Class A, 4 Watt, No Feedback, Simple Circuit, Great Sound - diyAudio
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 20th April 2013, 02:45 PM #1 diyAudio Member     Join Date: Dec 2005 Location: the north 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. __________________ lineup
diyAudio Member

Join Date: Sep 2010
Location: Seattle,Washington state,USA
Quote:
 Originally Posted by lineup 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.

diyAudio Member

Join Date: Dec 2005
Location: the north
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 ...
Attached Images
 4watt-simplified.jpg (23.8 KB, 2230 views)
__________________
lineup

diyAudio Member

Join Date: Dec 2005
Location: the north
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
Attached Images
 4watt-full-pub.jpg (43.7 KB, 2449 views)
__________________
lineup

 20th April 2013, 05:23 PM #5 diyAudio Member   Join Date: Mar 2004 Location: Krakow I like it very much __________________ regards, Pawel
 20th April 2013, 09:55 PM #6 diyAudio Member   Join Date: Dec 2007 Location: Italy Nice __________________ "The total harmonic distortion is not a measure of the degree of distastefulness to the listener and it is recommended that its use should be discontinued." D. Masa, 1938
 21st April 2013, 12:00 AM #7 diyAudio Member   Join Date: Sep 2010 Location: Seattle,Washington state,USA 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)
 21st April 2013, 01:44 AM #8 diyAudio Member   Join Date: Sep 2001 Location: Melbourne, Australia 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 __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com
 21st April 2013, 02:07 AM #9 diyAudio Member     Join Date: Sep 2007 Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though... Blog Entries: 145 What size (value and physical size) inductor would be called for? __________________ The heart ... first dictates the conclusion, then commands the head to provide the reasoning that will defend it. Anthony de Mello
 21st April 2013, 02:25 AM #10 diyAudio Member   Join Date: Sep 2001 Location: Melbourne, Australia 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 __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

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