Speaking of femto-distortion (TM) what ever happened to Halcro? Wasn't the exceedingly small amount of distortion and noise their trademark? Here one moment, gone the next.
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It looks like that we are deemed to hear distortion from the day we are born. And that the audio engineers try to make the the pain easier, i.e., the distortion in audio reproduction a most pleasing possible. The impressionists also faced a similar situation and have decided to represent
explicitly the "reality" with a distortion, that turned out to be a very nice idea. It seems that the audio engineers are on the same way, not so bad. Nevertheless, let me mention that i do distinguish and highly appreciate audio reproduction with "a little" distortion (0.001-0.005 is perhaps an acceptable range). Two class D Cherry amplifiers that i use now (a small integrated Maraschino and a larger Megamaraschino) do reproduce with little distortion, clear and detailed as far as i can see. I wonder if they give just one or several harmonic orders(???), i.e., whether it is a well-masked sound with the distortion (impressionists vs realists question; ironically i like more impressionists in painting - perhaps, that is why i spent the most of my time in the past auditioning tube amps). |
Two class D Cherry amplifiers that i use now (a small integrated Maraschino and a larger Megamaraschino) do reproduce with little distortion, clear and detailed as far as i can see.Class D might be the one way out of this. The issue is something called 'gain bandwidth product' and has to do with how much gain you have combined with bandwidth. That's easy enough to understand; where it gets tricky is when you apply feedback. If the bandwidth is limited, you can't apply much feedback because the amplifier will have phase shift at its bandwidth limits and this phase shift can result in the negative feedback becoming positive if something isn't done to limit it. But the problem is that the application of feedback introduces distortions of its own. An amplifier with good linearity prior to feedback, and having a fairly benign distortion signature (meaning a predominant 2nd or 3rd with not much above that) will have many more harmonics and intermodulations (which form at the feedback point), while doing a pretty good job of suppressing the lower orders. Since the ear converts all distortions into tonality, the addition of the higher orders and the IMD makes the amp sound brighter and harder. To get rid of this issue, you have to have enough feedback so that the feedback is able to compensate for the distortions it adds. Generally speaking this value is in excess of 35dB; if the amp has less the feedback has detrimental effects although it might look 'good' on paper. (This is why feedback has a bad reputation and why there are a good number of products that use none.) So to get 30dB of gain out of the amp, you need 75dB as a minimum if the amp is operated open loop (no feedback). That's a lot! That's why gain bandwidth product becomes a useful phrase because getting the gain and the bandwidth at the same time gets tricky to say the least. Now a class D amp can get around this problem through a fairly simple mechanism called self-oscillation. The idea here is to add so much feedback that the phase margin of the amp (where negative feedback becomes positive due to phase shift as I mentioned earlier) causes the amp to go into oscillation. You simply use that oscillation as the switching frequency. Class D amps make gain through the comparison of the switching waveform (usually a triangle wave; its fairly easy to convert a squarewave to triangle, so with a small bit of circuitry we use the switching of the amp itself for this) to the input waveform. So all you have to do is set the ratio between the two to set the gain, and then run as much feedback as you need. This can result in extremely low distortion and no phase shift, even if the output filter frequency is set fairly low. Time will tell if this proves out to be a viable path. |
@atmasphere , thanks for your comments. I am too far from understanding all this technical background, but am learning some new things. I would not ask you many questions, but please forgive me if my understanding of these things is too far from the reality and my questions are stupid. Feedback is not the only way amps can give the gane? Somehow class d amps use double feedback to get to the switching waveform to transform analog sound to digital one? But how digital amps transform that digital sound back to analog (do they have some integrated DACs)? |
Feedback is not the only way amps can give the gane?You have to have gain to be able to apply feedback to an amplifier design. The feedback kills some of that gain and how much is measured in dB (decibels). But you still need gain for the amp to amplify the signal, so overall the circuit needs enough gain for that and the feedback. Class D amps are analog, not digital. There is confusion because of the 'D'; it does not stand for 'digital'. Class A, B, and C were already taken when the idea was proposed in the 1950s. |
tried to listen to a pass amp at last AXPONA. unfortunately their display was static and visual only. most unusual at an audio show and highly disappointing. i see a lot of them listed for sale, dis-proportionately so. compared to the bigger players i have heard incl. jadis, parasound halo, mac ss and tube, esoteric, luxman a and ab, rega, hegel, line magnetic, primaluna, marantz, yamaha, bat, raven audio, cary ss and tube, manley, nad and more the only one i would take over my rogue audio integrated and seperates would be esoteric. |
