what to look for in a good amp?

[ImcLoud]

Was a few years ago and it still went in the garbage shortly after.

My brother had a set of 15" JL audio W1's in his car when he was younger, and while I don't remember what the subs ratings were my brother was feeding them 3 times that amount {say they were 500w each he had a pair of 1500 watt amps... And they never failed, he used them for years and never hurt the subs... He used to BLAST that system when ever he drove the car and they never gave up, he spoke with Jl about it back then and they said it was most likely due to the clean output, not having distortion kept the subs together, because they seen people blow them with 300watt amps, which makes less sense...

How can you blow a 500w speaker with 300watts but not 1500? Distortion and clipping kills drivers... My brother was using a high end head unit with very high end amplifiers, his actual attention was to replace the JL's with some other sub but was waiting for the funds and bought the jls just to get him music, but ended up keeping them until he sold the car...

Anyway, I have seen speakers perform way beyond their posted limits, and I have seen some die after a simple pop from removing RCAs while the system was on {ask me how I know that, set of Klipsch towers, it instantly killed the left towers tweeter and even after the tweet got fixed it never really sounded rite again..}

 

[RichB]

You are of course theoretically correct, but practically speaking, not if that 0.03% is THD+N over the spectrum of 20-20,000 Hz. Total is total, regardless of the order of the harmonics so even if it has more higher order harmonics. If the total is 0.03%, each of those higher order ones will be less than 0.03% because the invidual has to be less than the total.

0.03% at any order of harmonics within the 20-20,000 Hz is only audible to golden ears. Yes, there are other distortions unrelated to the music signals (such as crossover, intermodulation etc.) but I would think most amps including the low cost EMOs got that beat already, just ask EMO..

I do agree it is possible that certain below audible level distortions could cause long term listening fatigue (Irvrobinson also mentioned that more than once) but it is hard to prove and sort out the root cause of such fatigue. For example, try listening to some of Adele's albums, I love her songs, but find it hard to endure her distorted voice at the end of a verse when she ramps up in loudness and tone. I can only attribute that to the way her albums were recorded, including mike related issues. My point is, in long term listening related issues, it is hard to just blame the amp, it could be other things causing the fatigue.

I found an interesting tidbit in the Lexicon ZX7 review:

Lexicon ZX-7 Multi-Channel (300 watts x 7) Power Amplifier - Secrets of Home Theater and High Fidelity

Check out the 60Hz/2kHz tests where there is significant increase in ringing.

And at 20 volts, IMD was actually less, at 0.014%. If you look at the peaks around the 2 kHz fundamental, they are higher than the ones in the 5 volts graph. The reason the distortion number is less is because the fundamental is higher in relation to the distortion peaks than in the 5 volts test. Note also that there are more IM peaks around the 4 kHz, 6 kHz, 8 kHz regions (multiples of 2 kHz) than in the 5 volt test, but IM measurements only take into account the peaks at ± 250 Hz around the fundamental (2 kHz), so this is why showing the actual graph is important, rather than just giving a number.

So, it appears the specs for IM only need report the peaks with a 250Hz range.

I am not saying that this is audible, but the increate harmonins were measured was only two tones.
I have seen many amp measurements where the amount harmonics increase.
It seems reasonable, that with a more complex signal and load, the harmonics would also increase.

- Rich

 

[PENG]

I found an interesting tidbit in the Lexicon ZX7 review:

Lexicon ZX-7 Multi-Channel (300 watts x 7) Power Amplifier - Secrets of Home Theater and High Fidelity

Check out the 60Hz/2kHz tests where there is significant increase in ringing.



So, it appears the specs for IM only need report the peaks with a 250Hz range.

I am not saying that this is audible, but the increate harmonins were measured was only two tones.
I have seen many amp measurements where the amount harmonics increase.
It seems reasonable, that with a more complex signal and load, the harmonics would also increase.

- Rich

That's an interesting read. Still, what is inaudible to me will remain inaudible. I can't even hear my Ex-Oppo 95's fan from 13 ft away where I sat. By the way, since you seem to have good discerning hearing ability, could you hear Adele's distorted vocal? In my high quality recording thread I posted that observation of mine and none of those responded could hear the distortion that I heard on that album (Live at the Royal Albert Hall). You could try either the BR or the CD, and let me know what you think. Once I noticed the characteristics of the vocal distortion in that recording, I could no longer enjoy it as much as I did intially. I guess that would be a classical example of what Irvrobinson and others referred to as long term fatigue effect. I actually have a couple other CDs that have similar vocal distortions, both are Tierney Sutton's, one is even a SACD. I am really surpised that no one else posted on that thread could hear what I heard.

