Factors in Choosing a Power amplifier or AVR

[derrickdj1]

Factors in Choosing a Power amplifier or AVR

I enjoy my Klipsch speakers and this discussion forum. The nagging question that I have since joining the forum is what metrics determine proper system amplification for a particular system. Power amps and avr's choices are regularly discussed on this forum. What factors need to be considered when selecting an avr or power amp for HT or 2 channel setup? Is there a difference is sound quality at not only high levels, but also at lower levels? Being new to this forum, I thought this would be an interesting topic to share opinions and knowledge on the subject. For example, the warm sound attributed to tube amps: which is due to distortion in the 2nd harmonic's that so many enjoy. Most of the metrics that I have listed make no inferences on the amp or avr's wattage output. Which factors are most important in achieving good sound quality?

What are you looking for in a power amplifier or AVR for you HT system? Power amps or avr's need, high-current, high voltage, speed (slew rate) , and stability over the entire bandwidth, are some of the key features of a good power amplifier or avr. The slew rate, or the time required for an amp to go from 10% to 90% of it's total output voltage determines how fast the amp can change under various loads. The current delivered to charge the capacitor is also a key factor in the power amps performance. Under high current load an amp produces heat which must be dissipated to keep the unit from failing. If the output stage of the amp has a delay in charging and discharging the signal from the input stage, certain frequencies in the bandwidth will be out of phase. All of the above parameters are key to the amps/avr's performance. This is directly related to the sound quality, SQ. Certain qualities attributable to different types of amplifiers are a result of how well they are able to perform these functions.

To select a high speed, high voltage amplifier for a certain purpose, one has to look not only at the bandwidth and/or slew rate of the amplifier, but also at the expected capacitive load, the maximum sustainable output current and the possibility of overshoot voltages damaging the load. All of these are required for an optimal result. http://www.falco-systems.com/high_voltage_amplifiers.pdf.

Dampening Factor: this refers to how an amplifier has control over the loudspeaker cone. This control is needed for clarity and detailed sound reproduction of the source material. The quality of the speaker is also one of the most important factors at the final stage of sound reproduction. Signal to Noise ratio is also something to consider when selecting an amplifier. Make sure you are comparing apples to apples. Some S/N ratios are referenced at 1 watt and others are measured closer to peak wattage. The S/N ratio gives you an ideal of how quiet the amplifier is in operation. Klipschhorn owners can relate to this aspect of amplification. Channel separation is needed for sound imaging: and, once again the amps or avr's ability to perform these functions will be reflected in the sound quality for the listener. The number of amps in the HT system, number of transformer, rectifier and capacitors for each channel also influence the imaging properties of a HT system in conjunction with the speakers, room, crossover settings and other parameters. It is a bit like seduction, all things having to be working perfectly to achieve the ideal sound.

Impedance dips in amplifiers have a significant effect on speaker cone movement and frequency response.

An 8 ohm speaker can typically have an impedance dip to 4 ohms in the upper bass and rise to 20 ohms in the treble. Impedance dips can cause the spl in the tweeter and the woofer to be out of sync, or distortion.

Speaker cone movement becomes erratic. Loudspeakers must have a constant drive voltage to provide a constant acoustic output with changing impedance loads, and frequency fluctuations, http://www.Transcendent sound.com/Transcendent/Amplifier_Output_Impedance.html.  Impedance dips causes uncontrolled voltage to the speaker if the amplifier is not up to the task. These dips can cause amplifier and speaker strain with a deterioration in SQ.

The selection of speakers and speaker properties will impact the SQ, but that is another discussion.

[derrickdj1]

My document formatting did not appear in the final post for this thread. I apologize that the document is harder to read. Any help will be appreciated.

[Quiet_Hollow]

Open FireFox, click to edit the post, apply your formating, click post to update your message.

[russ69]

I didn't read your whole post but there is little you can tell by looking at specifications. Your ear is still the gold standard for sound quality.

[Quiet_Hollow]

Your ear is still the gold
standard for sound quality.

He might have thought his elbow was...

[leftwinger57]

I have agree w/ most of the guys here. your post reads like an engineering article and your wondering what sounds good.Do what I did find a store schmooze around w/o the salesman following you take some notes then wail into salesman the about what will power what speaker at what vol,and what avr will give me the movie experience if your into that.You have to decide wether your going both ways 2chl and h/t or just have an avr which most don't provide great music listening pleasure.As said before let your ears decide then do your calculations.....

