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Old 17th March 2013, 03:17 AM   #8681
a.wayne is offline a.wayne  United States
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Its 4 of 68K caps , 2 per side .....
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Old 17th March 2013, 01:31 PM   #8682
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I was thinking abouit this . If we take all of our commersial amps and solder in some nice bits of copper we might do some good . Doubtless the cross-section has some effect on sound ? I would focus on the Ground alone . The output transistors probably are more trouble than the existing amp arrangements so no great need to change that ( 0R22 emitter resistors ) ?

This says something in favour of the amps like LAB 47 . It's 9 mm feedback path is irrelevant as far as I can see . If the distance from it 's Ground is short and low resistance , that makes sense . The argument might be this ? Skin effect probably is important . Ideally 1 mm cross sections ? As I pointed out yesterday even a minute piece of 0.8 mm is loosing 0.03V at 0.2A . Setting aside skin effect we need a compact layout so as to make best use of the copper . Ideally a star point or a well thought out bus-bar . I say a well designed class AB can outperform a class A . In the PSU department it can . The high standing current is said to saturate the PSU ( if class A ) . Having the least standing current should produce less potenial difference in the 0 V rails ( must in fact ) . That will change things and I can only think for the better ? The output stage Dvv uses should promote very low distortion at very low standing currents ( triples , typically 7 mA per pair can be enough ) .

One thing people get wrong in design . Yes something should work . The practicality of getting it to work might have inconvenient consequences . It is a bit like the mid engined car and the boxer engine . We so nearly don't need to do it that we pretend it is a caprice . To work on a car is another matter or pay for the repairs when someone does . The front engined rear gearbox is intelligent . I heard Clarkson say rear wheel drive costs more to make and that's why BMW is better because they pay the extra . Rubbish . It will be more expensive now as it is less widely used . Initially the front wheel drive cost more as it had more difficult engineering . Clarkson forgets it was to get maximum interior space that dictated the change . Some argue BMW stayed with rear drive because it made them more money and was not without some merit . The money was not to retool and build a niche increasingly made vacant . They stayed with class AB if you like ?

One of the most inconvenient things about space rockets is the difference between weight of fuel and required thrust is a delicate balance ( almost not possible ) . Alan Bond ( and Val Cleaver et al ) in the UK solved it a bit . His early rockets were like a Coke can . It was stressed by the fuel . Problem is it was useless for a defense rocket as it took 30 minutes to fill and was stored empty . Shame we were so narrow as for commercial rockets it was ideal . The UK government always has a big supply of stupid pills to take every day . The latest Bond adventure might put some who read this into space one day . What is wrong with the world , penniless Britain of 1947 put jets into aircraft , now we can't even build locomotives . We had a saying here " the last one to leave the country please remember to switch the light off " . Irony is people flock to come here !
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Old 17th March 2013, 01:42 PM   #8683
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Sugden Masterclasses have nice metal plates forming the star point for the rectifier capacitors
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Old 17th March 2013, 02:01 PM   #8684
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The beauty of this is we might have it done in 20 minutes . The problem with PCB's is they are almost 2 D . Dead-bug is no big deal . I have some offcuts of Nordost 1.7 mm 60 micron silver plated OFC . That seems Ideal. Do a before and after for voltages .

In the UK we call that 2.5 sq mm twin and earth for electricity . It costs pennies . The silver helps a bit . I think it is 4 N's if Nordost .

( d x d x 22 ) /28 ( is OK for that ) (1.7 x 1.7 x 22 ) / 28 = 2.27 sq mm

22/ 7 = Pi 22/28 is related to Pi d sq/4

Last edited by nigel pearson; 17th March 2013 at 02:05 PM.
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Old 17th March 2013, 04:01 PM   #8685
DF96 is offline DF96  England
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You don't necessarily need thick metal, except when your design assumes superconductors everywhere (like Spice does?). If you assume every connection has some resistance and inductance, and design accordingly, then you can use ordinary wires. So the bigger improvement you get by scattering copper, the worse was the original design.
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Old 17th March 2013, 08:46 PM   #8686
dvv is offline dvv  Serbia
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Strictly speaking for myself, I find that no two models can be treated the same. Each is a story unto itself.

Changing the output transistors is a can of worms - no sense in doing that unless you also redo the protection circuits. If not, the amp will continue to behave as if you've done nothing. Your only possible gain might be in thermal behavior, given that more powerful transistors have a different derating curve.

