PrimaLuna Dialogue Premium Preamplifier. DESTROYS SPEAKERS!!

The OP said specifically it was DC and that he damaged his speaker, not his amp.

<< shrug >>

Not a big deal.

Right on both counts- but we sorted out pretty quickly that it wasn't DC- his amp blocks DC, so it had to be something else.

@ibocquin Hm, Its been a bit of a mystery to me as to why Krell has been spreading a false rumor that tube preamps push DC; I'm thinking that your experience might explain it.

@erik_squires  With regards to the PL preamp- if a high frequency snubber cap, the failure may have caused the preamp to make ultrasonic noise powerful enough that the amp made enough power to damage the speaker. If that is the case, my theory about the AC line may be out the window.

If, primaLuna is not a good match for electrostatics, and problems can arise, then BUYERS SHOULD BE WARNED, prominently written, in the owners manual.

Actually, there is nothing in my post that suggests that ESLs and the preamp are incompatible. As far as that goes, I'm not really saying that the amp and preamp are incompatible either.

What I am saying is that a host of issues led to this problem, and it might not even crop up if for example, your AC line to the power amp were a larger capacity, like 20 amps rather than the 15 amps you have now. I've seen things like this before with entirely different equipment; anytime you have such a high power amplifier you have to be careful!

When TWO pre amps, bought 6 weeks apart, FAIL, IN EXACTLY the same way, this points to a much deeper problem.

I agree, but the question is what is the deeper problem?

This preamp has been around a while without any reason to think there was a reliability problem. Yet two failed in the same installation. From a purely logical viewpoint, this points to something in the installation that is playing a role.

I don't think its wall paper...

The amp is equipped with 68uf input couping caps. This will prevent the amp from conducting any DC applied to its inputs. But the problem is not that the amp failed- the **power supplies** in the speakers failed- and not the matching transformers of the speaker. So we know its not DC that did the damage.

Its my opinion that the extreme power of the amplifier, coupled with a slight low frequency instability in the preamp is actually what caused the damage. When the LF instability showed up, in my theory the AC line voltage sagged, which then exacerbated the problem in the preamp, causing the amp to make the line voltage sag more, until finally the speaker couldn't take it any more.

Change any of the several variables here and its likely that there would have been no problem. For example, the amp draws a bit of power so it probably should be on its own 20Amp circuit. If its on the same circuit as the preamp, I think many preamps could have gotten into this trouble.

If the preamp had AC line conditioning, the additional time constant of the presence of the conditioner might have prevented this as well.

I personally don't think that the preamp had a severe failure. I suspect that in most systems there would have been no adverse effects at all.

IOW we would know if if there were 20 or 30 of the same preamp having the same part fail in a wide number of systems. But we don't see that- the preamp seems to be holding up just fine. We just have this rather weired occurrence in this **one** system! That's a red flag that its something in the system.

So the bottom line here is I don't think Kevin Deal has to do anything further in regards to the other preamps in the field.

The Bryston amps, as well as many other high end amps, DO NOT
have DC output protection.

Usually a relay is required for DC protection, but it can be implemented by other means such as crowbar circuit (which is a means of shorting out the power supply of the amp if the DC circuit is triggered).

From the STEREOPHILE review:
https://www.stereophile.com/solidpoweramps/108bry/index.html

Because the 28B-SST's components and circuits are rugged, the protection-circuit parameters are not as restrictive as are found in other amplifiers. Even so, the protection circuit is designed to handle most fault conditions, including shorts and DC offset.

It would not surprise me to find out that the above comment is actually false; that would not be a first for Stereophile.  Calls to Bryston here in the US and Canada did not get me to the bottom of it. I'll try again on Monday.

The Bryston is equipped with DC Offset protection. If the preamp made DC, the speakers would not be damaged unless the Bryston's protection circuit failed.

Well we have one part of the story, and my surmise was correct, it was an ESL. But I doubt the power supply was damaged. One other part of this missive is missing- the amplifier. What amplifier was used?

I don't think this event happened. If you look at the original post, you will see that the poster said that the power supply for the speaker failed- not the speaker itself.

If we presume for a minute that the preamp was putting out DC, and that also somehow this got by the amplifier without blowing up the amp and/or tripping its protection circuitry, then it would be the woofer of the speaker that would be at risk, not the 'power supply' (which suggests an ESL, but even then the power supply would be untouched).

So without further information, I'm calling this one a massive troll- and an attack on Kevin Deal. Kevin is a competitor on mine (we make amps and preamps) but he's always been straight with me.