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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
almarg's avatar
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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


solobone22 OP
88 posts
 
@almarg your suggestion is most appreciated - will do that this evening
gs5556
1,240 posts
 
The only way to get a handle on what's going on is to play a 50 hz 0 dBFS test signal through the Wadia and measure the output voltage. It should be 2.0 volts RMS (the 50 hz tone will be more accurately measured since most DMM's are optimized for 50/60 hz). The DC offset can vary as a signal is passed through so the 1.0 VDC reading with no signal won't give you the extent of the problem.

So the answer is the no signal condition will be there most of the time but the actual offset may not.
imhififan's avatar
imhififan
2,217 posts
 
The Adcom 535 Mk II is capacitor coupled at the input and the Creek and Carver are not. What you have is DC at the output which the Creek passed through to the speaker before going into protection mode. The Adcom's input cap blocked the DC and didn't pass the buzz-causing DC to the speaker. DC is enough to blow out a woofer.
Can you put a capacitor between  Wadia 121 output and input of the Carver to confirm that?
solobone22 OP
88 posts
 
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.

Testing with 50/60 hz test tone later today.
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