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Old 23rd November 2012, 06:16 PM   #7651
dvv is offline dvv  Serbia
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No. Spoof I can cope with, but spoof masquerading as reality is too much for me. When I watch a film/TV I like to know in advance whether it is comedy or drama. The exception is politics, which I know includes both.
There is comedy in politics?

News to me ...
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Old 23rd November 2012, 07:47 PM   #7652
DF96 is offline DF96  England
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Have you ever watched Prime Minister's Questions in the Westminster Parliament? Wednesday 12 noon to 12.30 (UK time). I understand it is major comedy viewing in the Netherlands.
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Old 23rd November 2012, 08:10 PM   #7653
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Old 24th November 2012, 07:47 AM   #7654
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Have you ever watched Prime Minister's Questions in the Westminster Parliament? Wednesday 12 noon to 12.30 (UK time). I understand it is major comedy viewing in the Netherlands.
Don't know about that, I don't watch TV much, and when I do, it's usually a movie or a series I like, for example, "Castle" (I'm something of a Nathan Fillion fan).

I am spending some time looking over my most recent purchase, a Toshiba (Aurex in some markets) SB-45 integrated amp. I have always trusted Toshiba products, but this one is something else.

It's an entry level integrated amp, but one with a twist. It's rated at 40 WRMS into 8 Ohms, basic functions only, but given it's date of birth (early 80ies), it has a LED power display. All in all, a typical representative of its breed - until you open it up.

In those days, most of its competitors had those hybrid power packs, the all-in-one powr amp. Switching by standard meachanical contacts, preamp most often using a few op amps.

But not this one. Yes, the preamp is still mostly by op amps, but in some places (phono RIAA) enriched with discrete dual devices. Switching uses a set of then popular VLSIs. The power amp is all discrete, and is of the type that in those days, you usually found on much more expensive devices, higher up the model line.

Well done voltage regulation, separate voltage regulator for the LED power display, dot type.

As expected, a small power transformer, although of appearently good quality, but people like us would use it to power a preamp. Two 6,800 uF electrolytic caps. Power devices rated at 80 Watts.

What I plan to do with it is to almost rebuild it, because I plan on changing carbon film 5% resistors with 1% metal film types in critical places, sticking in bigger electrolytic caps and very possibly exchanging the existing power devices with more powerful types - BD 249/250 C (Euro improved version of TI's TIP 35/36 C), and so forth.

The reason is that I want to end up with a surprisingly good (for its price class, of course) device I can fool around with some of my friends who think that if it costs less than $2,000, it can't really play music.

I mean, I paid $30 for it, and in a very good conditions - I just couldn't resist it.
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Old 24th November 2012, 10:48 AM   #7655
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I agree . As I said before fiction is the better truth as it announces itself . I watched a program about the Great Train Robbery recently which I enjoyed for it's attempt at accuracy of period detail ( some locomotives I suspect were wrong ) . It said that certain details changed for dramatic effect etc . I wish when then did that they would put a small star on the screen to say . My bet is if done with truth the star would be on much of time . Friends often say to me that something is a well known fact . I say " were you there " ?
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Old 25th November 2012, 07:34 AM   #7656
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I agree . As I said before fiction is the better truth as it announces itself . I watched a program about the Great Train Robbery recently which I enjoyed for it's attempt at accuracy of period detail ( some locomotives I suspect were wrong ) . It said that certain details changed for dramatic effect etc . I wish when then did that they would put a small star on the screen to say . My bet is if done with truth the star would be on much of time . Friends often say to me that something is a well known fact . I say " were you there " ?
Well Nige, water is definitely wet, and yes, I was there, and I am there every day.

But seriously, we must admit that our knowledge of human hearing is still defiicient. We have learnt a lot, but in my view, still not enough.

And in audio, we all have at some point faced a few audio inherent paradoxes. For example, we have the classic case of one amp measuring well and sounding mediocre, and another measuring poorly yet sounding much better.

I do believe most of us here could draw up a list of possible resons why this is so, but until we get our heads inside the two units, we're just guessing.

Not to use anyone else, I'll use myself. Over the years, I have come to the conclusion that everything else being equal, it often happens that an amp using medium high Ft (e.g. MJ110XX, MJ2119X, BD 249/250 C, etc) power devices SEEMS somehow more believable than many using much faster devices (Ft 30+ MHz). I can't explain it, and I wish I could, because this flies in the face of objective reasons, according to which the opposite should be happening.

I have swapped output transistors in many Japanese (now vintage) amps, and installed Motorola devices, and I have to say that NOT ONCE has this failed to produce better results. Yet, most devices I took out had spec sheets which exceeded Motorola's in most, even all aspects, save for power dissipation, as most of those taken out were rated at 100, 120 and 150 Watts, while Motorola's offerings were all rated at 250 Watts.

I understand this will definitely come into play when one is pushing the amp hard, i.e. nearer to its performance limits, but I cannot explain it when one is using the amp at an average power dissipation of 1 Watt or less.

As you know from the text you sent me, John Lindsey Hood voiced a very similar sentiment, and he is hardly a novice, or a dabbler. And he was talking about a pure class A power amp.

All I am left with is that perhaps the reason is the manufacturing process, the technology behind the products. Could it be that perhaps a triple diffused transistor is inherently better for audio, than the more current RET types, for example?