[wdrazek]

I tried to read your entire post, but came up a little short due to ADCD. Like the rest said, the sound of the amplifier or AVR should drive your selection. Specs only get you so far. When you hear a particular amp, do you get involved/ engaged in the music or does it leave you flat? Do you want to play air guitar, pick up the drumsticks, or the conductor's wand? Or do you sit back, your mind wandering, and come back only to analyze how the imaging, bass response or midrange detail are rendered? That is how I judge it. Hope this helps.

[Zen Traveler]

I tried to read your entire post, but came up a little short due to ADCD. Like the rest said, the sound of the amplifier or AVR should drive your selection....

I am with you on not being able to read the OP's post but want to give a contrary opinion....The amp shouldn't really impart any sound qualities but should have sufficient current to drive the speakers in question...I agree that the WPC numbers are useless but it is good to know if it can cover the impedance dips of your speakers at the volume that you want to listen.

That being said, the next thing to look at is the "bells and whistles," on an AVR or Processor and decide there what you need or prefer. THAT'S where the nuances of what your are hearing from your speakers is going to be generated.

[wdrazek]

I am with you on not being able to read the OP's post but want to give a contrary opinion....The amp shouldn't really impart any sound qualities but should have sufficient current to drive the speakers in question...I agree that the WPC numbers are useless but it is good to know if it can cover the impedance dips of your speakers at the volume that you want to listen.

That being said, the next thing to look at is the "bells and whistles," on an AVR or Processor and decide there what you need or prefer. THAT'S where the nuances of what your are hearing from your speakers is going to be generated.

While the amp "shouldn't really impart any sound qualities...", in my experience they often do. Sometimes it is subtle or impossible to hear them, other times it is obvious. And, while an amp's current capability can impact on the sound of a given loudspeaker, amps with equal quoted values will not always sound the same.

If you include circuit design and implementation in "bells and whistles", I would agree that nuances are found there. However, if you are stating that all amps of equal current capacity and feature sets sound alike, I'll have to politely differ.

[Zen Traveler]

.. However, if you are stating that all amps of equal current capacity and feature sets sound alike, I'll have to politely differ.

Well, this is the crux of many a debate and wager, but count me in after experimentation that I was one of the ones that couldn't discern a difference with all things being equal and no one in our group could...YMMV.

[Chris A]

The amp shouldn't really impart any sound qualities but should have sufficient current to drive the speakers in question...

[Y]

I would add:

"And sufficient dynamic performance (e.g., slew rate) to convincingly reproduce transients found in the source material", and

"Low enough output impedance to not impart 'its own sound' to your speakers", and

"High enough input impedance not to interact with the output impedance of your preamp in a non-linear way", and

"Low enough noise floor to not be distracting to your listening experience."

Chris []

[wdrazek]

.. However, if you are stating that all amps of equal current capacity and feature sets sound alike, I'll have to politely differ.

Well, this is the crux of many a debate and wager, but count me in after experimentation that I was one of the ones that couldn't discern a difference with all things being equal and no one in our group could...YMMV.

We agree to differ then, let the OP judge for himself.

[garyrc]

Some AVRs have fudged power figures. It's not that they are telling

lies exactly, but the power given is often with only two channels

operating, which is an easier test than with all 5, 6 or 7 channels

operating.

Dampening Factor: this refers to how an amplifier has control over the loudspeaker cone.

I'm no expert, but I really think it is "Damping factor," not "Dampening Factor." If I am right, then Star Trek was wrong[].

I wonder if this is one of those generational things, e.g., a great

number of younger people actually think "overachiever" means the same as

"high (or very high) achiever," thanks in part to the Orville

Redenbacker commercial of about 20 years ago. I read every review,

article, or advertisement I could through the late '50s, '60s, '70s and

'80s and never ran into the term "dampening factor," but prestigious

sources like McIntosh, JBL, and well respected reviewers discussed "damping factor."

By the way, JBL claimed that the "damping factor" could be too high.

[Chris A]

http://www.thefreedictionary.com/dampening

[garyrc]

http://www.thefreedictionary.com/dampening

No big deal, but I am still speculating that it is a generational
difference in word usage []. It also depends on which word you Google
.... I just typed in "damping" and, sure enough, the first 20 references
(maybe more -- I stopped) used the word "damping." One of the sources
was CROWN. Then I typed in "dampening" and, surprise, most of the
references used the word "dampening." In both cases I only counted the
references that described what we are discussing.

