simplest amplifier possible?
The question how to build the simplest possible amplifier using transistors intrigues me. I will report here my recent findings. To share the information with you and to hope for still further improvements.
My design criteria were:
* output power no real issue, around 1-5 Watts RMS is okay (translates to: 5 Watts would be great).
* input impedance above 33kOhm, sensitivity of around 1 Volts RMS or higher.
* two gain stages max.
* no fets or mosfets, just BJT's.
* class-A
* single-ended
* no global feed back
I came to this set after visiting Rudi Stor's website (www.rudistor.com/sound-lab). Here was the AR-3 head phone amp designed for simplicity and 8 ohms loads. I built this amp for fun and it sounds (contrary to my expectation) very very good with whatever phones you like (expensive Grado's, Sennheisers, AKG's, Sony's). I have several tube head amps for comparison (musical fidelity, Morgan Jones, Futterman). Actually, this is the first transistor amp that really intrigued me. The amp delivers around 50 mW RMS @ 8 Ohm. Just for fun I hooked up my Klipsch speakers: not bad at all.
So ....
Why not beef this amp using only 3 transistors (of which 2 2N3055's) to a few watts? I used around 1,25 Amps of idle current and an emittor resistor of 8,2 Ohms (50 Watts, becomes very hot of course) and a voltage of around 20-25 V DC.
The output power now is around 3/4 (ie 0.75!) Watts RMS. This is the best transistor amp I ever heard in my house. It betters the Hiraga and the John Linsley Hood, my references in simple class A transistor amps. Actually it rivals the better tube amps.
Now I started the quest for even more power. The power is limited in the design by the input stage that can not give enough swing. I changed some resistor values to get more swing and ended with around 3 Watts RMS (but a lower input impedance). The magical sound was gone however. I fiddled around using several other input transistors that can deal with more current. I did not succeed in getting the sound as good as I wanted it.
After more than one month of listening, soldering, experimenting, I finished the result ending up with one of the first trials, leaving me with around one (1) Watt of power.
If only this design could be brought to about 5 Watts of output ...
Who wants to take over the fiddling from me, I think this is it for me at this moment given the design criteria...?
Rudy
The question how to build the simplest possible amplifier using transistors intrigues me. I will report here my recent findings. To share the information with you and to hope for still further improvements.
My design criteria were:
* output power no real issue, around 1-5 Watts RMS is okay (translates to: 5 Watts would be great).
* input impedance above 33kOhm, sensitivity of around 1 Volts RMS or higher.
* two gain stages max.
* no fets or mosfets, just BJT's.
* class-A
* single-ended
* no global feed back
I came to this set after visiting Rudi Stor's website (www.rudistor.com/sound-lab). Here was the AR-3 head phone amp designed for simplicity and 8 ohms loads. I built this amp for fun and it sounds (contrary to my expectation) very very good with whatever phones you like (expensive Grado's, Sennheisers, AKG's, Sony's). I have several tube head amps for comparison (musical fidelity, Morgan Jones, Futterman). Actually, this is the first transistor amp that really intrigued me. The amp delivers around 50 mW RMS @ 8 Ohm. Just for fun I hooked up my Klipsch speakers: not bad at all.
So ....
Why not beef this amp using only 3 transistors (of which 2 2N3055's) to a few watts? I used around 1,25 Amps of idle current and an emittor resistor of 8,2 Ohms (50 Watts, becomes very hot of course) and a voltage of around 20-25 V DC.
The output power now is around 3/4 (ie 0.75!) Watts RMS. This is the best transistor amp I ever heard in my house. It betters the Hiraga and the John Linsley Hood, my references in simple class A transistor amps. Actually it rivals the better tube amps.
Now I started the quest for even more power. The power is limited in the design by the input stage that can not give enough swing. I changed some resistor values to get more swing and ended with around 3 Watts RMS (but a lower input impedance). The magical sound was gone however. I fiddled around using several other input transistors that can deal with more current. I did not succeed in getting the sound as good as I wanted it.
After more than one month of listening, soldering, experimenting, I finished the result ending up with one of the first trials, leaving me with around one (1) Watt of power.
If only this design could be brought to about 5 Watts of output ...
Who wants to take over the fiddling from me, I think this is it for me at this moment given the design criteria...?
Rudy