Why does a garden variety op amp (e.g. LF356, TLO71, and especially OP37) ALWAYS, by default, sound better to much better when it's endowed with a discrete current booster (consisting of garden variety transistors, such as say BC 639/640, MPSA 06/56, etc), when even initially the current requirements were WAY below the op amp's rating? The op amp is rated at say 10 mA of output current, it works in a circuit where 1 mA is all that would ever be asked of it, yet it sounds better with a current boost stage?

And, to add insult to injury, excatly the same is true of very elaborate, very expensive op amps as well.

These are the little mysteries of life which make it worth living, methinks.
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Old 25th November 2012, 08:37 AM   #7657
fas42 is offline fas42  Australia
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Originally Posted by dvv View Post
Why does a garden variety op amp (e.g. LF356, TLO71, and especially OP37) ALWAYS, by default, sound better to much better when it's endowed with a discrete current booster (consisting of garden variety transistors, such as say BC 639/640, MPSA 06/56, etc), when even initially the current requirements were WAY below the op amp's rating? The op amp is rated at say 10 mA of output current, it works in a circuit where 1 mA is all that would ever be asked of it, yet it sounds better with a current boost stage?

And, to add insult to injury, excatly the same is true of very elaborate, very expensive op amps as well.
That, at least to me, is not such a mystery: whatever you can do to help the op amp to not draw more than quiescent currents, at all times, will help. PSRR are never as good as they should be, and neither are power supply rails ...

Frank
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Old 25th November 2012, 08:55 AM   #7658
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I think the current booster idea is great . It is Mr Wayne's argument on the smaller scale . I bet like many things it it the least obvious of the real reasons that makes it so ? My bet would be keeping stuff out of the feedback loop . Just a guess and happy to be wrong .

I think we do in audio have to have faith in things which are hard to prove . Recently with my valve amp project I was forced by interest to use whatever was to hand , if not ideas sometimes slip away . Very often transistors that had voltage as their only virtue had to be used . All worked fabulously well . On seeing my circuits many made countless suggestions about devices I should use . Mostly that I should not use transistors . I was amused how many think that transistors would not be first choice device as current amps ( all my transistors are used as CCS's ) ! I then had a long hard think . Class A , 20 kHz on a rare day , 4 kHz peak . What is it that my 1 MHz transistor wasn't doing that a 30 MHZ one would ? The answer is nothing in this application . Faith would have been a mistake although I am probably as guilty as any for having my own little beliefs .

Having said that my hunch is I will use buffered op amps in future . I did a very long study on them as power amps . All those circuits will adapt nicely . As power amps by a very small margin complimentary feedback pairs with no loop feedback worked best . Distortion was almost as low as the op amp itself . With loop feedback was excellent , ears preferred without marginally . Two loops also ( 70/30 % or whatever ) . Something like OA604 BD135/ 136 works well . NE 5534 was very difficult , it suited without loop best . This perhaps it why 5534 is not well liked as it is easily upset ? I often use them as I have plenty . Then mostly to please others I use something better . Most designs I knew from the past that use them I strongly disliked . That is not the device , more the company it keeps .

This happens with wine . Poor soil and poor climate with indifferent grapes makes for poor quality wine . Montaud near Montpelier in the south of France made the usual low grade wine in 1982 when I first went there . Then they invested in carbonic maceration and asked some Australians how to do it . The result is rather good . The real shock is some Chardonnay they planted . They said to me you wouldn't know it isn't a New world wine . Oh yes I would , it is far better . For the majority of the wine the grapes and the soil are the same , even the people . Faith and science working together is how it changed . In this example tradition replaced with " we can do better " . The Chardonnay never makes it out of the Village . Funny thing is I always knew they cared , they just weren't able to process the grapes as easily as in cooler climates like Burgundy . Burgundy can loose it's grapes to frost so they perhaps have it worse now ?

BTW . Chardonnay is definitely the NE5534 of grapes in my mind . It is so often abused and ruined , too much oak .
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Old 25th November 2012, 09:08 AM   #7659
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That, at least to me, is not such a mystery: whatever you can do to help the op amp to not draw more than quiescent currents, at all times, will help. PSRR are never as good as they should be, and neither are power supply rails ...

Frank
Er, ... that's rather obvious, Frank.

If you do something, and it never fails to make a positive difference, with various products from various sources, then you obviously have a system of specifying things which is, to say the elast, lacking, or is overzealous when stating the specs.

Regarding PSRR, a long time ago, I too a cue from Beckman medical electronics and HP measuring gear, and later still, from Burr-Brown. To cut a long story short, instead of using typically a 10 Ohm resitor, followed by say 10uF in parallel with 0.1 uF as near the power input pins as possible, simply use no resistor, no parallels, but 10 uF quality tantalum caps. Factories don't because to them, it's a hassle to keep yet another component on their list, and a none too cheap one at that.

The last op amp which oscillated on me was so long ago that I don't even remember the event.

As for power supplies, I am usually called overzealous and thrifty locally, because I spare neither the effort, nor the materials for power supplies. For low signal level electronics, they are typicall of the shunt type, I have two "sizes", so to speak, one simpler and base on Motorola/ON Semi MJE 15030/15031 pass transistors, and one VERY complex and expensive, but, to the best of my knowledge, the best I have ever come across anywhere, at any price.

When the requirements are such, I will use more than one regulator per each channel, I'm no shy lilly.
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Old 25th November 2012, 09:19 AM   #7660
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This is a doodle I did , it is untried . The 10 M not a recommendation , nor 1 R . Just as high / low as . MC33079 also ( all 4 devices ) .

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