|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
63.111.2.217
Every now and then I visit the Elliott Sound Labs site for a refresher on almost anything audio - especially amplifier circuit design issues. From a psycho acoustic perspective, I always have considered that one of the more important aspects of stereo reproduction is the preservation of dynamics. Live signals show more dynamic range than most recordings. Of course this has lead to me experimenting with Dynamic Range "anti-compressors" in the 70's and 80's with some success. it is a genuine shame that with the digital era producers, in most cases, do not take advantage of the dynamic range afforded them.
Of course, with a high dynamic range comes tremendous responsibility - to preserve it in playback. This leads to one of my main thread topics over the years, clipping issues. Many think of clipping as a phenominon that creates a square wave - lopping off the signal - and creating all kinds of odd order harmonics - blowing out tweeters and other harsh & obviously audible phenomenon. It is my experience, that the clipping is one of the key culprits in a lot of audiophile observations. When we say the sound "loses detail", the "image focus drifts" and a host of other concerns that are far more subtle than what we believe are issues come into play...
OK finally to the topic at hand. In Audiophiledom, it is common to say let's avoid as many components as possible in the circuit path - with those nasty capacitors holding us up as prime targets. In a power amplifier, however, DC output at the terminals is certainly not desired. We do not want those main drivers (the low pass section) operating with an offset, even for a short while.
Elliott shows that even an AC coupled input amplifier when clipped for just 20 milliseconds with an asymmetrical waveform gives 2.7 volts DC output (almost two batteries in series) which would significantly disturb the loudspeakers' sound in the low frequencies.
His conclusion here makes a lot of sense:
"To what extent have the effects described here influenced reviewers (who typically never use any instrumentation, and usually never know if the amp under test is clipping or not)? I have no idea, but it is not unreasonable to assume that some degree of clipping must be experienced from time to time, and that will affect the outcome of a subjective test ... but with absolutely no technical detail to indicate the actual cause of the problem should it exist. Reviewer-speak will obfuscate the real issue(s), and the lack of instrumentation leaves us in the dark.
Finally, it must be pointed out that this shows that clipping with real-world (speech or music) signals creates not only the harmonics that have been described in innumerable web pages, but also generates a subsonic signal that is potentially very damaging to drivers, but is never mentioned. This signal has the capability to cause driver damage at worst, or unwanted cone modulation and additional loudspeaker distortion at best - neither can be considered a desirable outcome.
The moral of the story is to avoid clipping at all times - even momentary (supposedly inaudible) clipping will generate an unwanted low frequency or subsonic signal whose frequency will be completely unrelated to anything in the programme material. All it will achieve is cone displacement and increased intermodulation distortion"
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
Follow Ups:
Started to read the article,etc and soon quit. I tend to "listen" tl my ears more than the specs and scientific discussion. Over the past 50+ years I have found as a general common design condition capacitor outputs on the ss amps seem more pleasing to me. Not to say I have not found some great direct coupled amps but my long term preferred listeners seem to fall into the cap outcap category. Not sure why, not important to me as I would rather enjoy the music that dissect equipment design. It might be the speaker synergy. Most of my long time preferred speakers are from the days of tubes. I have no problem with an amp purposely cutting off frequencies that I can not hear, are not in the recorded range and, can be damaging. My only long term owned speakers not originally designed in the tube era sound better with a direct coupled amp.
Something about this hobby has always bothered me. Where we should recognize there is no best, no correct answer, no right nor wrong why are we so positional so much. Not new. Back in the early days the objective vs subjective opinion wars started and never ended. There is room for both.
Don Brian Levy, J.D.
Toronto ON Canada
Something about this hobby has always bothered me. Where we should recognize there is no best, no correct answer, no right nor wrong why are we so positional so much. Not new. Back in the early days the objective vs subjective opinion wars started and never ended. There is room for both.
+1
He knows how to make things work, but he certainly doesn't know anything about making good sound. In fact, just the opposite: he claims any metalized film cap is as good as any other. That's the kind of bias you must block with your mental capacitor!
Peace,
Tom E
Frankly, it undermines whatever useful he has to say. I wouldn't trust someone so profoundly clueless about so many aspects of audio to be able to design gear that sounds good.
Anti -Audiophile? What does that mean? Why would what he states in your link make him an anti-audiophile?
If I believe and trust that (most) cables do not change the signal audibly - am I an anti-Audiophile?
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
The math that shows that cables can make a difference is not profound.
They certainly can make a difference!
