Why do we hold amplifiers to such high standards?

[Joseph Crowe]

Even mention of THD and uper highs in same sentence makes me laugh. Second harmonic is A*2 so eventually up to 10 KHz it theoretically has some sense and only theoretically. In practice to about 6 or 6.25 KHz.

Yeah, it’s not H2 per se, but rather the energy required to produce H2, which drained out from the primary tone. This is where the audibility aspect comes into play. We can’t hear H2, but we can hear how it robs the primary tone of its transient peak energy on music. It’s the same principle as a studio dynamic compressor, which produces more and more H2 with more aggressive compression.

 

[ZolaIII]

Yeah, it’s not H2 per se, but rather the energy required to produce H2, which drained out from the primary tone. This is where the audibility aspect comes into play. We can’t hear H2, but we can hear how it robs the primary tone of its transient peak energy on music. It’s the same principle as a studio dynamic compressor, which produces more and more H2 with more aggressive compression.

I elaborated more elsewhere.

Looking beyond the single headline SINAD value...

Which amps offer the best distortion linearity? What I mean by distortion linearity (possibly the wrong term) is the most consistent (and lowest) distortion vs power across all frequencies. Here is the graph from the NCx500 review: The maximum SINAD before clipping (@15Khz) is about -75dB...

www.audiosciencereview.com

 

[SIY]

Re: impedance peaks in the bass, that's from loudspeaker resonance (electrical and mechanical)- so the peak means that the amp will be working less hard at those frequencies to accelerate the cone. The amp merely has to provide the same voltage that it did above the frequency of the resonance, but now at a lower current, to maintain constant SPL. Don't let watts mislead you, volts is where it's at; think of the difference between speaker sensitivity and efficiency.

 

[Axo1989]

So if we say that the sweep is at 2.83V, then at 15V output, there is +14.5 dB of gain. So the Topping can hit 99 dB at 70 Hz and 104.5 dB at 1 kHz.

At 1 kHz, it is pulling 56W (2.5A) and at 70 Hz, it is pulling 9.4W (0.625A).

If you “could” deliver 56W into 70 Hz, then your amp would need to push 36.6V, and that would be a 22.1 dB gain over 2.83V or 106.6 dB. Even though that is only 1.525A, the LA90 cannot hit 36.6V because this sweep shows that the max voltage is ~15V.

So the impact of the high impedance “somehow works out” is that if you have the FR response curve and maximum voltage of the amp, you can do the math.

The other way we can do it (since I based it off the 4 ohm measurements) is that 24 ohms should be 1/8th of 4 ohm and 1/4 of 8 ohm, or 7W-9W give or take, which matches my 9.5W calculation earlier because it might be easier for the amp to drive at high impedance.

The impact is the “90 dB @ 1 watt” sensitivity. Here, if you assumed the LA90 hit 46W into 6 ohms, you would see 106.6 dB predicted but you don’t really get that.

If you wanted 36.6V into 70 Hz, your amp would need to deliver 335W into 1 kHz, which is how the impedance affects the “power” of the amplifier you need when shopping, even though that is to get to 56W at 24 ohm.

But way too much maths. That's the point where I p*ss the Topping off for a joke and get an old Krell.

 

[ZolaIII]

Re: impedance peaks in the bass, that's from loudspeaker resonance (electrical and mechanical)- so the peak means that the amp will be working less hard at those frequencies to accelerate the cone. The amp merely has to provide the same voltage that it did above the frequency of the resonance, but now at a lower current, to maintain constant SPL. Don't let watts mislead you, volts is where it's at; think of the difference between speaker sensitivity and efficiency.

It's highly recommended especially with ported speakers to use high pass (as limiter) a tad above such at Fs or at least Fb (second and first peak in importance/phase plots and after the impedance peak where they meet up). That way it ease up things for both speakers excursion and amplifier. Of course Fs is for use with sub's.

 

[Joseph Crowe]

I elaborated more elsewhere.

Looking beyond the single headline SINAD value...

Which amps offer the best distortion linearity? What I mean by distortion linearity (possibly the wrong term) is the most consistent (and lowest) distortion vs power across all frequencies. Here is the graph from the NCx500 review: The maximum SINAD before clipping (@15Khz) is about -75dB...

www.audiosciencereview.com

I read that but I don't see how it relates to what I said. I think you might be talking past me.

 

[Ze Frog]

To be fair a lot of the measurements are certainly beyond the hearing of most mortals, for me measurements mean more in the sense with electronics as a denotation of how well engineered they are. Obviously you don't have to get the absolute best measuring, but at the same time you likely don't want to spend a massive wodge of cash on something that is beaten by something a fraction of the price.

