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PrimaLuna ProLogue Integrated - Help Needed

Hi everyone. I recently made a big upgrade (for me); I traded in all my aging mediocre equipment and purchased a pair of GoldenEar Triton Twos and a PrimaLuna Prologue integrated amp. I'm using Nordost Purple flare speaker cables. No power conditioning at this point.

The problem is this: when I turn up the volume past a certain point (about 95 dB sustained), the amp begins to produce a low-frequency "throb". The throb is of moderate volume, very audible during quiet passages. The throb is about two beats per second, I'd say. It manifests both audibly and visually (in the form of a pulsing blue light from the left channel power tubes).

I've done a lot of work to try to diagnose the issue, but would like your opinion. Has anyone heard of a problem like this? I've had all sorts of suggestions from the dealer and PrimaLuna, from microphonic feedback to bad power. I don't think it's feedback, as I've isolated the amp in a separate room from the speakers and still experience the problem.

I'll shut up and just link a video I made. If you use headphones, you can hear the throb pretty clearly.

https://www.youtube.com/watch?v=Juk1ILtarS8

Thanks for any help!
roblinx
zd542
5,339 posts
 
What's your source? Also, did you swap the tubes from the right and left channels to make sure there's no problem with your tubes themselves?

I haven't seen this problem before, but maybe someone else can answer this. Could his bias be off?
almarg's avatar
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almarg
9,670 posts
 
ZD, I think that if you read this you'll conclude that the problem, or at least its root cause, is unlikely to be related to biasing. And note in the video that the problem can be induced in the power tubes for BOTH channels, if the volume is increased sufficiently.

Mofi, your suggestion is very logical, but note that the OP indicated that the same symptom occurred even when he relocated the amp to an adjacent room.

My strong suspicion is that the root cause of the problem is a defect in the amp, which is resulting in "motorboating" as I described.

Best regards,
-- Al
mechans
3,048 posts
 
That's not your amp it's your heart beating when the music is turned up.
BTW does this happen with all sources?
roblinx OP
5 posts
 
Hi Everyone,

I'm overwhelmed by the positive and helpful responses. Let me try to address each:

Stereo5: the dealer sent out one of their consultants with a separate (solid-state) amp. We were not able to duplicate the problem with the other amp, only the PrimaLuna.

Mofimadness: I've tried your idea, even going so far as to unpower the Triton Twos. Even without the subwoofer powered, the problem still happens (though it's only audible when I apply power to the speakers). I even tried putting the speakers in another room, making sure no AC power crossed the cables. Still the same issue.

Zd542: I have not yet tried swapping the tubes; that might make an interesting piece of evidence for diagnosis, at least.

Almarg: I like your idea... I should press for further tests by the dealer. They tested all the tubes, but claimed to be unable to reproduce the problem in house. I want to go there and show them how to make it happen.
Also, can you please re-link the article you linked? The URL was broken for me.

Thanks, everyone. I really appreciate your input.

Rob
almarg's avatar
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almarg
9,670 posts
 
Hi Rob,

Not sure why there was a problem with the link. But just go to Wikipedia, and enter "motorboating" in its search box. One of the choices which will then appear beneath the search box will be "motorboating (electronics)." That is the page I was linking to.

Good luck. Regards,
-- Al
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