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Old 30th November 2011, 12:53 PM   #11
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Placing Q9 on a heatsink by itself is a recipe for disaster. It provides thermal compensation, therefore it must be on the same heatsink as the drivers (Q7 and Q8). The closer it is to them, the better it will work. This means that your existing layout will have to change drastically, but that is just the way these things work.

Last edited by ingenieus; 30th November 2011 at 01:09 PM.
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Old 30th November 2011, 01:01 PM   #12
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Quote:
Originally Posted by paranoid06 View Post
Thank you for your suggestions everybody, I've tried to edit the layout according to Alfonz's suggestions. Hope its better this time!

@sakis - what happens if the layout isn't up to the mark? Will it cause oscillations in the amp??
@kalmara - thank you for letting me know that! That was just something that cannot be avoided! And was out of carelessness.
@ingenius - Is it really necessary to keep them in a line? I was thinking of using U shaped heatsinks used for TO-220s

I've attached the edited layout.

Thanks and Regards
Hi paranoid06,

Re your layout - if Q7 and Q8 are vertically mounted on the PCB, you will need to move R13 & R14 away from the top board edge to allow for the heatsink. If you only intend Q7 & Q8 to mount flat on a right-angled bracket, this may not be a problem.

Regards,
currentflow
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Old 30th November 2011, 01:20 PM   #13
mdhull is offline mdhull  South Africa
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Quote:
Originally Posted by ingenieus View Post
Placing Q9 on a heatsink by itself is a recipe for disaster. It provides thermal compensation, therefore it must be on the same heatsink as the drivers (Q7 and Q8). The closer it is to them, the better it will work. This means that your existing layout will have to change drastically, but that is just the way these things work.
It's a CFP output stage so thermal linking of the Vbe mult bias transistor is not mandatory
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Old 30th November 2011, 03:13 PM   #14
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@ingenieus - I guess ur mistaken, Q9 is BC546!
@currentflow - I will be flat mounting them on a right angled aluminium bracket. So no worries! Anyways thanks!

Regards
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Old 30th November 2011, 03:28 PM   #15
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Another Edit!
Q4 and Q5 kept collinear.

Regards
Attached Images
File Type: jpg P3A Layout-4.jpg (132.9 KB, 1308 views)
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Old 30th November 2011, 04:08 PM   #16
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Originally Posted by mdhull View Post
It's a CFP output stage so thermal linking of the Vbe mult bias transistor is not mandatory
That applies for the pre-drivers but I'm not so sure about the Vbe multiplier. Douglas Self discusses the difference between thermal compensation for CFP and EF stages at some length in his book. He concludes that CFP has larger bias errors than EF and then describes ways to mount TO225 devices on TO3 or TO3P drivers.

Last edited by ingenieus; 30th November 2011 at 04:34 PM.
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Old 30th November 2011, 04:20 PM   #17
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do the reading of the forum regarding this issue
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Old 30th November 2011, 04:27 PM   #18
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Originally Posted by paranoid06 View Post
@ingenieus - I guess ur mistaken, Q9 is BC546!
It still has to go on to the heatsink. There are ways to do that. You could glue it on. You could also wrap it in a piece of copper tubing or copper sheet and bolt it down. I'm not sure about what works best. Somebody else might care to comment on this.
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Old 30th November 2011, 04:32 PM   #19
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Originally Posted by ingenieus View Post
That applies for the pre-drivers but I'm not so sure about the Vbe multiplier.
For CFP there is local feedback in the output stage and the Vbe multiplier should be in thermal contact with one or both of the drivers, not OPs, if any.

PS: ESP makes a living from his website, selling PCBs for his projects among other things.
Support him and get the 'reference' boards at the same time!

Last edited by discrete; 30th November 2011 at 04:35 PM.
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Old 30th November 2011, 04:34 PM   #20
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do the reading of the forum regarding this issue
Yes. I am!
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