I imagine that
the free dictionary is a newer, rather than older source. AOL spell
check now thinks "the sixties" should be abbreviated "the 60's," but
Arriana Huffington knows that it is "the '60s" (and wrote a good
article about it), and so does my copy of the MLA.. Yet "the 60's" is
becoming a more widely accepted way of writing it, thanks to the power
of the Internet.

Until about 1988, or so, the
word I always happened to see used in reference to amplifier damping
factor, or damping down physical vibrations was "damping." It may have
been on Star Trek: The Next Generation or Deep Space Nine that the word
"dampening," in our present context, hit me over the head. Prior to
than, "dampening" seemed to mean "making wet," or what you did to your
clothing when you heard a really great sound system

[billybob]

Not to detract from this illusory by the more modern crowd of long decided word usage(not all is misued) and verbage, when I spritz myself with apple cider vinegar, or vinegar bath, if overdone, I have defeated the purpose of being spritzed as it were, where I must change the definition if being truthful.

Yamaha M-70's are fairly quiet amps, I hear. The OP in this case appears to grasp the finer details as to what must be the aural issue.[^o)]

[derrickdj1]

Thanks for all the comments on a post that I thought no one would read. I do think that bandwidth stability, slew rate, impedance stability, dampening factor and the amp or avr's dynamic response do impact the SQ of a system. Slight variations in the spec's of one amp or avr compared to another, lead to a difference is the SQ of the units. I am not saying a night and day difference, but this may explain why some people claim that their system sounds better with a particular amp or avr. I also agree in a perfect world, that the amp or avr should not impact the SQ if all of the metrics in the opening post are well controlled. Most of the differences in SQ are more noticeable when listening to music with a broad frequency range. I also believe when selecting an amp or avr in trying them out for a few weeks in your system so that adequate listening time over a wide range of source is possible.

[Quiet_Hollow]

An "amp" will definitely impart a difference in sound if it's handling an entirely different type of source signal and amplifying it in a novel manner.

I truly believe this is where a lot of confusion stems from, when making broad comparisons between technologies....especially as of late.

Some technologies simply cannot be compared on a 1-1 basis. For starters the source going into the actual input stage of the amp has to be the same...and some of the new systems simply don't use the same source.

If it's analog. It's analog all the way whether its transistors (SS) or tubes. Even a digital source, once passed through a DAC is analog and is processed accordingly. Onkyo and many others do this. When you read "vector noise shaping" that's a brief way of saying "it's correcting for all error imparted by the feedback loops in the analog amplifier stages". It works very good, but it's complicated, and it's still analog.

True Digital, on the other hand, is not an analog signal. You can't simply tap into the bit stream and "hear" what the sound is. Even after it's been amplified, without the re-construction filter after the chipset it's still digital hash. The audible signal is literally formed at the amplifier output terminals once the speaker closes the loop.

So, when we plug in a Panasonic SA-XR57, Pioneer SC-55, or a NAD M-2..they are not an "amp" like a classic Sansui, Yamaha, or Carver in the strictest sense...When they (the former) are fed a digital bit stream, they are re-producing sound in an entirely different manner from anything else....and that's why they sound unlike anything else.

A good analogy would be trying to compare an electric vehicle to it's internal combustion powered variant. The first thing someone might try to compare is MPG. Well, they don't use the same energy source. Then people try to compare horse power. But either vehicle's prime mover doesn't develop toque in the same manner. In the end, they both go down the road, and look like cars, but that's where the similarities end. Need further proof, just take an late-model EV to the local mechanic and watch the bewilderment set in when they pop the hood.

Same with the chip amps. They can't even be bench tested in the same manner.

[derrickdj1]

Thanks for your input Quiet Hollow. One of my goal when I did this post was to try and generate a discussion on thing in an amp that will affect SQ. The new class D ice amp and the Class D3 amps are a whole different monster compared to conventional avr's and amps. I have seen recommendations on this forum for one amp or avr over another one and little sound discussion on why this one is better than that one, other than wattage, or vague terms such as neutral sound, warm sound or other descriptive terms. I have seen other topics on this forum discussed in great detail, such as, the recent discussion on power conditioners. I know this topic can become very technical and hard to follow. The easy way is to take forum recommendation, but I like to know why. This forum has taught me a lot over the past few months.