High End Class D

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Howard Stone

Jul 16, 2020, 1:17:58 AM7/16/20
I’m reading so many positive things about Neurochrome that I’m tempted. Anyone had any experience with “high end” class D (or is it Class T?)

Peter Wieck

Jul 16, 2020, 5:52:37 PM7/16/20

I see that, once again, you are nibbling around the edges of the "Brute Force Amp" concept. I kinda-sorta figured you would get there eventually. And, coincidentally, you missed out on a Harman-Kardon Citation 19 that I tripped over at a yard sale - my son-in-law laid claim to it the moment he saw it on the bench.

But, getting to your question directly: If you choose to move to Class D amplification do go for the most recent designs and do pay attention to how the signal is filtered to the speakers. Put as simply as possible: "Good Audio Quality" class D was only a concept as recently as 4 years ago. Today, distortions (all components) of less than 0.05% are routine. A few years ago, damping in Class D was very nearly non-existent. Today, it is approximately that of a 30-50 watt tube amp. Low, but definitely there.

A few things:
a) Class D amps do not like being run at/near rated output for long periods. They do not 'blow up' but they do get quite warm.
b) Based on the nature of sound and the decibel scale, if you are going to go to Class D, go BIG - Given that the next step after a 20 watt amp is a 200 watt amp, start there. Really. Do not try to gang them up, start with the highest power module you can afford and work from there (The 686 in Neurochrome, or any of several other brands:




As you can see, prices are all over the place and largely depend on how user-friendly and/or complete the various parts will be on arrival. But the overall audio quality will be largely indistinguishable **!IF!** you purchase an audio-purposed module initially vs. something for sound reinforcement.

My 'audio-snob' neighbor down the block built a Class D amp recently in a COVID-related fit of boredom to compare to his 300B-based flea-powered SET tube amp - he used the 150-watt mono modules, with separate power-supplies. I am not sure he is going back to tubes.

Repeat: GO BIG, or not at all - no need for extremes (1,100 watts, for example), but getting those transients is worth something.

Peter Wieck
Melrose Park, PA

Howard Stone

Jul 17, 2020, 8:07:51 AM7/17/20
That's really helpful Peter, thanks.

How serviceable are these amps. I mean, in 10 years, and Neurochrome no longer exists, and my expensive amp has a fault, is it going to be impossible to service because the parts (the chips?) are no longer available?

Trevor Wilson

Jul 19, 2020, 9:37:53 PM7/19/20
**In general, Class D amps are unservicable. Or at least they will be.
And here's the irony: Around 6 ~ 8 years ago, I was considering a
different occupation (apart from servicing audio equipment). I was in my
late 50s and found that the preponderance of surface mount components
and, in many cases, the complete lack of schematics for some products (I
had an NAD on the bench, that used an ICEPower module, for which no
service data was available, thus requiring an entire module
replacement). In the last few years, I've seen these trends accelerate.
Given the cost of Class D implementation is rapidly falling in cost, I
predict several things:

* Class D amps will not be worth repairing. Even expensive ones.
* High end manufacturers (like Rowland) that have embraced Class D will
* High end companies like ARC will likely survive, because sufficient
listeners will continue buying linear amplification.

The upshot for me is that, despite being at the end of my working life
(I'm 67 years old next month), I have never been busier. Most of the
guys in my business have switched to more profitable pursuits, or
retired. I get repair jobs in from all over the country (Australia).

I reckon that Class D amplification will sweep all before it. EXCEPT for
niche stuff. And there will likely be demand for that for a very long
time. Hell, I've started repairing cassette decks again! YIKES!

Postscript: Ya gotta love hipsters. As a group, they have pushed the
revival of old stuff along very nicely. I tips me hat to them.

Trevor Wilson

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Peter Wieck

Jul 20, 2020, 8:59:18 AM7/20/20

Serviceable - that is a heavily loaded question. Effectively, these modules are not serviceable in any conventional definition of the term. They are uncomplicated devices that if used within their design parameters should outlast all of us, and possibly our children's children. The best analogy I can think of without much thought is that a Class D module is very much like a well-made Klein or Estwing hammer. Unless you abuse it, it will last forever. It will also tolerate a limited amount of abuse, but not infinite abuse.


Buy a quality device in the first place. Build it well. Keep good clearances. Make sure the power-supply is capable. And keep it cool.

Trevor Wilson

Jul 21, 2020, 8:37:06 AM7/21/20
**All good advice. However, I would add a couple of riders:

* Most Class D amps, IME, fail more frequently that well built
pin-thru-hole products. That said, they are reasonably reliable. I have
4 subwoofers (different models), manufactured by a very highly regarded
US manufacturer in the workshop right now. All have faulty Class D
modules. None are worth repairing. I have a portable PA system with a
Class D amp. Repair is marginal and the client is still considering his
* By the time a Class D amp does fail (say: 5 ~ 7 years), it won't be
worth repairing, as technology will have moved on.

Howard Stone

Jul 21, 2020, 11:16:12 AM7/21/20
I’ve certainly had experience of failed DACs. Is that the same sort of thing?

The discussion has kind of put me off buying a Neurochrome. Also they’re not exactly cheap once you factor in the import duties from Canada to the UK.

But it’s a problem, finding an affordable GREAT amp. You guys know I have a Krell and a Radford, I’m addicted, I want a third!

(First world problems.)

Peter Wieck

Jul 21, 2020, 11:51:12 AM7/21/20
It has been my experience - albeit limited - that a class D module included as part of a powered speaker system is not the same as a purpose-build amp built from separately chosen parts. The one is driven by bean-counters searching for the the lowest possible cost, the other by the assembling individual with (presumably) fewer constrains. Keep that in mind. The biggest enemy of these amps is heat, then, heat, and did I mention heat? As the one-off builder, you would be able to accommodate ventilation and cooling that a mass-producer would not. That producer is building for "Warranty x 2" and you are building for the ages.
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