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Old 9th January 2012, 12:39 AM   #661
tvrgeek is offline tvrgeek  United States
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Quote:
Originally Posted by Wavebourn View Post
Expensive diodes allow you to do more of obvious errors in PS design and layout, nothing more. Vacuum tube rectifiers forgive even more obvious errors. But you may apply gray matter once, and it saves green matter that goes to each device in production. Think about each wire that has resistance and inductance, that are sources of voltage spikes caused by current spikes, to be happy. Less of measurements are needed when you know what you do...
I would bet a pint, as that is my maximum wager, you are correct that a standard bridge with snubbers, proper filtering, and proper dress, is just as good and $10 cheaper. I have seen only subjective babble and it is a simple thing to test. I put 4X the reserve as well as lower esr caps in the 120, so I thought it prudent to put in a larger bridge anyway, so why not? If I see a difference in the level and quantity of line harmonics in the output, we will know. If I don't, we will know. The wiring is not bad, but not optimum either. So second question, it is a worthwhile band-aid for an existing unit?
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Old 9th January 2012, 01:06 AM   #662
tvrgeek is offline tvrgeek  United States
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Can you elaborate on the "catching up" part?
With a scope, look at the amp input and the output from the mic.
Feed a steady 4K tone.
With a delay, you can basically overlay the traces.
Now, feed a computer generated 10 cycle pulse that starts at zero crossing.
Capture the result.
You will see the acoustic trace start later and basically look like it is a bit behind the drive. The first half wave is looks compressed in time and amplitude as it is told to reverse before it got going. Undersoot and slow. Within a few cycles, they are in sync. Of course, as you have the mass moving and all the spring-damping effects in place. This makes sense. BUT, how much is effected by different amps is what I noticed.

I am going to try to reproduce this so I can publish a picture. It was easiest to see on my analog scope, but no way to capture. I got it on Zalescope but it was not clear.

I also did some tests with a half wave and found how the driver behaved varied with different amps. My thinking was these are contrived and not realistic to music, but they are a dynamic test. It is a test that showed a difference. Relevant? I can't say as I have not done enough to correlate with my wife's super ears.

Off the wall thought. Could the delay be related to the slinky delay? This has been studied recently and confirmed as being caused by traveling waves within the spring. Probably not but who knows.
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Old 9th January 2012, 01:13 AM   #663
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Please use a current probe to see what is really happening with diodes. No other way will show you properly.
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Old 9th January 2012, 01:13 AM   #664
Pano is offline Pano  United States
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Thanks for the details, TVR. It just sounds like you're talking about phase, but I'd like to see what you've got. 10Hz is pretty low.

If you can measure at the amp output terminals (with speaker attached) it might be easier to see the effect than with a mic. And that would allow you to test into a resistive load, as well. If you can show that this difference corresponds to some of your subjective evaluations of the amps, that's worth something.
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Old 9th January 2012, 01:37 AM   #665
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Quote:
Originally Posted by john curl View Post
Please use a current probe to see what is really happening with diodes. No other way will show you properly.
I don't get a broken penny for what is going on outside of my wires. Even if devils jump on that wires, I do not care, if what I get after power supply is pristine clean (relatively, of course!)

However, if somebody connects ground wire of a mic pre directly to the ground wire of the bridge it means he or she better go to sell used cars.
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Old 9th January 2012, 01:58 AM   #666
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Wavebourn, your self-assurance will sometime catch up with you. I felt the same way, more than 20 years ago about high speed diodes, until I changed to them, though the efforts of a friend and future business partner, and then I MEASURED with a current probe and I KNEW I had overlooked something. It was embarrassing. It is now my D mod for the Vendetta Research. I don't like to do it, it is too difficult for myself to do, and I have to bring in a tech to do it, but I do offer it as a service in order to update 20 year old equipment, on occasion.
I have found that I don't know 'everything', that I will never know 'everything', and that is why I like to correspond with Russians, E-Germans, etc. because their background is DIFFERENT from mine and sometimes I learn something new, even while approaching 70 years of age.
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Old 9th January 2012, 06:03 AM   #667
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John;

Acceptance that I use models of reality that do work, but have no clue about reality itself how it works, looks and is organized, helps me to learn something new no matter how old I am and what others think about my knowledge, and where that models come to me from.

