So what AM I hearing in different solid state amps, or am I?

[SwedishChef]

With tonight's Audioholics amp video, it seems like a good time to ask for thoughts on something that's been bugging me. What have I been hearing - if anything - in different solid state amps/receivers over the years?

I hope not to start a fight - let's just brainstorm and share experiences, if we can. But I have this set of experiences with amplifiers that aren't completely consistent, and I can't really make sense of them. They lead me to not having a position on Why, and feeling like there's something going on I don't understand. I want to understand, and also understand how they relate to something measurable, if at all possible. Here are a few of these experiences.

Many years ago, I switched from a prior receiver (an NAD, I think) to a Harman Kardon AVR 7200 (supposedly 7x 100 watts). When I first bought it on closeout many years ago, I was amazed at how much better it sounded than my prior receiver, especially in two-channel use. Even on closeout, it was expensive for me back then, and I would have been happy and content to drive it right back to the store to get my money back if I'd found it lacking. I spent many hours comparing tracks played on a Rega Planet CD player.

While I'm pretty sure I was testing with 4 ohm 89db sensitivity speakers, it was also in a pretty small apartment, and I was not (and am not) one for playing things particularly loudly. I did not level-match the tests back then, but I don't think I was playing things significantly more loudly on the HK. There were so many improvements - the soundstage, the separation of instruments, the detail, the tighter bass. It was no contest.

The HK had been retired to 2-channel use in an office area when it died mysteriously, earlier this year, but it was getting nearly daily use. I replaced it with the cheapest thing I thought wouldn't be terrible, and picked up an NAD D3020 v2. It turned out that it bugged me constantly. (Was running to Paradigm Studio Reference 20 speakers). It's not like I was blasting anything whatsoever in that room. But it did seem to get worse if I deliberately tested louder music, when I started poking at it and trying to figure out what to do. (I also hauled out and tested some other speakers, but informally. It didn't seem a lot better with others.)

If the original amp was 50-60 watts - a guess, I could try to research more to nail it down - and the HK was 100, and the D3020 was 30 watts into 8 ohms (or 100 into 4 - those speakers dip to 4), we are talking different power levels. But it's hard to see how that should matter at these very moderate listening levels. (The recent HK usage was mostly playing ambient instrumental music in the background - you could easily have any conversation over it without turning it down in the slightest. I'd even leave it on during some meetings.)

I recently relieved a Marantz 6013 of its L C R duties by routing through three channels of a Harman Kardon Citation 7.1 power amplifier (to those unfamiliar, that 7.1 is just a model number, it has 4 channels of amplification). Again, I think things sound a little better, even in very moderate volume 2-channel scenarios - we're not just talking about near-reference movie situations here, where it might well help in a more obvious fashion.

To be clear, my experiences don't all cut in the same direction. I did some level-matched blinded listening comparing an Outlaw RR 2160 to the NAD D3020 v2 on some Canton speakers (model forgotten, as they weren't mine) a while back. And at low volumes, I had a harder time differentiating the two than I'd expected (though I could). The NAD didn't seem as bad. At louder levels, and with lower impedance, lower sensitivity speakers, it was much easier to distinguish the two. But I was under the impression that I just shouldn't be able to hear these kinds of differences unless the amp was pushed too far.

So when people talk about "Class D being good enough" these days - I just haven't heard those amplifiers yet. And when people talk about "solid state amplifiers sound roughly the same, and are all good enough, as long as you don't overdrive them," I see the measurements, and I kind of believe them. But I also feel like that hasn't matched my experience - I don't always HEAR that. So what am I hearing? If anything.

While I'm as susceptible to cognitive bias as anybody else, I hesitate to blame myself for that in all of these situations. For example, I definitely wanted to be satisfied with the D3020 - a problem quickly, inexpensively solved with a cute, small, space-saving amplifier that had bluetooth capabilities that were new to me, and fun to play with. But the sound just kept calling attention to itself again and again, and I kept wishing the HK hadn't died. I had to replace the D3020. (It is currently retired on a shelf.)

WHY did the HK seem like such an upgrade back in the day? And if it really did sound better, how can I explain that? And WHY did the D3020 seem so bad, even at moderately levels, in the recent past? Am I somehow THAT sensitive to distortion? Does the distortion perhaps start much farther down in the power (or volume knob) range than I'd thought? Was it just power? Was it current availability? It drives me nuts that I don't know, because in the modern world, where it's hard to "listen before you buy," I'm not even sure what to try to avoid - or characteristics I should try to buy for. Except, perhaps, trying to buy far more power than I think I'll need, so I don't risk running into distortion. But A) that's a guess, and B) it doesn't seem to match what other people say.

Color me confused. And interested in the thoughts of others. What measurable things might I be hearing in these situations? Or is it all in my head? And do you have similar experiences, and perhaps conclusions related to them? (If you've stuck with my question this far, your time and attention are appreciated.)

 

[Leemix]

HK are known to voice their stuff to something ppl like. So might be a reason.
The pre amp sections also matter.
In my experience all amps dont sound the same but i dont know why.
Many reasons why, and even if everything was ‘in your head’ that doesnt matter because if you like something for any reason you will enjoy it more. ...Which is the whole point

 

[Alex2507]

(If you've stuck with my question this far, your time and attention are appreciated.)

