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Old 7th February 2006, 12:13 PM   #1
bob_v5 is offline bob_v5  England
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Default Please help!!irf 740, simple amp

wondering if any one can give me a circuit diagram to build a very simple amp. I have zero budjet but feel like building something. I have a pc power supply, loads of resistors and capacitors, a stack of BC548, and an irf740. Plus anything i can pull from old gear thats lying about. I have found many simple circuits, but nothing that will work with only one power mosfet. I know an amp built with this stuff wouldnt be very good, but its just to keep me entertaind till i have some cash. I can get 5,12,17or 24 volts from the supply.
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Old 7th February 2006, 12:24 PM   #2
lineup is offline lineup  Sweden
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You can build an amp with only one IRF740 for output.
Should be good if you had some PNP small transistors
to work together with BC548, which is a NPN.

You can find any PNP?
Like BC557, BC558, BC556


What you also should look for is big power resistors.
They should be 22 Ohm or lower in value, downto 4.7 Ohm,
and physical size as big as possible.
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Old 7th February 2006, 03:42 PM   #3
bob_v5 is offline bob_v5  England
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not looking good. iv found a 709ce opamp, a few metal cased 4k7 resistors, mite be able to get more transistors from old computer parts.
I have transistors and a 22 ohm wire wound, which is quite big( about 3cm long and 1 round but old so probly not high power), from a faild project that blew up. (300w sub, worked great with 8 ohm speaker, 4 blew it ) Do you know how i could test them?
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Old 7th February 2006, 03:43 PM   #4
bob_v5 is offline bob_v5  England
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sorry jumbled message, too much caffene!
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Old 7th February 2006, 04:02 PM   #5
bob_v5 is offline bob_v5  England
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also have found
2n3906 pnp
2n3904 npn
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Old 7th February 2006, 04:24 PM   #6
lineup is offline lineup  Sweden
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Click the image to open in full size.

This is a very simple amp.
Using only one MOSFET.
It is the way Nelson Pass 'ZEN amplifier' works.

Where 'Current source' is where you can put a low value ( 4 - 10 Ohm )
Power resistor.
But it has to be big and be able to take a lot of heat.
They are mostly wire wound type.

Where says '8 Ohm Load' is where you connect your loudspeaker.

This picture is from ESP, ( Elliott Sound Products ) , project 36.
http://sound.westhost.com/project36.htm
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Old 7th February 2006, 04:33 PM   #7
bob_v5 is offline bob_v5  England
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cool cheers. was looking at the zen but i dont have an output transformer. Got a day off tomorow, guess what ill be doin!
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Old 7th February 2006, 04:35 PM   #8
lineup is offline lineup  Sweden
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Quote:
Originally posted by bob_v5
cool cheers. was looking at the zen but i dont have an output transformer. Got a day off tomorow, guess what ill be doin!
If you dont have it already,
here is the datasheet of IRF740:
http://www.irf.com/product-info/data...ata/irf740.pdf
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Old 7th February 2006, 05:20 PM   #9
bob_v5 is offline bob_v5  England
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allready got it but thanks for the help. Can you do my chemistry course work so i can build my amp instead?
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