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Old 13th June 2011, 06:47 PM   #1
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Default Layout critique

Made a layout for an EF amplifier with 60-100 W output into 8 ohm.

Most is based on Bob Cordells excellent examples in his book but with a few changes and additions here and there, some ideas are from this very forum, see Vbe multiplier. So nothing original and nothing I myself can take credit for.

However, interested in some (positive)critique of my layout.

It is not perfect but should be halfway decent, I hope so anyway.
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File Type: png Final Schematic.png (80.8 KB, 487 views)
File Type: png Final Layout.png (79.9 KB, 479 views)
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Old 13th June 2011, 07:19 PM   #2
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Realised the holes for the output coil were too small.
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Old 13th June 2011, 07:48 PM   #3
AndrewT is offline AndrewT  Scotland
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Why the big gap between the + & - power rails?
You repeat the same "gap" in the voltage amp stage.
Both these aerials will inject interference into all the adjacent circuits.
The very wide spacing of the outputs devices demands an enormously wide/tall heatsink.

Move the L//R of the Thiele Network off board.
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Old 13th June 2011, 07:59 PM   #4
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Quote:
Originally Posted by AndrewT View Post
Why the big gap between the + & - power rails?
You repeat the same "gap" in the voltage amp stage.
Both these aerials will inject interference into all the adjacent circuits.
The very wide spacing of the outputs devices demands an enormously wide/tall heatsink.

Move the L//R of the Thiele Network off board.
Ah yes, the big gap, that is one of the things that could be done better, but as always, making a layout is a compromise.

The board is 150 x 84 mm, going to use a 300 x 160/210 MM sink for each module. Modushop.biz Pessante Dissipante case standard sizes.

Why do you want the output coil+resistor offboard? That was my first thought but there is more than enough room for those on the PCB.

Some of the layout has taken ideas from the somewhat popular Lynx amplifier from Jan Dupont. It too has the same gaps between power rails and I have seen the same on many others. I would do it differently if there was an easy way to do so.

Last edited by Neutrality; 13th June 2011 at 08:04 PM.
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Old 14th June 2011, 09:10 AM   #5
AndrewT is offline AndrewT  Scotland
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The magnetic field emitted by the coil could have an adverse effect on the performance of the amplifier.
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Old 14th June 2011, 11:31 AM   #6
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beyond that pcb as said is too wide ...could be done much more compact ....
then also the usual mistakes are done ....

since you are going to pay for a double sided pcb you may as well skip the idea of suppling outputs and front stage speratelly ... There is a possibility that eventually you might run to ground loop issues

if you decide to stay with this design be sure that some capacitance and decoupling will be needed for the front stage also
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Old 14th June 2011, 01:22 PM   #7
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Quote:
Originally Posted by Neutrality View Post
Ah yes, the big gap, that is one of the things that could be done better, but as always, making a layout is a compromise.

The board is 150 x 84 mm, going to use a 300 x 160/210 MM sink for each module. Modushop.biz Pessante Dissipante case standard sizes.

Why do you want the output coil+resistor offboard? That was my first thought but there is more than enough room for those on the PCB.

Some of the layout has taken ideas from the somewhat popular Lynx amplifier from Jan Dupont. It too has the same gaps between power rails and I have seen the same on many others. I would do it differently if there was an easy way to do so.

Everybody is so "picky".

First the circuit -
1. Add 2.2R - 4.7R basestoppers to each output (covered in Bob's book).
Basestoppers on each driver , too. (22R - 47R)
2 . decouple both the current sources with the same resistive divider/cap (below 1) - minimizes "thump" (nearly eliminates it -both ccs's stabilize simultaneously)... Shown (below 1 -R9 ,10,22 and C5). Your call as far as what type CCS you want to use .

3. Look at my example as far as the input stage , the same adjustable CCS and offset control is used on about 50 amps now - it works very well.

The layout -
No problem with size and the coil (below 2 - inductor) sampson and all the OEM pro amp's put it in the same place. Saki's recommendation of local decoupling for the voltage stage is essential , either for common rail or boosted rail.

Your NPN Vbe to-126 device must be on the main heatsink to work. Just had had to let you know .. .

OS
Attached Images
File Type: gif ccs.gif (13.4 KB, 347 views)
File Type: gif op coil.gif (91.3 KB, 352 views)
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Old 14th June 2011, 01:43 PM   #8
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PICKY , PICKY ....

Most OEM output boards are large ... and for a reason...

You must spread the heat. The sampson above is 100mm X 200mm , most of the 3-4pair DIY EBAY boards are 75 X 175-200mm. To put 3-5 pair OP's on a 125mm board would be folly.

If you want a project to inspire , try Roender's thread - RMI-FC100, a single stage audio power amplifier

Larger board , all aspects covered.

OS
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Old 14th June 2011, 09:34 PM   #9
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Went back and added base stoppers, next up will be some added decoupling for the boosted front end. Something like 100uF//100nF pr. rail should be good enough.

As for the Vbe TO-126 device, my plan was to mount it on top of one of the output transistors for faster reaction to thermal changes.

As for decoupling of the CCS's I wont bother with it, Im going to make a DC speaker protection with turn on mute etc. so even if theres is a turn on thump I wont notice it anyway. But thanks for the suggestion, maybe I'll add it or maybe I wont, dont really know.
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Old 15th June 2011, 12:47 PM   #10
alex mm is offline alex mm  Romania
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Default First atempt to layout .......

...... Have spent ,few hours, to layout schematic from first page , so the result attach ......
Alex.
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