op-amp current source

[jackinnj]

Use LTSpice simulation to adjust resistor values, its best tool in this case.

Like JFETs, depletion MOSFETS, say the DN2540 will vary in terms of Idss and Vgth.

If you are matching two channels of a preamplifier for identical current you'll have to set one as the standard with Rset(1), adjusted for the ideal current, then trim the value of Rset(2) to match the other -- easily done with a 10k potentiometer in parallel.

SY's implementation discussed in his article
http://www.diyaudio.com/forums/diya...oise-thoroughly-modern-tube-phono-preamp.html

 

[vacuphile]

The inputs must not go outside the supply voltages of the op-amp.In one case an input is protected with two diodes at the supply and the other input with another two diodes connected to the first input.The second case has each input protected separately with respect to the supply with diodes.Not much difference.No, it is a current source but not a constant one 😕
It is a stabilised voltage supply with max.current limit.It seems that the R? you mension determins the max.current.But the schematic on entry 1 doesn't show that R.
Mona

There is a difference, in that D4 and D5 ensure that the common mode differential voltage is always smaller than 1 diode drop. In that sense they do not protect against input signals > power rails. I only had cursory look at schematic and gotta go now, if more questions will return later.

 

[sb****33]

There is a difference, in that D4 and D5 ensure that the common mode differential voltage is always smaller than 1 diode drop. In that sense they do not protect against input signals > power rails. I only had cursory look at schematic and gotta go now, if more questions will return later.

OK.
So why differential voltage should be < .6V ?
Why no such diodes device on the other regulator ?

 

[vacuphile]

OK.
So why differential voltage should be < .6V ?
Why no such diodes device on the other regulator ?

If the differential voltage is too large, things might break. Some opamps have internal clamping diodes and are thus protected, others are not. This may explain the differences in application. The specsheets of the opamps can tell you more.

 

[sb****33]

If the differential voltage is too large, things might break. Some opamps have internal clamping diodes and are thus protected, others are not. This may explain the differences in application. The specsheets of the opamps can tell you more.

MC34001 nor TL071 get diode in them.