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Old 12th July 2011, 08:07 AM   #121
AKSA is offline AKSA  Australia
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Why Sonnya? We don't want a 7W resistor here, a 5W would be more than sufficient.

Imagine 3.5A peak, that's 2.47A rms, and with 0R15 dissipation is one half of 2.47 squared x 0.15 which is 0.46W. This is continuous, 50W into 8R, absolutely flat strap. So 5W is more than enough as I usually simply triple the worst case!

It's 25mm, should be close enough for government work......

Hugh
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Last edited by AKSA; 12th July 2011 at 08:10 AM.
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Old 12th July 2011, 08:25 AM   #122
sonnya is offline sonnya  Denmark
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The bodylength of the Ohmite is 23.8/25.8mm and then you need a few mm in each en to bend the wires.

But again, this is if you would like to make space to the ohmite. There is plenty of room for the 3W 13FR150 in your layout at the present state.

Sorry for asking, it was not ment to question your layout. It surely looks good.
It is only to be sure, as i make the same mistake once in a while
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Old 12th July 2011, 08:26 AM   #123
srh is offline srh  New Zealand
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Hi Hugh, latest layout looks good. Now where is L1 damping resistor hiding? Under the board?(I hope.) Absolutely agree about the position of the take off point for the feedback.
Cheers,
Steve.
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Old 12th July 2011, 08:55 AM   #124
AKSA is offline AKSA  Australia
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Hey, Sonnya, give me tips by all means.

I'm leery of using resistors that are unnecessarily big. In truth a 3W source resistor is quite adequate. There is space there for 5W sandcast as well.

You are right about mistakes; I made my last in 1967, quite a serious one.....

Steve,

INSIDE the inductor, which accounts for the additional hole left and right at the centerline. It's a very compact way of doing it.

I think we have all bases covered now for the output stage fb take off point, thanks for bringing it up. I wasn't happy with the original either.

Cheers,

Hugh
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Old 12th July 2011, 10:32 AM   #125
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by AKSA View Post
....... what is important is that the feedback is taken from the midpoint.
D.Self disagrees.
I disagree, many disagree.

The NFB tapping point must come off the output trace. It must not be taken off the Re connecting trace.
Midpoint has nothing to do with correct NFB tapping point.
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Old 12th July 2011, 11:20 AM   #126
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Feeback should be taken after the summing point of both outputs. Whether or not the summing point is centered cannot matter any more then the Vbe diferences and emitter resistor variances, as long as the traces are large enough to carry their loads gracefully. Unless perhaps if EMI is a concern, but probably not?

If the both the output node and NFB are taken at the summing junction, small errors in the junction geometry will cause distortion. However much it matters is anyone's guess, but good practice is good practice. Especially when it holds back a frenzy of correction posts.

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Old 12th July 2011, 11:28 AM   #127
sonnya is offline sonnya  Denmark
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Quote:
Originally Posted by AndrewT View Post
D.Self disagrees.
I disagree, many disagree.

The NFB tapping point must come off the output trace. It must not be taken off the Re connecting trace.
Midpoint has nothing to do with correct NFB tapping point.
Well, it is taken from the centerpoint or should we say starpoint. And as long it is taken from the startpoint where the two resistors meets with the outputcoil it is perfectly ok. I do not expect any degration because of that.

Secondly Hugh has build many wellsounding amps according to the audience so he knows what he is doing.
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Old 12th July 2011, 11:38 AM   #128
AndrewT is offline AndrewT  Scotland
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Sonnya,
read kean's comment.

Aksa has written "midpoint". That is completely irrelevant, no matter what his opinion/reputation/skill/talent/previous products.
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Old 12th July 2011, 12:20 PM   #129
sonnya is offline sonnya  Denmark
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I also have the textbook. We are talking 10mm offset, in dself book... That is right. then i agree but in the latest layout Hugh has made we are talking 1 - 2mm offset if not less. But you can try calculate the sq.area of both sides of the junction/ summingpoint

A much bigger issue where the ground potential is taken for the Feedback loop. You have much less signal/noise ratio here than at the output.
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Old 12th July 2011, 11:16 PM   #130
AKSA is offline AKSA  Australia
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Interesting. I think I will let the experts slug it out.

Guys, let me know what I should be doing, and I will make the changes.

Cheers,

Hugh
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