traderbam said:
10V/us will render a slew rate limited bandwidth of about 22KHz. This is a level of performance (minus the power) you would expect from a boombox. Ever tried to calculate or measure the amount of TIM, DIM, PIM, etc... in such an amp? Does such an amp sound good to you?
traderbam said:
Huh? What voltages and currents are you talking about?
traderbam said:
This will put you on a collision course with JC and others. I agree there's not much of a difference between 400V/us and 600V/us but I do know that low distortion means nothing if the amp is slow. Slew rate induced dynamic distortions will kill your ears worse that 0.1% or third harmonic.
Traderbam, please leave some headroom in the slew rate or else you will get big TIM distortion. I thought this was universally understood by now. AND it can be measured.
traderbam said:
Did you say:
Bryston's 7B/14B amps claim slew rates of 120V/us. Given that the speaker output is separated from the amp output by a 2uH inductor in parallel with 5 ohms, I estimate that the slew rate at the amp output would need to exceed 600V/us to produce 120V/us at the speaker terminals.
Yes or No?
And why do you think I departed from wrong specs? Please specify.
traderbam said:
Bryston does NOT add a 'mass' to the system. As I've shown, the input of the Zobel network is purely resistive and constant, provided, of course, that the output is correctly terminated. The only thing it does is cutting off extreme high frequencies (Fc=-3dB at 400kHz). Is that a problem for you?
I suppose it is going off topic to start debating slew rate, so I'll be brief.
I have found that in engineering it is very important to get the specs right before devising a solution. Make sure you spec what is important and do not spec that which is incidental to a particular implementation. I may sound nit-picky, but I have seen people disappear down pointless blind alleys chasing incorrect specs. Unless you can show me otherwise, I don't see why a domestic audio amp needs to output frequencies higher than 20 or 30kHz nor slew faster than 10V/us.
Have you measured the maximum slew rate in a CD music signal? Stereophile have. Surely it follows that if an amplifier's output is ever slewing faster than this, then the amplifier is distorting.syn08 said:
The voltage and current sources withing the amplifiers circuit.
Gentle collisions lead to gretare understanding.
I am saying that high slew rate is not a requirement. You might argue that certain dynamic distortions are correlated with amplifier slew rate, in general, and that might be true, but high slew rate is not of itself a requirement.
I have found that in engineering it is very important to get the specs right before devising a solution. Make sure you spec what is important and do not spec that which is incidental to a particular implementation. I may sound nit-picky, but I have seen people disappear down pointless blind alleys chasing incorrect specs. Unless you can show me otherwise, I don't see why a domestic audio amp needs to output frequencies higher than 20 or 30kHz nor slew faster than 10V/us.
I understand your concern with TIM. I am talking about the slew rate at the amplifier output. I totally accept your past comments about vinyl sources and the vicious spikes that can arise from this type of source. My simple point is that if an amp is accurately reproducing a music signal then that reproduced signal should never have a greater slew rate than the source (as a % of peak). I don't know how that can be disputed.john curl said:
Ok, so it may be that a particular implementation of an amplifer to achieve the modest slew rate required at its output and a very low distortion, happens to exhibit very high slew rate capability. But I submit that it would be erroneous to specify high slew rate as a necessary end in itself. IOW, I think I would be wrong to criticize a design because it has an output slew rate limit of 10V/us. I don't see any implicit connection between the two.
Bob Cordell said:
Hi Bob,
If you look at my graphs, it becomes obvious why Bryston do it their way. Much more attenuation of RFI picked up by the speaker cables.
Cheers,
Edmond.
Since the GND line might also be prone to HF pickup (common mode), wouldn't an equal split of the output L//R between both send and return (which not always is GND, anyway) be the best practice? Something like I have proposed here:Edmond Stuart said:
http://www.diyaudio.com/forums/showthread.php?postid=1419373#post1419373
- Klaus
RFI
Hi Klaus,
Good point. When I was posting my comment, that was exactly what I was thinking about.
Thanks.
Cheers,
Edmond.
KSTR said:
Hi Klaus,
Good point. When I was posting my comment, that was exactly what I was thinking about.
Thanks.
Cheers,
Edmond.
That's all very well but where is your maths?john curl said:
My understanding is that Blu-ray will support 96/24. At the very worst, if they choose to record music for dogs (which they won't), a 100W amp will need to slew at 12V/us max.
Please tell me why you think I am wrong.
hi!
The Rane website is often very informative.
The have section that explains different words in Audio:
http://www.rane.com/digi-dic.html
Here is what info on Zobel
Zobel network or Zobel filter
(Also called Boucherot cell after Paul Boucherot
who worked extensively with electrical networks and power.)