 

[PENG]

Rich, after reading the review you linked, I re-visited Elliot Sound's article on IMD. I will do the same with the AH article on this topic as well.

Valves - Distortion+Intermod

Following are quotes from part of the article, for those who don't want to read the technicial stuff and don't mind just jumping to his conclusion.

"Any two amplifiers of good performance should sound the same, and if any difference exists there will be a good reason for it. The nonsense you may hear that some amps are hugely better than others is just silly - there is no logical or scientific reason that two amplifiers of similar overall specification can possibly sound different from each other. Strangely, the amps that are supposedly superior almost always have more distortion, higher output impedance and worse frequency response than their 'inferior' brethren. The basic criteria for hi-fi were established a long time ago, and have improved over the years, yet we have some reviewers claiming that valve equipment that was below par 50 years ago is better than transistor amps that trounce these 'new-old' amps in every respect. It's very hard not to be cynical."

"Intermodulation is a function of all non-linear circuits, and is not negotiable. The supposedly 'nice' even order (single ended) distortion creates more intermodulation products than the 'nasty' odd-order distortion - as might be found in minuscule amounts from very high quality push-pull valve amps, opamps and transistor power amps. These days, the levels are so low as to be difficult to measure, and are well below the threshold of audibility."

"It is critically important to understand that if two amplifiers sound different from each other (in a proper blind test), then one or both of them has a fault. There have been some extraordinarily good valve amps made, and without exception they are push-pull. Some of these amplifiers will be found to be virtually indistinguishable from a good transistor amp in a double-blind listening test. The extension of this is that if you can hear a difference between a valve amplifier (of any topology) and a good quality transistor amp, the valve amp is obviously making changes to the signal that the transistor amp is not. "

From the conclusion in the linked article http://sound.westhost.com/articles/intermodulation.htm:

"On the basis of this information, it is likely that the vast majority of intermodulation distortion tests are meaningless. Using a 19kHz and 20kHz tone and expecting to see 1kHz is fine, but it will only work if the amplifier being tested has asymmetrical distortion. With most real-world push-pull amplifiers, or any other topology that has very low levels of second harmonic distortion, the standard test will be decidedly optimistic, and may fail to show the real IMD caused by the amplifier."

I do not know if the author is correct in verything he wrote but the technical part makes sense to me. If you are interested in IMD, I suggest you read both articles from beginning to end.

 

[ski2xblack]

It seems reasonable, that with a more complex signal and load, the harmonics would also increase.

- Rich

A sine wave, or multiple sine waves for IMD tests, I'm pretty sure are more difficult for amps than music signals. The whole crest factor thing. (Correct me if I'm off base.)

 

[PENG]

A sine wave, or multiple sine waves for IMD tests, I'm pretty sure are more difficult for amps than music signals. The whole crest factor thing. (Correct me if I'm off base.)

Music waveforms are made up of sine waves of the fundamentals and associated harmonics but that's why like THD, % is typically used for comparison purposes.

 

[ski2xblack]

Music waveforms are made up of sine waves of the fundamentals and associated harmonics but that's why like THD, % is typically used for comparison purposes.

Isn't it the case that music composed of sine waves of the fundamentals and associated harmonics have a crest factor that is less taxing on amps than pure sine waves, generally speaking? I'm just trying to put things together in the context of Rich's statement about complex signals and increased distortion.

 

[RichB]

Music waveforms are made up of sine waves of the fundamentals and associated harmonics but that's why like THD, % is typically used for comparison purposes.

Isn't it the case that music composed of sine waves of the fundamentals and associated harmonics have a crest factor that is less taxing on amps than pure sine waves, generally speaking? I'm just trying to put things together in the context of Rich's statement about complex signals and increased distortion.

Those were interesting articles
I am not a EE, but just looking at the charts on HomeTheaterHifi. There is more ringing in the two tone tests than the single tone.
So, I am *thinking* that this trend with more complex waveforms.

Of course, they may also be harder to detect.

