Spatial Audio Raven Preamp

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.

Sheesh. If our stuff had been damaging speakers we'd not have been in business very long. Odd how a solid state manufacturer could get away with that!

Happens all the time in the small-production-run solid-state world. Oversights in manufacturing like no heat-conducting paste between transistors and heat sinks, for example. Or a wave solder machine not properly set up for EU-required leadfree solder, so the solder joints on a circuit board start going bad after a while.

There’s some pretty sketchy tube stuff too ... I remember seeing bulky, heavy electrolytic capacitors "attached" to the chassis with RTV silicone goo ... and no bolts, clamps, or other hardware! From a highly reviewed European manufacturer that is still in business twenty years later. Or a well-known American manufacturer that omitted, or forgot, the required 10~100 uF decoupling/stabilization capacitors for the multiple 3-pin voltage regulators, so they sang happily in the 10 MHz range. Easily visible on an RF spectrum analyzer, but not easily seen on a scope.

@lynn_olson 

Or a well-known American manufacturer that omitted, or forgot, the required 10~100 uF decoupling/stabilization capacitors for the multiple 3-pin voltage regulators, so they sang happily in the 10 MHz range.

I've seen preamps and amps where the parts were held in place with hot glue. All that had to happen was have it dropped in shipment and you have a shock or fire hazard. I've encountered oscillating regulators in some American built stuff so I know what you're talking about. Tends to make the 'regulated' circuit a bit noisy...

I have seen all sorts of things rebuilding old tube gear.  If it was original, then it was pretty well made and everything tied down.  If someone else had "restored it", all bets were off.   I won't name anyone, but there were a couple of well known vintage restoration places where I could not believe what I saw when I opened the hood.  50 cent caps with leads hanging in the air, etc....   The best story though, was an old Fender guitar amp I was fixing for a musician friend.   Someone had wired the hot side of AC to the chassis and neutral to the fuse!  The amp worked.... but if that guitarist has put his cold sweaty beer can down in just the right spot on top........