Is Jimmy Johns really that fast or are they just setting themselves up for failure by advertising to be?
Just wondering. have never experienced.
Just wondering. have never experienced.
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Bombaywalla, thanks for the additional thoughts. However, while I agree with your math, I don't completely agree with the conclusions you reached. As I'm sure you recognize, my hypothetical example involving 200 watts at 200 kHz, as well as the figures you cited in connection with Bruce's Ref150 of 150 watts at 66 kHz, are not remotely within the realm of real world operating conditions for a home audio system. Or at least a home audio system that is not in the process of self-destructing due to some unimaginable defect-induced oscillation :-) A key point to keep in mind is that under realistic operating conditions bandwidth and risetime should not be and in general will not be limited by slew rate, as I indicated in my long post dated 2-6-15 (see more on that below). And as I indicated in my previous response to Bruce: ... 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.Consider "VERY conservatively drawn thresholds" to mean parameters that are so extreme as to be well beyond the bounds of real world operating conditions. As you may realize but others may not, slew rate should be fast enough to avoid any possibility of the amplifier's output slewing under any realistic operating conditions. While bandwidth (and risetime) limitations mean that frequency components above a certain frequency are attenuated or filtered out, slewing results in essentially all frequencies that represent sonically meaningful information being filtered out and/or distorted. In a sense it can therefore be considered analogous to what happens in hard clipping, although of course that relates to amplitude limitations rather than speed limitations. I note, btw, that the ARC Ref 150 has a specified 3 db bandwidth of 120 kHz (at 1 watt, with an 80 kHz "power bandwidth" also being specified), and JA's measurements indicate a bandwidth of approximately 100 kHz (for an 8 ohm load connected to the 8 ohm tap), with excellent reproduction of a 10 kHz square wave (under small signal conditions, as noted under the graph). So while I don't think we can completely rule out the possibility of audible phase shifts occurring in the upper treble region under some circumstances, given the bandwidth of the Ref150, I would not expect that to be as much of an issue as your conclusion would seem to indicate. And to put that into context, I'll point out that more than a few other very highly regarded amps, including some tube amps costing vastly more than the ca. $13K Ref150, have bandwidths which are considerably more limited. Best regards, -- Al |
I note, btw, that the ARC Ref 150 has a specified 3 db bandwidth of 120 kHz (at 1 watt, with an 80 kHz "power bandwidth" also being specified), and JA's measurements indicate a bandwidth of approximately 100 kHz (for an 8 ohm load connected to the 8 ohm tap), with excellent reproduction of a 10 kHz square wave (under small signal conditions, as noted under the graph).Hi Almarg, thanks for the feedback. I did also note the very same specs as you wrote above & also noted that these were mostly under small-signal conditions while slew-rate is a large-signal parameter (as you already noted in an earlier post). When the amp is outputting a lot more power then i believe that the distortion will be much higher & the various BWs cited in JA's measurements will constrict & that 10KHz sq wave won't look so pretty anymore . That's why a 66KHz BW at max rated power under the stated 13V/us slew rate did not seem unreasonable to me. The effect of the excess phase shift would thus be more discernible (vs. lower power outputs). |
Bombaywalla, I generally get your points about slew rate specs and the impact on bandwidth, especially if there are large power demands placed on the amp at higher frequencies. FWIW, I seem to recall many years ago that I spoke with Leonard, ARC's former customer service rep, about the slew rate issue. Len explained that the design of an amp takes into account many factors and compromises, slew rate being just one of many. The same hold true for negative feedback, DF and so forth. So, in the end, Len wisely said that it comes down to how does the amp in question sound in real life operating conditions taking into account all of these design considerations and trade-offs. That's what engineers do all the time. As to your specific point that a 10K square wave pic might not look so pretty at high power outputs ... well that might be true. But as we all know, most of an amp's power demands are in the bass and midrange frequency spectrum. I surmise that listening to an amp pumping even 50 watts of power into moderately sensitive speakers at 10K Hz would likely melt your ears ... assuming the tweeters could take the load. Al ... what are your thoughts?? |
