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Old 11th May 2007, 10:49 PM   #21
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Sorry again, forgot the picture
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Old 11th May 2007, 10:51 PM   #22
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Refering to: http://www.ortodoxism.ro/datasheets/...ld/IRFP240.pdf ... the MOSFET output cans should be well "greased" and on reasonable sized heat sinks. ( I did it this way: http://3dotaudio.com/ampics.html = aluminum sinks about the size of a post card, ~3/4" deep fins, one for each amp of max. 150 watts.)

Refering to: http://focus.ti.com/lit/ds/symlink/opa445.pdf ... absolute max voltage is +/- 50 VDC, well filtered ... so +/- 45 is not a serious concern unless your power supply "springs a leak" = pop, sizzle, smoke, ... power supply rejection is only about 30 db @ 20K Htz., so filter up = say 20,000 uF per rail in the supply (I think 220 uF is enough close to the op-amp and MOSFETs, but not near enough back at the diode bridge/PS) ... plus the 22uF or more should be close coupled at the op-amp power pins and don't forget those 0.1 uF plastic snubbing caps ... stack 'em up like they were makin' love.

If you figured out the resistors right, this will be a very nice sounding amp ... got a PC board? ... (can I have one or two?)

I'm a littl puzzled about that pot off of op-amp pin 6 ... that's for DC offest adjustments, right? ... TI's Page 8 shows a little different way to do it ...
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Old 11th May 2007, 11:15 PM   #23
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Hi, fastEDY

I'll keep in mind your advice about the heat sinks and PS.

Remember my post n11
"PS: electronics is a hobby to me, I'm a dentist".

I'm a rooky, thath why I make my own PCB's design with "Express PCB" then make a transfer with Press'nPeel. Of course I can make a PCB design too, and share.
Cheers
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Old 11th May 2007, 11:19 PM   #24
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Quote:
I'm a littl puzzled about that pot off of op-amp pin 6 ... that's for DC offest adjustments, right? ... TI's Page 8 shows a little different way to do it ... [/B]

"You could put a 100-250 ohm trimpot between R5 and R6 and balance out the even harmonic distortion fairly easily. Did it 40 years ago, it should still work."

Thath was a suggestion of John curl, post#19

Cheers
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Old 12th May 2007, 05:08 AM   #25
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Quote:
Originally posted by bracoraab



"You could put a 100-250 ohm trimpot between R5 and R6 and balance out the even harmonic distortion fairly easily. Did it 40 years ago, it should still work."

Thath was a suggestion of John curl, post#19

Cheers
right...it can be done this way too...
before first turn on put it in the middle and then trimm the value to the lowest dc ...wait until the amp is a bit warm or warm fully and then trimm again...
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Old 12th May 2007, 11:26 AM   #26
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Hi Daniel, I'll keep in my mind too.
Hvala lijepa.
Braco
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Old 12th May 2007, 01:05 PM   #27
cs is offline cs  United Kingdom
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One more thing Braco :-

The OPA445 only has a gain-BW product of 2MHz, so the distortion at a closed loop gain of 30 may not be that good.

This is why I used a closed loop gain of 2, then used another (lower voltage) op amp as a driver with a gain of 10-20.

CS
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Old 12th May 2007, 01:40 PM   #28
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Hi, CS

Thanks for the concepts, then, you suggest to change the opa445 to opa552 12MHz bandwith?
Sorry for the cuestion, my electronics knowledge is too basic.

Well, I worked on the PCB and here are the results:
The PCB design
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Old 12th May 2007, 01:40 PM   #29
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bracoraab,

You need to check on the power dissipation of the op amp. The bias circuit on its output will draw quite a bit of power if the output swing of the amp is large. Take a look at the safe operating area and heatsink information on the data sheet.

Rick
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Old 12th May 2007, 01:41 PM   #30
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And the components layout
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