"Fast" means not so much unless you are speaking of a system.
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'Fast' often refers to risetime or slew rate. Spectrals have always been very 'fast' in this regard. 100V/microsecond is generally considered 'fast'.
Most tube amps are 'slow' by comparison- 15V/microsecond being typical. Our amps are 600V/microsecond- IOW they have speeds similar to the best solid state. Tubes are not inherently slow (after all, if they were, color television would not have been possible...). But there can be design elements that can slow any circuit down.
'Fast' and 'slow' should not be confused with 'bright' and 'dull'; these are entirely different things, even if an amp that is 'fast' is also 'bright'. There are different reasons for these things!
Fast, in this case, means how fast you bank account empties once you buy a Spectral item."
That's always the case. That's what credit cards are for.
"'Fast' and 'slow' should not be confused with 'bright' and 'dull'; these are entirely different things, even if an amp that is 'fast' is also 'bright'. There are different reasons for these things!"
We may not all have the same exact thing in mind when it comes to fast. After reading Douglas_schroeder's comment, I'm just not clear as to what he meant.
A lot of newer amps use very high damping factors which enables speakers to react faster to the signal. Damping factor on my Bel Canto Class D amps is 1000 I believe. It's as fast and clean as can be. Also not inherently bright sounding as many amps with high damping can be. Its a good class D design IMHO, as most likely is Spectral.
Overall benefits of amp high damping will vary with speaker but will always bias towards being "fast". On some speakers, particularly smaller ones that might be a bit light on bass in some cases, teh results might sound a tad lean, but adjustments to speaker placement based on room acoustics can help.
I run large full range speakers with 12" drivers (OHM F5) that mate well with high damping for the best "fastest" sound. I also use smaller monitors from Dynaudio and Triangle that sound their "fastest" with the high damped Class D amps I use now compared to others in the past. The Triangles are smallest and have somewhat limited bass extension. Only those tend towards being a bit lean sounding with the high damping on conventional ear hight stands. Placement closer to the floor on acoustic isolating stands works well to get full articulate bass.
See my system pics for all these examples.
My point was simply that no component is heard in isolation, and that the composition of the system largely determines the perception of how "fast" it is.
i.e. Put a "fast" amp with a dynamic speaker and it may not sound to the ear as quick as a "slower" amp with an ESL speaker.
Apples to apples there are amps which sound "faster" than others, but once you begin switching around components, all bets are off which amp will be perceived as "faster".
@Mapman ... I seem to recall Ralph (Atmasphere) posted comments some years back about the impact and import of high damping factors (DF) on woofer control. DF, of course is simply speaker impedance at a particular frequency (usually in the bass range), divided by the amp's output impedance at the same frequency.
As I also recall, Ralph may have said that a DF over 20 doesn't make that much of a difference in woofer control. In fact ... the dark side of a high DF is that it is oftentimes achieved by using high negative feedback (NF) which is used to achieve in part low output impedance, which augments high DF. Ralph has written much about the sonic downsides of using NF.
If Ralph picks up this post, I'm sure he'll fill in the gaps.
P.S. -- FWIW, the slew rate of my ARC Ref 150 is 13 volts/microsecond. The vaunted ARC GS-150 is the same. The mighty ARC Ref 750 is 20 volts/microsecond.
My point ... I have no idea what it all means.
But top rated and reviewed ARC amps like the Ref 150, the GS 150 and the mighty Ref 750 have slew rates nowhere near Ralph's amps which he says are 600 volts/microsecond.
Maybe Ralph can put this spec into perspective for us.
Bifwynne, yes you got that all right. I think. Damping is overkill at some point. Exactly at what point that is is somewhat debatable and would vary case by case I suspect. There is a correlation between damping and speaker control but not a hard formula. Like most things in this hobby theory and results may not always jive. In general though I believe it beneficial for an amp to have proper control over speaker transducer operation just like it is important that component impedances match beyond a certain range for best results.
The negative feedback argument is a mixed bag as well I think. Some things work well together and others don't. No one aspect of design determines results. Fast slew rates are surely a good thing though.
Ptss 02-05-15Ptss, if I recall correctly you have a DMA-180. I compared the specs on that amp with those of the currently produced DMA-200S S2, DMA-260 S2, and DMA-300. All of the speed-related specs (frequency response/bandwidth, risetime, settling time, and slew rate) on all four amps are identical, except that the DMA-300 has a slew rate of 800 V/us while the others are 600 V/us.
Most of the other specs are also very similar, the most notable differences being that the three newer amps have a much lower input impedance (10K) than the input impedance of your amp (100K), which could be problematical with some preamps, and the three newer amps have rated maximum power capabilities which increase into decreasing load impedances more slowly than in the case of your amp.