What I find makes the most difference per buck is putting in some high or higher quality electrolytics, also adding some size as well. For example, take out the 15,000uF caps and put in some 22,000uF, preferably of known good quality. If nothing else, you will get a better controlled bass.

Another thing which often works well (as for example in Marantz' 7000 series integrated amps) is to change the mundane NJR op amps with some quality fare from say Analog Devices. It makes the sound more transparent, been done often enough.

But fiddling around with ground is, in my view, a highly risky business. If they got it wrong in the first go, you will be spitting blood by the time you redo it the right way. You MIGHT play around with an existing potential equalizing resistor value, if you've just changed the caps, it might shift a value or two up or down, say from 15 Ohms to 10-20 Ohms, something like that.

You might wish to change its internal wiring from original copper to say pure silver, or high grade OFC copper, but that one you have to play by ear.

Or, change a weedy little wire from the amp output to the speaker binding post with something more substantial of known good quality. On occasion, this can audibly change the sound for the better, at least for more substantial, with more gravitas.

Or, as in case of my own HK 6550, you might throw away the crappy volume pot and install an ALPS Blue in its place. This produced literally stunning difference in my case.
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Old 17th March 2013, 11:33 PM   #8687
fas42 is online now fas42  Australia
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Quote:
Originally Posted by nigel pearson View Post
It's 9 mm feedback path is irrelevant as far as I can see . If the distance from it 's Ground is short and low resistance , that makes sense . The argument might be this ? Skin effect probably is important
IME the feedback path is extremely critical, as is grounding and power supplies. Skin effect to me is one of those "fashion" fads, I never once contemplated that being relevant.

To me, it's looking for the real weaknesses, and fixing 'em. I'm not interested in a 10% improvement, I want a 10 x step up in behaviour in the areas of weakness - this I believe is where the real gains are made, the ones that count, that one's ears are particularly sensitive to ...

Frank
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Old 18th March 2013, 03:21 AM   #8688
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hi guys an occasional reader/poster on here came here after a search on Perreaux brought this thread up. noticed it was an interesting title.
I have come across a guy who has a PMF5150B a MOSFET Power amp long story short I checked Perreaux schematics which I have on file but never used in anger.

they make some serious and significant claims on their site. checked the drawings...

It is the "Hitachi" app circuitwith a tiny variation but it is often very liked and applauded for sonic quality. so 5 small signal BJT's driving several pairs of comp MOSFETS is how it done eh???

just goes to show sonics are subjective and cumulative depending on what else is in the chain personal taste also counts in this equation.
But the Perreaux guys must be "generous" with truth too, as they claim to be the 1st "World company" to use MOSFET's perhaps they invented them then and not Hitachi or in indeed loosely Sony (for their Vertical FET's
in a nutshell specs can mean little if it dont sound "nice" or "musical" or just plain how you like it!!!!
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Old 18th March 2013, 07:44 AM   #8689
dvv is offline dvv  Serbia
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Originally Posted by CHARLIEB999 View Post
...
But the Perreaux guys must be "generous" with truth too, as they claim to be the 1st "World company" to use MOSFET's perhaps they invented them then and not Hitachi or in indeed loosely Sony (for their Vertical FET's
in a nutshell specs can mean little if it dont sound "nice" or "musical" or just plain how you like it!!!!
That particular version of MOSFETs perhaps, but if memory serves, Hitachi was the first on the market with MOSFETs in thei HCA/HMA pre and main amps some years before anyone had ever even heard of Perraux outside New Zealand.

That said, and repeating that I am not a great fan of MOSFETs, I have to admit Perraux's 100 WPC MOSFET amp was one of the few such amps I really liked. Heard it in London in the early 80ies. No idea why, it just sounded "right" to me driving big KEF speakers in a deačer's showroom. They sort of "clicked together".

As for "being generous with the truth", aren't they all?
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Old 18th March 2013, 07:47 AM   #8690
dvv is offline dvv  Serbia
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Originally Posted by fas42 View Post
IME the feedback path is extremely critical, as is grounding and power supplies. Skin effect to me is one of those "fashion" fads, I never once contemplated that being relevant.

To me, it's looking for the real weaknesses, and fixing 'em. I'm not interested in a 10% improvement, I want a 10 x step up in behaviour in the areas of weakness - this I believe is where the real gains are made, the ones that count, that one's ears are particularly sensitive to ...

Frank
But it all adds up, Frank, 5% there and 10% here, in the end, you might wind up with a significantly improved sound.
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