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Old 15th October 2012, 11:16 AM   #7431
dvv is offline dvv  Serbia
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If MOSFETs are your cup of tea ...

I have yet to hear a MOSFET design whose bass lines are as convincing as those of the bipolars.

As for Roy Gandi's advice, it seems quite simple and reasonable. If you simultaneously change two items in anything, and a difference occurs, you have no way of knowing whether the difference was made by both, or just one, and if so which one, or by some interaction between the two.

Regarding our limit of hearing THD, I read somewhere it could be as high as 2% if the decay of the harmonics is as it should be, but could be as low as 0.1% if not. As for IM dostortion, the same text argued that 0.3% was already audible by quite a number of people. But I must say I think this was Otala's original text in IEEE, and that was in 1976, quite possibly we have learnt otherwise since then.

My view is that proper decay of harmonics is far more important and audible than simple THD as such. I base this on my own experience - I've heard amps rated at 0.1% sound way better than many rated at 0.001%. Otala's own amp, as proposed in the said IEEE paper, sounds much better than most offerings with both more power AND lower THD specs. And it's rated at 0.3% THD across the audible band, poor by today's standards.
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Old 15th October 2012, 11:22 AM   #7432
dvv is offline dvv  Serbia
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BTW, Nige, I suggest you look over the old (1980 and onwards) issues of ELEKTOR. They had a fully complementary power MOSFET design which they revisited several times and by now, I reckon what was there has to have been squeezed out of it. A mature design, I'd say. And very good sounding. It was very popular locally, so I've seen and heard quite a number of them, certainly enough to say it sounds good.

You already know I believe thet, as John would say "all other things being equal", a fully complementary design will usually sound better than a classic design you show above. Not guaranteed, but certainly possible.
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Old 15th October 2012, 12:19 PM   #7433
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Hi DVV , I've got the ELEKTOR somewhere .

If the output stage is changed to conventional vbe bias and Complimentary Feedback Pairs it generally improves . Equally adding FET's gives better bass power . I know what you mean about FET bass . However all the amps I heard like that were bad amps . Did you try them in your design ? No source resistors required if buying from Exicon who match at no cost . Having looked closely at your amp I suspect it would be great with them in place . 3 sets 300 mA bias .

I suspect complimentary will be a marginal improvement as the curves say it will . Without ever trying it it seems high order distortion is reduced .

I think 0.1 % IM is the target .

My design is saying what if we had FET's earlier . We might have had this . It's like we went from Monkey to Human in one step . In amps we did . This is the Neanderthal if you like . We now know they were not so stupid from the tools they used . Us lot probably killed them off .

This is my Boeing 707 if you like . 747 is generic . I hear there is a move to go just below supersonic with conventional designs . About time . One hour or better saved to NY .
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Old 15th October 2012, 01:26 PM   #7434
dvv is offline dvv  Serbia
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Quote:
Originally Posted by nigel pearson View Post
...

This is my Boeing 707 if you like . 747 is generic . I hear there is a move to go just below supersonic with conventional designs . About time . One hour or better saved to NY .
That's only until they construct a jet engine which uses cow dung for fuel. Norweigian style, I understand they are already using cow poo to manufacture bio diesel within your local friendly bio diesel pump station.

After that, Mach 3.15 should be easy peasy. Saves like 4 hours London to NY. Hey man, if you've got it, flaunt it.
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Old 15th October 2012, 07:48 PM   #7435
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You may laugh . My friend Pippa ex BBC World Service and secretary to Alan Bond . He has just perfected a rocket / jet hybrid . UK to Australia in 45 minutes possibly in out lifetimes . To go to Spain would take longer as it would circle the Earth first . Perhaps the cost will be competitive ( $20 000 / kg I think at present ) . The main idea is to transport into space cheaply or was when I last took an interest .

http://www.reactionengines.co.uk/pre...ULY%202012.pdf
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Old 15th October 2012, 08:47 PM   #7436
gpapag is offline gpapag  Greece
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Talking of bandlimiting, here is the old and famous (much questioned and criticized) study from Bell Labs.

http://www.alcatel-lucent.com/bstj/v...tj10-4-616.pdf

I find data on pages 621-625 as important.

George

>Edit:This opens the door to a most valuable archive:

Bell System Technical Journal, 1922-1983

http://www.alcatel-lucent.com/bstj/
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Last edited by gpapag; 15th October 2012 at 09:00 PM.
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Old 15th October 2012, 09:36 PM   #7437
bcarso is offline bcarso  United States
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Quote:
Originally Posted by gpapag View Post
Talking of bandlimiting, here is the old and famous (much questioned and criticized) study from Bell Labs.

http://www.alcatel-lucent.com/bstj/v...tj10-4-616.pdf

I find data on pages 621-625 as important.

George

>Edit:This opens the door to a most valuable archive:

Bell System Technical Journal, 1922-1983

Bell System Technical Journal, 1922-1983
Thanks for that BSTJ link! There are a number of interesting things I'd wanted to follow up on.
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Old 16th October 2012, 06:42 AM   #7438
dvv is offline dvv  Serbia
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Quote:
Originally Posted by gpapag View Post
Talking of bandlimiting, here is the old and famous (much questioned and criticized) study from Bell Labs.

http://www.alcatel-lucent.com/bstj/v...tj10-4-616.pdf

I find data on pages 621-625 as important.