The bottom line, IMO.
Many Krell and Classe amps I have heard over the years sounded
particularly "fast" to me. Don't know their slew rates. I tend to
associate fast sound ie a combo of high slew rate and matching ability of
speaker transducer to respond accordingly with a high capacity for
delivering holographic sound. Low mass transducers like electrostats and
planers seem particularly amenable for that. Dynamic drivers operating in
Walsh wave bending mode also seem good at this to me. Mass and inertia
associated with typical dynamic transducers are the biggest barrier to
achieving fast sound much like it is with a phono stylus transducer.
I don't know a slew rate spec for the bel canto class d amps I use but they
are ice power based and the holography is quite high. Shockingly so when
I heard them the first time compared to amps I owned prior. As class d
amps continue to improve I wonder if their ability in this area in general
continues to go up perhaps even raising the bar beyond other design
I've read some diy discussions asserting that slew rate specs are irrelevant
for class d and perhaps some other amp architectures much as are very
high damping factors in most cases. Would not surprise me but I am not an
ee so dunno for sure.
I'll take al's wise advice and not worry about it much and just be happy it all
works and sounds as good as it does.
Al, can you please clarify where in the frequency spectrum slew rate vs rise time is relevant? My understanding is that for the most part sonically, slew rate correlates to bass performance and rise time to treble. This is what I've been told by the tech who's worked on some of my amps.
Also, that slew rates past a certain level become irrelevant like DF. Rise times lower than 2u sec. are about where the source material becomes the limiting factor.
Does musicality suffer when these thresholds are breached in an effort which may typically result only in marketing strategy?
Hi Peter (Csontos),
Yes, slew rate, risetime, and bandwidth will in the case of many designs extend well beyond the point of being overkill with respect to effects that may have DIRECT audible significance. The Spectral amplifiers being extreme examples in that respect. As I'll get into in a moment, though, that does not necessarily mean that the only benefit is to those who write marketing literature. But first for some quantitative perspective on these numbers:
A very conservative (i.e., safe) rule of thumb for bandwidth, that would rule out the possibility of perceptible phase shifts within the audible spectrum, and that would take into account the possibility that, as some have claimed, frequencies well above 20 kHz may be sensed by some listeners when accompanied by lower frequencies, would be to multiply 20 kHz by a factor of 10, meaning 200 kHz.
Then consider that the relation between risetime and 3db bandwidth (i.e., the frequency at which response has rolled off by 3 db) is, for a first order (6 db/octave) rolloff:
risetime = 0.35/bandwidth
where the units are chosen consistently between the two parameters (i.e., seconds and Hz, or milliseconds and kHz, or microseconds and mHz).
Based on that relation, a first order response that is down 3 db at 200 kHz corresponds to a risetime of 1.75 us (microseconds), very close to the 2 us figure you cited.
Slew rate, which is the fastest rate at which the amplifier output can change (presumably under large signal conditions), should be fast enough to provide a wide margin relative to values that might limit the other two parameters. If we consider the somewhat extreme example of a 200W amp, 200 watts into 8 ohms corresponds to 40 volts rms, which for a sine wave corresponds to 113 volts peak-to-peak. The half-period corresponding to a frequency of 200 kHz (i.e., the time required for a peak-to-peak swing at that frequency) is 2.5 us. 113 volts/2.5 us is about 45 volts/us. A slew rate of 100 volts/us, which Ralph (Atmasphere) rightly characterized as "fast," seems comfortable relative to that figure, considering especially that 200 watts at 20 kHz, much less 200 kHz, is an unlikely scenario :-)
Now consider in those contexts the specs on the four Spectral amps I referred to:
Bandwidth (3 db): 1.8 mHz
Risetime: 0.4 us
Slew rate: 600 v/us (800 v/us in one case)
Obviously way overkill relative to any conceivable effects that are DIRECTLY audible.
So why have I put the word directly in caps? Well, I would presume the designers feel that by designing ultra-fast circuitry they can avoid or minimize effects which may be audibly significant. For example, they may be able to realize the benefits of increased amounts of negative feedback while avoiding or minimizing what would normally be its adverse effects, such as transient intermodulation distortion. Or the higher speed circuitry might help to minimize crossover distortion, or the effects of unwanted energy storage in devices, etc.
So what can be said about that? Well, its an approach, and a philosophy. As is usual in audio, how good or bad the results are will depend on quality of implementation, system matching, and listener preference.
