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Post by RightinLA on Feb 19, 2014 10:15:14 GMT -5
It's funny I'm singing the graces of audio transformers and sorta slighting Mcintosh considering their amplifier designs! LOL I was listening to some music using my MA6900 and got a chuckle from that. Yes, this is quite ironic, but the autotransformers are used for entirely different purposes. By the way, we all need autotransformers. All the transmission power system transformers are autotransformers. Without them we would have no power for our equipment.
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KeithL
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Post by KeithL on Feb 19, 2014 12:28:59 GMT -5
His explanation is quite... reasonable... and, no, I don't see anything in there that I would say isn't entirely true. But, as with any good product marketing, he does manage to "accentuate the positive", and to switch back and forth between the theoretical and the practical as it suits him. Transformers are a VERY complicated subject, and there's no way to discuss them in detail without resorting to a lot of engineering jargon (and no way to understand that without some engineering background). He starts out (early on) by saying that "most people think they sound better".... hmmmm.... Now, let's assume that even a halfway decent resistor has distortion and noise that are so low they're difficult to measure. Accepting this as a given, then how can some other form of volume control sound "better"? In what way can it alter the signal less than the low noise and distortion of a resistor? And would that difference be audible if it did? Remember that "openness" and "naturalness" are made up human constructs. You can't measure "openness"; it is either some combination of actual factors (which you could measure if you knew what they are) or it is strictly in your imagination. If you want to credibly claim that this works "better" than a plain old resistor, then you'd better be able to point to something that the resistor is doing wrong. (Of course, resistor-based PASSIVE preamps have drawbacks as well, which is why most people use ACTIVE preamps.) Now let's move on to his (admittedly) "simplified" model of source and destination impedance. The theory (and the reality) is that, if both the source and the destination are pure resistors, and the transformer is "perfect", then the source will see a purely resisitive equivalent of the load multiplied by a constant (determined by the winding ratio of the transformer). However, nothing is perfect, so the transformer includes stray capacitance and inductance, as well as resistance, and the interconnect cables introduce capacitance as part of the source and of the load. The result is that you get resonance peaks (determined by how the inductance and capacitance of the transformer and the load interact). Read any thorough review - WITH MEASUREMENTS - of any autoformer-based passive attenuator. You will see frequency response anomalies; including usually one or more big peaks in frequency response in the ultrasonic range - which do affect the upper audible frequencies to some degree - and which varies depending on the exact load and source you use. You will usually find that, because of this, the frequency response varies by quite a bit depending on where the knob is set, and depending on what source and destination you connect to it. (Now, I'm not saying that these effects will be deal-breakers, but they are a serious down-side of transformers.) Of course, he does "admit" that the impedance "seen" by the source will vary depending on the setting - which is something that would normally be considered bad. (Most powered preamps have a fixed input impedance because they involve some sort of buffering. Without that, depending on your source component, you may find that your frequency response and other characteristics change audibly as you turn that autoformer volume control up and down.) And my final gripe is his resorting to the concept that a transformer is more "efficient" than a potentiometer because the potentiometer "turns a lot of the signal into heat". In that case, the reality is that he's entirely.... correct . However, with line level signals, it simply doesn't matter. (Some microphones, and some phono cartridges, put out such tiny amounts of signal that "discarding" any of it may result in degraded noise performance. In 'the old days" this was significant, which is one reason why most older pro equipment used "matching transformers". This is why some MC preamps and microphone preamps use transformers - still; and, if you're going into a tube input stage, whose input impedance is ridiculously high, then the "free voltage gain" you get from an input