Feedback is not the only way amps can give the gane? It's "gain" as in "to add or receive." And feedback in linear amplifiers actually reduces gain. You can learn some of this with op amp text books. Somehow class d amps use double feedback to get to the switching waveform to transform analog sound to digital one? I'm not aware of double feedback loops, but I am aware of multiple types of feedback being used with different Class D designs. As Ralph (atma) mentions, it's not digital, but the feedback controls the switching. To be a truly digital amp the signal at least has to go through an analog to digital conversion, which doesn't really happen in Class D. The control of the on/off switching is in the analog domain and that's where the feedback is used. The latest Technics Class D amps may in fact be considered digital, as there is an analog to digital conversion at the input, as well as DSP applied for impedance compensation. These types of amps are quite rare. Many, including Ralph, argue that since the output is analog no audio amplifier can be digital. I side with Technics though, it's sufficiently digital to be called a digital amplifier. |
I don’t really know or care much for specs. Voicing of any component is, to me, most important. For a designer to be a musician is not necessarily prerequisite but it helps. Vital is that the designer not only needs to understand what music sounds like but is able to voice their “instruments” reflecting that knowledge. Then, ultimately, an amp/speaker combination needs to reflect the taste of the listener. Obviously, an amp can only be evaluated when powering a speaker-the “two hands clapping” in any system. |
It is then an interdisciplinary thing, very desirable but perhaps it rarely happens an engineer to be a musician, but it will help if he is an audio fan. Eric, i thought feedback was something to create the gain. I am too far from this field, but will try to have a look on some books (e.g. why the feedback is unavoidable). Could something similar to switching waveform be used to create a correct and accurate digital signal from the source analog signal and "amply it digitally" without any distortion? Is there no way to amplify a digital signal directly from the digital sources (e.g., CD player), what this would really mean? Then you will again need a DAC just to output the amplified digital signal to the speakers (but i understand that "amplified digital signal" cannot exist, a binary number cannot be amplified and that that the conventional amplification is analog). I was not aware of Technics class D players which is interesting. Cherry amps are produced by a US company called Digital Amplifier Company (DAC), there should be some reason for this name. |
@riaa. no padded cell here. rogue products are highly rated by stereophile currently class A and anything but garbage. my tube pre amp and tube power amp has that elusive combination of dynamics, high output, huge soundstage, transparency and world class refinement at an affordable price. they are currently unable to keep up with demand and are building a new production facility. |
Nope. That’s Steve Hoffman Forum bottom feeder gear. Stereophile gives great reviews to anybody that advertises with them. If you gave a favorable comparison to say PS Audio then I would say OK....MAYBE. Esoteric isnt known for great amps either....just good Disc Spinners which your in a constant 2 year Upgrade cycle and constantly chasing your tail. Their amps are sterile sounding. Many of the brands you listed are Minor league to say the least. Luxman vs Rogue?? No idea what your talking about. Highly doubtful you’ve ever heard the M900U/C900U Combo....if you did you would leave your Rogue out at the Curb. Your right they DID move. From Swanky Bucks County (VERY Expensive to live) to the middle of freakin NOWHERE in NE PA Pocono Mountain Region where property is dirt cheap. That's progress for ya!! A house up there is 1/4 of what it cost in Bucks and taxes are probably 80% Cheaper. Business must be booming....HAHA Next Stop....West Virginia Coal Miner Country |
Thank you all for delving into the femto distortion/feedback/ gain/switching wave forms/harmonic orders. I fear all this self-oscillation is causing me harmonic disorder. Whether we do or do not go rogue doesn’t matter. I prefer commando. As for static Pass labs displays at Axpona last April, I would like to propose a suggestion for any company who brings equipment across the country to allow visual examination only. Save some money and tape up some fancy photos as that does not frustrate me as much. There must have been a couple rooms using Pass gear at Axpona but I can not recall a year back that well. Let’s all book flights to Schaumburg in August now while ticket prices are still low. I did!!! |
Hey Joeinid, Before you start trashing gear in my collection can you do me the courtesy of waiting until I sell it first?? ESPECIALLY cause you sold it to me in the first place. That would be the considerate thing to do right? LOL I might have to start a rumor about AG Speakers...like if you get the Copper Colored Horn ones and place them too close to a window they can act as a Magnifying glass with the sunlight and burn your house down!! :) Happy Easter Buddy |
As mentioned above, it speaker/amplifier match always matters. Try putting 500 watts and a high damping factor on a high sensitivity full range driver, or an 8 watt SET on a YG acoustics and see what it gets you. Too bad there’s not a database where someone tracked every amp/speaker combination used at the various audio shows. Would be useful to see what combinations people used when working to sell their gear. |