My understanding is that for the most part sonically, slew rate correlates to bass performance and rise time to treble. This is what I've been told by the tech who's worked on some of my amps.That can probably be said to have a vaguely definable basis in situations where risetime and slew rate are slow enough to verge on having DIRECT audible significance, given as I said that risetime is inversely related to bandwidth (and thus potentially to upper treble extension), and bass frequencies are generally present at much greater amplitudes than upper treble frequencies (slew rate probably being best considered as a large signal parameter, as I said earlier). But the statement strikes me as a crude oversimplification at best, and one which does not have much relevance in situations where both parameters have comfortable margins relative to audible thresholds.
Al, do you think what you describe might correlate to an amps ability to deliver "holographic imaging" as part of those more nebulous sonic artifacts? I tend to relate high performance as measured in things like bandwidth slew rate and rise time with resolution and resolution is a factor for holography I believe.
So Al, what does that mean in the context of ARC ref amps. As I mentioned above, the slew rate for my amp (150 wpc) is a paltry 13 volts/microsecond and the rise time is a sluggish 2 microseconds. The top of the line Ref 750 has a slew rate of 20 volts/microsecond and a rise time of 1.5 microseconds.
Based on your comments, I gather a CD will be over before the amp is able to get a signal to the speakers. Almost like playing a 45 rpm record at 33 rpm on a turntable. :)
Of course, I'm being tongue in cheek, but I gather there is some overkill in the specs. Kinda like an amp with a DF of 1000 ... way overkill. Ralph has mentioned that a DF over 20 is a waste.
Bruce (Bifwynne), a basic point in my analysis was to show that even relative to VERY conservatively drawn thresholds the speed-related parameters of the Spectral amps are **in themselves** extreme overkill. While at the same time citing the possibility that the overkill might provide indirect benefits in the design.
The numbers you cited for your ARC amp don't seem to me to be unreasonable in any way, they just represent a different philosophy and a different approach, which result in less margin (but arguably still very reasonable margin) in those particular parameters.
Mapman, re your question, I'm not really sure. I too believe that there is a strong relation between resolution and holography/dimensionality etc., but my instinct is that linearity, distortion, and noise performance more often than not tend to affect resolution more significantly than the speed-related parameters. Just MHO.
Al; where the heck did you get this knowledge?I'm an EE with extensive analog and digital design experience (for defense electronics, not for audio), and I've been an audiophile for about 35 years. Audio has always been of interest to me from a technical standpoint as well as a musical standpoint.
My understanding is that for the most part sonically, slew rate correlates to bass performance and rise time to treble. This is what I've been told by the tech who's worked on some of my amps.
Actually slew rate has almost nothing to do with bass, in case Al had not made that clear earlier.
Damping factor also has nothing to do with bandwidth, slew rate or risetime. However, A high risetime and slew rate can improve the effectiveness of the use of loop feedback, assuming the feedback parameters are properly worked out. So it may be that with higher risetime and slew rate, an amplifier with a greater damping factor can be built.
The thing is, no speaker needs more than about 20:1 for a damping factor- in fact if the speaker is over-damped, quite often a loss of bass impact is experienced (and is also measurable).
As Deep Thought was want to say: "Tricky."
It might be hard to quantify or even identify but it makes sense to me that higher performance in general enables design options that might not be viable otherwise. To what extent any of those are beneficial or not of course may still be up in the air, but it is always a good thing to have options in design, at least that has been my experience over the years in other areas of engineering.
Isn't that what "high end audio" is really about from a technical perspective? Doing things bigger, better faster....sometimes just because you can.
I think it would be useful to get a subjective description of just what the attributes of a 'fast' amp are sonically. What does speed sound like in an amp in comparison to mediocrity? Anyone?"
All components contribute to a systems illusion of speed, so its hard to isolate just the amp. But overall, from a subjective perspective, you need to listen to how the system is reproducing the attack, resonance and decay of whatever instruments are on the recording. When the attack, or leading edge of a note is being highlighted more so than the other 2, you'll probably interpret that as speed, or PRAT.
Can you give an example of an amp that is outstanding in this regard?"
I bought a Musical Fidelity A3.5 integrated. It had way too much attack, or speed. So much so, that unless you have a really dull sounding system that needs a band aid fix like that, it just wears you down and starts to sound like a gimmick. Its kind of hard to find an example like that any more, because most designers have been trying to get their designs to have more of a balanced sound to them. And for the most part, they've been successful. Tube designers try to get they're gear to have more SS qualities, and SS designers trying to get some tube aspects in their designs. That type of thing.
Is "fast" a desirable attribute?
Yes. The human ear/brain system has a tipping point wherein if the reproduction of music is not 'fast' enough, the processing moves from the limbic system (emotional center) to the cerebral cortex (intellectual center).
