Hi ! i have a maybe weird question about solid state circuits topologies
I see a lot of discussion about discrete opamps topologies (I see a kind of race to get the best THD performance)
The designers have done a wonderful job and with great results in some cases
Very naively i took a commercial discrete opamp (because i found the schematic in the web) and tried to raise the power supply voltages, put more powerful output transistors, appropriately change the output resistors to have an amplification stage capable of adequately driving an 8 ohm load
A V gain of 10 times with a 1V input should provide about 12.5W/8 ohm that with a high efficiency speaker should be more than enough in a not too big room
The result of the simulation has been not that exciting in terms of THD. It works but not well enough (that for me would be about -80dB ? advice kindly required on this issue)
Is this type of approach wrong ? that is, starting from a good discrete opamp and doing a sort of scale up in voltage supplies and power of the various components or is the circuit design for an amplifier is based on completely different principles ?
I see a lot of discussion about discrete opamps topologies (I see a kind of race to get the best THD performance)
The designers have done a wonderful job and with great results in some cases
Very naively i took a commercial discrete opamp (because i found the schematic in the web) and tried to raise the power supply voltages, put more powerful output transistors, appropriately change the output resistors to have an amplification stage capable of adequately driving an 8 ohm load
A V gain of 10 times with a 1V input should provide about 12.5W/8 ohm that with a high efficiency speaker should be more than enough in a not too big room
The result of the simulation has been not that exciting in terms of THD. It works but not well enough (that for me would be about -80dB ? advice kindly required on this issue)
Is this type of approach wrong ? that is, starting from a good discrete opamp and doing a sort of scale up in voltage supplies and power of the various components or is the circuit design for an amplifier is based on completely different principles ?
Hi and thank you for the very kind and valuable advice. I have done some attempts and as always i was trivializing the issue like many ambitious ignorants
do often.
My rational was that in the end i could look at a power amp stage like a discrete opamp with higher gain, higher power delivery on lower ohmic loads
The usual discrete opamps are found in line stages and that is what i did.
So i took a commercial (i.e. working) discrete op-amp intended for line stage found in the web (i would like to mention it but the last thing i want is to start a quarrel)
I changed the output devices with more robust parts and the results are ... disastrous
This is one of the two output pair bjts
maybe they are not adequate ?
The voltage amplification part is the same I have checked the dissipation of drivers and it is ok It is the output stage that provides weird figures
Can i attach the schematic without upsetting anyone ?
do often.
My rational was that in the end i could look at a power amp stage like a discrete opamp with higher gain, higher power delivery on lower ohmic loads
The usual discrete opamps are found in line stages and that is what i did.
So i took a commercial (i.e. working) discrete op-amp intended for line stage found in the web (i would like to mention it but the last thing i want is to start a quarrel)
I changed the output devices with more robust parts and the results are ... disastrous
This is one of the two output pair bjts
maybe they are not adequate ?
The voltage amplification part is the same I have checked the dissipation of drivers and it is ok It is the output stage that provides weird figures
Can i attach the schematic without upsetting anyone ?