Hi MIKEKS
I think that is an intelligent solution for a thermally compensated stage,with a similar-current mirror circuit.
The problem with this circuit is the difficulty to apply a NFB with all the one which achieves:a need of a selection of Q1 and Q2, that they must be equal in both channels of a stereo amplifier yield more tightening for the lack of the emitter resistors.
Another little problem is the signal noise ratio,held low for the high current flow. I don't have the datasheet of the ZTX 696 but with a standard VBE of 0.65 the current in Q1 and Q2 is 15 mA each approx:very high for a low noise input stage.
If you neglects this the circuit is a good way for a good music listening,with the possibility of drive a capacitive loads.
I think that is an intelligent solution for a thermally compensated stage,with a similar-current mirror circuit.
The problem with this circuit is the difficulty to apply a NFB with all the one which achieves:a need of a selection of Q1 and Q2, that they must be equal in both channels of a stereo amplifier yield more tightening for the lack of the emitter resistors.
Another little problem is the signal noise ratio,held low for the high current flow. I don't have the datasheet of the ZTX 696 but with a standard VBE of 0.65 the current in Q1 and Q2 is 15 mA each approx:very high for a low noise input stage.
If you neglects this the circuit is a good way for a good music listening,with the possibility of drive a capacitive loads.
Well, I agree it is obvious why that is the case, but the curious thing is when you start thinking about what this implies for its application.
It got me thinking, the same thing happens with a "normal" EF if you start sinking current into it, but not if you source current from its output. So this one has a more symmetrical response.
If I were designing a circuit like this, a unity gain buffer with no DC shift, unless the load was very light, I'd just use another emitter follower at the output, and use the diff pair as a controller for the EF. At least that way I have the "unlimited" output drive in one direction. This one appears to be too simple for its own good.
It got me thinking, the same thing happens with a "normal" EF if you start sinking current into it, but not if you source current from its output. So this one has a more symmetrical response.
If I were designing a circuit like this, a unity gain buffer with no DC shift, unless the load was very light, I'd just use another emitter follower at the output, and use the diff pair as a controller for the EF. At least that way I have the "unlimited" output drive in one direction. This one appears to be too simple for its own good.
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