I am now studying a complementary symmetrical Jfet IPS to complete my most recent power amp lineup.
Initially I started with a complementary differential Jfet IPS mirror loaded but did not continue due to the difficulties found in avoiding VAS operating point variations due to beta differences and temperature variations.
So now I am using a more typical design without mirrors but in order to increase OLG I placed a Darlington over each input Jfet.
Simulations look very good but I would appreciate input from the experts before I start laying out a pcb.
1 - I am using KSC1845 as the darlington bjt for the positive IPS side that uses K170 jfets. Should I use a higher beta bjt ? What would be the best choice here ?
2 - The same question must be placed regarding the negative LTP where I am using KSA992 and LSJ74 jefts.
3 - For the VAS I chose to use a beta enhanced connection in both sides. Should I contemplate the option of cascoding the VAS instead ?
Hope this design rises enough interest so we can have a good discussion regarding this type of symmetrical amp.
Initially I started with a complementary differential Jfet IPS mirror loaded but did not continue due to the difficulties found in avoiding VAS operating point variations due to beta differences and temperature variations.
So now I am using a more typical design without mirrors but in order to increase OLG I placed a Darlington over each input Jfet.
Simulations look very good but I would appreciate input from the experts before I start laying out a pcb.
1 - I am using KSC1845 as the darlington bjt for the positive IPS side that uses K170 jfets. Should I use a higher beta bjt ? What would be the best choice here ?
2 - The same question must be placed regarding the negative LTP where I am using KSA992 and LSJ74 jefts.
3 - For the VAS I chose to use a beta enhanced connection in both sides. Should I contemplate the option of cascoding the VAS instead ?
Hope this design rises enough interest so we can have a good discussion regarding this type of symmetrical amp.
Attachments
I also tried a CFP instead of the Darlington's for the IPS but found the circuit needing much higher miller caps to be stable.