Loud popping sounds after warm-up

I run a Unison Unico hybrid integrated amp which uses a pair of 12au7 tubes in the preamp side.  Over the weekend it started acting up.  After about 1 - 1.5 hrs of listening (with both tuner and cd), there started a very loud popping sound every 3-5 seconds.  As I was worried about damaging my speakers, I immediately turned things off, so not sure if the sound was from both channels or just one (my wife seemed to think it was only from one channel).  The popping occurs even after turning down the volume to '0'.  Initial thought was that one or both tubes were going bad, but the problem reoccurred after swapping out to another set of tubes.

Would appreciate any thoughts on what the problem might be, or how I could explore the problem further without damaging the speakers.
It sounds like a grounding problem...so many times people look at the tubes right away ...I have found this NOT to be the case (I run 10 tubes in my front end). Try using a cheap power strip with a ground plug (3 prongs), then plug everything into the strip. It sounds like you have plugs going to different sockets and that can lead to problems with too many ground plugs going every which way. I take it your not using a turntable at all right?  Also, Maybe the amp needs to be looked at ??

Matt M
if it is 15 or 20 years old, you may have electrolytic caps that are going bad

----> serious business as they could blow your speakers AND the rest of the amp
I had an amp that popped intermittently and it was the caps....fortunately i pulled it out before any damage.
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If the popping is just as loud with the volume down and is in one channel, I would suspect a bad solder joint on or near an output transistor.
" As I was worried about damaging my speakers, I immediately turned things off". You were right and turned them off right away. I had the same issue and did not turn them off soon enough, so it fried one of my speakers. I later learnt from reading other stuff that it could be power current leakage from the capacitor. Yours issue could be different though.
Thanks all for your feedback.  Based on everyone's comments, it looks like either a bad capacitor or maybe an output transistor.  I recently had the unit modified with all new capacitors, resistors, and some diodes, and it is still under warranty for anything associated with the mod.  The unit has now been sent back for repair and hopefully the problem is associated with a solder joint associated with one of these mods.

As an aside, my speakers suffered no damage, and putting back in my old Acurus preamp/Parasound amp combo, I was pleasantly reminded how good my old setup sounded (and still does).
I doubt that its a filter capacitor or output device. Popping is not a symptom of either in failure mode! A bad solderjoint is far more likely.


I believe I am having the same issue with my Unico. Have you fixed your problem? I would really appreciate your feedback, maybe it can help with my issue.

Thank you.

Regards, Josip