*** Boucherot, Paul (1869-1943)
French engineer who studied the phenomena of electric conduction,
introducing the concept of reactive power
and inventing the synchronous electric motor in 1898.
So we see here, this is nothing new.
it goes way back to Bell Labs and January of 1923.
😀 😀
And anyone of us, think we can add some revolutionary idea ...
Would not think so, my friends 😉
Weblink:
http://www.rane.com/par-z.html#Zobel
The Rane website is often very informative.
The have section that explains different words in Audio:
http://www.rane.com/digi-dic.html
Here is what info on Zobel
Zobel network or Zobel filter
(Also called Boucherot cell after Paul Boucherot
who worked extensively with electrical networks and power.)
*** Boucherot, Paul (1869-1943)
French engineer who studied the phenomena of electric conduction,
introducing the concept of reactive power
and inventing the synchronous electric motor in 1898.
So we see here, this is nothing new.
it goes way back to Bell Labs and January of 1923.
😀 😀
And anyone of us, think we can add some revolutionary idea ...
Would not think so, my friends 😉
Weblink:
http://www.rane.com/par-z.html#Zobel
I like Zobel networks with feedback amplifiers. In fact, I think that it is almost necessary, but I could be proven wrong.
john curl said:
Infact you are very right,according to investigations of
D Self B Sc phD it was found that the o/p works best with
zobel😉
That Stereophile test of DVD-A and SACD shows that the highest slew rate measured was less than that of a full amplitude, 12kHz sinewave.john curl said:
I suppose a CD source could, in theory, output up to 23kHz full scale. I'm not even sure they can do much above 21kHz, though, their brick-wall filters see to that in order to minimize aliasing.
If you have evidence to the contrary I would like you to share it with me. Then I would have to argue that it is unecessary to allow inaudible frequency content into an amp in the first place.
Seriously, I think your posts are confusing what the spec. of music is with the relationship between DIM and slew rate in certain classes of NFB amplifier. I think it is misleading to mix up correlation with cause-effect.
My complaint is, if you make a blanket statement that implies all amplifiers will produce audible DIM unless their slew rate is 10x or more higher than the input source, you overly constrain the design problem for the creative amateur.
My approach is that a certain audible distortion target has to be met. Obviously, an amp has to be able to slew at least as fast as the source, but beyond this it is up to the designer to trade things off in the circuit design. Same applies to frequency response. I don't favour saying something has to be a certain way if it really doesn't.
Traderbam, we spent 10 years reviewing slew rate limitiations. I have worked with Walt Jung, Matti Otala, John Meyer, and even published a paper on worst case slew rate for the IEEE in 1978. Trying to argue with you at this point is useless. You MUST include significant headroom, just like an auto, to be at its best, needs a greater top speed potential than you would normally drive at. Now please don't tell me that this auto analogy is wrong. I once owned a Renault Dauphine with 32HP for 95,000 miles, and know that more horsepower would have been very convenient in many occasions.
We usually add a factor of about 5 for worst case effortless headroom for slew rate. We developed this 'rule of thumb' from 100's, YES, 100's of test measurements over a period of years. It is SOMETIMES possible to get away with less slew rate, just like I got away with a 32HP auto for 5 years, but it IS a compromise that I would not go back to.
What you do is your own business, but convincing others that slew rate is unimportant from a few calculations that we first did 40 years ago, is unfortunate.
We usually add a factor of about 5 for worst case effortless headroom for slew rate. We developed this 'rule of thumb' from 100's, YES, 100's of test measurements over a period of years. It is SOMETIMES possible to get away with less slew rate, just like I got away with a 32HP auto for 5 years, but it IS a compromise that I would not go back to.
What you do is your own business, but convincing others that slew rate is unimportant from a few calculations that we first did 40 years ago, is unfortunate.
'mass'
Theoretically, we don't need more slew rate than the max. SR of the input source. In real life however, most amplifiers (i.e. amps with a high degree of global NFB) show up a direct connection between SR, (open loop) bandwidth and distortion. Think of the Miller compensation for example. The higher the Miller cap ('mass', using your terminology) the less bandwidth. That means less NFB loop gain and more distortion.
So most likely that an amp with only 10V/us SR produces far more distortion than an amp with 100V/us SR.
traderbam said:
Theoretically, we don't need more slew rate than the max. SR of the input source. In real life however, most amplifiers (i.e. amps with a high degree of global NFB) show up a direct connection between SR, (open loop) bandwidth and distortion. Think of the Miller compensation for example. The higher the Miller cap ('mass', using your terminology) the less bandwidth. That means less NFB loop gain and more distortion.
So most likely that an amp with only 10V/us SR produces far more distortion than an amp with 100V/us SR.