Eric, i thought feedback was something to create the gain. I am too far from this field, but will try to have a look on some books (e.g. why the feedback is unavoidable). You can have gain without feedback. There are class A, AB and D amplifiers that use no feedback. The problem with what you propose in the 2nd paragraph above is that digital audio switches at speeds far too low to be practical to amplify directly, and at some point you do have to create an analog signal to drive your loudspeakers. So what some products do is they accept the digital input and then convert the switching of the digital to a much higher frequency that is practical for a switching power amp. Some amount of DSP is required for this approach. But a switching amplifier itself is an analog process plain and simple. |
Thanks for these notes. Then you need a good DSP unit I guess. Perhaps in future a miracle can happen and digital speakers without any amplification will reproduce the sound. Meanwhile, another related practical question. Conrad Johnson preamplifiers have notably high thd I saw in specs of all the recent models et6 et7 and gat it is 0.15 (I was surprised to see this). I didn't have a chance to audition them but I assume they sound good. Do they (do the higher order harmonics help)? I ask this question also because am considering to try one of these preamplifiers. Thanks |
Then you need a good DSP unit I guess.The DSP is built-in to such amps that have a direct digital input. Conrad Johnson preamplifiers have notably high thd I saw in specs of all the recent models et6 et7 and gat it is 0.15 (I was surprised to see this). I didn't have a chance to audition them but I assume they sound good.There is a huge difference between high THD and higher ordered harmonics! Higher ordered harmonics as distortion is bad and highly audible, but high THD might not be so bad, if the harmonic content is mostly lower orders (2nd, 3rd and 4th) as the ear is far less sensitive to them. |
but high THD might not be so bad, if the harmonic content is mostly lower orders (2nd, 3rd and 4th) as the ear is far less sensitive to them. Can we know, based on specs, whether THD referes to a lower or higher order harmonics? Is there another common parameter that refers to the higher order harmonics? I.e., is then a way to know about the "real" distortion (one we do not like) based on the specs? |
too fuzzy. this is what Jeff Fischel answered on my question on the distortion: "CONRAD-JOHNSON preamps are designed for optimal sonic performance , yet this is not always reflected in the specifications of distortion." well, we know CJ amps and preams sound well,where from comes this high distortion, or can it be good high distortion or CJ amps sound good despite high distortion (or because of that)? i have three alternatives for a preamp for my Cherry Megaschino (now I am using $650 class A SS Nuprime HPA 9 headphone amp/pre which is not really bad, still might be worth to look for a replacement) : Pass Labs XP-12 Conrad Johnson ET6, and Conrad Johnson ET7 all of them have some promo, Pass is a demo unit. Did some of you guys compare XP-12 with a CJ prse, or ET6 with ET7 (ET7 costs double of ET6!)? |
RIAA, please clarify your position; are you simultaneously ridiculing an audio engineering company and two different US geographic regions? Why are you all butt hurt that others might actually enjoy Rogue gear? I sure hope you are just joking; if so please disregard this message; if not, well that’s just pretty sad all around bro. |
response to the earlier post. i was also considering pass xa25 (according to reviews it gives neutral tuby sound) but i think made a correct decision because this amp would not drive well my thiel cs6 speakers. i am very staisfied with megaschino so far. perhaps, the overall performance might further be improved by replacing the nuprime hpa 9 with one of the preamps from my list, though i have no idea of how much it might really be improved. pha 9 is not bad and the cost of the replacement would be very considerable. both, pass labs and conrad johnson recommend to leave their stuff on all the time, which i do not do in my current settings. |
I know this is a little off topic, but is there supposed to be a difference in sound between the XA25 and INT25? I was reading some reviews and they are talking about JFET, Vertical FET, BoboFET, but they don't really explain what it does, or why it's better. For those of you that are quoting text, are you just clicking the " button then copying and pasting the text from their post? Sorry, I'm new and have been reading more than posting. |
That would be these. https://avahifi.com/products/dva-m225-mono-block-solid-state-amplifier They're very good. |
@chorus Thanks for the reply. I was looking at a lot of amps and amp/preamp stacks and at the end I purchased a new First Watt F8, since it's the latest from Nelson Pass and comes with a full warranty. Those monoblocks look awesome, but I just put in an order for a BHK Pre-amp, which seems to have a history of working best with a BHK amp... and by working best, I mean it will have less quirks, noises, issues, etc... A lot of people seem to keep the BHK pre despite these little quirks, so it was a leap of faith, since I will be running it with my F8. Part of the fun is experimenting with new gear, hopefully I won't regret this. I want to try those monoblock amps now! Thanks for the link @twoleftears |
