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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

Showing 5 responses by almarg

almarg's avatar
almarg
9,670 posts
 
Not sure what to suggest at this point, other than measuring the DAC’s output on the 200 volt AC scale as was suggested (while no music is playing).

It would be nice if it were possible to also measure the output voltage(s) of the DAC’s external switching power supply, but that would seem to be impracticable due to the nature of the connector and the lack of definition as to how it is wired.  I suppose it's possible that it has been intermittently misbehaving, and caused the failure of the internal supply.

Good luck. Regards,

-- Al


almarg's avatar
almarg
9,670 posts
 
I tested using meter set to the V with the 3 dashes below the solid line.  

That's correct, and that is what I assumed you were doing.

I suppose it is possible for a large DC output to occur intermittently, but it seems unlikely.  Especially if the problem has occurred when no signal was being provided to the DAC (i.e., when a CD was not being played).

Regards,

-- Al
 

almarg's avatar
almarg
9,670 posts
 
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
almarg's avatar
almarg
9,670 posts
 
P.S: Now that I think of it I presume that "2-pin" and "3-pin" were references to the number of prongs on the power plugs of the amps. And since the problem appeared when you used the Carver which has a two-prong plug that would seem to further confirm that the problem was unrelated to a ground loop.

Regards,

-- Al
almarg's avatar
almarg
9,670 posts
 
It’s not clear to me what you mean when you refer to a "2 pin connection" and a "3 pin connection." Initially I thought you might have meant RCA vs. XLR, but several rear panel photos I found as well as the manual for the Creek amp (which you described as "3 pin") show it to only have RCA inputs. And the cable you indicated was being used between the DAC and the amps is an RCA cable. Can you clarify that?

Also, by any chance were you using XLR-to-RCA adapters between the DAC and any of the amps?

In any event, I agree with Dan that it does not sound like the problem was caused by a ground loop.

Good luck. Regards,

-- Al



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