I want to build a 1-2W class a amplifier for use in a 5,25" pc expansion slot - diyAudio
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Old 21st April 2013, 04:39 AM   #1
Shamron is offline Shamron  Norway
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Default I want to build a 1-2W class a amplifier for use in a 5,25" pc expansion slot

Hi everyone.

As the topic says, i want to build a small class a amplifier (1-2W) for use in my pc and to make it fit in a 5.25" (cd-rom slot).

I love the JLH a lot and i got both 2x10, 2x15 and 2x40W versions of it and they all use either sc5200 or mj15003 output transistors. Is it possible to use something smaller for this project? Something similar to bd140?

I've googled a bit but the closest i come is 3-5W which would generate too much heat i guess.

Anyone got schematics or could give me a few tips? What modifications would i need to do to the original JLH to downscale it to 1-2W?

Thanks in advance.
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Old 21st April 2013, 05:55 AM   #2
lineup is offline lineup  Sweden
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I would be able to design such an amplifier.
I think you can get away with TO-220 transistors in the output.
The power supply would be 12V DC from the PC.

You are very right to say it would be 1-2 Watt.
The circuit could be very simple, of course, but Class A would be fine.

You can take a look at my new Class A circuit: Class A, 4 Watt, No Feedback, Simple Circuit, Great Sound
This would be good for 12 VDC supply, too.
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Old 21st April 2013, 06:30 AM   #3
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JLH 69' scaled for 1 watt. Can be plugged into the PC's 12volt line for power. Heat generated is about 4 watts or so per channel with 350mA bias. Heatsinks sized to the dimensions of the height and length of the bay should work fine.
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Old 21st April 2013, 09:07 AM   #4
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What about downscaling this: http://www.firstwatt.com/pdf/art_beast.pdf
EDIT: Not a good idea. Just single 12V supply.

Last edited by franzm; 21st April 2013 at 09:16 AM.
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Old 21st April 2013, 10:18 AM   #5
Shamron is offline Shamron  Norway
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Quote:
Originally Posted by jerluwoo View Post
JLH 69' scaled for 1 watt. Can be plugged into the PC's 12volt line for power. Heat generated is about 4 watts or so per channel with 350mA bias. Heatsinks sized to the dimensions of the height and length of the bay should work fine.
Thanks a lot, i think i will go for this one as i have the bd139's and only need to order the other 2 transistors.

What program did you use to create the circuit?

@Lineup: I actually found that thread in google, but i want to avoid using sc5200's unless i'll get less heat with them?

Thanks to you others as well. :-)

Last edited by Shamron; 21st April 2013 at 10:19 AM. Reason: typo
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Old 21st April 2013, 11:00 AM   #6
Telstar is offline Telstar  Italy
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Some headphone amps have the caracteristics you are looking for, such as the jlh for hp. The circuit posted above is very nice, and you can find cheap pcbs from the usual Chinese ebayers (jimsaudio for instance).
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Old 21st April 2013, 11:03 AM   #7
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Bigger transistors make less heat than small ones (at the same power)

It's OK to use them for the little amp.
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Old 21st April 2013, 12:56 PM   #8
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Originally Posted by EWorkshop1708 View Post
Bigger transistors make less heat than small ones (at the same power)

It's OK to use them for the little amp.
????? 4W is 4W. no mather if its TO-220 or TO-247. With the bigger one you get less heat pr square inch.
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Old 27th April 2013, 01:53 PM   #9
Telstar is offline Telstar  Italy
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Not only, but the big power transistors are less linear at small currents. The OP should check the datasheets well before choosing.
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