Hi Al(marg). Your informed and considerate posts are "very" much appreciated. Your background provides a great platform for your insights. My Dad was a Civil Engineer so I appreciate how thorough and appropriate an Engineer can be on a topic of interest. (Dad was a woodworking craftsman and built the boat that so enhanced my youth). Your comments invite me to further research. On a non technical side, I've checked your system indicates stock power cords. Please don't be offended at my totally subjective suggestion that you at least try an MIT Oracle AC 3 (non-networked) power cord. In my Spectral based system these have proven to be extremely effective in all components,including digital,--batting much higher than their approx $600.00 cost via Joe Abrams,their online dealer/discounter for Audiogon. I hope you will sense increased speed and refinement :- ) |
Thanks, Ptss. I appreciate the nice words and the suggestion. And I've noted in the past your frequent advocacy of the importance of addressing power quality and power-related issues. I'll keep your specific suggestion in mind, for a future time. Next on my list, though, as you've seen in the DEQX thread you initiated, is purchase of an HDP-5 in the next month or two :-) Best regards, -- Al |
Hi Al(marg). Your informed and considerate posts are "very" much appreciated. Your background provides a great platform for your insights. My Dad was a Civil Engineer so I appreciate how thorough and appropriate an Engineer can be on a topic of interest. (Dad was a woodworking craftsman and built the boat that so enhanced my youth). Your comments invite me to further research. On a non technical side, I've checked your system indicates stock power cords. Please don't be offended at my totally subjective suggestion that you at least try an MIT Oracle AC 3 (non-networked) power cord. In my Spectral based system these have proven to be extremely effective in all components,including digital,--batting much higher than their approx $600.00 cost via Joe Abrams,their online dealer/discounter for Audiogon. I hope you will sense increased speed and refinement :- ) |
Al, as you and Ralph are obviously the two most technically knowledgeable, I think it most appropriate for the two of you to also define/describe amplifier 'speed' from a subjective/sonic perspective. As yet, no one has given a description of what a 'fast' amp sounds like in comparison to something unremarkable. This goes to the op in reference to it's effect on the music. I'd like to hear references beyond HF transient performance/attack and bottom end definition. Grooming is necessary in this hobby just because of it's inherent limitations. The moon is too far away. |
"define/describe amplifier 'speed' from a subjective/sonic perspective. As yet, no one has given a description of what a 'fast' amp sounds like in comparison to something unremarkable." If you recall, you did ask this question a few days ago. I did my best to give you an answer and you got mad at me because of it. Have another look. "02-09-15: Csontos 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." "02-09-15: Csontos 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. Zd542 (Threads | Answers | This Thread)" And for those answers, I got this. "02-10-15: Csontos 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. " "02-11-15: Csontos 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." To sum up, you asked for a subjective opinion and I gave you one. Then you asked me for an example, so I gave you one. What exactly do you think the word subjective means? Maybe we don't think its the same thing. If someone else dares to give you an answer, are you going to attack them as well? |
02-18-15: CsontosFrom a subjective perspective, I think of "fast" as referring to the ability to reproduce musical transients in a "clean" and accurate manner, as opposed to a "sloppy" and inaccurate manner. As ZD said on 2-9-15, "you need to listen to how the system is reproducing the attack, resonance and decay of whatever instruments are on the recording." I would emphasize, though, that speed from a subjective standpoint and speed as characterized by risetime, bandwidth, and slew rate are two different things, which do not have a necessary or direct relation. It seems entirely conceivable to me that an amp having a 100 kHz bandwidth could be subjectively "faster" than one having a 1 mHz bandwidth. Although in many cases there may be an indirect relation between faster bandwidth/risetime/slew rate and subjective speed. For example, use of a given amount of feedback in a really high speed circuit may not result in as much Transient Intermodulation Distortion compared to its use in a slower circuit (as Ralph, Psag, and I alluded to earlier). Less TIM distortion meaning more accurate reproduction of musical transients, by definition. BTW, re "the two most technically knowledgeable," let's not overlook Bombaywalla, who is certainly no slouch when it comes to EE technical matters, and perhaps some of the others who have responded as well. Best regards, -- Al |
