[abernardi]

I'm not sure if this is the right circle as this isn't a DIY issue, but it is technical.... and I'm not... but I'm hoping someone here may have some insight.

Recently I purchased a Signature 15 amp from Vinnie at Red Wine Audio.  As soon as I put it in the system I started getting regular dropouts, often preceded by a slight tick of distortion.  It happened consistently on sharp transients, a loud drum hit or the attack of sax, etc.  But it also seemed to happen at random times as well as random sound levels. 

Vinnie and I tried to trouble shoot the problem and tried everything we could think of, but we were left baffled.  I sent him back the amp, he put it on the bench and could find nothing wrong.  He sent me another unit and I had the same problems.  We never figured out what was wrong. 

Fast forward a few months and I get my hands on that little TBI Millenia MG3 amp that's on tour right now, and... you guessed it, the same problem cropped up.  Exactly the same issue. 

Here's my system:

2011 Mac Mini, 5GB RAM, SSD, OS 10.8, WD USB external HD with media, running Audirvana.
Toslink to an Audio-gd NFB-2 DAC
Latest Dodd battery pre-amp
Dodd battery Tube amp (but using a custom power supply, as Gary hasn't got the battery pack in production yet)
Avlar Prodigy Speakers: two way with SEAS 8" woofer and a Heil type AMT, 100db/1W sensitivity, 8ohm
Tuan's (Sonny on AC) Sweet Spot ICs
Robert's (HT c0z on AC) speaker cable

I swapped cables, checked for shorts, I moved the problem components away from the others, I moved the power supplies away from the components, I tried different pre-amps, I tried no preamps, I tried a passive pre-amp!,  I tried a Squeezebox instead of the Mac and DAC.

I don't know if this has any significance, but both the SIG 15 and the TBI are battery powered.

When I first put the SIG 15 in the system, I used a Virtue Sensation (also on batteries) as the pre-amp.  I ran the SIG 15 off A/C and as I said I got the dropouts.  Then when I ran it off batteries, the dropouts went away, except the channels reversed!  I was hearing the left in the right and right in the left.  I thought I was hallucinating.  I shut everything down.  Powered it all up again and the channels were correct, but the dropouts reappeared.  I took the Sensation out of the loop and ran the amp straight from the DAC controlling the volume with iTunes, the dropouts went away!  So now I'm thinking, obviously there's something screwy with the Sensation.  Maybe some wires are crossed in the pre-amp outs or something.  I put the Sensation back in and now got no sound at all!  I shut everything down for the night.
Next day I took the Sensation out and put in a little Kingrex pre-amp.  The dropouts were back.  So it wasn't the Sensation.  And now I discover the dropouts were happening only in the right speaker.  It didn't seem to matter which channel either, I swapped channels.  Even stranger, I have two sets of speaker inputs for biamping and found that the dropout was happening only with the woofer.  So now I'm thinking it's the speaker.  I poke around the speaker and test for shorts, damage, etc, can't find anything.  I test the resistance, confirm it's 8 Ohms (7.1 actually).  But I'm thinking there has to be some damage to this woofer, so I take the SIG 15 out and put the Sensation back in and sure enough, I'm getting dropouts in that woofer.  OK then, bad woofer.
Next day, I fire it up and the dropouts are gone!  OK, let's try the SIG 15 again.  The dropouts come back, but now it's BOTH SPEAKERS....argh!  I put the Sensation back, no dropouts.  Sig 15, dropouts.  I even tried going directly from iTunes again like the day before, but now the dropouts were still happening.  Finally I took the speakers out and put in some bookshelf speakers and the the dropouts went away.  OK, so that was consistent.  I couldn't get the bookshelves to misbehave, so the Avlars were the only constant in this dropout problem.  And the dropouts only started with the SIG 15, otherwise the Avlars behaved.
Next day, I'm thinking, maybe the DAC is losing lock with this amplifier for some reason.  Vinnie thinks, yeah, maybe the power supply is interfering with the DAC.  So I disconnect the power supply from the wall, but still getting dropouts.  Then I take the Mac and DAC out all together and use a Squeezebox Touch and its internal DAC as the source.  No dropouts.  Then I take the digital coax out from the Squeezebox to the Audio-gd DAC and... no dropouts.  Wow, maybe it's the Mac?
No such luck.  Next day the dropouts come back regardless of the source 
Finally I tried using an old DVD player as a source, no computer, no HD.  Still got the dropouts. 