Speakers are somewhat different, good measurements here allow you to know what the speakers characteristics are. Even if you don't want to listen to a flat response, starting there allows far more effective EQ and tailoring of the sound. Also factors such as directivity and such allow you to get a better idea of how it will interact in a room. If a speaker has loads of peaks and troughs, you end up with something where in some cases you just won't have enough EQ available to fix, and if you did it will degrade the sound quite markedly. So best to build or buy flat and then tailor to your own liking.

 

[Tell]

0.1% THD was SOTA in the late 70s in an amp. And 0.005% was late 80s, early 90s. At least for McIntosh gear.

If a manufacturer is not at least 0.005% THD today, what are they doing? To me, it's a measure of competency.

But if humans can't hear distortion over 0.1% then anything below is academic anyways? But yeah sure, if they can build better without charging to much extra for it go ahead, but personally I don't care that much at all anymore as long as I get enough power.
I mean I've had a few class D amps with the best being maybe 0.01% and I never heard any distortion from it unless it's clipping, but the one I was using started just a few weeks ago making awful high pitched noises because of a bad PSU, so instead I started using an old Marantz 2015 that I inherited from my late grandmother. The specs from Marantz says 0.9% THD and 79dB SNR, and to my ears it sounds very clean and absolutely noise free. I might maaybe hear some graininess to the sound, but that might very well be all in my head just because I know it's old and what the specs says. But then of course, just before I started using with Marantz my daughter was born so I haven't really been playing particularly loud anyways so I'm quite sure than any distortion is far below the noise floor in my room.

But even so, sometime in the not too distant future I will be building myself an TPA3255 PFFB amp with some sexy VU meters, just because it's fun and a bit of feel good

 

[egellings]

Agree. Once distortion gets acceptably low so that it becomes inaudible, I don't see any point in striving for lower amounts outside of getting a better handle on the engineering involved in achieving that. No point in ordering a drop forge when all you need is a tack hammer. Audio amplification is a solved problem and has been for some time now.

 

[rdenney]

I place a higher priority on no distortion. It is relatively easy to get plenty of power now. And I'm glad it doesn't require megabucks to get both.

Not me. Lack of power leads to clipping, which is far more audible than any harmonic distortion short of clipping.

Quiescent noise is also something I look at.

You are right that power is now easy to get and affordable, and so is low distortion. More difficult is attaining both of those objectives at near-short loads, so if I had speakers that dipped down to 2 ohms or less, I’d pay attention to that, too.

Back to the OP’s topic, lots of high end audio stuff is sold based on the star power of the designer. It’s a club for the wealthy whose concerns are only nominally about audio fidelity. We should remember that the likes of Dan D’Agostino and Nelson Pass (and, for that matter, Bob Carver) made their reputations in designing and building high-power, low-distortion amps when it really was difficult.

But good engineering doesn’t sell, and salesmen always make more money than engineers.

Bruno Putzeys—as much as anyone the reason we have inexpensive high-power, low-distortion amps—should have that star power but he does only among geeks like us on this forum.

Rick “an engineer” Denney

 

[JohnnyAudio]

I just want one that looks nice.

 

[MattHooper]

I used tubes for my power amps so it’s not like I’m chasing the lowest distortion.

But when I wanted to try out a solid preamp against my tube preamp, I went with a benchmark LA4.

Reasons: I was looking for a neutral signal and I could no doubt get that from plenty of other preamps, it was nice to have the guarantee from the measurements done by Amir and others. Plus, it had the features that I wanted, and bought secondhand it wasn’t too expensive for me.

Also, since I’m actually running a second preamp through the benchmark inputs - my tube preamp for when I want to listen with tubes in the chain - the super low noise from the benchmark gives me peace of mind that running another preamp through it will be transparent.

Finally, just owning a product that I know is so well engineered to the degree of measuring lower distortion and most other similar products, adds some pride of ownership and conceptual satisfaction.

 

[Descartes]

I just want one that looks nice.

In addition itt needs to sound neutral, does not cost an arm and a leg, measure well and doesn’t heat up to much!

 

[Waxx]

granted. if you want a KW amp, it will be higher THD. That said, there are low THD high wattage amps, for a premium price.

But how much is needed for home hifi vs PA system?

I have a McIntosh 2205 from 1975 - 1981 rated at 0.1% THD for 400w (mono) into 0.5 - 4R or 200wpc into 1-8R. Their current lineup of 450 or 600 wpc amps are 0.005%. The MC1.25KW is 0.005% THD. Sure, the current lineup is much more $ than crown.

But for what I would consider suitable for an average home room hifi, does one need much more than 300wpc? 400 wpc? That's should cover a decent sized room with reasonable sensitivity speakers.

A home setup i installed recently needed a lot more. The custom subwoofers (there are 4 installed) alone need about 2000W each, and the main speakers (JBL M2) are rated at 1200W for the woofer alone, the tweeter is 250w rated. This is installed in a room of 12x7x4m (a larger size EU living room). The amps he uses are Lab Gruppen theater amps, with build in Lake dsp.

