Audioengr ( hi !! ),
What part do you think vswr and impedance mismatches between source, cable and load play when it comes to transferring signals from transport to DAC ? Since we are dealing with an RF based signal, transmission line theories DO directly apply here.
Your statements about low dielectric absorption intrigue me. Shouldn't a cable that has a higher velocity factor be less prone to signal deterioration / absorption due to the signal spending less time in the cable ? If that is correct, than a cable that is "slower", such as those that make use of a teflon dielectric configured in a standard coaxial design, would be a relatively poor performer. If that is the case, cheaper "foam" insulated cables "should" perform appr 13% better than more costly Teflon versions given equivalent conductor materials. Any thoughts or comments on this ? Sean
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Jt, rather than clog up your inbox and have to make several individual replies, how about posting your comments here ? I for one would like to know what you have gotten such good results with, especially since both I and my Brother along with several others here are running EVS DAC's.
Before you comment, you should be aware that there is NO such thing as a 75 ohm RCA connection. This is true regardless of what Canare states. Nor is the nominal impedance of the wiring from the digital input to the circuit board inside the EVS 75 ohms. None the less, you may have stumbled onto something in terms of increased power transfer / minimized loss / reduced standing waves. The last part ( reduced standing waves ) is directly related to a reduction in jitter. Sean
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For sake of clarity, i am not Sean125. I didn't want anyone to confuse my departure with his arrival. Given our different points of view on power cords, it should be obvious that we aren't one and the same. Toodles... Sean
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John: I don't think that you'll find anyone here that would deny that brands / prices / cosmetics may have more influence over what we hear than many of us would like to admit. I try to forget about all of this stuff and just listen. Obviousy, i try to start off with products that are at least well designed to begin with, but one sometimes does not even have that much info to work with when auditioning specific items. Sean
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While it is strictly a matter of semantics, the actual digital out signal from a transport is sent at 2.822 MHz. If one could resonate a cable that introduced a perfect non-reactive 75 ohm load at that frequency, you would end up with no standing waves. Bare in mind that terminating and feedpoint impedances are a LOT more complex than just selecting a 75 ohm cable ( we wish it was that simple ). This would allow the transport to load up easier due to a complete lack of reflections and a clearer signal path to transmit the data, which theoretically should drastically reduce jitter. This takes for granted that the transport and dac would both have nominal 75 ohm inputs & outputs though. This is something that i've been meaning to check into but just haven't gotten around to it. Sean
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Audioengr: Tara worked with terminating impedances years ago. Silver center conductor, Teflon insulation, Silver braided shield, 75 ohm resistor from center to shield at the load end. It is a very nice sounding cable and not bright in the slightest bit.
As far as having to use a resistor(s) to terminate the load, you would not need to do that IF the actual output impedance of the transport is 75 ohms, the cable is 75 ohms and the input of the DAC is 75 ohms. The problem is that none of these are exactly the correct impedance, so you have VSWR at the feedpoint, VSWR within the cable and VSWR at the load. If one could find out the actual output impedance of the transport and the input impedance of the DAC, it would be easy to make up a section of cable that would act as an impedance transformer. This would minimize standing waves / reflections and maximize power transfer. THAT was the point that i was trying to explain. Obviously, you could not market this cable as the specific values would change component by component.
As far as terminating the cable with a resistor at the load end, that would NOT solve an impedance mismatch at the source end. An impedance bump ANYWHERE along the signal / data path will result in reflections back to the source. Sean
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A 10% mismatch ( VSWR of 2.0 ) at RF frequencies ( which digital data is transferred via RF ) can begin to play MAJOR havoc with some circuitry. I know that text-book theory states otherwise, but you have to realize that much of that theory was based on tube circuitry that made use of matchingn networks and tank circuits. Most SS gear does not have this type of circuitry, so loading characteristics become far more critical.
The severity of how much the operation of a device would be affected obviously depends on the stability of the circuitry and whether or not the impedance mismatch was of a reactive or resistive nature. Not only would the sending unit have to deal with the reflections playing games with the output section, signal loss is increased. The resultant decline in detail is increased due to loading via the "back-pressure" within the transmission line. This is not to mention that line loss increases as VSWR increases, compounding the factors involved drastically. As such, ANY type of vswr / signal reflections tend to start a very drastic downward spiral effect once they come into play. This is FAR more apparent with SS gear, but then again, i don't know of any transport or CD player that uses a tubed digital output section.
