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I have seen amps with a Slew Rate of 120 and another 60 both good amps but I would like an explanation of the differences why one may be better or different. Thanks
Slew rate (if you speak calculus) is the absolute value of the derivitive of the voltage signal at the amplifier output. Any amplifier has a maximum positive and negative slew rate, which are often DIFFERENT.From this, you can calculate the full-power bandwidth of the amplifier by simply dividing the slew rate of the amplifier by 2*pi*p, where p is the single-ended peak value of the amplifier.
While people argue that 20kHz is a safe number, it's been my experience that even on bandlimited things, distortion, noise, clock leakage, etc, will introduce some frequencies well above 20kHz. I'd suggest that a minimum is about 150 kHz myself.
Now, they really oughta give the slew rate in both directions, measured separately, into a real load. But that's another chapter in "why the specs given for amplifiers are nonsense".
High slew rate is very necessary for a clean transparent sound...checkout www.avahifi.com....my OMEGAIII Hafler rebuild amp from Frank VA, has 300V/uS slew rate, the sound comparison to the original Hafler DH500 ckt, which had a slew rate of about 50 is like you put on a new pair of correct prescription glasses...the sound opened up, the highs were crystal clear, no edge, the bass went as deep as anything you ever heard....how bout a 16Hz signal on a pair of Legacy FOCUS speakers...it's awesome...Slew Rate matters.....same slew rate for the pre amp driving it the OMEGA III..as with RMS watts of 300 per channel for the VAN ALstine OMEGA III rebuilt Hafler...there can never be too many good watts and fast slew rate..it makes teh music come alive...the faster the better..music is full of sharp transients and attacks, the amp needs to be able to respond to it...the AVA do it well....read about slew rate on the site....www.avahifi.com
I think we understand that you are
a fan of, or salesperson for, AVA
by now.Several of the moderators are
suggesting you give it a rest.Thank you.
æ
I have no affiliation with AVA...they make some great stuff.....that is all......would it be better if I complained about other brands....I have some Audio Control products also(C-131 and R-130)...works great, but it hisses like a leaky steam pipe.....so I would hardly think that the ckt design is so great...since HISS is distortion, noise....well designed products have no noise.....since I am spoiled by (here we go) AVA...which is total silence on no signal...guess that means it's better ckt. design...or is that wrong to say?
Nice one, sneaking in another plug. Just like the boy who runs to his mom to say "Mommy, Johnny just said @#$%" and then wonders why HE is getting his mouth washed out with soap.Yeh, if you like AVA...cool. Like Legacy...great. But, unfortunately, the initials CE carry their own legacy, so a bit of discretion may go a long way.
Your reputation from AR precedes
you (and it ain't pretty).Consider yourself warned and
play nice while you're here.Thanks.
æ
***I have seen amps with a Slew Rate of 120 and another 60 both good amps but I would like an explanation of the differences why one may be better or different. ThanksHigh slew rate is a GOOD thing to have. Having said that, there is no way to predict which one of the two amps above is going to sound better TO YOU.
Being a good thing doesn't mean one has to sacrifice everything to get as much of it as possible. Every parameter on the amp spec sheet is but one brick. Surely it makes sense to make every brick quite good. However, given even perfect bricks one surely could built one ugly outhouse.
A skillful mason can build a perfect palace, even if some of the bricks he uses are less impressive if simply taken alone.
Engineering is mostly the art of finding good combinations, not the one of pushing any single parameter to its limit (although this is sometimes the case too).
Again, the amp that sounds better to you is the better amp.
Victor, I don't know if you saw...I left you some info on Ponomarev CDs at the Music Asylum a few days ago.
***Victor, I don't know if you saw...I left you some info on Ponomarev CDs at the Music Asylum a few days ago.Sorry, I missed it, but I saw it now. Thank you. As burried as I am nowdays, I should still try it. As far as Godunov, he is not with us any more as I am sure you know... he must be the same place his older namesake Boris is...
But you are right in substance - it is not always the best that gets accepted, often it is kitch... boy, how could someone like Warchol, Rothko and Pollack ever be considered artists... here they don't have a conveninent excuse of a "I had to paint Lenin to survive" kind. It is more like "I had to make trash to live well".