And there are ways to prevent them from doing that, again by applying math.
... how vocal you are about your convictions, which amount to simple lack of experience with cables in a context of a resolving system . The same goes for amplifiers, capacitors, and whatever else he doesn't think matters for sonic results.
If you are as vocal as Elliott, devoting multiple pages on his web site to this clueless gargabe - you certainly are anti-audiophile.
Yeah, I though Audiophiledom was about the experience of listening and enjoying recorded music. Correct me if it is not.
I completely understand and have experienced the effect cables can have on perception of reproduced sound. I also know that is has absolutely nothing to do with changes in the signal! One experience is complete independent of the other. You can search my comments and understanding of the experience of reproduced music. There are engineers and scientist out there - not just cult-like convicted arrogant folks like you that might believe I can't have the exact same enjoyable experience listening to Bartok on my MMG's, HK Receiver, $600 Crown Pro Amps, standard power cords and Walmart and Monoprice sourced under $10 interconnects - Engineers and scientist dating back to Helmholz (yeah that guy) and more recently, Heyser - that worked diligently to not only address the correct ways to measure audio equipment but also understand whty measurements of signals do not correlate well with the observations of man (or woman).
I would like to even submit that you would enjoy the experience on my system.
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
"I also know that is has absolutely nothing to do with changes in the signal! "
Beg your pardon but it has everything with changes in the signal. What else would it be...unless you are saying that it is pure psychological?
I do not participate in discussions with opponents who are irrational, in addition to lacking experience with the matters discussed, sorry.
When you listen to a recorded signal on your playback equipment it your primary interest or desire to:
A. recreate a life-like event in your listening room - with the multiple dimensions that implies?
B. Review the recording for it's production characteristics or the artist(s)' performance abilities
C. Observe the fidelity and or preservation of the intent of the performer and the producer your reproduction system provides?
You can pick one or more or add another.
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
capacitor coupled amps were the main design of almost all the vintage gear from the 60's and 70's. Seemed to work out pretty well for them!
Seems like more a sales pitch. Especially when someone uses the word "obfuscate".
A well engineered design works well with many types of amps.
Don't fear the cap.
charles
In general I would state that one should never use a marketing web site to help one understand electronic engineering. Use a good book. 'Vacuum Tube Amplifiers' by Morgan Jones is excellent but you get very little solid state understanding. However, AC and DC electronic theory is that same for SS or tubes.
If the "take away" from your understanding of this essay is that capacitor coupled amplifiers could be evil, then I believe that the author has mislead the reader. It appears to be an essay more along hte lines of, "these are the facts I have selected to support my theory."
As the article demonstrates
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
over most every SS amplifier for musical realism, especially in the critical midrange, despite their use of output caps. The linearity, however, of those caps makes a pretty big difference in audio quality. Which is among the reasons why old/cheap tube amps lack transparency.
Evil? Are you kidding?
And yes, clipping is bad. Simple to correct. Don't!
If this were really a problem we would be hearing about a lot more damaged woofers in the world!
Getting rid of all coupling caps in the signal path is asking for trouble though. The first problem is that as soon as there is a direct coupled path, the circuit now has a lower timing constant than its power supply. This opens the door to intermodulations. Of course this can be overcome by a much larger supply, but it can also be overcome by a small coupling cap at the input of the circuit.
I prefer to have the coupling cap in the middle of the amp somewhere, so that intermodulations in the amplifier itself do not result in modulations to the supply. This really helps keep IMD down...
The input pole should predominate, followed by the feedback pole, then followed by the supply pole (as a function of the load impedance).
Staggering the poles in this fashion makes the amplifier behave better at high levels.
Of course the NAD 'soft clipping circuit' really helps too, by clipping the input signal rather than allowing the amplifier to become unstable when the feedback loop clips.
We use passive EQ in our preamps with no feedback. This reduces ticks and pops at the output, even though we have plenty of bandwidth.
Passive RIAA in a preamp is an excellent idea.
The music just shines through the ticks and pops that otherwise cause strange behavior in the preamp. It's like the junk is in a different plane from the music, easier to hear through.
Actually, I find that preamps with active EQ can exacerbate ticks and pops. They are often a lot less audible on preamps that use passive EQ, even though the bandwidth is the same or better.
When I first encountered this phenomena it was a real eye-opener!
"Actually, I find that preamps with active EQ can exacerbate ticks and pops. "
Yes indeed.
Without the feedback the music is in a different plane than the junk and the junk is easily ignored.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: