Please help!!irf 740, simple amp

bob_v5 · 7th February 2006, 12:13 PM

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.

lineup · 7th February 2006, 12:24 PM

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.

bob_v5 · 7th February 2006, 03:42 PM

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?

bob_v5 · 7th February 2006, 03:43 PM

sorry jumbled message, too much caffene!

bob_v5 · 7th February 2006, 04:02 PM

also have found
2n3906 pnp
2n3904 npn

lineup · 7th February 2006, 04:24 PM

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

bob_v5 · 7th February 2006, 04:33 PM

cool cheers. was looking at the zen but i dont have an output transformer. Got a day off tomorow, guess what ill be doin!

lineup · 7th February 2006, 04:35 PM

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

bob_v5 · 7th February 2006, 05:20 PM

allready got it but thanks for the help. Can you do my chemistry course work so i can build my amp instead?

7th February 2006, 12:13 PM	#1
bob_v5 diyAudio Member Join Date: Sep 2005	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.

7th February 2006, 12:24 PM	#2
lineup diyAudio Member Join Date: Dec 2005 Location: the north	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. __________________ lineup

7th February 2006, 04:24 PM	#6
lineup diyAudio Member Join Date: Dec 2005 Location: the north	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 __________________ lineup

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7th February 2006, 03:42 PM	#3
bob_v5 diyAudio Member Join Date: Sep 2005	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?

7th February 2006, 03:43 PM	#4
bob_v5 diyAudio Member Join Date: Sep 2005	sorry jumbled message, too much caffene!

7th February 2006, 04:02 PM	#5
bob_v5 diyAudio Member Join Date: Sep 2005	also have found 2n3906 pnp 2n3904 npn

7th February 2006, 04:33 PM	#7
bob_v5 diyAudio Member Join Date: Sep 2005	cool cheers. was looking at the zen but i dont have an output transformer. Got a day off tomorow, guess what ill be doin!

7th February 2006, 05:20 PM	#9
bob_v5 diyAudio Member Join Date: Sep 2005	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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