Thank you Al. I thought there is always going to be a direct causal effect of actual amp speed and subjective/sonic speed. That's very interesting. I understand the obvious descriptors of a really good amp but there's another effect/indicator of subjective speed which is observable. It may be that I have a too limited perspective on what transient performance is. The things I'm referring to are effects of ambiance being injected where you can hear it's instantaneous up front presence less subtly than the engineer may have intended probably expecting it not to be noticeable, and maybe with a sparkling almost grainy effect. As if you can hear that sound being constructed. Also for example a string being stretched or when they are sliding up or down the neck of the instrument, or soft consonants like the word 'you' for example where after the initial attack the remainder of the tone is so consistently immediate as to convey the same sense of speed as the transient. Or the precisely contained decay of a kick drum where you can hear reverberations clearly/sharply. Or even a trombone doing it's thing with a sense of strength and immediacy that denotes speed. I have a pair of Meridian 105s that are uncanny in their ability to convey this sense of speed. I also have a pair of the famed LOW TIM LSR&D Superamp monos designed by the late Dr. Marshall Leach of Georgia Tech. Although they both display equally competent transient performance, the Meridians have that sense of immediacy that raises them a notch above. I also have a GAS500 that has this sense of immediacy but not quite as fast in transient performance. If the relationship between technical parameters and subjective perception is indirect or vague, then how does someone set out to design a 'subjectively fast' amp? Is it just a crap shoot? Technically, what descriptors must an amp possess in order to facilitate subjective speed? Isn't this the goal? I do recognize those here with knowledge and pay attention to their conversations. But it's you and Ralph who seem to stand out among the others for me. |
If things are going well you will not hear 'speed' in an amplifier. If you do seem to recognize such based simply on highs and transient response, IMO/IME that is likely due to a coloration and not anything else (and often caused by trace amounts of higher ordered harmonic distortion). Real speed is evident if the soundstage is deep and wide but not unnaturally so (this is because with speed comes correct phase response); the amp will be relaxed at high frequencies but obviously able to play them with a black background. I hesitate to say any more as so many other factors are involved/so many variables can exist... |
To me, "Speed" seems more of a real issue with various transducers than with amplifiers. |
"02-19-15: Csontos But there's another question that hasn't come up and that's 'how much of an influence does a pre amp have in perceived speed'?" Actually, I did bring that up. lol. All components in the system have an effect on a systems "speed". A good example is Naim because they are associated with the whole PRAT issue. I spoke to them and asked them about this and they suggested that I start off with a preamp if I really wanted to see what the Naim sound was all about. Ultimately, Naim wasn't for me, but its a good example of how other components effect a systems speed. When I said in my other post my MF integrated had a sound that was kind of like a "gimmick", for lack of a better term, there was just too much attack. It definitely had the speed that is a big part of the PRAT sound, but the sound fell short because there was no foundation to the music. For a more complete sound, and not necessarily just speed on the attack, but tempered with resonance and decay, some good examples would be my old ARC VT-100 and Quicksilver V-4's for tubes, and for SS, Ayre is the best I've heard in this respect. With these products, they components sense of speed is balanced with other qualities that give a more complete sound. |
02-19-15: CsontosThanks for the nice words in your post, Peter. I'm not sure how to answer your question, though. Consistent with Ralph's comment, there are simply too many variables that can be expected to be involved to be able to formulate a meaningful general purpose answer. It stands to reason that wide bandwidth and fast risetime and slew rate will tend to be helpful, but only indirectly if at all once they get above a certain point (for example, the 200 kHz bandwidth figure I cited earlier, corresponding to 10x the nominal upper limit of audibility). As with most sonic characteristics of audio components, I would expect accurate reproduction of those sonic attributes which contribute to a realistic perception of "speed" to be more than anything else a function of the knowledge, experience, and thoroughness of the particular designer, and of his or her priorities in addressing the innumerable tradeoffs that enter into any design. Best regards, -- Al |
