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Old 3rd February 2012, 07:50 PM   #1721
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Quote:
Originally Posted by mr_push_pull View Post
really...
Really. Human bodies have all the same topology, but anyway doctors use lots of different diagnostic methods to check if the person is in good health or not. Why do you expect the single set of criteria to check which amp will sound better in all conditions?

Edit:
Speaking of health... The whole week I had been weak... Influenza. What kind of measurements would you propose in this case? The answer is simple: specific measurements, according to symptoms. The same with amps: symptoms can be very different, and no measurements can be used to tell which one is better. Especially, when you hear some symptoms, but have no experience to tell what can cause them. Like in my case: absence of appetite can be caused by common gastritis, while I know it had been caused by virus. Experienced doctor can tell. Experienced designer can tell. But you can't choose the single set of measurements to judge doctors' and desighers' results. Except subjective measurements: feeling of health, feeling of reality of sounds.
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Last edited by Wavebourn; 3rd February 2012 at 07:56 PM.
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Old 3rd February 2012, 07:58 PM   #1722
wahab is offline wahab  Algeria
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Quote:
Originally Posted by bcarso View Post

To wit: the slew rate of the stock DH-120 is fairly low and asymmetrical. The slew rate of the alternate design from wahab is symmetrical and much higher. Both slew rates are compatible more-or-less with a full-rated-power 20kHz sinusoid, but wahab's amp has lots of slew rate to spare as it were.

So we have, possibly, the opportunity to explore questions about symmetry and slew rate's effect on audio quality.
Perhaps that reducing the slew rate , if it s high , would be worth it,
by increasing the relevant cap from 39pF to 47/68pF.

This would increase THD and IMD slightly but would provide robust stability,
and thus would prevent any risk of oscillation.

In an experiementation , better to be cautious....
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Old 3rd February 2012, 08:00 PM   #1723
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by Wavebourn View Post
Really. Human bodies have all the same topology, but anyway doctors use lots of different diagnostic methods to check if the person is in good health or not. Why do you expect the single set of criteria to check which amp will sound better in all conditions?

Edit:
Speaking of health... The whole week I had been weak... Influenza. What kind of measurements would you propose in this case? The answer is simple: specific measurements, according to symptoms. The same with amps: symptoms can be very different, and no measurements can be used to tell which one is better. Especially, when you hear some symptoms, but have no experience to tell what can cause them. Like in my case: absence of appetite can be caused by common gastritis, while I know it had been caused by virus. Experienced doctor can tell. Experienced designer can tell. But you can't choose the single set of measurements to judge doctors' and desighers' results. Except subjective measurements: feeling of health, feeling of reality of sounds.
I highly recommend 2 oz of 150 overproof rum with a full lime squeeze, and a spoon of honey, warmed , take it twice a day, the virus or you will be dead in 2 days, usually the virus ....
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Old 3rd February 2012, 08:03 PM   #1724
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Don't slow down, except to remove output coils OR for better stability.
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Old 3rd February 2012, 08:04 PM   #1725
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Thanks Wayne. However, I don't use alcohol, but lemon and honey use regularly the whole week. Can you recommend this cure for all illnesses, including allergy to honey?
The same about amps. They are more different than our bodies. Try to give 2 oz of 150 overproof rum to chicken and see what happens...
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Old 3rd February 2012, 08:21 PM   #1726
a.wayne is offline a.wayne  United States
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You can forget the honey wave, the trick is the over proof rum/lime. Funny , you won't try alcohol, but instead will use the drugs fostered by it .
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Old 3rd February 2012, 08:25 PM   #1727
jcx is offline jcx  United States
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pooge-ing the Hafler may be a fine pursuit but I don't see how it is useful to the thread topic - particularly if you literally rebuild the existing amp there is far too much room for skepticism over "results" reported from you/your wife's memory of the baseline performance

given the poor quality of the Hafler pcb layout and number of proposed changes you may as well build a new amp entirely so you can compare side-by-side
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Old 3rd February 2012, 08:33 PM   #1728
dvv is offline dvv  Serbia
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The problem with measurements is that they have polarized people to the extreme.