transformer may well justify the drawbacks.) However, modern solid state components have become so quiet that this is rarely a concern any more, which is why you don't see too many input transformers any more. The old idea of "matching source and destination impedance for best power transfer" hasn't been an important consideration for years. Please note that I'm not at all saying that an autoformer volume control won't work; in fact, it may work well... but there are both benefits and drawbacks. The obvious benefit is that an autoformer shouldn't introduce any thermal noise (no noise due to the operation of active components - because there are none, and very little noise due to current flowing through resistance since the resistance of the windings should be quite low). It also won't produce any of the distortions you often see with active circuits; although it trades them for other distortions due to non-linearities in the magnetic transfer "process" (there are whole books filled with the details of what can go wrong with transformers and how to work around it). The drawbacks, however, include: an impedance that changes with setting; distortion due to the transformer (saturation effects, etc); frequency response anomalies due to interactions between the transformer and the impedance of the source, load, and cables; frequency response anomalies due to the design of the transformer itself; possible magnetic noise pickup (hum) - depending on how well it is shielded and what hum fields are in the area; and, finally, those nice big steps you're stuck with since each volume control "tap" requires an extra wire (and connection) inside the transformer. (Because of all this, his great distortion spec - with no source or destination impedances specified, is largely meaningless... since we have no idea under what conditions it was measured, and we DO know that it will be different depending on what you have connected to it.) I checked out the forum link - and I do see some interesting (and scholarly) discussions there about transformer design..... but I also saw some stuff about interconnects with gold and silver conductors, and even winding transformers with silver conductors.... Unfortunately, I was unable to read into the ones about the rare metals.... sadly my astrologer is locked in a life and death struggle with a local witch doctor (luckily, confined to the spiritual plain), so I am currently unable to seek professional advice about whether this is a good week for me to look into rare-earth interconnects and transformers. I'm afraid that, after reading a few posts about how different metals "sound" in the laminations, I start reaching for my old Aleister Crowley mystical book collection. (Yes, different lamination materials will result in different magnetic properties, which may well in turn lead to different frequency response and saturation characteristics, which may in turn lead to audible differences - but it's far more complicated and less direct that "nickel laminations sound bright and silver wire sounds clear". That sort of thinking is basically a way of simplifying something that is not at all simple so it seems easier to "understand" - except, of course, the results aren't actually valid - for the obvious reasons.) Really, though, there was a lot of good information about transformer design for those who are willing and able to understand it... Before I bow out of this discussion, though, I will say that (other than cost), IF YOU INSIST ON A PASSIVE VOLUME CONTROL, an autoformer does indeed have several advantages over a purely potentiometer-based passive volume control. (Although I have no idea how this particular one compares to the others available, it at least seems to be well designed. However, I think I'd look for a review, with measurements, before considering buying one.) Personally, however, I find that the benefits of an active volume control (aka "a preamp") so far outweigh any type of passive that it's not much of a contest. OK, I'll bite, how do you make a volume control with no resistors? Actually, I see that Tap-X uses autoformers (that would be the way) - and they also make some pretty impressive claims for them.... Now, I do kind of wonder under what conditions they measured those impressive specs; since it does sort of matter. (We all know that the frequency response and THD of a transformer will vary wildly depending on the source and load impedance, right? In fact, and even though they claim the contrary, the capacitance of the cable will make a significant difference as well - and that will vary with cable length. In fact, in general, transformers introduce a lot more coloration to the sound than resistors. I would love to hear how they managed to avoid all the normal