I am absolutely amazed to find this out Al. So it's more or less a matter of alchemy? Like an unguarded secret by someone successful in coming up with the right recipe but in the end not being able to put their finger on just what makes or breaks the design. So a great mind with knowledge and experience still must exercise some trial and error in designing a circuit. Like art. I've heard it said you're not an artist til someone else says you are. I think there's some merit in that saying. |
Its not alchemy, but a designer does have to know what he is doing and it is the mark of a good engineer to know what is 'negligible' and what is not. Beyond the alchemy part of your post, it is pretty much correct. Even a talented engineer will fall well short of possibility if he or she does not remain a student of the practice (or 'art'), especially that of the specific product and its goals. There is always something new to learn- I find that engineering/technical types that make the assumption that we know everything there is to know about audio are the same ones that have terrible stereos. You have to have an open mind and in particular, be open to the fact that you don't know everything!! |
I get that Ralph. But even the alchemists were careful not to make the same mistake after an explosion. I don't know why I thought it was basically cut and dried. I don't have two amps that sound the same, even among identical examples. I guess I just think it should be entirely straight forward as to how to achieve a pre-conceived sonic result. I thought the differences are borne entirely of preference and not ability. IOW, lots of designers need conceptual adjustment. I suppose it's yes and no/know. |
^^ that has been my experience. The ear/brain system is the final arbiter and not enough is known about how we perceive sound to be able to go off of bench specs (which rarely have anything to do with human perceptual rules) to create a good design. Those who rely entirely on a goal of good bench specs tend to make lousy sounding equipment. |
I'm with you Atmasphere. Soundstage is a far 'deeper'effect of speed. Even with just the Spectral gear I use (supposedly 'fast') I've had an education on speed with experimentation of AC isolation and conditioning. The cleaner the signal the faster my equipment sounds. My experience is the faster the end signal the better the clarity of the different instruments and their place in the mix. "Speed" provides a deeper experience of the 'timbre' and 'nuance'of the instruments and the sense of air around them, delicacy in spite of a complex orchestral piece. For smaller combos speed provides a greatly enhanced appreciation of the genius of the players. Without "speed" these emotionally exciting cues simply don't have time to be created. Speed is far more than that immediate crash of the cymbals; and it gives me a deeper pleasure in all types of music. Slow is simply far less involving. |
"02-24-15: Atmasphere We've had a polarity switch on our preamps since 1989. Its only audible if the recording uses a minimalist microphone technique, like two mics to record everything." It took me years to finally hear that. Everyone always said that it was a bass issue, but to me, it sounds like a slight timing issue. " Does anyone out there appreciate appropriate polarity for the recording?" Its kind of hard to when the recording engineers don't. Its about a 50/50 split. |
Well Atmasphere I think it's good you at least have the polarity switch for those of us who have systems refined enough to be desirous of the correct polarity for "every single orchestral piece" we sit down to enjoy (I say we assuming there are many others like me : ) . Same for our Jazz or even solo flute or violin recordings. How about solo guitar, anyone? I remember being bothered years ago by Jazz recordings by CTI recordings. Different instruments having different polarity. Only years later did I discover this was done purposely ; maybe something to do with the "big" 'wall of sound' popular with the people with crappy equipment and white metal zip cord of about 20 gauge for speaker wire. :( And yes i think it also isn't too important for those listening through iPhones either; just like the majority of old cassette decks. Oh dear. Thank goodness SPECTRAL and MIT, EQUITECH and SOUND APPLICATION gear is there for those of us who don't want to listen to "fuzz". This reminds me that now I'm retired I should go into "Consulting" ; setting up systems so the owners will be properly thrilled by their good quality equipment - from wall plugs to speaker placement and damping to seating positions. Heck I understand the average lack of sensitivity to these items. It's true that most won't hear - and won't care - ( until maybe it's pointed out to them). I have gone into a number of shops selling high end gear only to have to point out they have the channels reversed - and I think it's because countless "sound advisors" have never been to a live orchestral concert in a decent hall. Polarity comes up next when they or I put on a solo piano, played and recorded beautifully, only to have it sound like the artist is playing with gloves on. Yuck. I have always appreciated my dearly beloved hi-fi enthusiast HARRY PEARSON who had the ears and sensitivity that a good system "properly set up" should come close to achieving the sound of real instruments in real space. My hat remains doffed to his lofty goal. |