We studied slew rate limiting about 20 years ago. We wrote several technical papers on the subject for the AES, IEEE, 'Audio', 'Audio Amateur' and several other publications. We have found that a mimimum slew rate of .5V/V (peak to peak) is adaquate for virtually all amps and preamps. This is 50V/us with a 100W amp. Lower slew rates will give TIM (SID) distortion, with moving coil cartridges or other difficult sources. We have done virtually hundreds of tests that show this. It is relatively easy to have high slew rate power amps today, because output devices are much faster than they were 25 years ago. Also, Gm control of the input stage increases slew rate potential as well. Correspondingly, slew rates in IC's have risen from 0.5V/us to over 20V/us and much more, over the decades since they were first introduced for the same reason.
Slew rate is the maximum rate at which the output of the amplifier can move. It's generally measured in V/usec. Fortunately, it need only be adequate for the purpose. There's no advantage in simply increasing the number without limit. Slew rate is related to peak voltage and frequency by the equation:Slew rate = 2*pi*f*Vp where Vp is the peak output voltage of the amplifier and f is the frequency of interest.
For example, to get a 50 volt peak sine wave out of an amplifier at 20kHz requires an amplifier with a slew rate of 6.28 volts/usec. With a slight safety margin there's no reason to go faster.
WRONG...just listen...a slow amp sounds constricted and lifeless.....with high power and fast slewing...the sound is ALIVE.....after using my VanAlstine OMEGA III Hafler DH500 rebuild, nothing less than 300V/uS at over 300 RMS watts will ever make LIVE music, all else sounds lifeless and flat....same for the pre amp slew rate.....high speed brings the music alive.
This is way oversimplified. It may be that for CD playback, you could get by with sufficient slew rate to reproduce a 20 kHz sine wave at full power due to the bandlimited CD digital audio. The fact that most cymbal crashes and other difficult waveforms may contain several (perhaps hundreds) of frequency components all right around 20 kHz and even above, and that some vinyl playback systems are quite capable of reproducing that, means that a single 20 kHz sine wave does not stress the amp sufficiently for such use.Another factor is that AT the slew rate limit, the amp is operating completely non-linearly, that is, it is slewing, or trying to change it's output as fast as it can to catch up to the original signal. At the slew rate limit to reproduce a 20 kHz sine wave, the ampo has no further margin, no ability to handle ANY other signals present at the same time, ANY additional signal will increase the required slew to maintain gross overall linearity. Margins are needed to allow for more than ragged edge performance, and for more than CD bandwidths and capabilities. It is very likely that with the introduction of the higher bandwidth SACD and DVDA playback systems, such power amps would need to be capable of providing a slew free sinewave of 96 kHz or higher. Now we are up to in excess of 30 V/uS.
How slight your safety margin meeds to be of course, depends on just how well the amp was implimented in the first place. If proper attention to details occured up front, instead of as a bandaid later, then the amp should be able to slew quite a bit faster than necessary, and the whole concept of slewing and non-linear distortion would become a moot point.
One more thing concerning slew rates and amps, in my opinion, the best way to approach it is to make the power amp as linearly fast as you can without compromising other parameters, and then RC filter it to exhibit a constant risetime regardless of power level. That way, the amps sonic character never changes with level, and the unit can not readily be driven into slew rate limiting, it becomes impossible to drive it hard enough with out gross clipping as a result.
The one power amp I have heard that did not make it's presence known had a raw power bandwidth of over 2 Mhz, and was bandlimited via an input RC network to around 200 kHz. Most of the audible signs of there being a power amp present were gone, and all that could be heard as due to the amp were minor parts quality issues, which were easy to improve and make virtually invisible.
Of course, all fot he above is rather simplistic, but at least accessible to the layman.
Jon Risch
***For example, to get a 50 volt peak sine wave out of an amplifier at 20kHz requires an amplifier with a slew rate of 6.28 volts/usec. With a slight safety margin there's no reason to go faster.There is no reason to make a car that can go any faster than 55mph. No reason for $500,000 violin. $52M painting. $500 wine. No reason to have more money than one needs to cover the today's lunch.
Heck, if you are an American, then there is absolutely no reason to spend over $5 per year on clothing... Works for my friend Joe, so it will work for you, too.
Really, Norm, this is boring.
Well I guess you showed me. Put me down as being wrong.