- Rich

 

[RichB]

That's an interesting read. Still, what is inaudible to me will remain inaudible. I can't even hear my Ex-Oppo 95's fan from 13 ft away where I sat. By the way, since you seem to have good discerning hearing ability, could you hear Adele's distorted vocal? In my high quality recording thread I posted that observation of mine and none of those responded could hear the distortion that I heard on that album (Live at the Royal Albert Hall). You could try either the BR or the CD, and let me know what you think. Once I noticed the characteristics of the vocal distortion in that recording, I could no longer enjoy it as much as I did intially. I guess that would be a classical example of what Irvrobinson and others referred to as long term fatigue effect. I actually have a couple other CDs that have similar vocal distortions, both are Tierney Sutton's, one is even a SACD. I am really surpised that no one else posted on that thread could hear what I heard.

I do not have that recording, but I have the 19 and 21 CD's and they are only acceptable recordings.

So should I get the BD or do you think it isn't worth it?

- Rich

 

[PENG]

I do not have that recording, but I have the 19 and 21 CD's and they are only acceptable recordings.

So should I get the BD or do you think it isn't worth it?

- Rich

I highly recommend that BR disc. The orchestral part is great, just Adele's vocal part I found distorted at the high end, almost sounded like she overloaded the mike, again I seem to be the only one noticing that. I did do some power Googling and found one (may be two) who reported the same but thought it was in her voice, I doubt that though. I have the 19 and 21 albums and still noticed similar distortions.

 

[PENG]

Isn't it the case that music composed of sine waves of the fundamentals and associated harmonics have a crest factor that is less taxing on amps than pure sine waves, generally speaking? I'm just trying to put things together in the context of Rich's statement about complex signals and increased distortion.

Two points, 1) Crest factor of sine wave is square root of 2, or approx. 1.414.

2) Music waveform typically has a higher crest factor but the individual sine wave frequency components of the fundamental and the harmonics would still be 1.414.

I think you may be thinking about the talk that using sine waves to test an amp's output is more taxing than using actual music waveforms with the same peak voltage. That would be true because by definition, given the same peak voltage, the average value of the power using a pure sine wave will be higher than that of a waveform with a higher crest factor. I don't think that is relevant to IMD though.

Rich got me interested in this topic and I am working on trying to understand the concepts and theory of all sorts of distortion. Lots of readings ahead of me in the days ahead..

 

[PENG]

For non EE's here's an easy read on sine wave, music wave etc. http://hyperphysics.phy-astr.gsu.edu/hbase/audio/fourier.html It is not easy to understand but I think it is important to understand the basic concepts of the Fourier theorem if we are interested in the topics related to waveforms. For EE's, espeically those in the heavy current or telecommunication streams, they all must have done their fair shares of Fourier analysis, but it is quite possible that many of those graduated years ago would have forgotten the details.

 

[RichB]

I highly recommend that BR disc. The orchestral part is great, just Adele's vocal part I found distorted at the high end, almost sounded like she overloaded the mike, again I seem to be the only one noticing that. I did do some power Googling and found one (may be two) who reported the same but thought it was in her voice, I doubt that though. I have the 19 and 21 albums and still noticed similar distortions.

Many vocalists have their favorite MIC's maybe she likes them that way.

I'll order that BD/CD pair,

Thanks.

- Rich

 

[anamorphic96]

$230 Sony 520 power output for 2Ch into 8 ohms/ 2Ch into 4 ohms/ 5Ch into 8 ohms @ 1% THD: 141.7WPC/ 160.6WPC / 81.3WPC.

So yeah, if a $230 AVR can output 161 WPC into 4 ohms x 2Ch for music, that is more than enough. You would need 320 WPC to increase the volume by 3dB.

I bet you ten to one that Sony shuts down and does not even come close to that figure when that 4 ohm figure is full bandwidth instead of 1khz. Which is what all those figures are measured at.

 

[PENG]

I bet you ten to one that Sony shuts down and does not even come close to that figure when that 4 ohm figure is full bandwidth instead of 1khz. Which is what all those figures are measured at.

I wouldn't bet anything without first defining what "come close to..." means. Whatever that means it probably would come much closer than you think. I am guessing but have seen enough data to know 1 kHz output vs 20-20,000 Hz typically aren't that far apart, there are going to be exceptions but probably most of the time within 10 to 20%.

