Thanks ,
I have found similar already ,
But i need the current source feed from +Vs signal. Actually , i am trying to design an A class amplifier with an IC , one NPN transistor , and a current source - but i am restricted to use NPN devices for a current source too , because it is a high - voltage amp.
What should i use instead of I1 ? Restor seems to add too much distortion.
Regards ,
Lukas
I have found similar already ,
But i need the current source feed from +Vs signal. Actually , i am trying to design an A class amplifier with an IC , one NPN transistor , and a current source - but i am restricted to use NPN devices for a current source too , because it is a high - voltage amp.
What should i use instead of I1 ? Restor seems to add too much distortion.
Regards ,
Lukas
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diy esl headphone - ouch, that could hurt
probably related to:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=72967
where a high V floating ccs is wanted
jan's battery bias would work as a proof of concept test to see if the ccs helps much but a more permanent solution requires a way to generate bias for the ccs pass device, with a bipolar Q this is hard, a Supertex depletion mode fet LD150 used as a ~1ma ccs could bias a npn ccs
a enhancement mode VN0545 mosfet (DigiKey) could be biased with a opto driver designed for solid state relay control http://www.irf.com/product-info/datasheets/data/pvi5013r.pdf (DigiKey)
with the opto gate driver looking like a battery and a souce series R setting the current
Digikey also has VP0545 p channel mosfet which could make a single ended ccs hanging from the V++ supply
another possible improvement is to linearize the pass transitor - the Baxendal "super-pair" may be useful here: (mje340 not recommended at this V, its just that I think the model comes with LtSpice)
(the dc bias is hiding in the input Vsource)
probably related to:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=72967
where a high V floating ccs is wanted
jan's battery bias would work as a proof of concept test to see if the ccs helps much but a more permanent solution requires a way to generate bias for the ccs pass device, with a bipolar Q this is hard, a Supertex depletion mode fet LD150 used as a ~1ma ccs could bias a npn ccs
a enhancement mode VN0545 mosfet (DigiKey) could be biased with a opto driver designed for solid state relay control http://www.irf.com/product-info/datasheets/data/pvi5013r.pdf (DigiKey)
with the opto gate driver looking like a battery and a souce series R setting the current
Digikey also has VP0545 p channel mosfet which could make a single ended ccs hanging from the V++ supply
another possible improvement is to linearize the pass transitor - the Baxendal "super-pair" may be useful here: (mje340 not recommended at this V, its just that I think the model comes with LtSpice)
(the dc bias is hiding in the input Vsource)
The LM317 can be used with an external BJT or MOSFET so your higher operating voltage is just about choosing the right external BJT. A resistor is a distortionless component, all things being equal a CCS will result in higher distortion. Have you considered using a source follower output stage instead of your common emitter ???
Like everything in audio its debatable. Ill give you the engineering arguement. A source follower will have magnitudes of order lower output impedence so your amp will have a much lower damping factor. Also you DONT need any more open loop gain then the opamp provides so you dont need the gain a common emitter output stage would provide. Just the facts, feel free to go with what ever your heart tells you 
HFGuy said:Like everything in audio its debatable. Ill give you the engineering arguement. A source follower will have magnitudes of order lower output impedence so your amp will have a much lower damping factor. Also you DONT need any more open loop gain then the opamp provides so you dont need the gain a common emitter output stage would provide. Just the facts, feel free to go with what ever your heart tells you
If only the facts were correct...
Lower output impedance increases dampiing factor (or were you talking about Q?). Current source is nor necesairly used only when you want high gain, but also when you want a better defined slew rate and/or output voltage swing. Depending on what amplifying device you use for the other end, a current source may linearize it and produce lower distortion.
Facts are correct, thats what makes them facts. Yes i ment to say increased damping factor, mark that up to short attention span or dyslexia. Loading a common emitter with a CCS will provide you with a very high gain, the imp looking into the CCS is very high therefore the gian is very high. A resistor is much more linear then even the best active device, as for the output stage linearity it will be taken care of by the feedback loop.
Bazukaz said:Sorry , didnt read last reply
Yes , it is related to another thread
So , as i understand , i would need a separate low voltage source to set bias for Q3 ?
Lukas
You can use a floating shunt voltage source like the LM431, with two resistors in series to the supply. Then connect a bootstrap C from the output to the middle point of two resistors, that way the supply for the shunt reg can go way above the supply voltage.
Jan Didden
If you dont mind me asking what is your rail voltage ?? How high is it ?? And what is this amp for ? A typical audio power amp doesnt need anything that would be considered high. I also dont think tubes will work, any kinda output power tube will require more grid voltage then the opamp will likely provide.
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