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I can't help but wonder if the distortion is dominated by a grounding issue. The distortion mechanism that I struggled with for a while was figuring out how to handle the ground for the output stage decoupling caps. I've seen quite a few amplifiers that exhibit this behavior, so I suspect I'm...

This pretty much agrees with my own measurements of similar Rotel equipment - decent linearity (I measured right around 0.01% THD+N), pretty decent build quality, tasteful styling, and generally a fairly simple design. They tend to be pretty easy to fix too.

Samwha have been "okay" in my experience. Not great, but not awful. I wouldn't replace them unless they've failed.

Here's one thing I've learned: People are absolutely brutal to equipment that isn't theirs, isn't important, and is in their way. Some of the worst abuse I've seen takes place during decommissioning. Doesn't matter that it's a $40,000 network analyzer that's only 4 years old, people will drag...

Yeah, that's an interesting situation. Still, I should point out that protection mechanisms are often a better solution than throwing lots of power transistors at the problem. MC2 amplifiers have relatively few output transistors for the power level (I think 5 pairs in the MC650, and 3 or 4...

Nothing about 1 kHz is fast. Even an Arduino Uno could implement a protection scheme fast enough to deal with this. Designing a good protection circuit that detects overcurrent in less than 50 us is trivial. Thermal runaway shouldn't be an issue in competently designed amplifiers. This issue...

Not likely to be a cap in this case. It's much less of an issue now, doesn't manifest itself for a few years, and while heat is a factor, 3 minutes of very hot running won't do much to kill them. The cap plague thing had everything to do with bad electrolyte formulations.

That has more to do with the waveform than the load. A typical musical waveform into a resistive load is pretty easy on an amp, since the average power level is pretty low, even if its peak power is high. The main issue with reactive loads is that it's a worse situation from a SOA perspective...

As a note, there are two issues here: safe operating area (SOA) and thermal issues. SOA is an issue even for music, because it deals with short timescales (much less than a second), and a loud bass note is plenty. Of course, any competent engineer will look at SOA for an amplifier that is...

2-ohms is hardly and edge case. A worse situation for an amplifier is a short, which is incredibly common (loose strand in a speaker wire, for example). Lots of speakers dip down below 3 ohms in the bass region. Some go below 2. Worse still, you can get a 3 ohm reactive load. Quite frankly, any...

Any modern amplifier that blew up under 2-ohm testing for a short sine wave sweep is defective in my book. If it's not meant to handle 2-ohm loads, then it better have suitable VI limiting. There are 8-ohm rated speakers that dip down to 2 ohms (and often 2 ohms reactive!) at certain frequencies...

Okay, compared to 3000-year-old speakers from the Roman Empire, the OP's speakers are spring chickens.

I doubt it. I'm fairly familiar with the Elac speakers from that era. The sandwich cone midwoofers and the JET ribbon tweeters perform pretty darn well, and the measurements I have taken show that these speakers are objectively pretty good. The directivity control probably isn't up to Genelec...

It's probably worth differentiating between transducers and electronics in this discussion. It's no secret that the differences between speakers are pretty audible, and that there are a lot of really lousy speakers on the market. In contrast, barring power limitations, and assuming we aren't...

Maybe time to check of the pins on the connectors are even connected to anything... I wouldn't be surprised if this is just an aluminum tube with a connector mounted on the end.

@JohnYang1997 Any chance you'd be willing to discuss the topology used here a little? I'm genuinely curious how you've gotten the distortion this low.

Hey, those lawn mowers are great for small city lots. I used one for years until a good battery-powered mower came my way. Way less of a pain than a gas mower, and way less garage space too.

6BQ5 amps can very comfortably run 15 WPC while keeping distortion far lower than this. I've built a few, @SIY has built many of them, and there are a good number of commercial designs that do it as well, with the ST35 being one of the better known (but not necessarily highest performing)...

95% of the places buying this type of equipment are not a "ground up" build. It's an upgrade to an existing install in a studio / concert hall / whatever, and finding 4U of free rack space is never easy in any established system. If there is 4U of free space, who's to say it's all in the same...

Ugh... I really don't need more RJ45 in my life. About the only things going for that connector are cost and ease of field termination.