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In Reply to: RE: Measuring properties or changing operation? posted by bjh on June 24, 2009 at 11:40:54
"things like power line conditioning and power cords *do* often still make a difference. "
Yes, it's true perhaps but when it's true then also it is evidence that the power supply design is incomplete.
Noise "can" be a problem if your design doesn't deal with it, then an external bandaid can help beyond decoration.
Since it is possible to make power supplies which are extremly immune to huge line noise, possible to make radio transmitters with sensitive audio circuitry, even possible to make sensitive electronics operate in close proximity to an xenon arc lamp, what would be the reason (other than cost or knowledge) not to design for noise immunity like that in modern hifi gear?
This problem is not new either, one couldn't design a tube amplifier in the old days without addressing RF and noise.
Most output tubes and all small signal tubes would work perfectly happily up to Citizen's band (27 MHz) if allowed to, not like transistors which have vastly lower open bandwidth.
In the old days there were mare severe sources of noise too, in the last 20 years these sources were replaced to permit the cell phone and wireless era high up in frequency.
My point is as a designer, one is left thinking the job is not done if an external shield / AC cord etc actually changes the operation.
Think about it this way, It is "foolish engineering" to leave the proper operation of a circuit or system to depend on having "the right" kind of AC, especially since one can remove that issue at least over some range with proper design.
Testing the actual operating voltage range and tolerance / immunity to input distortion / noise is normal stuff, at least when making test equipment.
Possible reasons for the way it is;
Audio design, especially power analogue circuitry, is a much much smaller business than "test equipment", fewer Ham's and DIY'rs now in the field, who are good self taught designers and perhaps the very presence of the "mystery of the magic cord" and such enhances part of the industry's image and romance among the buyers
Just a wild guess.
..., in your opinion, designed power supply, that is immune to power cords.
Of course, with details of the system this piece of equipment was tested in.
Forgive my scepticism - but I've never faced one since my system became more or less resolving. However, I can see that to be the case in the context of cheap receiver and CD changer, connected to $100 speakers - but the reason, obviously, would be quite different from power supply being designed "properly".
Sure, here are two, old and new, A Xilica 4080 speaker controller / processor operates over a wide range of input voltages, has no sound, or audible pickup when used near xenon and old florescent lighting or next to switching power supplies and amplifiers.
It’s balanced inputs make concerns about exotic cables irrelevant and the market and sales of exotic cables is vastly smaller by percentage in pro.
A McIntosh mx110 tube pre-amp / tuner also had a huge tolerance to RFI and EMI noise and could be used next to the room with an RF induction heater.
In general tube gear, including the tube amplifiers from Grommes where I worked in the 70’s, were very tolerant of line and radiated noise but much less so on the range of line Voltages.
Lastly an example of a sort of audio situation I had to resolve personally.
I was given the task of re-designing and then building and testing the control electronics for an Acoustic levitation system which was to be flown on the shuttle but first on sounding rockets.
The science problem driving this being that there were many materials which reacted with the container when melted or required such a high temperature that there were no containers available.
The solution was to use high intensity sound to position a sample in the middle of a really hot furnace, to melt and cool the sample without contact.
The existing sound source had a capacitive pickup, like a condenser microphone, which was charged to 200Vdc.
The sound source was a resonant bar of titanium, the pickup’s job was to pick up the tiny signal from the vibration at 16KHz and use the pll circuit I designed to lock on to the resonance, keeping it in tune and at a constant amplitude.
This had to be done on shuttle power, which could vary from 24 to 42Volts (28VDC nominal) with a boat load of noise spectrum up to low RF.
Our experiment power was set to 100Amps so the furnace modulator (4 phase pwm) had to monitor a current shunt to regulate at no more than 100 Amps while heating.
Here is a link to that stuff, now 20 years ago.
http://www.springerlink.com/content/42375j4148345603/
Anyway my point was that even when dealing with the most sensitive signals like a “naked” condenser microphone, buried within an extraordinarily electronically noisy environment, you can still engineer around it, if doing that is part of the task.
Unless there are unusual circumstances, the level of conducted and radiated noise in the home is certainly much less than in industrial and many commercial uses of electronics, including audio.
Lastly, keep in mind that in addition to any real change electronically or not, other things can also effect ones perception of a given event.