The answers are the tricky part. I recall lusting after the H/K 7300 and still consider it a beast. It may be that the NAD had some short comings which you were able to identify by the sound signature on familiar music. Without test gear and/or the kind of time it takes for a semi-proper comparison, all I really have to go by is how much I like something and how often I go back to it.

For a real discussion on the matter I defer to the myriad of Brainiacs that responded to this thread:

Which power amps (or all of them) have their own sound signatures, and why, by design, or just happened to be?

If you read and believe the linked Audiosciencereview.com review on the Benchmark AHB2, it should be beyond doubt that such an amplifier will just do its job, without introducing any tonal characteristics to the input signal. The reviewer received two samples. Do you think some golden ears...

forums.audioholics.com

 

[Kvn_Walker]

You said you level matched, so that would rule out "louder is better" ... assuming you did that for every comparison. Our brains can mistake a difference in loudness to a difference in quality.

I think all well-built solid state amps should sound close enough that little difference could be heard if they are driven within operating spec.

If I get another Class D amp in the future it'll be based on Hypex N-Core. Those are the real deal, and the measurements back it up.

 

[Swerd]

First of all, @SwedishChef. Welcome to AH, and thanks for your question. It was well worded and carefully though out.

What have I been hearing - if anything - in different solid state amps/receivers over the years?

Many years ago, I switched from a prior receiver (an NAD, I think) to a Harman Kardon AVR 7200 (supposedly 7x 100 watts). When I first bought it on closeout many years ago, I was amazed at how much better it sounded than my prior receiver, especially in two-channel use. Even on closeout, it was expensive for me back then, and I would have been happy and content to drive it right back to the store to get my money back if I'd found it lacking. I spent many hours comparing tracks played on a Rega Planet CD player.

While I'm pretty sure I was testing with 4 ohm 89db sensitivity speakers, it was also in a pretty small apartment, and I was not (and am not) one for playing things particularly loudly. I did not level-match the tests back then, but I don't think I was playing things significantly more loudly on the HK. There were so many improvements - the soundstage, the separation of instruments, the detail, the tighter bass. It was no contest.

Your question can be difficult to answer clearly because the differences from a larger amp can be subtle and hard to easily describe in words. It depends on how powerful the amps are, how much reserve power they have, and how demanding the speakers are.

A number of years ago I added an external 200 wpc amp to my existing AVR. The 2 channel amp drove my front left and right speakers. The AVR was a modest Denon rated at 70 wpc. So the power increase was about triple.

At first, I couldn't say I noticed anything had changed. But soon I noticed that the speaker's bass seemed a little more crisp and firm (less bloated?) on certain musical selections. It was subtle, and depended on the music, so it wasn't always noticeable. Within a few weeks, I started noticing that the cues for sound that was comfortably loud and too loud had changed. I could listen at louder levels without noticing that it was uncomfortably loud. After that, I started turning it down.

Apparently, with the AVR I had judged when to turn it down by the amount of noise or distortion I was hearing. When I started using the bigger amp, those cues were less noticeable. It's not unlike driving a car, where I could estimate my speed by listening to the road noise. If I got new tires, or drove on smoother pavement, those cues changed and my sense of speed was wrong. The more powerful amp was apparently quieter, as in less noisy than the smaller amp, while at the same time, driving the speakers louder.

I hope that makes sense. Please note that all what I described was with the same speakers.

 

[Swerd]

This next post will try to tackle the MAJOR issue that some speakers are easy to drive and some are hard to drive.

Such differences in speakers can create the false impression that different amps or receivers sound different when it's really brought on by the speaker-amp combination. I believe that speakers with somewhat demanding power requirements tend to sound different when driven by different amps – where one amp easily drives the speakers, and another amp struggles to drive them.

It would be easy to misinterpret this by saying that higher watts always equals better sound. Meaning 300wpc would sound better than a 80wpc amp at the same decibels, same amp build quality. Is this just because of "headroom”? In a single word, yes, more headroom is the reason.

But few things are really that simple. More watts can lead to better sound only if your speakers were limited by fewer watts in the first place. Different speakers have different power requirements. You need more power only up to a certain threshold, a "good enough" point. Beyond "good enough", more is not better.

Back to your case. What were the speakers you used with those various NAD and HK amps? What were their power requirements? Specifically, what were their sensitivities and impedance? Please note that sensitivity is a single measured value expressed as dB/watt or dB/2.83 volts, but impedance is not constant, it varies with the frequency. You must see a speaker's frequency vs. impedance curve.

For example, your Paradigm Studio Reference 20 speakers. (Soundstage Network is a good source of reliable measurements of speakers. Few speaker manufacturers publish these type of measurements.) That page says their sensitivity is 88.5 dB (measured at 1 meter with a 2.83 V signal, averaged from 300 Hz to 3 kHz). Their impedance vs. frequency curve (below) shows they should be considered as 4 ohm speakers.