issues and pitfalls associated with putting audio signals through transformers.) Q - What is an autoformer? A - An autoformer (short for autotransformer) is a special type of transformer with an especially simple winding arraignment. The simplicity means that it can't be substituted for an ordinary transformer in most applications, but when it can be used the result is a device with higher performance. To be more specific, an ordinary transformer has separate primary (input) and secondary (output) windings, while an autoformer shares some part of the winding between the two. Note that the ordinary transformer provides DC isolation between the input and output windings. In many applications this is an important feature. However, when DC isolation is not required then an autoformer will often outperform an ordinary transformer. This is because virtually all electronic devices exhibit some imperfections; they are not ideal. But compared to an ordinary transformer, an autoformer can often be made with fewer (or smaller) imperfections. The behavior of an autoformer is often closer to ideal. You might have noticed that the autoformer is a simple three-terminal device with a common ground. This makes it a direct replacement for resistive voltage dividers like potentiometers or stepped attenuators. Q - Why use an autoformer volume control? I've been happy with a good quality potentiometer. A - The simple answer is that most people find that the autoformer volume control sounds significantly better than even the best potentiometer or stepped attenuator. And it's not a subtle difference; most people report that the autoformer has such an open, effortless sound that they would not consider going back to a resistive device. Exactly why they sound better is still under debate, but one theory is that it's because an autoformer doesn't attenuate by wasting energy. A fairly good analogy can be made to the transmission in a car. If you need to drive at a slow steady speed which method would you choose: (1) leave the transmission in high gear and apply the brakes to keep from going too fast, or (2) downshift into a lower gear that will allow the car to go the desired speed with minimum effort? An autoformer is essentially an electronic gearbox that operates without wasting significant energy. Potentiometers and stepped attenuators adjust the signal level by literally turning the excess signal into heat. On the other hand, when an autoformer is adjusted for low volume level it actually makes things easier for the source, much like a low gear makes things easy for your car engine. It becomes quickly apparent that the reflective load can be ignored in this case since it is many multiples of the inductance in parallel with it. Inductance gives you a impedance = 2*pi*Frequncy*L(inductance) or Z=2piFL. Its this simple formula that tells you what you need to know about the impedance presented ot the source. Q - What is the impedance presented to the source? A - It is the reflected load in parallel with the inductive reactance of the autoformer. When set for no attenuation, the reflected load is simply whatever follows the volume control in the signal chain. However, that load is cut in half (resistance is doubled) for every 3dB of attenuation. At -20dB the reflected load is reduced by a factor of 100. At -40dB it is reduced by a factor of 10,000 which is 10,000 times the resistance! The simplified approach is to determine the desired load taking into consideration the lowest frequency of interest and doing a few simple calculations. For example: If your source is a CD player with a 50 ohm Z-out and you want to adhere to the 1:10 ratio of source to load many suggest all you need ot do is pick a suitable low frequency (often 20hz) and plug the numbers into the Z=2piFL formula to get, 500=2*pi*20*L. Solving for L gives you a required 4hy inductance to provide a 500 ohm load to a 50 ohm source. Our Autoformers come shipped with a butt gap which provides approximately 20hy's of inductance. If your situation requires more inductance it is quite simple to restack the lams to get inductance values up to 170hy's. Q - What if I don't want to stack the lams? A - They come stacked with a butt-joint , but stacking a core is not a difficult job and takes only a few minutes. I find this interesting... Q - Aren't 3db steps rather coarse? A - For some reason (that we don't understand) 3dB steps on a magnetic attenuator seem finer than the same size steps on a resistive device. In any case, few people find this configuration adequate. Here is the page. www.intactaudio.com/atten_FAQ.htmlHe wants a lot of money for those little transformers for certain but the design/manufacture is very tight. Basically he wants 200 bones to to wind you one.
