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
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;
An externally hosted image should be here but it was not working when we last tested it.
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
The SAP devices by Sanken would work well here too.
Datasheet:
http://www.farnell.com/datasheets/82862.pdf
Cheers,
Glen
Datasheet:
http://www.farnell.com/datasheets/82862.pdf
Cheers,
Glen
Tube_Dude said: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
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.
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.
AHhhhhh!Output coupling cap!
AH, a modern design...
was popular almost 40 years ago.
Kapibara said:This amplifier is class B or class AB ?
It's only a bad joke now in 2007...
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That certainly does look like a 70's app. note. It's class C, almost to class B. A little more bias so the junctions are really almost on might help it out a lot. Even 1 mA of current would really help. It is not in any danger of going into thermal runaway as long as the bias components are on the heat sink or transistor cases.
-Chris
Fer sure!Never liked them....... colored sound
-Chris
Hello
Hey guy's I know it's a 30 years old circuit, but it's so simple and it's working since I've built one 8 years ago, it was good as a so simple circuit can be and I heard much worse amp with 5 time more transistors, he he he, but it's an easy amp for the beginer.
Linuxguru suggest those mods;
-------
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.
-------
Gaetan
Hey guy's I know it's a 30 years old circuit, but it's so simple and it's working since I've built one 8 years ago, it was good as a so simple circuit can be and I heard much worse amp with 5 time more transistors, he he he, but it's an easy amp for the beginer.
Linuxguru suggest those mods;
-------
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.
-------
Gaetan
Hello
I did a schematic with the Linuxguru suggested mods, and I added a 500 ohm bias trim pot and a 15 pf bypass cap on the nfb resistors, but no active Vbe multiplier, better to keep the amp simple. All mods have a * near them. And if I've done error in the schematic mods, no problemo just tell me.
Bye
Gaetan
I did a schematic with the Linuxguru suggested mods, and I added a 500 ohm bias trim pot and a 15 pf bypass cap on the nfb resistors, but no active Vbe multiplier, better to keep the amp simple. All mods have a * near them. And if I've done error in the schematic mods, no problemo just tell me.
Bye
Gaetan
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