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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
atmasphere's avatar
atmasphere
12,067 posts
 
I'm trying to think of a way that a simple ground loop, DC or ultrasonic noise would destroy a woofer and leave the amp intact.
None of those seem to be the issue; a ground loop can't do that, DC is blocked in any sane design by coupling capacitors and ultrasonics take out tweeters, not woofers.
So what could cause a really loud angry buzz before outright failure of the woofer? I'm guessing the 'snap' was the woofer voice coil bottoming out. AC line voltage is one possibility- but this happened without the Creek being damaged.
I tested the amp and it seems to be ok through another pair of speakers.
I'm wondering if the DAC is grounded correctly. If the green wire and white wire were exchanged on the IEC it might be able to do something like this. A DVM should tell the story- measure the resistance from the center pin of the IEC connector to the chassis and see what you get. It should read 0.something ohms- shorted. What is the resistance to ground of the other two pins? If either is shorted to ground its a problem!

jea48
4,652 posts
 
@atmasphere

You must have missed the OP’s last post.
solobone22 OP

11 posts   
04-28-2019 2:47pm Update:

I went to test the Creek and it wouldn’t power on. Opening it up I found the 2 fuses on the board were blown. Unfortunately they didn’t blow before the speaker was damaged. The unit even worked a short period after the initial incident. Checked the fuses and they were the correct rating.


atmasphere's avatar
atmasphere
12,067 posts
 
You must have missed the OP’s last post.
I did see that. But what we know is that the amp didn't fail- those fuses provide power to the amp, but the amp worked because filter caps in the power supply still held some voltage. That's my assumption that checks all the boxes anyway. We'll know more after the fuses are replaced and the amp tested.
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