As such, i would think that all of my experience with RF loading characteristics and impedance mismatches would directly apply to digital data transfer. I would suspect that the output section of most transports / cd players would not be very stable due to lack of a buffer circuit or complex impedance matching network. Therefore, ANY gains in terms of increased power transfer / minimization of reflections would be of multi-fold benefit for the aforementioned reasons. I have not verified this personally, but see no reason why this would differ from any other RF based SS circuit loading up. I really do want to start measuring and experimenting in these areas, but just have not had the time to do so. Sean
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Taxes are not "mandatory", nor are "mismatches" and "reflections". The more that one becomes familiar with and "works" the system, the less of each they may have to deal with. If one is really good and / or dedicated, it is possible to reduce any of the above to a point of negligence. Just because they are there does not mean that they should be "accepted".
Such is the case for signal reflection and vswr within a system. Why settle for 90% efficiency when one can have 99 - 100% ? The only difference is how much effort and money one is willing to invest to achieve that 10% improvement? When dealing with mass manufactured products, it is probably good enough. When dealing with small quantities of "high tech" products ( such as "high end" audio ), that is too much "waste" as far as i'm concerned. "Settling for" mediocrity or what is "good enough" never made me happy. Sean
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Spluta: I was primarily refering to audio and low frequency RF gear. When you start hitting high frequency RF, you can have it. Things can get WAY "squirelly" REAL fast. I can understand that you have to take what you can get in situations like that, as there just aren't a lot of alternatives out there.
Foreverhifi: Out of curiosity, what was Dunlavy running for electronics at their factory ? I would assume that he had his Z-6 speaker cables, but do you know what was used to connect all of the gear ?
This brings up another topic. If the gear / speakers being used within a manufacturer's reference system sounds like "hell" and / or is set up poorly, how is it that they can really tell if something sounds "better" or if they have actually made an improvement to a product during listening tests ??? This is not to pick on John Dunlavy in specific, as i surely respect him for his knowledge and experience. Sean
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Foreverhifi: I might agree with John Dunlavy regarding his comments "God himself couldn't hear the difference in two wires/cables measuring the same values!"
If the cables presented identical loads to the source component with the same level of signal transfer into the load component, they "should" sound identical. However, it would be possible to measure cables and have them come up the same yet be electrically VERY different from one another.
One could use a cable constructed like Kimber 8TC and insert inductors in each leg of the run and then take a run of 10 gauge zip cord and insert capacitors in each leg of the run. The total resistance, inductance, capacitance and impedance for both cables may measure the same on a meter but the fact that some components were lumped and others were evenly distributed would cause current to flow VERY differently along the length of the lines. As such, "tuned networks" within a small area may not be as effective as achieving similar electrical characteristics over a wider spread and vice-versa. Much of this will depend on what you are trying to achieve and the rest of the circumstances involved. Whether or not we can actually hear such things is a good question and one that i would love to be able to know ( and prove ).
As to the cables that Dunlavy was using, i would have thought that he would have been using some of his own speaker cables and interconnects. As to his choice of gain stages, he should have known better than to say that "an amp is an amp" etc... He used to design and market components back in the 1970's and they were very well thought out in terms of circuitry. I don't know how well they were constructed or if he paid attention to parts selection, but he knew enough to try and design something that was "technically correct" to say the least. He is a very smart guy but whether or not he applied everything that he knew at all times is another matter. Sean
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Red: I've heard very similar sonic traits when using certain analogue cables as digital cables. Since the impedances between transport to DAC would normally be very different from DAC to preamp, another line level source to preamp or preamp to amp, i don't know why this is. Having said that, some folks that i've talked to that have cables built to their spec insist that every manufacturer introduces their own sonic signature into what they make. That is, the grade of copper or silver, how the wire is formed or drawn, etc... all plays a key in the sonic signature. As such, some folks have had cabling made to the same spec by several different manufacturers and they all sound different. This is the kind of stuff that boggles the mind yet would probably reveal quite a bit if someone were willing to devote the time to research the subject. Then again, maybe that's why "audiophile" cables cost so much i.e. we have to pay for all of the R&D that's taking place : ) Sean
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