Let's stop calling Class D amplifiers "efficient" when they are not.

[rdenney]

Amps like the Quad are a bit legendary. But there are mountains of A/B amps that were respected in the day but are now in scrap heaps. How many people still run SAE amps? Spectro Acoustics? Even later brands like Carver, Adcom and B&K—I’ll bet the majority of these have been scrapped. Even traditional high-end amps like McIntosh. I’d even bet that the number of Quads in use is the minority of those made. And I’m not even going into the Japanese brands.

There just aren’t enough Restorer John’s to go around (and I mean that in all senses).

Rick “life-cycle efficiency isn’t obvious” Denney

 

[dlaloum]

Amps like the Quad are a bit legendary. But there are mountains of A/B amps that were respected in the day but are now in scrap heaps. How many people still run SAE amps? Spectro Acoustics? Even later brands like Carver, Adcom and B&K—I’ll bet the majority of these have been scrapped. Even traditional high-end amps like McIntosh. I’d even bet that the number of Quads in use is the minority of those made. And I’m not even going into the Japanese brands.

There just aren’t enough Restorer John’s to go around (and I mean that in all senses).

Rick “life-cycle efficiency isn’t obvious” Denney

I did not like the sound of the Adcom 555 when I had it... it got moved on relatively quickly - the Quad stayed.

I think most SAE amps get held onto and refurbished too...

I see the occasional Carver Sunfire amp come up for sale, and they seem to get snapped up fairly quickly - some of the designs are a lot more complicated to maintain/refurbish .... the Quads are relatively easy... Peter Walker was always keen on keeping things repairable/maintainable

 

[SIY]

I did not like the sound of the Adcom 555 when I had it...

How did you determine that it was the sound that you didn't like? Controls for ears-only? Or is this "I know what I know, and I will make a conclusion without an actual experiment?"

AFAIK, the Adcom doesn't actually have a "sound," it just amplifies voltage accurately enough to be better than any reasonable audible threshold.

 

[dlaloum]

How did you determine that it was the sound that you didn't like? Controls for ears-only? Or is this "I know what I know, and I will make a conclusion without an actual experiment?"

AFAIK, the Adcom doesn't actually have a "sound," it just amplifies voltage accurately enough to be better than any reasonable audible threshold.

The 555 vs a Quad 606 and a Quad 405 (also a Revox Integrated I had at the time)....

It was a subjective evaluation, using a pair of Klipsch Forte's (III I think?)

I had a Radio Shack SPL meter, which I used for level matching...

The 555 always sounded harsh, the Quad's and the Revox sounded smoother, more "together".

Knowing what I know now, chances are the 555 was unhappy with the impedance/phase profile of the Forte's

I purchased the Forte's and the 555 as a set together... kept the Forte's for a while, before they ended up with my brother...
Was never happy with the sound of the 555 combined with the Forte's - all my other amps sounded better (the other three, in fact sounded identical).

The buyer who came for the 555 listened to the setup, and was happy with the sound....

 

[Ken1951]

How did you determine that it was the sound that you didn't like? Controls for ears-only? Or is this "I know what I know, and I will make a conclusion without an actual experiment?"

AFAIK, the Adcom doesn't actually have a "sound," it just amplifies voltage accurately enough to be better than any reasonable audible threshold.

If my 555 has any sound of it's own I've never noticed it and it was first used when new with a pair of Magnepan MG-1Bs. Currently powering a pair of Paradigm Signature S8 v.1. Never bothered to do any sort of test because everything has always just sounded great to my ears and still does.

 

[SIY]

It was a subjective evaluation, using a pair of Klipsch Forte's (III I think?)

So by "subjective," you mean "peeking." No basic controls.

Knowing what I know now, chances are the 555 was unhappy with the impedance/phase profile of the Forte's

The 555 does exceptionally well with difficult loads. That's always been its strength.

 

[dlaloum]

So by "subjective," you mean "peeking." No basic controls.

The 555 does exceptionally well with difficult loads. That's always been its strength.

Yes...

And I very much wanted to like the "vaunted" and very positively reviewed 555 ...

But yeah - whatever the reason was... It did not make a good impression ... this was in the early to mid 1990's...

