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Old 19th April 2006, 11:50 AM   #1
aetosa is offline aetosa  Greece
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Default AN948 amp project

I'm trying to built the amplifier I found at http://www.irf.com/technical-info/appnotes/an-948.pdf
In fact I've built it, but some things are missing, because the PCB is not very clear. I've attached the PCB with the components drawn on it. Can you tell me if it is correct? If it needs something more?
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Old 19th April 2006, 11:55 AM   #2
aetosa is offline aetosa  Greece
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I enlarged it .
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Old 19th April 2006, 02:21 PM   #3
djk is offline djk
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That was not a design from an audio engineer, the boad layout leaves a lot to be desired.

The gate of Q6 needs to go through a resistor (try 220R) to the collector of Q4, the drain goes to the negative rail voltage.

Q3 must be attached to the heatsink, and have a cap across CE on the board (0.1F~10F).

C2 needs a 0.1F in parallel, as does C3.

Q1, Q2 are in wrong, depends on the pin-out of the devices used, but they are wrong in any event.

Considering that this may be your first project, I would choose something different, this would be too much of a challenge.
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Old 19th April 2006, 03:08 PM   #4
aetosa is offline aetosa  Greece
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Sorry, I forgot to mention that I have replaced Q1, Q2, Q3, Q4.
Q1=BC640 Q2=BC560 Q3=MPSA43 Q4=BC549.
I have built quite a lot of other projects. It's just that this one, even though DOES have a PCB layout BUT is not very clear and some things (like bridges(I mean wires from one point to another)) are missing.
I have attached the layout of the transistors.
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Old 19th April 2006, 03:12 PM   #5
aetosa is offline aetosa  Greece
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This must look better.
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Old 20th April 2006, 11:26 AM   #6
djk is offline djk
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You clearly have either Q1 or Q2 in backwards. The basic IRF design is poor, so is their board layout.

The grounding scheme stinks. As a bare minimum, cut the trace on R1, C1, R7 away from ground, and add 10 ohms between the two. Drill a pair of holes near R15, one for power ground, the other for the speaker ground.

You will need clamp diodes on the outputs, and a gate resistor on Q6, probably some compensation on Q4 as well. L1 needs a damping resistor.

I would rather adapt the $6 A40 board:

http://www.audioxpress.com/bksprods/pcbs/nelsonpass.htm

http://www.passdiy.com/pdf/a40.pdf
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Old 21st April 2006, 07:55 AM   #7
aetosa is offline aetosa  Greece
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'You clearly have either Q1 or Q2 in backwards'.
I'm posting the layout (Schematic and Board) I've made in Eagle .
(In the scematic I'm using, Q3=BF391)
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Old 21st April 2006, 08:08 AM   #8
aetosa is offline aetosa  Greece
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Sorry I forgot the attachment!!!
Here it is...
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Old 21st April 2006, 08:30 AM   #9
aetosa is offline aetosa  Greece
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As you will see, in the BOARD,pin 1 of Q3 , I havent made it. I left as you see it, only because I wanted it to look like my PCB (the real one, tha I have made)
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Old 21st April 2006, 08:46 AM   #10
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hi aetosa,

I had a quick look at your eagle files, and, althougn I'm not an expert, I would like to add a word of caution. You need to carefully check all the small signal transistor pins.

Also, Q1 should be the same as Q2 and the output devices on the PCBs usually have the heatsink facing the edge of the board.

good luck
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