We cannot measure everything that is relevant, but not everything we can measure is relevant.

To wit: say you have an amp with a THD spec of say 0.001%. Say you have another amp with the same spec of of say 0.05%, or fifty times more (sic!).

On the face of it, one would be tempted to say the first one will sound better. I would venture a guess that the second has a better chance of sounding better.

I would do so based on my own experience of designing and building audio gear. I don't think, I *KNOW* what are the reasonable limits of distortion you can have from a decently designed piece of gear without using tremendous amounts of negative feedback. To be specifi, for me, "low feedback" assumes no more than 20 dB of NFB, "medium" raises this to say 28 dB, and"high" is above that. Obviously a very personal qualification.

Over the years, I have consistently discovered and rediscovered that the best overall performance, at least for mw, is achieved by the "medium" class, followed by the "low" class. Some peopkle are willing to sacrfice stability for low NFB figures, while I am not.

THIS is the additional piece of data we all need to be able to judge those THD figures properly. Tell me 0.05% THD with 26 dB of NFB versus 0.001% THD with say 40 dB of NFB, and my money will be on the first one.

So, the problem is not so much a matter of measurements as such, but of their completness, of what has been published and what has not.

Measurements are an indespensible tool while desigining and prototyping because they are the inital set of parameters which tell you how you did the job in rough terms, and perhaps push you to improve on it. Once you have many years of measuring under your belt, believe it or not, but based on a set of well taken measurements you can actually have a rough idea of what to expect from an amp. Not precise, true, and exceptions are always possible, but in general, it is so.

When you see the sweep signal on your spectrum analyzer, and see that the decay of the even and odd harmonics is as it should be, you know that amp is likely to sound clean and clear.

When you measure your open loop full power response and get something like 60 or 80 kHz, you know that amp will not sound congested, lazy and slow. Of course, getting such figures is the trick.

If your open loop full power measurements show that your harmonic distortion is 0.3% 20...20,000 Hz, then you don't NEED much feedback in general.

But, this is designer/engineer stuff and means little to the typical customer. In that sense, to him, practically all measurements are meaningless simply because he doesn't know how to interpret them properly. Nor is that his job. He is paying for somebody else to take care of such matters.

Having no better choice, the audio industry tries to convince us that theirs is a great product because it has practically nonexistent distortion. They carefully opmit telling us HOW they achieved those figures.

This is why specifications cannot faithfully describe gear: 1) we don't know HOW they did it, by super careful design, or by adding tons of feedback, and 2) the average customer has no idea of how to interpet those fugures, all he knows is that they should be as low as possible.

By the same token, calling measurements irrelevant is overdoing it just the same as calling them everything, just in the opposite direction.

@Wavebourn
For a natural riddance of flue and influenca, try heating up a glass of red wine as high as you can to be able to swallow it, then add a soup spoon of natural honey. Sip it at once, make sure it rolls down your throat constantly but slowly. Drink it in the evening, just before going to bed. Be aware you will sweat a LOT that night, but in the process, you will sweat out the culprit as well. Look mama, no aspirin! Worked for my ancvestors and me every time.
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Old 3rd February 2012, 08:40 PM   #1729
a.wayne is offline a.wayne  United States
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Name a high feedback back amplifier considered to be good sounding , contrary name a low or zero feedback amp considered bad sounding . The Audio Note UK amp discussed previously , failed every test known to man , yet it got a pass for sound ...


PS: Please quantify high feedback and low feedback ..........
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Old 3rd February 2012, 08:46 PM   #1730
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Thank you dvv for such good analysis!

Also, thank you for the recipe. But I am afraid for me a glass of vine would mean a death, like 20 dB of feedback to the conditionally stable amp that will inevitably oscillate on frequency lethal for output transistors.
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