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Old 14th March 2013, 10:12 AM   #8631
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I think it was King George VI Equerry who received a letter saying " Did the King know it was bad taste to have brown shoes with a blue pinstripe suit " ? The Equerry wrote back " He does , therefore it isn't " .

That's the point . We know and we choose to do differently .

My other point is I often sit at my modest test gear and play " what if " . I know for a fact Formula One guys do this . No one can say they lack facilitates or brains ( how many here would be able to live in that world , engineer or not ? ) . I looked at a Renault on test day . I said your problem is the back end is too light and you are not getting the power down . We all knew it was the regulations and not wanting extra weight . I suggested hairspray on the tyres . We laughed as we knew it would be banned . However two races might be the time to get banned . The idea came from Speedway racing , it was banned . Doubtless it wouldn't work as the speedway was thought to be dirt sticking to the tyres giving 1 second a lap . But who knows without trying ? The scientists of 1880 must have thought they knew most things . Most never guessed what was around the corner ? Listening to live Beethoven the other day told me we got nearer in 1938 than now . The recording engineers can not be 100 % of the problem . Vitally no recording I hear sounds like Beethoven . To sum up , real Beethoven sounds like direct cut 78's , it's magical . Maybe something that comes from another dimension can not be trapped so easily . Like us it has a soul whatever that might be ? Some of those 78's reached 32 kHz on the stampers if pressed on Vinyl ( post war FFRR , 7 kHz on the disk and only for one play ) ! Bob Stuart was saying this in the 1970's " Causes of distortion in audio amplifiers due to loss of information " i.e the soul .

TAS 194: Meridian Audio's Bob Stuart Talks with Robert Harley | The Absolute Sound

I took the chief engineer of Thoren's with me to FI test day . He only went to prevent me asking his wife ? She was furious as she is a journalist and she would have had access to the German drivers ( Silverstone test day ) . Kurt did say to Renault that the Red Bull were faster with the same engine as the car sounded different into corners ( rough ) . The engine the same and the mapping the same . It was the " Blown Diffuser " . They smiled at Kurt politely . He was right . Kurt is as penniless as me , that would have been a nice little number for him . The crumbs from the table of F1 would feed us nicely .

FET's measure worse . They are very obliging . Usually all their problems can be solved . Too many people read various things and it becomes " fact " . Facts + belief = mediocrity . Think about it . If the facts are the facts then only one solution is correct . That being true only price matters . As F1 proves . You can have all the facts and still loose a race . It is the unseen factors that count . That rock from space proves that .

I was looking at TDA 2030 this week . It is not far from being as good as we need . I have been driving a motor with it . I am impressed as they even at the UK's inflated prices cost $1.50 ( 5 off RS , PCB about same price ) . It might be a bit mediocre , dam well measures OK . I am so tempted to use it in feed-forward with some dumpers to crack 1R ( 10 V rms ) . In bridge 20 V rms ! Here is the irony , it might be better than a muscle amp into that load ? I dare say the 2030 can be stacked as did Douglas Self with NE5532 . After all the 2030 is just an op amp with grunt .
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Old 14th March 2013, 10:26 AM   #8632
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Indeed TDA2030's can be stacked - I did it 4 wide for the bass mids on these amps. Doesn't help with their sucky RF rejection though : http://www.diyaudio.com/forums/blogs...i-p6020438.jpg
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Old 14th March 2013, 10:51 AM   #8633
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I bet they still would run rings around valve amps on that problem ? When Henry Ford grafted two model T engines together the world never was the same . Suddenly an engine so very humble was not . The Flathead Ford V8 . Model T was remarkable . With the state of our roads maybe that's what I need ? People who laugh at model T do not realize it's special design . If the going gets tough is almost a 4x4 and no complexity .

Any tips on stacking 2030's ?
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Old 14th March 2013, 11:01 AM   #8634
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Yeah - for audio there are better choices than TDA2030 I reckon. Not very transparent because of their RF susceptibility. I abandoned arrays of TDA2030s primarily though because sometimes on start-up they'd crowbar the supply, which was fine running from my bench supply because I could set the current limit so nothing got blown up. But I was unwilling to troubleshoot this problem as it was intermittent. Another reason for avoiding the TDA2030 was its lack of mute.

If you want to stack chips then TDA7293 would be my choice - its much easier as it has a master-slave facility built in. It also has mute. Its not quite as cheap though as TDA2030 (I was using the A version which has slightly higher max supply voltage).
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Old 14th March 2013, 11:16 AM   #8635
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Funny you say that . For a Pabst motor TDA7293 is a great choice ( and so cheap ) . It has many options . It is like a postage stamp so doubt it is good for more than 20 watts continuous . However a short term test suggested otherwise .


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Old 14th March 2013, 11:32 AM   #8636
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There I was thinking you were planning some serious stacking : 7 TDA7293 in Parallel 555W Mono Subwoofer Power Amplifier Board | eBay
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Old 14th March 2013, 11:39 AM   #8637
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Originally Posted by jcx View Post
its interesting how these low numbers of global feedback keep getting bandied about - this is still in the region where Baxandal's "harmonic multiplication" math shows some higher harmonics may be increased by the negative feedback

while >40 dB over audio bandwidth is quite practical today with RET or MOSFET output Q speed - the Linear Audio Putzeys article is unusually clear but the result that negative feedback should be maximized when used at all if you value accuracy is a standard feeback theory result

Putzeys Bruno (you have to cruise the site for the free sample of the article)

and at higher loop gains the higher order harmonic "hump" gets pushed into the noise floor - all visible harmonics are decreasing with order

DF 96 wrote about that sometime ago . As far as I can see ( under his guidance ) all that happens with increasing negative feedback is we are left with the harmonics which the failing gain of the amp can not fix ? I looked very carefully after that and found they were always there and looked the same . I had thought previously they emerged . If the amp goes unstable that is another matter . I did notice trends .These sometimes suggest an optimum feedback level has been reached . This might be , I can have 20% more wattage but it looks very ugly . I can still have that wattage and it will be 10% distortion all in perfect harmonic reduction in the harmonics . So what should I do ? Have the 10 % distortion and not the 2% . The reason being the below 80% matters much more . If designing transistor amps these trends still exist and can be manipulated . Best one I know of is let the driver amp clip first . No text books says that ? You can always have a switch to do it how you have been told to . Also makes for very quiet drivers ( and cheap , RC filter ) . Why use regulated power supplies when the output transistors are happy to do the same if not driven into ripple ? And it is so dam fast !
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Old 14th March 2013, 11:43 AM   #8638
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Originally Posted by abraxalito View Post
There I was thinking you were planning some serious stacking : 7 TDA7293 in Parallel 555W Mono Subwoofer Power Amplifier Board | eBay
COOL ( or hot )
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Old 14th March 2013, 08:05 PM   #8639
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Originally Posted by nigel pearson View Post
COOL ( or hot )
Depends on the quiescent bias current.
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Old 14th March 2013, 08:10 PM   #8640
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I think that as technology advances we will be seeing more and more all-in-one power amp chips.

I suspect that in say 10 years' time, discrete will be only in luxury items, while the Lo Fi and Lower Mid Fi will use power chips. Many already are.

On the other hand, I believe people will refine the sound of the power chips.

For example, here's one for Nige to ponder over - would a power chip sound better if it was buffered by a FET input op amp? I have a nagging feeling that it really might sound better, at least in this stage of their development.
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