But by and of itself speed is not the final arbiter- it must occur within an otherwise musical framework.
Zd, I would think the opposite is the case in fact. Deliberately not designing true to life character seems to be the gimmick among tube amp designers especially. Just because of the well known quirky expectations of their market base. From what I gather, tubes sounding closer to ss is more trendy than vise versa. If the sound is 'balanced' as you say, it will display serious speed and attack...like reality does. If that's not what you want, it's okay to be honest and not obfuscate or try to reinvent the English language.
Btw, a soa amp will always display serious speed and attack.
Zd, I would think the opposite is the case in fact. Deliberately not designing true to life character seems to be the gimmick among tube amp designers especially. Just because of the well known quirky expectations of their market base. From what I gather, tubes sounding closer to ss is more trendy than vise versa. If the sound is 'balanced' as you say, it will display serious speed and attack...like reality does. If that's not what you want, it's okay to be honest and not obfuscate or try to reinvent the English language. "
You asked the question and for some reason, it looks like you're not happy because I was able to answer it. You make up all this crap and back it up with guesses. It doesn't work that way, regardless of what you think. The only way you can legitimately challenge my findings is if you have some of your own to back yourself up with. You can't do that. I've owned the amp and based my findings on reality. If you want someone to listen to you and take you seriously, then put your money where your mouth is and get one yourself. But we all know that's not going to happen, so keep reading the magazines, come up with more useless crap and keep us entertained.
"Btw, a soa amp will always display serious speed and attack."
Btw, more useless crap. Audio Note, Shindo, Jadis... The list goes on, and no, I'm not explaining it to you when you pretend like you don't understand. Everyone else will. (although you probably wouldn't be pretending)
Zd, I do own a few amps. You clearly favor tubes so I responded commensurate with your bent. Not everyone considers your subjective view as reality btw. I'm perfectly happy with your answer. I just think it's bullshit, that's all. I expected as much.
Oh, I've never read or bothered with one of those mags.
Soulution advertises 'fast' amps. My understanding is that this enables them to use large amounts of negative feedback in order to achieve low distortion. Because they are 'ultrafast' negative feedback loops, they do not degrade the sound. So says Jonathan Valin as he currently sings their praises in The Absolute Sound.
Zd, I do own a few amps. You clearly favor tubes so I responded commensurate with your bent. Not everyone considers your subjective view as reality btw. I'm perfectly happy with your answer. I just think it's bullshit, that's all. I expected as much. "
Well, it took you long enough. Trying to figure out how to "win" and make yourself look good. Take as long as you want, but you'll never get it. The secret to winning an argument is don't argue. Just use facts. Why? Because you can't argue facts. Facts are facts regardless of what you, me or anyone else says. Can't do a thing about it.
I referenced a Musical Fidelity A3.5. You can't agree or disagree with me, subjective or otherwise. Why? Again, because you never heard one. Its a factual statement. Neither one of can change it. But we know you'll try and fail anyway.
Also, wrong on my preference for tubes. I knew you wouldn't get the example. I don't have a preference for anything, I just pick what I think sounds best (from actually listening, not guesswork). Right now, my entire main system is all SS.
02-06-15: BifwynneBifwynne, doing the math for your ARC Ref 150 tube amp -
if the amp is outputting its full/rated 150W into 8 Ohms that would mean a RMS voltage of 34.6Vrms of a sinusoidal waveform & a peak of approx 49Vp of the same sine waveform. I.E. the peak-peak voltage of the sine wave would be 98Vpp. If amp traversed the 98Vpp such that the slew rate of the amp is 13V/us (as spec'd) then the maximum frequency that the amp could handle with this slew rate would be 66KHz. So, it appears that the freq BW of your amp is 20Hz (or 5Hz?) - 66KHz.
Compared to the (fictitious?) example Almarg gave where the amp was a 200W unit & had a slew rate of atleast 45V/us such that it could handle a signal as high as 200KHz.
So, the ARC Ref 150 has quite a bit lower slew rate compared the Almarg's example power amp & accordingly lower frequency bandwidth.
This also means that since the ARC Ref 150 bandwidth is just 3X (rather than 8X or 10X) the music bandwidth (of 20KHz) one can expect to hear the amp impart its own phase shift onto the higher frequencies of the music. This can manifest itself in a few ways - the highs could sound rolled-off or they could sound warmer or there could be less sparkle/shimmer compared to an amp of higher bandwidth. Nothing wrong with this sort of attribute of a power amp - many like it & many others don't. Something keep in mind.
Just some additional info, FWIW.