Here's a 20 watt amp, very simple but sound good

gaetan8888 · 17th July 2007, 10:11 PM

Hello

Here's a 20 watt amp, very simple but sound good, for those who want a small power amp, it's from Fairchild Semiconductor, 1974

Here's the shematic;

For the output darlington transistor you can use 2N6388 and 2N6668 , made by On Semiconductor, cost arround $1. at Mouser.com

I did made one for a friend, few years ago, it was sound very good.

Here's what I did get on my HP333 distortion analyser.

Distortion vs frequency

1khz .07 %
10khz .08 %
20khz .1 %
30khz .12 %

Distortion vs power output at 1 khz

.5 watt .17 %
1.5 watt .12 %
4 watt .05 %
12 watt .16 %
17 watt .5 %
20 watt 4 %

Try it and say your listening impressions.

Gaetan

GK · 17th July 2007, 11:23 PM

The SAP devices by Sanken would work well here too.

Datasheet:
http://www.farnell.com/datasheets/82862.pdf

Cheers,
Glen

Kapibara · 24th September 2007, 10:28 PM

Look very nice.
I will testing soon.

Tube_Dude · 24th September 2007, 11:30 PM

Hi

Without emitter resistors in the darlingtons , I'm afraid the quiescent current is not stable , and thermal runway can occur ...

Jorge

GK · 25th September 2007, 01:05 AM

Quote:

Originally posted by Tube_Dude
Hi

Without emitter resistors in the darlingtons , I'm afraid the quiescent current is not stable , and thermal runway can occur ...

Jorge

No. In that design the darlingtions are biased cut-off (ie < ClassB), so emitter resistors are not required, as there is no quiescent current.
It would generate heaps of crossover distortion.
That's why I mentioned the Sanken parts..........

Cheers,
Glen

linuxguru · 25th September 2007, 05:16 AM

Probably worth increasing the bootstrap cap to 100-220 uF, 50v - should improve the bass response below 30 Hz. Also a small bypass cap - say 1-22 uF, around the diode/resistor Vbe bias chain should improve the highs.

A small miller capacitance of around 33-100pF between the base and collector of Q1 should help suppress AC instability.

I've built something similar to this, but with a Vbe multiplier for crossover biasing, bias stabilization resistors of 0.2R in the emitters of Q2 & Q3, and 2N6054/59 TO-3 output darlingtons.

Leolabs · 25th September 2007, 02:57 PM

AHhhhhh!Output coupling cap!

robo7 · 25th September 2007, 03:41 PM

Quote:

AHhhhhh!Output coupling cap!

AH, a modern design...

was popular almost 40 years ago.

Kapibara · 25th September 2007, 05:24 PM

This amplifier is class B or class AB ?

Dzsoni · 25th September 2007, 06:05 PM

Quote:

Originally posted by Kapibara
This amplifier is class B or class AB ?

It's only a bad joke now in 2007...

17th July 2007, 10:11 PM	#1
gaetan8888 diyAudio Member Join Date: Apr 2007	Here's a 20 watt amp, very simple but sound good Hello Here's a 20 watt amp, very simple but sound good, for those who want a small power amp, it's from Fairchild Semiconductor, 1974 Here's the shematic; For the output darlington transistor you can use 2N6388 and 2N6668 , made by On Semiconductor, cost arround $1. at Mouser.com I did made one for a friend, few years ago, it was sound very good. Here's what I did get on my HP333 distortion analyser. Distortion vs frequency 1khz .07 % 10khz .08 % 20khz .1 % 30khz .12 % Distortion vs power output at 1 khz .5 watt .17 % 1.5 watt .12 % 4 watt .05 % 12 watt .16 % 17 watt .5 % 20 watt 4 % Try it and say your listening impressions. Gaetan

24th September 2007, 11:30 PM	#4
Tube_Dude diyAudio Member Join Date: Mar 2002 Location: Aveiro-Portugal	Hi Without emitter resistors in the darlingtons , I'm afraid the quiescent current is not stable , and thermal runway can occur ... Jorge __________________ Jorge

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17th July 2007, 11:23 PM	#2
GK Account disabled at member's request Join Date: Jan 2006	The SAP devices by Sanken would work well here too. Datasheet: http://www.farnell.com/datasheets/82862.pdf Cheers, Glen

24th September 2007, 10:28 PM	#3
Kapibara diyAudio Member Join Date: May 2007	Look very nice. I will testing soon.

25th September 2007, 05:16 AM	#6
linuxguru diyAudio Member Join Date: Sep 2007	Probably worth increasing the bootstrap cap to 100-220 uF, 50v - should improve the bass response below 30 Hz. Also a small bypass cap - say 1-22 uF, around the diode/resistor Vbe bias chain should improve the highs. A small miller capacitance of around 33-100pF between the base and collector of Q1 should help suppress AC instability. I've built something similar to this, but with a Vbe multiplier for crossover biasing, bias stabilization resistors of 0.2R in the emitters of Q2 & Q3, and 2N6054/59 TO-3 output darlingtons.

25th September 2007, 02:57 PM	#7
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	AHhhhhh!Output coupling cap!

25th September 2007, 05:24 PM	#9
Kapibara diyAudio Member Join Date: May 2007	This amplifier is class B or class AB ?

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