Ian Thompson-Bell wrote:

Nick Gorham wrote:
Ian Thompson-Bell wrote:
Nick Gorham wrote:

Ian Thompson-Bell wrote:


Don't forget this is a mic pre not a power amp so current draw is
less than 10mA and as its class A it is also constant.


Just to pick up ona small point, the current draw of a class A
single ended stage is not constant, I think you may be thinking of a
push pull or differential stage.


Provided the stage has its HT decoupled (RC) across the operating
bandwidth then the current draw of a single ended class A stage is in
fact constant. I agree if you consider the stage in isolation of its
decoupling that it is not so, but I don't plan to build a preamp
without decoupling ;-) Even then, the average current is constant.



Fine, please yourself, alter your definition of constant and where the
class A stage starts, and hey presto, you are right.


Sorry to have upset you but this was in the context of the power supply
for the preamp. I did agree with you that the stage in isolation does
not draw a constant current. But looking from the power supply into the
preamp (with its decoupling) which was the context of the comment, it is
correct. I am not altering anything, just trying to be accurate. From
the point of view of PSU design, the current draw from a preamp is constant.

Cheers

Ian

Indeed for a preamp which makes perhaps 1Vrms output, the change in Idc
is utterly negligible.

Patrick Turner.