***Well I guess you showed me. Put me down as being wrong.It seems that you are doing this to yourself.
Ever since the civilization had began the mankind has been striving for more, faster, better, easier, more productive, more fun, you name it. All the while there have been people arguing that what we have now is enough and no further progress is needed. Every time the mankind just drove by them.
Generally speaking, arguing that 5 is good enough when 20 can be done never works. People will always want to see what is behind the mountain.
You seem to have a mission of convincing everyone that $1 per watt and 20kHz are sufficient. That just plain will not work.
It is a hobby and is all about fun. People WANT to try things and telling them "you don't need it" will irritate many. People also have the right to try and even like all those silly things they do to tweak their systems - all this is totally innocent and quite natural.
It s really not the matter of right and wrong - no one can say that collecting stamps is right but fishing is wrong.
What about collecting stamps with fish on em'?
That's okay, but NOT collecting fish with stamps on them.
Right on, Victor! I thought that we got through this question of slew rate dacades ago. Your comparison of an auto that does only 55 mph is fitting. I owned a Renault Dauphine (32 hp) and drove it for over 90,000 miles. It can be done, but why bother?
For the record, it is difficult to make a low slew rate power amp that works well right up to the slew rate limit. This is because the input stage will start to add distortion, well before the slew rate limit is reached. If you add local feedback to the input stage to make it more linear before the slew rate limit is reached, then the slew rate will increase from its initial value. To reduce the slew rate back to it's initial value, it would be necessary to reduce the gain-bandwidth of the amp, increasing its high frequency distortion. Today, we can make amps with over 50V/us, with little effort.
***For the record, it is difficult to make a low slew rate power amp that works well right up to the slew rate limit. This is because the input stage will start to add distortion, well before the slew rate limit is reached. If you add local feedback to the input stage to make it more linear before the slew rate limit is reached, then the slew rate will increase from its initial value. To reduce the slew rate back to it's initial value, it would be necessary to reduce the gain-bandwidth of the amp, increasing its high frequency distortion. Today, we can make amps with over 50V/us, with little effort.In today's environment we pretty much don't worry about the slew rate as design parameter (we don't build the laser gun mirrors for the Star Wars). We just make sure everything else is done right and then good slew rate and bandwidth naturally follow. It is then what it is and usually is high enough.
Which is not to say that other designers may not take a radically different approach and achieve good results. There is no simple answer, but in case of most parameters you don't want to stop at the minimum required. And you are right, it is almost harder nowdays to design well for limited "programmed" slew rate.
Frank Van Alstine and crew have 300V/uS....engineering gurus, electrical wizzards......www.avahifi.com......sonic bliss.
Hardly. Dave Spiegel was doing 350 V/uS back in 1974. His prototype amps in 1979 were doing over 1000 V/uS (Audio Horizons Winter issue, 1979). Like i said before, his designs were light years ahead of their time. Most products back then were running in the 30 V/uS to 50/VuS range with some of them WAY below that.Another guy that has really pushed the design envelope is John Curl. Do some browsing through both old & new audio mags and you might be surprised how often you see his name associated with some of the freshest designs. You'll find out how blessed we are to have him here with us. Sean
>
Back in the 1970's, we had a slew rate race, because we did not know whether an ultra high slew rate would make a significant difference. At the same time, we researched REAL audio sources for potentially high slew rates. The term 50V/us is a rational minimum. We always design higher slew rates in most amplifiers. Typically, 100V/us is easy to do today. One trade-off is between ultra high slew rate or the use of output inductors. Most modern audio amps have removed the 1-5 uH output coil on the output of the amps, (as well as the output fuses), because it tends to ring with capacitive loads, such as electrostatic loudspeakers. Parasound, for example, doesn't use output coils anymore, yet has very high slew rates on its amps. Using an output coil allows for ultra high slew rates, but the necessity for this, is debatable. With inductors, ultra high slew rates of 750V/us or more are practical.
***Frank Van Alstine and crew have 300V/uS....engineering gurus, electrical wizzards......www.avahifi.com......sonic bliss.With today's component base numbers from 200 to 500 are fairly easily achievable, if that is the goal. I believe Spectral has it at about 600, but don't quote me on that. We usually stop in the 200-300 area, because other considerations seem to take over at that point, at least in our case.
Also, another important element - when your product has to interface with many unknown components, including the cables, network boxes, etc. very wide bandwith can get you into trouble in no time at all, if you don't have enough margin.
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