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KeithL
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Post by KeithL on Feb 19, 2014 14:38:21 GMT -5
I'd have to say that the nicest preamp I ever heard... well... I didn't hear it... because a preamp is supposed to have no sound whatsoever (a "straight wire with gain"). This does make testing easy; just set the gain to 1, and switch it in and out; if you hear ANY difference, then there's something wrong. This is why I always have trouble with people who spend endless hours comparing the way components sound. To me, it's pretty simply. If three components sound different, then there are two logical possibilities: either one of the three is right, or they're all wrong. (Since there is only one possible "entirely right", it is logically impossible for two to sound different, yet both be right. Now, in most cases, since there is no perfect, the fact is indeed that all three are wrong, and so you're stuck trying to minimize the flaws, which is often a matter of personal preference). The thing that specifically worries me about that autoformer preamp is that it may sound very different depending on what you connect it to. Other than the fact that this violates one of what I consider to be a major theoretical tenet of good design (that something that really works well does so without being overly sensitive to what you connect it to), it means that neither you nor I can count on its sounding the way we expect in OUR systems (and the fact that it sounds good in your system in no way suggests that it will sound good in mine, or vice versa - even assuming we use exactly the same judgment criteria.) My interpretation of what the DDDAC folks said about the Sowter output transformer is as follows: Obviously, since adding the transformer improved something, there was something wrong to begin with. Since we have now proven that there was a flaw that needed fixing, I wonder what that flaw actually is, what options there are for fixing it, and which is the best one. For example, if their conjecture that the transformer "sounded better" because it lowered the output impedance is correct, and we assume that the flaw with the original design is an excessively high output impedance, then we have several options for fixing it.... and at least one of them is technically superior - and a lot cheaper (a simple buffer). Another (Still cheaper) option would be to use a larger coupling capacitor. And, if the transformer fixes this problem, but introduces a frequency response anomaly, or more distortion, then we've spent extra money to fix one problem - and create another. Such is the trap of trying things with no clear goal in mind. Unfortunately, without that goal, I'm left to wonder if the transformer actually improved the performance at all (objectively), or if it simply added some distortion that several people found pleasing. or, for that matter, if it created some anomaly that happened to cancel out some anomaly in the "reference system" they were using, and so produced an improvement that wouldn't be "valid" with any other combination of components. (Since big horns, powered by small tube amplifiers, obviously have some pretty serious coloration, I'm not really sure what they heard, or why, or how much of it gets credited to the DAC. For most engineering-based analyses, absolute neutrality is the first and main requirement for a "reference system" of any sort.) If I was being cynical, I would suggest that they avoided using a good solid-state active I/V stage (which is recommended as optimum on every DAC chip manufacturer's data sheet I've ever seen) for no good reason - and that such an I/V stage would have had an admirably low output impedance.... and, as such, they "stuck with" a technically inferior passive I/V stage - because they were convinced it "sounds better", and then were forced to resort to extra design to correct the flaws that resulted from this decision. Personally, if I had built their DAC, and was at this "point" in the process, I would like to see if eliminating the transformer, and then replacing the passive I/V stage with a more traditional active one, might achieve the same performance - and sound quality - a lot more easily and cheaply.) (I'm also not sold on their choice of an input converter - which, since it has a major effect on the jitter of the signal being decoded by the DAC, could have a major influence on sound...) LEST YOU THINK THAT I'M PICKING ON THESE GUYS... I should take the opportunity at this point to say that their entire project was well thought out, well documented, and beautifully presented. The website presents all the facts as they are known, details the entire design and construction aspects of it, and is in fact one of the best DIY projects I have ever seen. And, if you like DIY, and want to experiment with different DAC topologies and component options, I would highly recommend it. (It's just that, as an engineer, if you're looking for the most direct way to get yourself the most accurate DAC you possibly can, I'm not convinced theirs is the shortest path to this goal.) OK, I'll bite, how do you make a volume control with no resistors? Actually, I see that Tap-X uses autoformers (that would be the way) - and they also make some pretty impressive claims for them.... Now, I do kind of wonder under what conditions they measured those impressive specs; since it does sort of matter. (We all know that the frequency response and THD of a transformer will vary wildly depending on the source and load impedance, right? In fact, and even though they claim the contrary, the capacitance of the cable will make a significant difference as well - and that will vary with cable length. In fact, in general, transformers introduce a lot more coloration to the sound than resistors. I would love to hear how they managed to avoid all the normal issues and pitfalls associated with putting audio signals through transformers.) LOL I have no idea why it just sounds "better" and yes your input/output impedance matching is critical if working in passive mode. I'm reading this to try and gain better comprehension... www.jensen-transformers.com/an/Audio%20Transformers%20Chapter.pdfIt is the nicest preamp I've heard honestly. I thought Bent did some contract work for Jade/Emo... Why don't you ask him or bring in a unit for testing? Those guys in Europe that built that crazy DAC use a transformer for balanced to single ended conversion from their DAC. www.dddac.com/dddac1794_sound.html Read what they have to say about that Sowter transformer.