George

>Edit:This opens the door to a most valuable archive:

Bell System Technical Journal, 1922-1983

Bell System Technical Journal, 1922-1983
Well done, George, thank you.

I will find the time to read it carefully
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Old 16th October 2012, 07:00 AM   #7439
dvv is offline dvv  Serbia
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Originally Posted by nigel pearson View Post
You may laugh . My friend Pippa ex BBC World Service and secretary to Alan Bond . He has just perfected a rocket / jet hybrid . UK to Australia in 45 minutes possibly in out lifetimes . To go to Spain would take longer as it would circle the Earth first . Perhaps the cost will be competitive ( $20 000 / kg I think at present ) . The main idea is to transport into space cheaply or was when I last took an interest .

http://www.reactionengines.co.uk/pre...ULY%202012.pdf
Nige, please don't misunderstand me, it's just that I find the idea of manufacturing fuel, on a local level, from cow poo so fascinating and yes, a bit amusing as well.

But this is by no means a "mad scientist" idea, the Norwegians are actually developing a network of fuel pump stations across the country which do just that, and of course, they have developed one model and are developing more small city cars which use that fuel. It's no joke, no far off vision, it's today's reality. And if it works, who am I to complain?

My only real fear is that the price of beef will rise, and then some. Baby beef will become a true luxury item. Who wants to slaughter a power manufacturing organism?

As for the development of new modes of traveling, I only took a short look at the link you supplied (I'll read it in detaila later), but it seems to me this is the slingshot theory at work. The idea being to shoot a projectile into space, which takes some fuel to do, and then almost sail back down to your desired destination. Overall, one saves quite a bit of fuel in comparison with our rather wasteful jet planes of today, AND you gain in traveling time.

I don't know if it will happen in my lifetime, but I sure am hopeful. I will always support an idea which does its job and saves in natural resources. This may sound whacky, but I am angry at GM's tardiness in introducing small, eco friendly turbocharged 1.4 litre engines in the car model I own, Chevrolet Cruze. I was forced to buy a classic version of the model, with a naturally aspirated 1.8 litre engine simply because they could not make enough of the smaller turbo engines to offer them across the board. So that energy and exhaust friendly engine if offer only in the rich West (USA, Australia) and not in the poor East. Sure, it's an Euro 5 compliant engine, very clean, but the smaller one is cleaner still, AND uses less fuel.
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Old 16th October 2012, 10:06 AM   #7440
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Dvv . It wasn't that . Pippa and I were walking one day . I have known her for years . She suddenly says " you would have liked my old boss ". I had no idea she did that , she is BBC Pippa not space scientist Pippa . Alas all of the things she typed , not one fact had stayed with her ! Very frustrating . It was always a mystery to me why a certain power in 1943 didn't strap pulse jets onto their aircraft ? What a stupid use they did put them to . My dad was delivering news papers and hid behind the wall when hearing one stop . A minute or two later two old ladies were puling him out of the dust and rubble . The street was gone ( Sutton , London ) . When I was a baby I used to play on one in the back garden in Rye Sussex of my grandfather . apparently when taken to a museum years later it was still live ! I even twiddled its propeller distance measuring thing !


I don't know if anyone noticed the amp I drew had almost no bandwidth limiting and fair bit of feedback ? I have built these amps and they are totally OK and can be tweaked with two pole VAS compensation to further increase high frequency negative feedback .

The big deal is the lack of low frequency restriction seems highly desirable . Even with warped records no real problems found . Each choice shown was about using the best ideas for each section . I suspect very low bass enhances a feeling of space in the music ? This is not bass power , just the corner frequency . OK it might not be in the recording . That is not an excuse to say don't bother . In fact if already a problem don't make it worse .

Going back to pulse engines . My interest in electronics came from my dad teaching me the basics aged 4 . As I was highly interested in my grandfathers flying bomb he taught me that also . Locomotives and motorcycles came next . I was allowed to clean the carburetor of his BSA . I took my dad to the steam railway the other day . They insisted he drive the train and not me . That was correct . To be honest I didn't want to . He insisted I was the train lover . To which I said not me . He is 81 .

The Bell labs paper . I will print that as printed seems to work better for me .

About engines . Why not a double 4 cylinder V8 synchronize ? One engine switches off when not required via a clutch . In addition hybrid electric drive ( 50 kW ) ? The nice thing about hybrid is it can provide 4 wheel drive when needed . The engines can be direct drive via a clutch to the wheels . The beauty is the V8 becomes available when true performance required . For example a long drive in Germany . Now the master card . The car uses the engines in rotation . Every time one starts the car the engine least used is put into use . In addition in failure mode one engine could be switched off . The two engines would share a water supply so as to have the unused one ready for use . These could be no heavier that a usual V8 if discounting the extra crank . An economy version with one engine could be made . I would suggest 2000 cc per engine to make it a true super car . One could even have a V8 and a four together if wanting to be exceptional . That could be a 6 litre T12 as in Napier circa 1930 .
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