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Old 20th April 2013, 02:45 PM   #1
lineup is offline lineup  Sweden
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Default Class A, 4 Watt, No Feedback, Simple Circuit, Great Sound

Here I will present a good way to produce 4 Watt in a simple way without global negative feedback and still have low distortion.
Uses only common transistors, type BC547B.
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Old 20th April 2013, 03:26 PM   #2
thanong is offline thanong  United States
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Quote:
Originally Posted by lineup View Post
Here I will present a good way to produce 4 Watt in a simple way without global negative feedback and still have low distortion.
Uses only common transistors, type BC547B.
Cool,lineup.Can you please show your circuit and informations,Thank.
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Old 20th April 2013, 03:48 PM   #3
lineup is offline lineup  Sweden
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Thanks thanong.
Here is first the simplified idea. See my attached diagram!

Q1 is the voltage amplifier.
The voltage gain is ruffly R1/R5 = 1800/270 ~6.6

After the voltage gain is one buffer follower = U1
The follower is biased by a CCS constant current source = I1

The final circuit uses heavy local feedback and so the distortion is rather low.
The circuit is very easy to setup and try and gives good Class A sound.

I show the complete circuit in my next post.
I am very happy for anyone who try this simple experiment.
It may sound better than you think - with only Class A 4 Watt ...
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Old 20th April 2013, 05:09 PM   #4
lineup is offline lineup  Sweden
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Here is the full circuit.
It delivers 4 Watt RMS into 8 Ohm with max 0.1 % distortion.
The output big transistors can be 2SC5200, MJL3281 or MJ21194.

The output DC voltage should be adjusted to V/2+0.8 Volt. Where V is the supply voltage.
Suitable transformer is 2x15 VAC. You use one winding for each channel.
One winding will give like 20-21 Volt DC supply voltage.

Enjoy
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Old 20th April 2013, 05:23 PM   #5
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I like it very much
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Old 20th April 2013, 09:55 PM   #6
Telstar is offline Telstar  Italy
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Nice
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Old 21st April 2013, 12:00 AM   #7
thanong is offline thanong  United States
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Thanks lineup,I will try.I very love small class A amp.I'm not listening to lound I guess maybe 1-2 watt (my room is small and I don't want to disturbing other poeple in my renting house.)I have a small tube single end class A receiver(Silvertone) that I took from console.Its sound nice but a little bit hum and I don't know how to fix.My system is pioneer cd player and alesis monitor one speaker.I listening to mostly jazz,blues,60's rock and country.Hope your circuit is not to hard to try ( I have background about electronics but not fluent in tube honestly)
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Old 21st April 2013, 01:44 AM   #8
AKSA is offline AKSA  Australia
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Lineup,

A very nice circuit. Elegant driver. Do you think you could almost double efficiency with an inductor in place of the CCS?

You have added something very worthwhile and good sounding to DIYaudio! Congratulations!

Hugh
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Old 21st April 2013, 02:07 AM   #9
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What size (value and physical size) inductor would be called for?
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Old 21st April 2013, 02:25 AM   #10
AKSA is offline AKSA  Australia
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Typicallly 80mH and DCR of around 0R5. This is a BIG, heavy lump. But it can double efficiency to about 30% for a Class A.

Hugh
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