ZD, I appreciated a post you made about I/C's or speaker cables and mentioned that if one can't hear a difference they shouldn't claim there IS no difference - only state "they" don't hear a difference. Correct polarity and absolute phase are the same. However, the whole system has to be refined enough-- and set-up well enough - for one to be able to clearly notice the difference. |
I also believe most natural instrument music lovers will learn to appreciate the difference very easily when they have some coaching by a knowledgeable person who is not simply interested in selling a piece of equipment. Maybe there is an opportunity for me to establish a consulting service for those who really want their system properly set up-- not sell gear? Now I'm single and son is grown and on his own consulting and travelling may be quite enjoyable. Hmm. Any thoughts? Ideas? Would that service be of value to anyone? |
Regarding absolute phase/polarity, I would make two points: 1)It should be kept in mind that if a preamp provides a polarity switch, when the setting of that switch is changed not only is the polarity of the signal being inverted, but the circuit configuration that is being used within the preamp is being changed. In the case of a preamp having a balanced internal signal path, such as Ralph's designs, I would expect that to not be of much if any significance from a sonic standpoint, since the polarity change can be implemented in balanced designs by simply interchanging signal connections somewhere in the signal path. However in the case of preamps having an unbalanced internal signal path, I wouldn't rule out the possibility that the preamp's sonics could change noticeably when the setting of that switch is changed. Perhaps more noticeably than the resulting "correction" of the polarity of the recording. 2)I disagree with the notion of a 50/50 split, because I believe that for most recordings neither setting can be thought of as being correct. My suspicion is that on 90+ percent of recordings the whole concept of maintaining absolute phase or polarity is meaningless. The great majority of pop recordings, and the majority of classical recordings as well, are captured with a multitude of microphones (dozens in the case of many orchestral recordings), and then the signals from all of those mics are processed through elaborate multi-track consoles where they are mixed, equalized, compressed, limited, and subject to who knows what additional effects. The end result, when it comes to absolute phase or polarity, is inevitably in those cases a random hodge-podge of different sounds with different phases. So if one setting of the polarity switch on a preamp sounds better than the other on a particular recording it figures to be more likely the result of random synergy and subjective preference than the result of the system preserving the "polarity" of the recording. I therefore agree with Ralph that the benefit of a well implemented polarity changing function in a preamp will primarily be to the unfortunately very small percentage of recordings that are engineered using minimal/purist mic techniques, and that are engineered with minimal post-processing. But then again, those tend to be the kind of sonically high quality recordings that many audiophiles (including me) particularly seek out. Regards, -- Al |
"2)I disagree with the notion of a 50/50 split, because I believe that for most recordings neither setting can be thought of as being correct." Just to clarify that, the 50/50 split seems to be the established mainstream opinion. Personally, I can't verify it, and think of as a rule of thumb that most people seem to go by. "02-24-15: Ptss I also believe most natural instrument music lovers will learn to appreciate the difference very easily when they have some coaching by a knowledgeable person who is not simply interested in selling a piece of equipment." We may not be talking about the same thing. The polarity inversion that I'm referring to is a very subtle difference. So subtle in fact, that even though I could hear something happening when I invert phase, I couldn't even decide what position sounded better. Only in the last few years, and with a very detailed system that has excellent overall timing, can I reliably hear differences. But the difference is still fairly small. Just to add one small thing to the discussion, most good CD players and digital separates also have a phase invert switch. So if your preamp doesn't have that feature, your digital source may. |
Almarg. I feel I should have stated my comments applied to Spectral Audio gear as that is what I researched, bought and continue to own and follow. Their website will clarify their designs. Regarding subtlety, I certainly acknowledge that the more refined your system the clearer the difference exhibits. If your system is not well set up you won't hear or care about polarity, just like if you were listening with ear muffs on : - ) |