Once again, I don't care what currents flow outside of my loop, if that loop is connected with mine in the single point only. In order for current to flow 2 minimum points are required. If to deny that, the world as we know it does not exist anymore, and we can do nothing.
In order to be able to do something real I have to stick with models that work and leave alone musings that do not.
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Old 9th January 2012, 06:45 AM   #668
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10Hz is pretty low.
I think he meant 10 cycles of 4 KHz, not 10Hz.
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Old 9th January 2012, 06:58 AM   #669
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I do not know, myself, how to 'isolate' a rectifier bridge from the power supply caps, effectively. And even if a common mode choke would help, it would not completely be successful. It is very easy just to use the 'right' rectifier, and eliminate the problem at its source.
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Old 9th January 2012, 11:03 AM   #670
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Wavebourne:
I understand and am not looking for a measurement that "tells all". But is there some set of measurements, perhaps a set that could be combined, that will be closer to a "Sound Quality Index"? We know that within reason FR and THD are not indicative. That's a dead horse.
I have to question the whole notion of a "Sound Quality Index", if by that you mean taking a variety of different types of measurements, combining them together with some weighting or algorithm, and then producing a single scalar value like a 0 to 100 scale covering "awful" to "outstanding".

The problem with this is that it assumes that different types of flaws can counter balance each other, when they can't. For example does a more extended bass response (which is a desirable trait on its own) make up for a harsh resonance in the midrange ? Any sort of weighted Sound Quality Index would imply yes, but I say no.

Does an ultra flat frequency response make up for a lack of dynamic range ? Not in my opinion. Conversely does an extremely good dynamic range make up for an extremely non flat frequency response ? No, not in my opinion.

I don't see how its possible to have a single scalar value like a "Sound Quality Index" to rank speakers with various differing deficiencies against one another, without of necessity incorporating the individual listeners preferences.

By preferences I mean the relative importance you give to various aspects of performance. Some people might place more emphasis on tonal accuracy, some on dynamic performance, some frequency extension, and so on. Based on these differing priorities the same set of speakers may be ranked differently by differing listeners, because you're comparing Apples to Oranges. There isn't necessarily a clear order of precedence.

Some of the tests performed by Toole do seem to suggest that there is a universal ranking order for speakers regardless of listener preference based on a fairly limited set of measurements, but as far as I can see, radically different topologies of speakers were not compared in his tests, nearly all being typical 2/3 way cone and dome designs, with only one token electrostat dipole, no horns, either CD or non CD, and no line arrays either, let alone other more exotic topologies.

From this the only conclusion I can draw is that speakers of a similar overall design topology can perhaps be ranked in linear preference order (using a single scalar value) but that says nothing about comparing radically different topologies, so I think its dangerous to over-generalize his conclusions beyond the limited topologies tested. (EG cone+dome designs will all tend to have the same sort of failings to greater or lesser degrees)

As an analogy, how would you go about defining a "Picture Quality Index" for the picture on Televisions ? Unlike hearing, what we can see is a lot better defined and understood, and a lot less subjective than hearing.

There are a ton of measurements that can be taken and there are a ton of different ways in which pictures can be deficient. For example:

Convergence errors, geometric distortions (barrel distortion etc) grey scale tracking, black level, banding on gradients, colour balance, (highlights and lowlights) update rate/ghosting, resolution and sharpness, motion compensation processing, noise, halo effects, the list is nearly endless. Some screen technologies suffer from some problems, some from others, just like certain speaker topologies tend to suffer more from certain problems.

All these things can be measured fairly easily with the right tools, most can be seen individually with the naked eye with the right test patterns, they are all well understood, but could you measure them all numerically (without any visual inspection) and calculate a single quality index figure that would agree with the subjective ranking of TV sets by individuals ? Maybe, maybe not, but should we even be trying ?

Clearly in audio we still don't even really know what measurements correspond well with what we hear, beyond the obvious ones like frequency response, which are important, but don't tell the full story.

I'm all for finding out which measurements do matter and which don't, and having a rough idea of their importance, but I don't see any particular benefit from trying to merge a set of measurements into a "Sound Quality Index", or even that it's possible when you're comparing such radically different potential flaws to each other.

A Sound Quality Index rating doesn't help you improve the design of a speaker, only individual measurements will do that. Lets figure out what those measurements are...

PS yes I know much of this thread is focused on amplifiers not speakers, but speakers are a much more 3 dimensional problem than amplifiers, with far more potential for complex flaws, especially considering they are transducers whose input and output are not even in the same domain.

At lest with an amplifier you have voltage in and voltage out, two quantities that are directly comparable, with scaling. You have no such luxury with speakers.
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