@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. Bruce 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. Regards, -- Al |
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 approaches? 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. 😄😃😀😋 |