I had the opportunity to audition 7 different high end integrated amps at Suncoast Audio. They included: Naim Supernait 3, Gryphon Diablo 300, Moon/Simaudio 340i, VAC 170i (all tube), Luxman 509x, Hegel H390, and Pass INT 60. Every one of those amps were outstanding and I would have been perfectly satisfied with any of them. However, my ears really liked the Pass INT 60. And, liking the Pass signature sound I went with the INT 250. I was a little afraid at the time that the INT 60 would not have quite enough horsepower. Turns out I was wrong, but I went with the INT 250 anyway. I LOVE it!! I won't take the time to go into all the technical reasons I like Pass Labs products so much. But after almost 2 years with my INT 250 I've become a HUGE Pass Labs fan. The amp has opened up beautifully. Great synergy with my Harbeth Super HL 5+ 40th Anniversary (XD) speakers. I know there are amps out there that may sound as good as Pass amps but I just really like the Pass Labs flavor of sound. And their customer service is second to none. Nothin' not to like and gobs to like. |
I’ll start right up front with saying I’m a huge Pass Labs fan. I chose to purchase a Pass INT 250 after auditioning 6 other integrated amps. The first Pass amp I auditioned was an INT 60. I wasn’t even planning on auditioning any Pass Labs amps at all. But the INT 60 really shocked me with it’s accuracy, fine detail, deep and wide sound stage, clean, clear, and strong bass, crystal mids and top end, and how well balanced it was. Some call it a "chocolate" sounding amp. But at the risk of sounding cliche’-ish, it has such a smoothness yet clarity about it. Very difficult to explain in words. Anyway, I obviously really, really, like both amps. Another reason I like the INT 60 and INT 250 so well I’m sure has to do with it’s synergy with my Harbeth Super HL 5+ 40th Anniversary speakers. They’re perfect for my small-ish (27’ x 16’) listening room. Those speakers and those amps like each other a lot. When I auditioned all 7 amps mentioned above I made sure to use the same speakers I had at home. Another selling point with me was the build quality of Pass Labs components. And, Pass Labs has a rep for some of the best customer service you’ll find anywhere. So, there ya go. That’s why I’m a major league Pass Labs fan. Do I think they’re "better" than anything else out there? Not necessarily. But I think they’re just as good as anything in their price range. There are just so many amps on the market that I’ve never heard. That’s another reason I can’t claim to have "the best" amp. And neither can anyone else, unless they’ve listened to them all. Since we’re talking thousands of amps extremely few, if any, people have done that. Anyway, from a sonic standpoint, it’s not about whether my amp (or any other component) is "better." As usual, it all comes down to preference and the flavor of sound you want, based on YOUR ears. Sorry for the rambling post. |
audiofoundIn what way was the int250 different from the Diablo 300? |
Different strokes...it's all about preferences. I'm a "Passaholic." I love the Pass sound. It's so rich sounding to my ears. Most people feel the same way about their gear. That's OK! It's alright. It really is. Nothing wrong with differing opinions. I happen to also really like Luxman products. But there have been some posts on this forum where the OP didn't care for Luxman. We seem to have difficulty with the concepts of opinion vs fact. I occasionally have had that same problem. Two years ago I booked a flight and made the trip to my favorite audio dealer and auditioned 7 different integrated amps. They were ALL outstanding and I would have been happy with any of them. However, as you might expect my ears liked some more than others. The audition included products from Pass Labs, NAIM, Moon/Simaudio, VAC (tube amp), Hegel, Luxman, and Gryphon. I ended up purchasing a Pass Labs INT 250. I love it and my ears love it. All the other amps sounded superb. But I can virtually guarantee you there are people that prefer something other than the amps I tried. Are all people going to like the INT 250 as much as I do? Of course not. Pass Labs has a pretty lengthy list of very happy owners and fans, so they must be doing something right. You all know all this stuff. We see it daily on the forums. The differing opinions are one of the things that make the forums so much fun. But some people take the differing opinions personally and are actually threatened by opinions different from theirs. Anyway, nothing new here. I've seen it on music forums too. I guess it's part of the nature of forums. It would make a great study...the psychology of forums. Anyone care to take that one on? |
About the F4's distortion, Nelson Pass said ".....the distortion is 2nd and 3rd harmonic in character, rising or declining in linear proportion to the output
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Be that as it probable is, it’s probably more true of Pass’ First Watt than of his Pass Labs amps. In any case, I believe it’s well established that the FW amps are primarily marketed to those with high efficiency speakers; 93db and above, and not falling much below 8 ohms. And while I can’t swear to it, I think that typical distortion levels from at least some of the FW models driving speakers like those are respectably low. However, I've yet to see much in the way of a full set of independent distortion and other measurements done on most FW amps-certainly not on the F4, which I own and plan to use with my new speakers. The one exception I know of was the Stereophile review of the FW J2, where JA did his usual array of tests. IIRC, the J2 did quite well with 8 ohm loads. |