H,
Udip's schematic shows output Re=10r.
How do you calculate the output impedance?
For both the open loop and closed loop (gain =A) would be useful.
Udip's schematic shows output Re=10r.
How do you calculate the output impedance?
For both the open loop and closed loop (gain =A) would be useful.
Discrete Op-Amp.
O.k. I give up - can someone tell me how the two diodes, at the current through them, can lift the bias voltage sufficiently to achieve 17mA quiescent current. There are two diodes “feeding” two transistor junctions; so isn’t the net voltage across the two Re’s nominally zero? Where does the extra voltage come from to provide the 340mV required? A 33R resistor in series with the diode string would do it, or an extra diode, as has been suggested, but then Re would have to go down to about 4R7 for the required 17 mA.
Or am I totally wrong?
Brian.
O.k. I give up - can someone tell me how the two diodes, at the current through them, can lift the bias voltage sufficiently to achieve 17mA quiescent current. There are two diodes “feeding” two transistor junctions; so isn’t the net voltage across the two Re’s nominally zero? Where does the extra voltage come from to provide the 340mV required? A 33R resistor in series with the diode string would do it, or an extra diode, as has been suggested, but then Re would have to go down to about 4R7 for the required 17 mA.
Or am I totally wrong?
Brian.
Hi,
I have never measured the Vdrop of a diode as a biasing component, but I suspect the diode drop is higher than the Vbe of the outputs. diodes 0.65 to 0.7v cf transistors 0.6 to 0.63v.
Has anyone measured these?
I have never measured the Vdrop of a diode as a biasing component, but I suspect the diode drop is higher than the Vbe of the outputs. diodes 0.65 to 0.7v cf transistors 0.6 to 0.63v.
Has anyone measured these?
Thanks, Andrew,
I'm very much a learner with LTSpice, but simulation shows a current of about 3.6mV, ie 72mV difference between the diode pair, and the BJT pair.
Brian.
I'm very much a learner with LTSpice, but simulation shows a current of about 3.6mV, ie 72mV difference between the diode pair, and the BJT pair.
Brian.
Re: bump
Hello my mate AndrewT
Somebody can inform you! I am sure!
Personally I never bother at all to find output impedance,
not within my voltage+power amplifier, inside the feedback loop.
I know, if I did design my amplifier properly according to my knowledge,
it will have a figure that is good enough for the job.
And output Z wil be fairly constant,
when used with intended loads (loudspeaker Z variations in audiable band)
and within its restricted power bandwidth (=not too high).
This is maybe why I never bother to calculate, estimate
'damping factor' of my amplifiers, either.
If an amplifier is good and properly design for its task
then wont matter much with trying to catch such numbers.
I know Nelson Pass has expressed similiar ideas.
In this forum and at his websites.
This makes me feel totally relaxed, about this issue.
😎
AndrewT said:
AndrewT said:
Hello my mate AndrewT
Somebody can inform you! I am sure!
Personally I never bother at all to find output impedance,
not within my voltage+power amplifier, inside the feedback loop.
I know, if I did design my amplifier properly according to my knowledge,
it will have a figure that is good enough for the job.
And output Z wil be fairly constant,
when used with intended loads (loudspeaker Z variations in audiable band)
and within its restricted power bandwidth (=not too high).
This is maybe why I never bother to calculate, estimate
'damping factor' of my amplifiers, either.
If an amplifier is good and properly design for its task
then wont matter much with trying to catch such numbers.
I know Nelson Pass has expressed similiar ideas.
In this forum and at his websites.
This makes me feel totally relaxed, about this issue.
😎
Hi,
I am not thinking about speaker driving nor damping factor.
I am thinking about source impedance for the next stage, whether it be a filter or a balanced inamp. Both needing accurate knowledge of the output impedance of the previous stage.
I am not thinking about speaker driving nor damping factor.
I am thinking about source impedance for the next stage, whether it be a filter or a balanced inamp. Both needing accurate knowledge of the output impedance of the previous stage.
ooh
sorry
we are talking preamps here
i forgot
anyway, somebody will inform/tell you, i'm sure
😉
sorry
we are talking preamps here
i forgot
anyway, somebody will inform/tell you, i'm sure
😉
Hi,
I don't think so, maybe high impedance speakers over 300ohms but even then I think current ability will be struggling.
This circuit can be scaled to drive 600r with a tiny bit of parasitic capacitance, but asking it to drive a reactive load is a different ball game.
Low impedance! how low? 8ohm, 16ohm? 32ohm?
I don't think so, maybe high impedance speakers over 300ohms but even then I think current ability will be struggling.
This circuit can be scaled to drive 600r with a tiny bit of parasitic capacitance, but asking it to drive a reactive load is a different ball game.
Low impedance! how low? 8ohm, 16ohm? 32ohm?
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