And I am NOT a great believer in amps "sounding different" - quite the opposite!
But I do know that amps do behave differently when handling loads outside their specced performance envelope... so with "easy" speakers (within the rated spec envelope) - all amps sound alike.... once you start to get extreme phase angles and low impedances.... the ones that are outside their rated design spec start to become audibly different.

The 555 according to stereophiles 1989 review, blew its fuses when asked to drive a 2 ohm load to high levels... so I would not describe it as an amp well suited to difficult loads! But I was blissfully unaware of amp/impedance matching in those days... and the 555 was/is indeed a high value powerhouse - sadly...(my emotions at the time) - it just didn't sound great into my setup.

 

[rdenney]

I did not like the sound of the Adcom 555 when I had it... it got moved on relatively quickly - the Quad stayed.

I think most SAE amps get held onto and refurbished too...

I see the occasional Carver Sunfire amp come up for sale, and they seem to get snapped up fairly quickly - some of the designs are a lot more complicated to maintain/refurbish .... the Quads are relatively easy... Peter Walker was always keen on keeping things repairable/maintainable

I would say those that remain are preserved at a higher rate because only real enthusiasts preserve them. But how many ended up in the landfill before they were “collectible”? I’m not thinking of Carver Sunfire, but of Carver Corporation products. Or even Carver’s previous Phase Linear amps, and those were legendary, too. How people are using Phase Linear amps in their systems any more? Where did your 555 end up?

I have an Adcom GFA-535 that I use every day in my office and it sounds like all my other amps when not overdriven.

Rick “thinking enthusiasts tend to extrapolate their own interest to broader markets” Denney

 

[Galliardist]

I don't doubt it a bit, and there have been some excellent examples of bad thermal management here on ASR. I meant it when I said I was not sure when thermal management was introduced, should have clarified that I was not surprised that it was, but was just looking at the John's first post.

Specsmanship is as much a part of marketing class D as anything else. Most components do not provide a chart show how efficiency varies with power, from which many folk might realize their class D amp is not much if any better than class AB at their average power levels. I think that was @restorer-john 's main point.

Maybe the title of this thread should be "Let's stop calling class D amplifiers where they are not"?

 

[Audio Science Pal]

Yamaha. Class A/B, 47W @ idle, 120V.

 

[Head_Unit]

I'm pissed that the EMF property of AMPS keeps pushing my electrons OUT of the amp. How am I supposed to burn them in if they are always leaving? how are they supposed to get good at amplifying?

It's a damn good question. Research has shown you need 10,000 hours of practice to get good at something. I don't see how those electrons can get their 10,000 hours if they don't stick around

 

[KMM]

Did a very simple, non-scientific test to determine the efficiency of a classic A/B type amp (Nubert Amp A. 2*540 W 4 Ohm (0,5% THD+N) and a Audiophonics NCore NC2050 MP 2*250 W 4 Ohm THD=1%.
Speakers: Nubert Nuvero 140 440W/600W
Cable: Goldkabel LS440 Rhodium
Streamer/PreAmp: Audiophonics Sabre Evo via balanced output
Pink noise from test CD
Adjusted volume on both amp to 80 Db(A) at the same location using a iOS app and a microphone stand

Both amps warmed up for 1 hour

Idle power demand (10 min average)
Audiophonics 17.4 W
Nubert 103.5 W

Load power demand (10 min average@80 Db(A)
Audiophonics 20.7 W
Nubert 107,5 W

Idle power consumption is the obvious difference and this simple test should at least give a hint which design is the more efficient in terms of power demand. I limited the output to a listening room friendly 80 Db(A). Likely, at much higher SPLs the difference will be smaller, but I ain't gonna test it. My Nuvero 140 are very efficient.............

 

[radix]

Idle power demand (10 min average)
Audiophonics 17.4 W
Nubert 103.5 W

Load power demand (10 min average@80 Db(A)
Audiophonics 20.7 W
Nubert 107,5 W

Idle power consumption is the obvious difference and this simple test should at least give a hint which design is the more efficient in terms of power demand. I limited the output to a listening room friendly 80 Db(A). Likely, at much higher SPLs the difference will be smaller, but I ain't gonna test it. My Nuvero 140 are very efficient.............

What did you measure the power with? Just curious.

 

[KMM]

Simple power meter plugged into the wall outlet. Good enough for this type of triage. Like this. https://amzn.eu/d/7nr0wh1