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Post by pedrocols on Feb 19, 2014 15:29:35 GMT -5
So in other words....just stick with Emotiva products...
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hemster
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Post by hemster on Feb 19, 2014 15:50:36 GMT -5
So in other words....just stick with Emotiva products... Oh come on.. Where did he say that? I thought his response was detailed with reasoning and insightful if one makes the effort to understand it.
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Post by roadster on Feb 19, 2014 16:07:06 GMT -5
Oh come on.. Where did he say that? I thought his response was detailed with reasoning and insightful if one makes the effort to understand it. +1
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Post by pr1 on Feb 19, 2014 16:40:34 GMT -5
I understand the xps-1 phono stage is only $100 unit.. I normally run a ps audio GCPH but right now i have their new "Nuwave Phono Converter" for a 30 day trial. Before i spent good money on the Mac i would demo one of these units for a couple of reasons.. 1- ensure your setup is working properly... 2- see what you think of a dedicated phono preamp for $1800 vs much more for the Mac.. The other functions of the XPS-1 are totally solid as i would imagine you agree.. the nuwave phono converter has an ADC so you can record your vinyl.. thats what i am doing now and it sounds great minus my TT shortcomings..
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Post by solidstate on Feb 19, 2014 16:50:26 GMT -5
That's the easiest way to right justify 24bits. They could have gone with a more complex way of doing this but who's to say that wouldn't have also increased jitter. Jitter is a concern with the delay logic for certain. As I said prior I'm not an EE designer so I have no idea what other "better" solutions could be made. PS DIYer audio nut EEs have reported better performance from shut regulation mods to each "deck"
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Post by solidstate on Feb 19, 2014 16:56:56 GMT -5
I have heard differences in a loudspeaker system that could not be measured with test equipment...
100% HONEST
Scouts Honor!
Psychoacoustics at work?
I don't know... I try to be as objective as I can be and all audio sessions are blind IE closed eyes/blindfold to prevent McGurk like effects with third party swap.
There is a lot to human audio perception that we do not understand.
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Post by solidstate on Feb 19, 2014 17:01:06 GMT -5
Here is an interesting paper written by one John Curl. John has said a lot of things that I initially thought as BS pseudoscience but that man is willing to TRY alternate design under the criteria that HIS EARS are the most important factor in determining certain design elements not his test equipment. www.q-audio.com/johncurl.pdfI wonder if John isn't actually onto something in that paper.
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Post by solidstate on Feb 19, 2014 17:35:42 GMT -5
Let us all remember due to "interaural time dely" and double arrivals we are not hearing a natural sound are we from any two channel system. There is also the concern, though discarded years ago, that "doppler distortion" could have a perceived psychoacoustic element.
Bob discusses interaural time delay issues with stereo system during an interview done with TWiT. Remember you will receive FOUR ARRIVALS from a sound coming from two speakers from loudspeaker ear crosstalk. Have any of you heard a Carver C4000 Control Console with it's pre-subtract filter?
THIS IS A FANTASTIC INTERVIEW!
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Post by lionear on Feb 23, 2014 16:23:04 GMT -5
Here is an interesting paper written by one John Curl. John has said a lot of things that I initially thought as BS pseudoscience but that man is willing to TRY alternate design under the criteria that HIS EARS are the most important factor in determining certain design elements not his test equipment. www.q-audio.com/johncurl.pdfI wonder if John isn't actually onto something in that paper. This is an amazing document. I read the whole thing - there's a lot that is beyond my head, but there are some amazing insights in plain English, too. The biggest lesson I take from it is "trust your ears". If something doesn't sound right, then keep searching for a solution or a replacement. We don't need to know the reason why we don't like it. I had no idea that PNP transistors are "better" than NPN transistors - but then I don't have to. I just have to trust my ears.
