Spatial Audio Raven Preamp

@mbmi Glad you are enjoying your preamp. Not sure how it is relevant to this thread.

The most dangerous of all are DC-coupled preamps and power amps. If the DC servo system in a preamp fails, the failure can propagate all the way to the loudspeaker. I saw this happen when I was visiting the home of a reviewer.

@lynn_olson The highlighted statement above is false.

I don’t contest what you saw.

We’ve been making preamps with a direct-coupled output (which we patented) and its been one of the most reliable design aspects of the preamps over the last 35 years. If it were to fail, our preamps wouldn’t make a high Voltage anyway, even as it warms up. As a result this is something that we’ve never seen.

If a tube amplifier was used, DC at the input would not have caused damage.

If a solid state amplifier was used, it should have gone into protect mode as any competent solid state amp will have a proper protection circuit!

So IMO if this anecdote is true, the designers of both the amp and preamp didn’t know what they were doing. Equipment should always be fail safe!!

Was the preamp of this story a tube preamp?

The anecdote is true, not fictional. I was there and saw it happen.

Not surprisingly, the preamp and power amp were all solid-state and were stupendously expensive, in the $100,000 range. As we old-timers know, price does not guarantee quality in our business, unfortunately.

DC servo failure is not rare in the high-end solid-state world. It should be, but isn’t. When it happens, the results are very expensive, not to mention the cost of down time.

Looking back, my guess is poor solder technique somewhere in the preamp, or maybe a regulator in the plus or minus supply gave up, yanking the preamp output to 15V or more. Or a DC servo went nuts. Results were the same, a destroyed power amp and loudspeaker. The only unusual thing was a designer (me) seeing the failure in real time, in a domestic setting. You usually see this kind of drama on a test bench, not in the context of an ultra-deluxe system in a home.

Should it have been better designed? Of course! But how is the consumer to know? They assume [higher price = better product].

That’s the real difference between pro gear and audiophile equipment. The pro stuff is reliable, because it has to be.

That’s the real difference between pro gear and audiophile equipment. The pro stuff is reliable, because it has to be.

@lynn_olson If you're going to stay in business for the long haul producing high end audio products they have to be reliable too. I can't imagine how anyone thought that a solid state amp without the ability to protect itself from something like this was a good idea. At the very least if the amp smoked it should have blown a fuse...

Oh it blew a fuse all right. After the output section was completely destroyed, and a massive DC pulse killed the woofer. This was European oligarch-class audio gear from a well-known manufacturer.

The manufacturer is still around, twenty years later. The buyers are expected to suck it up and not complain, I guess.

The joke amongst designers of transistor gear is transistors do a great job protecting the fuses (because transistors fail in milliseconds, while fuses can take a half second or longer). Transistors fail much faster than any human response time, whether on a bench or across the listening room. And a good, solid DC pulse will destroy any woofer ... audiophile-grade woofers can only take 1 watt (or less) of DC on the voice coil. Professional 15" woofers with 4" voice coils can take a little more DC, but certainly not 200 watts.