If you feed the inputs both to one long-tailed-pair you'd have much higher common-mode impedance and fewer input devices contributing noise I think.
Point here is a single diff pair is already balanced and the second is not required.
Of course the feedback scheme would have to be adapted accordingly.
What about CMRR in your circuit 11301 ?
Of course the feedback scheme would have to be adapted accordingly.
What about CMRR in your circuit 11301 ?
I have not calculated it. For me this is a hybrid Intrumentation Amplifier. With discrete input transisors i see the main advantage in low voltage noise. As far as i can tell the better this input transisors are matched and thermo coupled, the better CMRR will be. Plus precission resistors .
An integrated INA does not get better then around 1nVqHz.
This one can be as low as 0,2nVqH with the right transistors and relatively high idle, say 20mA per pair.
An integrated INA does not get better then around 1nVqHz.
This one can be as low as 0,2nVqH with the right transistors and relatively high idle, say 20mA per pair.
Something like this maybe?
The feedback goes to the emitters via a filter network (Z1 and Z2), then the outputs proceed to further balanced passive filtering and diff amp?
Then you have only one transistors' worth of noise for each input rather than two, I believe. Wasn't sure what loading you are going for.
I was thinking of an input loading of around 1kOhm. For low voltage noise Z2 should have a low value.
This circuit is interesting.
This circuit is interesting.
How do you set the gain Joachim ?
The need for two RIAA circuits bothers me a little.
It might need a bigger emitter resistor instead of the 3ohm
The need for two RIAA circuits bothers me a little.
It might need a bigger emitter resistor instead of the 3ohm
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For balanced in-out, I find Scott's more interesting :
A simplified universal differential or single ended phono preamp
Patrick
A simplified universal differential or single ended phono preamp
Patrick
Thank you Joachim... Now it is clear.
In my sim the voltage reference in the opamps uninventing inputs must be set to -1v otherwise the circuit oscillates.
In my sim the voltage reference in the opamps uninventing inputs must be set to -1v otherwise the circuit oscillates.
(Re post 11314) No.
RCruz said:
This is re post 11309. No, the circuit does not work with dc condition like this.
I do not have the opportunity to simulate but obviously the collector voltage should be higher than the emitter voltage.