And their impedance phase angle vs. frequency curve (below) shows that the impedance phase angle (in degrees) in this speaker varies by no more than about 90° through the audio frequency range. This is especially important in the bass to lower mid range region, roughly 50 to 500 Hz, where changes of impedance phase angle greater than 90° result in hard-to-drive speakers.

All this indicates that the Paradigm Reference Studio 20 speakers aren't particularly hard to drive, even though they are 4 ohm speakers. However, they probably do sound better when driven by more potent amps than with smaller amps.

Perhaps – and I can only speculate about this without knowing more about your amps' power output – the NAD amp had insufficient power to drive these speakers well, while the HK had more than enough power.

 

[Leemix]

Cut post to relevant lines for question:

Please note that sensitivity is a single measured value expressed as dB/watt or dB/2.83 volts
That page says their sensitivity is 88.5 dB (measured at 1 meter with a 2.83 V signal, averaged from 300 Hz to 3 kHz).

I have read a few places that sensitivity is only measured down to 300Hz but i have never seen a reason why. I would think that below 300Hz to the -3dB point of the speaker would be very relevant because thats where most power is needed and where amp power differences should be important for a set SPL calculation when calculating how much power is needed to run X speaker to X dB SPL.
Do you(or anyone else reading the thread) know why its only down to 300Hz?

 

[Swerd]

I have read a few places that sensitivity is only measured down to 300Hz but i have never seen a reason why. I would think that below 300Hz to the -3dB point of the speaker would be very relevant because thats where most power is needed and where amp power differences should be important for a set SPL calculation when calculating how much power is needed to run X speaker to X dB SPL.
Do you(or anyone else reading the thread) know why its only down to 300Hz?

I don't know why for certain, but I can make a guess.

Below 300 Hz, most rooms make significant contributions to a measured SPL value. This can be both plus and minus contributions. To avoid that, sensitivity measurements keep things above 300 Hz.

In fact, some manufacturers seem to avoid using sensitivity numbers determined in anechoic or simulated anechoic conditions. Do their in-room sensitivity numbers make use of speaker placements that take advantage of wall or corner reinforcements? This can easily result in unusually high sensitivity values.

 

[lovinthehd]

My general experience with solid state amps is mostly of the "it doesn't matter as long as you're using them in their comfort zone" variety, so to speak. Like Swerd, I have had the experience of changing various amps, including much more powerful amps, with the same speakers in the same room and have done so several times. While I may hear a slight "difference" (which I can't define) upon first making a change, it's very minor and fleeting/soon forgotten (let alone would I be able to readily identify which amp was in use later....and there have been times I've made a change I have forgotten about and not noticed at all until I go and make another change). I have several different systems going now, and several different power amps on hand, and I can interchange the various electronics with relatively seamless results. Maybe I'm just not sensitive enough.

Maybe it goes back a ways. I inherited a Fisher receiver from my dad to start my first good system with, but it started having issues after a while and I replaced it with a new receiver a year or so later. I did not notice a particular sound quality difference, nor even any particular ability to get significantly louder with the same speakers as I was using before but the two receivers were probably within 2dB of each other, too (altho I only knew about watts at that point, the new receiver being around 70 wpc at 8 ohm, the old one 45 or so), which was slightly puzzling but didn't dwell on too much (too busy digging the music). Later when I changed that receiver out for a separate pre-amp/power amp setup again no significant change with the same speakers, altho could get a bit louder I thought but no significant change in sq. I was actually a bit disappointed after all the talk about how the more powerful amp would be such a huge upgrade....

Every now and then I make changes or switch gear in/out (cuz that's what we audioholics do?) and the amp or pre-amp makes no significant difference to my ears, it's the speakers/rooms that are the changes that make differences that are readily noticeable. I don't think any of my speakers have been particularly "hard to drive" otoh.

I did start to watch the amp video shortly after it was posted by Gene/Matthew but not terribly interested in tubes so thought I'd wait and see what showed up here in print....

 

[TLS Guy]

I think it has to do with the amp loudspeaker interface. The load presented by speakers to amps is all over the map. I do think that many speakers present an unreasonably difficult load to amps.

A test bench resistor is not a speaker load by a long shot. We talk a lot about the ability to provide current as impedance drops. A very closely related issue is the source resistance of an amp. We don't talk about this a lot. Well the higher the source resistance of an amp the more it will follow the impedance curve of the speaker.

This is an issue that Peter Walker of Quad and Raymond Cooke founder of KEF who were very close friends talked about a lot. Raymond Cooke was stressed the importance of minimizing impedance swings and phase angels in his designs. Peter Walker was very concerned to get the source impedance of his amps very low.

My speakers are all tested and used with Quad amps. Basically I believe that ideally speakers and amps should be designed as a unit, and so did both the above mentioned gentlemen. I think this is at the bottom of your observations.

Quad amps have about the lowest source resistance of any amps.

The bottom line is that many amps will look the same on the test bench, but will not measure or sound the same driving a variety of speakers and that is the problem.
So that is why I only use Quad amps. First they are good amps and basically my speakers are tweaked using Quad amps, and so essentially my speakers and amps are a unit.

 

[ski2xblack]

@SwedishChef , HERE is another fairly comprehensive article to chew on...