S-Man
StrivingON
Hi,
I just ran a simulation, and set one resistor to 68ohms, and the other to 1kohm. The DC operating point simulation for the resistors shows the 68ohm resistor has 3.1mA, and the 1kohm resistor has 0.21uA.
This is not with the LTP input stage used in isolation, but connected to a VAS and output stage with DC offset servo.
Can you run a simulation and confirm ?.
Thanks and regards,
Shadders.
Measurement trumps simulation!
Are you taking into account that for the amp to work properly the VAS transistor "regulates" the voltage across the input transistor's collector resistor at ~0.6V.
Simulating at LTP in isolation will not work.
Here are the measurements from both channels of my NCC200 at quiescent with +/-40V supplies.
Voltages measured across resistors:
1K 0.500V 0.501V (= 0.5mA i.e. ~1/2 of the tail current)
22K 10.75V 10.66V (= 0.48mA)
620R 0.632V 0.628V (= ~1mA tail current)
68R 0.716 0.705V (~10.3mA VAS current)
220R in + rail 2.52V 2.49V
220R in - rail 2.86V 2.82V
If you change the 22K resistor to 1K you will still get about 0.5mA through it!