 

[PENG]

I have seen many amp measurements where the amount harmonics increase.
It seems reasonable, that with a more complex signal and load, the harmonics would also increase.

- Rich

After having some time to think about, I would say that won't be the case. Since distortions are expressed in %, or -XdB, and a complex wave is simply fundamental plus bunch of harmonics, and the harmonics that are the make-up of the original complex wave are not "Distortions", so in terms of %, complex wave don't necessarily mean more distortions, just more harmonics. I hope I fail to confuse you, sorry if I did..

 

[RichB]

After having some time to think about, I would say that won't be the case. Since distortions are expressed in %, or -XdB, and a complex wave is simply fundamental plus bunch of harmonics, and the harmonics that are the make-up of the original complex wave are not "Distortions", so in terms of %, complex wave don't necessarily mean more distortions, just more harmonics. I hope I fail to confuse you, sorry if I did..

Some.

I have found the answer of what to look for in an AMP:

Shite loads of power, low distortion, killer looks.

I had a dealer tell me that "Amps are mostly a male item" ; They are basically an indoor muscle car.
What could possibly be wrong with that

- Rich

 

[ImcLoud]

I think people get too hung up on which amp,
pick one with a long warranty, a good company track record {My b&k's had silly service issues like power button, led light , broken connectors, and since they were "shut down" parts were not available and it just sucked, it also hurts resale value when the comapany is no longer around},
pick an amp with the specs you need, physical size, watts per channel, channel count, rca and or balanced inputs, impedance stability, triggers, ect.
pick an amp that fits in your budget,
pick an amp that has the aesthetics you like,
and pick an amp that you can live with.

For HT, I tend to just go with what works, AVR's get outdated fast, so I say buy the cheapest one with the features you want then if that isnt enough power get an amp for your front 3, this way when your avr quits, or when its outdated you can simply buy another one with the features you want or need...

For music, I like mono blocks and get the power you need, if its for a desk top system and you sit 15"s from the speakers, then get an amp that will give you 95db at 1m, most likely 20-50watts will be more than enough, but if you have a 500sq ft room with 20ft cathedral ceilings, and sit 18 ft from the speakers get a lot of amp 200w to 400w {400w would be about the max for full range speakers for me, and that is probably a lot more than most people would need... 200w seems to be the sweet spot especially if you cross to a sub amp, that will be enough for most any residential room...

Amps are part of hi fi, whether its built into an avr or 7 separates stacked on top of each other, they are an essential part, we all have our preferences, so buy what you like, and when someone asks "which amp should I choose?" answer with your preference, as long as you are honest and know what you like you can't be wrong, if you have no experience with separates and never owned modern pres, pros, and amps, then I would include that in your post, I have owned everything from $2000+ avr's to $3000K 2 channel amps with $1500 preamps. I tend to like to stay at the bottom of the "hi" end, I want a system for $3K that sounds "better" than the systems I listen to that people spend $10K on... Its not hard to do, first thing to get rid of is the "name game", then the "middle man", then the "snake oil" , then look for sales, and you will get your self a decent system for short money...

Looks are also important, some may not care about looks {I don't care too much about the HT system, its a living room, mostly used by "us" and guests usually don't come over to watch TV.... If they do the lights are off so no one can tell my ascends have a horrid black vinyl finish, lol.... With music, I like the amp stands, and fancy speaker wires {that I make myself, for $10 each, lol}, the fancy veneers or piano finishes are a nice touch, a stack of amps, and a preamp with an aluminum face, what ever, just something that looks like poeple put thought into it...

Well thats enough from me, I am rambling, I think I hurt my shoulder again, so I took some pain meds tonight and feel loopy..... sorry if non of this made sense...

 

[PENG]

Some.

I have found the answer of what to look for in an AMP:

Shite loads of power, low distortion, killer looks.

I had a dealer tell me that "Amps are mostly a male item" ; They are basically an indoor muscle car.
What could possibly be wrong with that

- Rich

Agree, I would add gigantic analog power meters to the killer look.

 

[anamorphic96]

I wouldn't bet anything without first defining what "come close to..." means. Whatever that means it probably would come much closer than you think. I am guessing but have seen enough data to know 1 kHz output vs 20-20,000 Hz typically aren't that far apart, there are going to be exceptions but probably most of the time within 10 to 20%.

I agree with you into an 8 ohm load. But not a 4 ohm load. Not with that Sony.