300b lovers

I understand that you are referring to the approach you use with judicious application of negative feedback. I was referring to Lynn’s comparison to the “golden age “ PP amplifier which typically used 20db of NFB. Your current class D amplifiers do not fit this description.

@charles1dad 

They don't! However, Futterman claimed 60dB of feedback in his OTLs. That was during the 'golden age'... Also Kron-Hite made a transformer coupled tube amplifier (UF-101) that claimed even more feedback! It was built for laboratory use but works great for audio as well. Its specs are astonishingly impressive and having had a set (they were single channel) I can say they sounded quite decent. That was a long time ago but we compared them to an ARC amplifier which got its doors blown off.

If feedback is applied properly it is really beneficial. If its not then it will mess things up with the amounts normally found in tube amps (12-20dB...).

In the last couple of years, I had the VTV Audio EVO 1200 Class D amp with the Purifi module, with the aftermarket ministrations of Ric Schultz, and while the sound was as Ralph describes it,

@whitestix I'm going to contest this; I was not describing those amps at all and haven't heard them. You can tell something is up that isn't right since when you go on the web, you see really variable reports about their 'sound'. I notice that doesn't happen with tubes- everyone agrees that tubes sound smoother and often have more detail and so on. To what degree and what emphasis is the differences between the tube amps. I'm saying I've been playing a class D that you would think is in that category if you heard it. Going back to tubes you don't find that tubes are bringing anything more to the party. I get that seems like a tall statement. Keep in mind that OTLs have ruled the roost in the transparency department of the tube amplifier world and I've been building them since 1977 or so. During that time I've heard many tube amps; I repaired audio for a living as I put myself thru college and afterwards until Atma-Sphere was able to keep me busy full time. So I know what tubes bring and I'm telling you there's at least one class D out there that does the same thing. I suspect there are others.

Sorry I won't be able to participate in this thread for a while- I'll be out of town for 4-5 weeks. Y'all have fun and be well! 

I've lived through many new equipment break-in events over the years. As my experience level increases and the resolving capabilities of my system increases, it has been easier to track changes through the duration of the event. In a moment of judgement, it can be difficult to make statements of progress or regression as we aren't very good at making absolute comparisons, unlike numerical measurements. It's always relative and our powers of perception are better at establishing trends over time than snap judgements. It is possible to fool yourself in a single session. More valid impressions form through multiple sessions.

Here are several notable examples where break-in from new was significant and long in duration.

Antipodes K50 Server. From new, un-listenable for 9.5 days of continuous power up. Utter dreck. By two weeks of on time the performance was quite good. After 1 month, exceptional. After 6 months, fully plateaued. My experience, corroborated by others, and the manufacturer. The reason - power supply capacitor break in.

Daedalus Apollo 11 speakers. Pretty rough on arrival. Grainy HF. Over days the bass would come and go. By 110 hours the sea began to part. The grain and hearing fatigue began to lift. Bass came in. By 150 hours they were quite good. The manufacturer claims 400 hours for full break in. Guess my hearing isn't that good. Mundorf capacitors are the main culprit here.

Taiko Extreme music server. Sounded OK on arrival. After a couple weeks, quite good. After 1 month exceptional. Here's the rub on this one, even after fully broken in. If you shut it down for 15 minutes, unpowered, it takes 4 hours to recover. If you unpower for over 1 day, it takes 4 days to recover. All of a sudden the drapes open and it's a nice sunny day. These experiences are corroborated by the manufacturer too. Cause - power supply capacitors.

The common ingredients in these events are the capacitors. I suspect that these parts are the special sauce that makes this level of performance possible.

I have not heard a power amplifier exhibit this extreme of behavior from new, but that does not mean these parts don't require break in and overall performance will benefit from more run time.

If you are throwing parts in the bin after 30 minutes, I think you are missing out on some opportunities.

I've read plenty of attempts at explaining why parts, particularly capacitors change during break-in (they do plateau, they don't keep changing) but it doesn't matter unless you are a capacitor designer/manufacturer. Results are results. The reasons why don't matter for users.

Engineering is the prostitution of science. Even scientists don't have all the science worked out yet. Not even close.

My concern is reliability and unknown, undocumented processes going on in critical components. This is just bad engineering. Imagine an expensive car where the horsepower and handling changed from day to day, and the manufacturer had no idea why. Cars are 100x more complex than an audio product ... the average car has 35,000 parts, 5,000 of which are moving parts, nearly all of which are critical to performance, reliability, and safety. A single-part failure can make the entire car useless.

What’s the capacitor manufacturer’s excuse? "This is how we’ve always done it" isn’t good enough. "We don’t understand what we are making" is even worse. There’s good engineering, making reliable products that people enjoy, and bad engineering, where mysterious things occur and nobody knows why. Regrettably, this is the situation for much of high-end audio.

For all I know, Don, Thom, and I might end up designing a capacitor conditioner for one of the cap companies. Back when I was working with Gary Pimm, he came up with a gizmo that did that ... pushing through 10 kHz square waves at 1/4 of the cap’s rated breakdown voltage. After twenty minutes of that, it either survived or not. Actually, nearly all survived, and they were "broken-in" for sure after that treatment. And it weeded out the parts that were going to fail anyway.

By contrast, using the cap in a normal circuit, with music stimulus, is barely tickling it. No wonder it takes forever.

My concern for the customer experience might sound big-hearted, but actually it’s purely selfish. Neither Don nor I want ’em coming back. I am 100% retired, Don is thinking about it, and we both want the preamp and power amp to be reliable and good-sounding right out of the box. People tell their friends, etc. etc. So every part going in has to earn its keep in terms of reliability and sonics.

 A Cornell Dublier engineer once explained to me that the difference between a 150V rated cap and one rated at 175V was the way the cap was formed up and nothing else. Forming is a process where voltage is applied to the capacitor with a target of the rated voltage; something that is done only once in the factory.

But the cap is almost never used at the forming voltage. Usually for best reliability, they are to be run at about 80% of the rated voltage.

So the cap is not as efficient at the new voltage when new. It takes time for the cap to 'form' to the new voltage. Its important to understand that electrolytic caps have some properties in common with batteries and so are fundamentally different from film caps in this regard. Charging them and polarity are two examples of this similarity. Forming is one way they are unique.

Anyway, when the cap forms up to the new voltage used inside the amp or preamp it will be a more efficient bypass. Its my theory this is what people hear during break-in. I've found it measurable too- the voltage once the caps are formed is every so slightly higher and the supply is less noisy.