A simple test which may be useful to help in seperating these.
Sit down and listen back and forth between the two cables which show the largest difference. Pick music that makes the difference obvious as possible and go back and forth.
When you feel it’s the right time un plug them, have a friend come in and have them pick one of the two and plug it in and you listen again, now not knowing which cable it was.
Have the friend switch back and forth making sure you can’t see and he doesn’t tell you which one is in use.
The results of these fall one of two ways generally.
Most often, the audible difference is smaller to much smaller or even gone when you don’t know which is which and you only use your ears.
If there is a difference even if small this way, without prior knowledge, then you are on to something in the engineering side that can be tracked down to a source, ideally before it is sold as a product.
If not, don't feel bad, in fact your in good company.
In the recording and mixing community there is a story told to remind themselves they are not infallible even if they do it for a living.
It goes like this, the engineer spends 10 min doing minute tweaks on an eq or processor strip getting the sound "just right".
Then when sitting back to enjoy, notices the "bypass" button is / was pressed the whole time.
To a very real degree, we hear what we want to hear and only part of that is related to electrons etc.
You're right, but it was not a great sounding piece of gear. Rolled off on the top end with a most definite lack of detail and information.
Therein lies a major issue with audio gear. While test gear is often oriented to optimize one or maybe two specific parameters, audio gear has a range of parameters to satisfy. The goal is not to meet a standard but to surpass those standards. Considering the wide bandwidth, the dynamic range desired, the great mix of frequencies and levels involved in any mix, that is a pretty tall order. Then couple that with the various range of human tastes.
Audio gear is geared to extreme sensitivity. Very often our test gear is not even designed to measure such parameters which can be detected by the human ear. As an example there is the rather groundbreaking work done by Matti Otala concerning TIM distortion, which was relatively unknown until he published his works. If test gear exists it is often astronomically priced. I recall a Rhode and Schwartz real time analyzer used by one company to measure a particular parameter in wire construction which cost them at the time $100K and of which only five units in the world had been manufactured.
In many pieces of audio gear you sacrifice one aspect of music to optimize another. In many instances what is theoretically negligible can be audible, despite engineering theory.
I recall one manufacturer displaying a prototype of a preamp and commented that his new design using the identical layout and parts should sound better than his original which had multiple individual phono sections. His reply that from a theoretical point of view there should be absolutely no difference as the power supply was sufficiently large to exclude any current draw differences even if all the sections were running (they were not at the time). Yet a direct comparison revealed, obviously, that there was a sonic difference.
Declaring that human perceptions can vary, while very true, ignores the basic fact that some listeners can hear certain changes. You can cater to the lowest common denominator or you can cater to the extremely discriminating.
You can be happy with the relatively lossy mp-3 player or you can demand the very high end piece of audio gear. Both can offer great satisfaction to many users. But just because the listener with the poorer component is happy does not necessarily mean that anything "better" is a figment of the user's imagination.
Let's face it: there are huge ranges in human perception and that is simply part of the challenge. I once placed five different types of hook up wire in my preamp's five inputs. There was enough differences so that even the two inch length made a difference, however, subtle you may believe it to be. In a system I was familiar with I could consistently identify each input even in a blind test. I do not claim "golden ear" status, but I have spent an inordinate amount of time actually listening to music, critically.
While I barely made it through aural training classes at the local university, continued listening in the manner I was taught can reveal certain aspects which many others do not hear. It has nothing to do with the condition of your ears, but more to do with the mind-ear connection. In doing research on hearing, I am consistently struck by the fact that any of the senses can be trained if you embark on a program to do so.
Think of it in terms of the aficionados of wines and how much practice they have to go through in order to become an expert. If you're into video games, think of how much time you need on a particular game in order to excel at it. Still in music, it is the subtleties which define the a great performance or a great virtuoso. A great performer can make even a student model instrument sound decent, but he will do much better with a a great one. The pursuit of the subtleties in music is what drives many to "better" audio gear. If not, the world would be happy with a transistor radio.
Stu
You basically said the same all over again... got it the first time, doesn't change the situation for me anyway.
Everything matters, don't forget to tweak your placebos!
Ok, just wanted to be clear on how that works technically.
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