2. amps-preamps
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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

Showing 5 responses by roblinx

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
roblinx OP
5 posts
 
Thanks Almarg... I actually meant the link in your second post, that went to the PrimaLuna site.

BTW, I didn't reply to Mechans: Yes, all sources. I've tried the CD and AUX inputs. Didn't try the bypass circuit, as I don't have an external preamp.
roblinx OP
5 posts
 
This is a followup for everyone: the working theory is that this is some sort of distortion-based feedback loop that happens apparently exclusively with the GoldenEar Triton speakers.

I took my PrimaLuna to a friend's house and tested with his B&W 80somethings. No matter how hard I pushed it, the pulsing issue did not occur.

I took the PrimaLuna to the dealer today and tried it with their floor model Triton Twos. I was able to reproduce the problem just as at home.

We hooked the amp up to some higher-end speakers (can't recall the model now) and could not reproduce the problem.

At this point the tech commented that I was simply pushing the amp too hard, and the Tritons were causing some sort of electronic or microphonic feedback. I don't entirely buy this explanation, but it does seem to be specific to the Tritons.

He then had the idea to replace the stock EL-34s with some KT-88s that he had on the floor.

Presto, problem solved. Problem no longer happens with the Tritons.

Again, I don't pretend to understand the issue, but apparently the EL-34s were freaked out about playing loud with the Triton Twos.

Thanks to everyone for their suggestions!
roblinx OP
5 posts
 
Al,

Thanks for your additional detailed reply! I'm eager to try your resistor idea. Are we talking about something like this AG50 resistor? http://www.ohmite.com/cat/res_audiogold.pdf

I'm disappointed to report that the PrimaLuna is still showing the same issue with the swapped-in KT-88 tubes. The problem manifests in basically the same way, but the "motorboating" effect is much less noticeable (and the blue light "throbbing" is harder to see with these tubes), so I didn't see it right away.

I'm thinking I may have to abandon either the PL or the Tritons. I'm much enamored with the PL sound, so it might be the Tritons that get the boot.

Thank you again for your help.

Rob L.
roblinx OP
5 posts
 
Al, you're a genius!

The resistors fixed the problem, at least as far as I can tell (and that's the important part).

I find it interesting that I'm the first person to experience this issue. I guess I'll attempt to report it to someone who might care. Would be a shame to not publicize this solution.

Thank you very much for your help!

Rob
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