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Old 26th January 2006, 05:32 PM   #1
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Default class a elektor headphone amp

Does anyone know this amplifier ?
Click the image to open in full size.

I got it with a heatsink a few years ago and was told that it was an elektor class a headphone amp that could also deliver around 10 watts into 8 ohms.

Anyone recognice it ?
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Old 26th January 2006, 06:20 PM   #2
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Class A, discrete 10 Watt in 8 Ohm.
I do not remember this Elektor headphone amplifier.

What are those 4 ouput transistors?
BD139/BD140?
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Old 26th January 2006, 06:36 PM   #3
Nisbeth is offline Nisbeth  Denmark
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A headphone-amp that provides 10W output? That's a little unnecessary. Why don't you email elektor with the PCB-number and see if they can help you?


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Old 26th January 2006, 06:51 PM   #4
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I have build this Headphone amp too.
And somewhere i have the orignal article ...

But 10W is to mutch for this headsinks ...
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Old 26th January 2006, 06:54 PM   #5
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I remember this amp. 10 W with these transistors is a bit weak but if the supply voltage was +- 15 volts it's possible to get a couple of watts from the amp. Beware of the thin traces from the output.

Why do you ask?

I have the article somewhere in my collection. If you could tell me when it was published it would help me.
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Old 26th January 2006, 07:03 PM   #6
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Elektor did that design in 2 versions, the first one was part of their 80s discrete modular preamplifier design.
Second version was identical but doubled output devices, also BD139/140.
Bias was 0.1 amps.
I still have both articles.
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Old 26th January 2006, 09:21 PM   #7
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I soldered those trannies on today, the originals were fried/stolen a few years ago, i still have the heatsink that came with the amp when i got it from a forum member of a swedish hifi forum.

It originally used BD139/140, the ones there now is similar ones but are drivers from a broken poweramp.

It was the previous owner that said the thing could deliver around 10 watts in 8 ohms while it operated in class A driving 32ohm headphones.

I believe its either the 1983 mag 4 headphone amp, the mag 7 1984 mini crescendo, the mag 1 1986 AXL amp, the mag 9 1986 or the mag 10 1986 mini stereoamp.

Board number EPS83022-7 if it helps.
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Old 26th January 2006, 09:28 PM   #8
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It does nearly 10 watts in class AB.
With 4 BD139/140 per channel i managed to get 2 watts in class A and keep the devices alive.
Sound on a K1000 isn't bad

The board number stands for 1983
I can post a picture of the 2 device version i built, same as yours.
I used it on efficient loudspeakers, amazing what such a little amplifier can do.
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Old 26th January 2006, 09:34 PM   #9
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I find the sound suprisingly good with just a cd-rom drive as source.

My output transistors are: 2SD669A ond its complement 2SB649.

If anyone have the issue with this amp, i´d like a scan of the info sheet and schematic.
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Old 26th January 2006, 10:04 PM   #10
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Maybe i should add that i run it with a pc power supply, also i have it hooked up to a pair of old 4 ohm speakers.
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