly noise and little music.  The headphone side was fine.

As the unit wasn't functioning properly I hadn't had the chance to hook it up and use it.  When I got it back and hooked it up there was a nasty ground loop(?) that led to a blown speaker (Thiel 1.6).  The buzz produced was the angry bee buzz followed by a loud electrical sounding crack and the woofer was gone.  The amp (Creek Classic A53) went into protect mode and I shut it off.  I then disconnected the Wadia and hooked up a Mytek Brooklyn+ and there was no buzz.  Same cables same outlets same everything except the DAC.  I tested the amp and it seems to be ok through another pair of speakers.

At this point I wasn't sure what was going on.  I tested 3 different amps with the Wadia and 2 of the 3 buzzed.  With the Mytek none of them buzzed.  Of the 2 amps that buzzed one of them had a 2 pin connection and the other a 3 pin.  The only amp that didn't buzz was a 2 pin Adcom 535 MkII.  The other amps were a 3 pin Creek and a 2 pin Carver.

Here is the full chain:

Primare CD31 --> Madrigal AES Cable --> Wadia/Mytek DAC/preamp --> Chord Cobra Vee RCA --> Creek/Adcom/Carver amps --> Tara Labs spkr cable --> Thiel 1.6/B&W CDM1SE speakers

I used the same wall outlets for the DACs and amps.  The same interconnects were used between components as well as from the amps to speakers.

I tested the wall outlets with a cabling tester and it said they were wired correctly.

Could there be something else that I'm missing that would be causing this?  The only amp I am comfortable with using to test is the Carver as it has a variable level on the front panel.

Any help or thoughts on this would be greatly appreciated.

solobone22
gregdude 

51 posts   
04-23-2019 10:52pm


A ground loop would be characterized as a hum. What you say you heard was a buzz, that blew out a woofer, almost definitely DC


Not always. Not if there are higher frequency harmonics riding on the equipment grounding conductor.
https://www.youtube.com/watch?time_continue=5&v=FBRPHojSGAs

https://www.youtube.com/watch?v=Nakpj_Mee0Q
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solobone22 OP

7 posts
04-24-2019 11:04am

I have a Klein Tools MM300. I set the meter to 200m and tested the RCA output touching the positive line inside the connector and the negative line to the outer barrel.

The left channel read 1.0.
The right channel read -0.1.

This looks to be the culprit.

@ solobone22 ,

How about setting the meter to DC volts and preform the same tests.

Then just for the heck of it set the meter to AC volts and preform the same test.
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Hi Jim (Jea48),

Looking at a photo of the particular meter shown here I see that there are two settings of the mode switch marked "200m." One is for DC current, which it seems safe to assume is not the one the OP used, and the other is the most sensitive of the DC volts settings. So it sounds like the worst case of any of the readings the OP reported was 1 mv (millivolt) DC, which won’t hurt anything.

I second your suggestion of trying an AC volts measurement, although the most sensitive AC volts setting provided by this meter has a full scale of 200 volts.

Best regards,

-- Al
Al,

Thanks for the better picture of the meter. I wondered why the OP was measuring DC current.

https://data.kleintools.com/sites/all/product_assets/hires/klein/mm300_photo.jpg

gs5556 theory makes sense to me. I just thought the DC voltage at the outputs of the DAC would have been higher.

The left channel read 1.0.
The right channel read -0.1.


Jim
I tested using meter set to the V with the 3 dashes below the solid line.  That is the setting for DC.  Anyone have further thoughts on this?

@gs5556 Is this something that would present itself all of the time or only intermittently? I'm referring to the DC issue.