So there you have it.  I'm sure if you've read this far you're probably as frustrated as I am just from time wasted reading this thing 

I wasn't going to pursue the issue, but then when the TBI amp did the same thing, I have to think there's something that my Avlar speakers are not liking with these two amps.  I've had about 5 other amps in the system at one time or another and they were fine, it's just these two amps. 

Any ideas?

[ZLS]

Try checking the connection to the external HD;
also make sure you are using the maximum memory buffer for Audirvana. 
Perhaps just run iTunes and see if the dropout problem continues. 

[wilsynet]

I am not really technical in this way, but doesn't it seem like there's a short in the speaker?  Measuring 7.1 ohms isn't the same as driving the speaker and putting the amps under load just like connecting an 8 ohm resistor to an amplifier isn't the same as connecting speakers to an amplifier.

If I recall correctly, the Sensation has more power than both the RWA and TBI amplifiers.  I'd guess the lower powered amps are behaving differently than the higher powered Sensation.

[jtwrace]

What version Audirvana?  Dropouts are a known issue wtih the current release of A+.  You might want to not use A+ and see what it does.

[srb]

Try checking the connection to the external HD; also make sure you are using the maximum memory buffer for Audirvana.  Perhaps just run iTunes and see if the dropout problem continues.

What version Audirvana? Dropouts are a known issue wtih the current release of A+. You might want to not use A+ and see what it does.

But abernardi had said he still has dropouts even with a disc player as a source ...
 

Finally I tried using an old DVD player as a source, no computer, no HD. Still got the dropouts. 

[jtwrace]

Have you tried different interconnect and speaker wires?  More likely to be a defective interconnect though. 

Have you checked the power outlet (voltage) to make sure it's not doing anything crazy?

[abernardi]

Try checking the connection to the external HD;
also make sure you are using the maximum memory buffer for Audirvana. 
Perhaps just run iTunes and see if the dropout problem continues.

HD seems OK, I tried it with iTunes only and other sources, but no luck.  Running Audirvana in hog mode, max memory

I'd guess the lower powered amps are behaving differently than the higher powered Sensation.

Good guess, but my Dodd amp is 15W, same as the RWA, and that's playing reeeeeaaaaallll nice right now.   
And i think the TBI is more than that.

Have you tried different interconnect and speaker wires?  More likely to be a defective interconnect though. 

Have you checked the power outlet (voltage) to make sure it's not doing anything crazy?

Yes, tried all different cables.  You have an interesting point about the power outlet, my power is bad.  But I'm using a PS Audio power condtioner and both these amps were running off batteries.


Like I said, I'm not well versed in this technically, but could there be some magnetic field or RFI thing going on?  There are some high power lines about 1/4 mile from me and a powerful radio tower about 1/2 a mile from me.  When I drive under that tower, my car radio goes crazy.  But I always figured I was far enough away from these things.

[Speedskater]

There are some high power lines about 1/4 mile from me and a powerful radio tower about 1/2 a mile from me.

Both of these sources operate 24 by 7.  They won't cause intermittent problems.

[rollo]

   My guess is either a tube or cold solder joint. Next time you get a drop out try raising the volume up several notches up and see if it kicks in. I had the same issue recently with the left channel going in and out. It was a tube in the preamp power supply.
All gone when new tube installed. It was driving me nuts. We had both issues at once, a cold solder joint at the coupling cap in the Pre then the tube. When I discovered the solder joint , thought it was over. Actually was both however the real culprit was the tube. 
    Hope all works out for ya.


charles