One transistor power amp
An amplifier, as close as possible to an amplifying copper wire !
This is a single transistor (mosfet) power amplifier.
It produces about 5W RMS per channel.
No overall or local feedback. Only one MOSFET in the signal path!
It sounds amazing, produces no noise at all, and has an audio detail and a stereo image I have never heard before.
I think I will grow old with this amp :-)
Building suggestions:
- use metal film resistors only
- use oversized output capacitors: distortion happens only at the cut of frequency, so go as low as your ears and body can handle!
- use a large heatsink, this is a class A amplifier, and has an efficiency of about 25% (omg so bad, but hey I like the heat, esp. in winter times! )
- I use a 24V fan at low speed on my little heatsink, with extra filter to avoid motor hum. Use a bigger heatsink to avoid the fan setup.
- I use an old 24V laptop power supply, with extra filter to avoid switching noise. See scope images, it works pretty well !
- Clipping the amplifier brings a tube style distortion which is pleasant to the ear. (see scope image)
- Distortion firgures probably aren't that good but hey, it sounds just great the way it is !
(most of all) ENJOY!
It produces about 5W RMS per channel.
No overall or local feedback. Only one MOSFET in the signal path!
It sounds amazing, produces no noise at all, and has an audio detail and a stereo image I have never heard before.
I think I will grow old with this amp :-)
Building suggestions:
- use metal film resistors only
- use oversized output capacitors: distortion happens only at the cut of frequency, so go as low as your ears and body can handle!
- use a large heatsink, this is a class A amplifier, and has an efficiency of about 25% (omg so bad, but hey I like the heat, esp. in winter times! )
- I use a 24V fan at low speed on my little heatsink, with extra filter to avoid motor hum. Use a bigger heatsink to avoid the fan setup.
- I use an old 24V laptop power supply, with extra filter to avoid switching noise. See scope images, it works pretty well !
- Clipping the amplifier brings a tube style distortion which is pleasant to the ear. (see scope image)
- Distortion firgures probably aren't that good but hey, it sounds just great the way it is !
(most of all) ENJOY!
Discussie (2 opmerking(en))
Martin Jäger 8 maanden geleden
As I'm not really a specialist in amplifier design, please allow me a question: Could I use 10,000 uF capacitors I have as output capacitors in this design?
How does the capacity relate to the cut-off frequency?
Thanks, I sincerely appreciate your help.
Martin
frederik 8 maanden geleden
About output capacitors, the rule is very simple.... the bigger the better ! I learned so much from Mr Douglas Self (See his book Small signal audio design)
Electrolytic capacitors are no problem in any signal path as long you avoid the "cut off region" as there most distortion happens. So if you go big, all should be fine!!
If you use 10000uF, the cut off frequency at 8 ohm load is around 2Hz (1/(2pi R C) = 1/(2x3.14x8x10000.10-6) ) so well below audio band.
Have fun !
Frederik
Senior Editor, Elektor 9 maanden geleden
Thanks for this interesting project!
Roberto
frederik 9 maanden geleden
I used a 1kHz square wave, and measured the output with an 8ohm resistor load. I think we are around 1V/us.
sodapdf-converted-28.jpg (29kb)