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Post by Deleted on Feb 23, 2014 17:10:09 GMT -5
Here is an interesting paper written by one John Curl. John has said a lot of things that I initially thought as BS pseudoscience but that man is willing to TRY alternate design under the criteria that HIS EARS are the most important factor in determining certain design elements not his test equipment. www.q-audio.com/johncurl.pdfI wonder if John isn't actually onto something in that paper. This is an amazing document. I read the whole thing - there's a lot that is beyond my head, but there are some amazing insights in plain English, too. The biggest lesson I take from it is "trust your ears". If something doesn't sound right, then keep searching for a solution or a replacement. We don't need to know the reason why we don't like it. I had no idea that PNP transistors are "better" than NPN transistors - but then I don't have to. I just have to trust my ears. Agreed 100%. I ran across that paper about a few years back and read with great interest. Well written, and excellent advice. Thanks for posting that.
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Post by solidstate on Jul 10, 2014 20:26:17 GMT -5
OK, I'll bite, how do you make a volume control with no resistors? Actually, I see that Tap-X uses autoformers (that would be the way) - and they also make some pretty impressive claims for them.... Now, I do kind of wonder under what conditions they measured those impressive specs; since it does sort of matter. (We all know that the frequency response and THD of a transformer will vary wildly depending on the source and load impedance, right? In fact, and even though they claim the contrary, the capacitance of the cable will make a significant difference as well - and that will vary with cable length. In fact, in general, transformers introduce a lot more coloration to the sound than resistors. I would love to hear how they managed to avoid all the normal issues and pitfalls associated with putting audio signals through transformers.) And that TAP-X kit BESTS ALL OF THEM.100% transparent with the best volume solution possible IE no resistors. It can be built as a balanced or single ended unit with the balanced unit costing almost twice the amount for obvious reasons. Some more interesting reads on transformers and audio electronics design that might interest you and Emo/Jade. soundstage.com/maxdb/maxdb071998.htm
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Post by Boomzilla on Jul 10, 2014 20:41:46 GMT -5
IMHO McIntosh makes EXCELLENT sounding preamplifiers. Before buying one, though, I'd also audition Audio Research. Just my two cents...
Boomzilla
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Post by Boomzilla on Jul 10, 2014 20:46:03 GMT -5
...This is why I always have trouble with people who spend endless hours comparing the way components sound. To me, it's pretty simply. If three components sound different, then there are two logical possibilities: either one of the three is right, or they're all wrong. (Since there is only one possible "entirely right", it is logically impossible for two to sound different, yet both be right. Now, in most cases, since there is no perfect, the fact is indeed that all three are wrong, and so you're stuck trying to minimize the flaws, which is often a matter of personal preference). Amen, brother Keith. The preamp that sounds the most like real, live music is the accurate one. Of course, NO preamp sounds exactly like that. Therefore, minimizing the flaws (aka choosing the one that sounds best to you) is the name of the game.
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Post by Deleted on Jul 10, 2014 21:53:32 GMT -5
This is a great interview. I have heard sonic holography and it really sounds good. I am wondering why other manufacturers have not created or made this available to two channel systems. With REW and Dirac you can EQ and even deal with impulse response but it will still not deal with four sound arrivals vs. two. I also found it interesting to heard Bob talk about hoe a tube amp in effect "listens" to the room. If anyone is going to know about the merits of solid state versus tub it will be Bob Carver because he has designed great examples of both and examples of ss to mimic tube. Let us all remember due to "interaural time dely" and double arrivals we are not hearing a natural sound are we from any two channel system. There is also the concern, though discarded years ago, that "doppler distortion" could have a perceived psychoacoustic element. Bob discusses interaural time delay issues with stereo system during an interview done with TWiT. Remember you will receive FOUR ARRIVALS from a sound coming from two speakers from loudspeaker ear crosstalk. Have any of you heard a Carver C4000 Control Console with it's pre-subtract filter? THIS IS A FANTASTIC INTERVIEW!
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