Does anyone know the sensitivity (or overall gain) of Mighty Midget?
Also, can I use 5K OPT? I know the power and THD will be higher. Since I have them already, I just want any reasons NOT to try them first.
Also, can I use 5K OPT? I know the power and THD will be higher. Since I have them already, I just want any reasons NOT to try them first.
Power output will be lower. The final is biased around 290V/40mA or about 7k. Sure it will work.
Maybe I misunderstood what you are saying, but the output stage DC bias conditions aren't directly related to OPT primary impedance. The reflected OPT primary impedance is calculated as the secondary load impedance multiplied by the square of the turns ratio of the transformer. Pete's write-up said that his measurements were taken with an OPT with a 7k primary impedance, giving power out of about 3.5 watts. A lower reflected primary impedance, like 5k, will result in more power, not less, for the same output stage drive because this implies a lower transformer turns ratio, meaning that the signal voltage is "stepped down" less than with a 7k OPT, and the signal voltage reaching the speaker is therefore larger.
But the difference between a 7k OPT and a 5k OPT usually isn't enough to be concerned about.
But the difference between a 7k OPT and a 5k OPT usually isn't enough to be concerned about.
True. But you have moved the ball. Why would we have "same output stage drive"? Gain is cheap.
The maximum output of a low-distortion class A power stage is the power device V/I and any transformation ratio.