We don't all listen to the smallest speaker we can get away from, some like bigger speakers, and have the space and money (and family that don't mind them) to do this. And there are more of those than most think.

I know in reality once you pass a sinad of +95dB, the sound is fully transparent, and even amps of a sinad of 75 can sound good. Chasing the highest sinad number is like rating cars on their maximum speed, while in reality you can only drive max 120km/H (at least in Belgium).

 

[Waxx]

I think a lot of people here (but certainly not all) forget what is the most important on this subject, the system is a tool with a purpose: to enjoy music. And for one person an absolute clean system is needed for that, but most don't need that, they enjoy music on systems that are not sota and don't care about it. This site has mainly the former off course. But if you are happy with an amp that has a sinad of 60dB, the purpose is still fullfilled.

This does not mean science and scientific review is not needed, it's very needed. We all know the unrealistic claims from many companies in hifi (and audio in general) and science helps to make a good decision, but it's a tool for most, not a purpose. I'm also a bit a freak, and got a few systems in my house. And some have amps with very low sinad (Hypex NCore), but i also got a pair of Nelson Pass ACA's, that measure poor but are loved by many. And i love both options and are thankfull that i can have both (and a few amps in between) and know why i love both.

Science and sites like this one helps you determine what you love and make a science based decision, that has a way better chance on success than other sites with subjective reviews, that are often sponsored by the same companies that they review. And sites like this one also show that you don't need to spend a fortune to have a sota system like many other sites claim.

 

[radix]

A home setup i installed recently needed a lot more. The custom subwoofers (there are 4 installed) alone need about 2000W each, and the main speakers (JBL M2) are rated at 1200W for the woofer alone, the tweeter is 250w rated. This is installed in a room of 12x7x4m (a larger size EU living room). The amps he uses are Lab Gruppen theater amps, with build in Lake dsp.

We don't all listen to the smallest speaker we can get away from, some like bigger speakers, and have the space and money (and family that don't mind them) to do this. And there are more of those than most think.

I know in reality once you pass a sinad of +95dB, the sound is fully transparent, and even amps of a sinad of 75 can sound good. Chasing the highest sinad number is like rating cars on their maximum speed, while in reality you can only drive max 120km/H (at least in Belgium).

I did try to slip in that waffle word "average" which in the US for a living room is 12x18 ft (3.7m x 5.5m).

Yes, I can see 1000wpc (or more) for a room over twice that size. Really, for 98 dB SPL @ 10m with 92 dB speakers and good headroom, I could see 1200 or more depending on the dynamic range desired and max desired party volume. Just don't walk to the front of the room

I'm all for getting a system that puts out the desired SPL at the desired distance, with plenty of headroom. And is clean without audible hiss or noise.

 

[Cbdb2]

I guess it "matters" because your amplifier, being at the end of the signal chain, is really what is determining the maximum theoretical dynamic range of your system - either bottlenecking or providing headroom for whatever comes before it -

The dynamic range of your system will be limited by the one piece of gear with the lowest dynamic range (weakest link) and the noise adds up from all the gear sort of. BUT as far as hifi electronics go the power amp is the hardest to design with high sinad. High gain and high power. So, often this is the weakest link.

 

[Cbdb2]

View attachment 354268

50 times increase is BS. First any increase after 10k is useless. They don't tell you what the actual amount of NFB is. So an amp with a 1khz NFB pole and 20db more NFB will have less 10khz distortion than this Amp with a 50khz pole. And complex compensation to achieve this result has been around for ever, this is nothing new.

 

[Cbdb2]

Maybe I don’t truly understand this the way that I think I understand it.

If the Topping LA90 can produce 15V max, how loud could that Polk floorstander play a 1 kHz test tone (at 6 ohms impedance) versus a 70 Hz test tone (at 24 ohms impedance)?

If the speaker has flat freq. response it will be the same loudness. The speaker is much more efficient at 70hz than 1khz. The efficiency of a (flat) speaker follows the impedance curve, or, the power vs freq. the speaker uses is the inverse of the impedance curve, flip it upside down.

 

[Cbdb2]

Yeah, it’s not H2 per se, but rather the energy required to produce H2, which drained out from the primary tone. This is where the audibility aspect comes into play. We can’t hear H2, but we can hear how it robs the primary tone of its transient peak energy on music. It’s the same principle as a studio dynamic compressor, which produces more and more H2 with more aggressive compression.

I don't think the math agrees with you. Take a quick transient, a square wave and filter out some of the harmonics. The rise time will decrease. Take a sine wave and add some harmonics, the rise time will increase. Transferring power to the harmonics will decrease the peak amplitude, and we are talking about less than -60db of power.