Transistor currint morror in anode - as dynamic load?

[NovaPA]

Hello, dear colleagues.

There is idea to use current mirror in the anode circuit of the double triode differential stage, and current sourse in cathode.
To get higher gain on low voltage supply.

There are some doubts... Please, advice, will it work? Or only on high woltage, with higher current?

 

[Neperdun]

Some times ago I wished to assembly almost the same preamp.
But I was going to use transistor current sourse instead LM337 because it is too noisy!

Please tell me if You'll assemble it!

 

[moamps]

I never liked using the 3 pin regs as current sources for the audio signal. The question here is whether CCS can work properly because the regulator needs more than 3V to work. So the vacuum tube grids should be at a minimum of -4V or more, which is probably not the optimal operating point for vacuum tube in this case. An additional negative power supply should be used here. And so on....

 

[thor.zmt]

Hello, dear colleagues.

There is idea to use current mirror in the anode circuit of the double triode differential stage, and current sourse in cathode.
To get higher gain on low voltage supply.

There are some doubts... Please, advice, will it work? Or only on high woltage, with higher current?
View attachment 121346

The LM337 as CCS will be noisy. I would suggest a cascoded CCS using 3.3V Zener diodes, this gives ~2.5V across the current set resistor and close to zero tempco. See also WAlt Jung's current source Article. The voltage across the whole CCS should be 7.5V plus any signal swing. Use a negative voltage if needed.

The current mirror load does NOT WORK like this for a differential output. One side is loaded in effect into the diode impedance of the transistors BE junction, while the other side is loaded into a very high impedance. So gain will be extremely different between the two phases.

The correct solution would be to use a low capacitance N-MOSFET in a "Mu-Follower" configuration per phase, with a CCS tail for the differential tube amplifier.


Essentially the above circuit doubled up.

Thor

 

[NovaPA]

Thank You for, I think, the best explaination!

One only doubt: current mirror is typically used in differentian stages in OpAmps... why it works there?