>In a really simple circuit, say a battery across which is a lamp. The lamp
>will glow at a particular brightness. Now before the battery goes flat,
>stick a resistor across the battery - the lamp goes dimmer as current is
>being used by the resistor, which is therefore not available to the lamp.
This experient is demonstrating how the internal resistance of the battery
affects the terminal voltage (& hence output current) as the load changes.
The resistor you added didn't directly make current unavailable to the lamp,
it only decreased the total load resistance.
Have you studied voltage division? As the ratio of the load resistance to
the internal resistance changes, so does the voltage across each resistance.
It's the dropping terminal voltage that results in less current.
It's a subtle distinction maybe, but I'm not sure your mental model is
entirely accurate. If it's not clear enough I'll draw a picture for you in
PSP or something.
If you performed the same experiment with a good power supply, the lamp
would *not* vary in brightness as you connected other loads in parallel.
>The way I see it, the analogue stage in the MiniDisc player is like the
>bulb
>(it is dependant on power at a particular voltage and current being
>available to sound a particular way),
Yeah, it definitely has supply requirements.
>the optical and co-axial inputs are
>like putting two different resistors across the supply. I know this is very
>much an over simplification - but hopefully it tells you how I'm thinking.
I understand where you're coming from, but it's not quite right.
It's an oversimplification because the power supply is regulated, so under
normal conditions it has virtually no internal resistance - the output
voltage does not change under load. Loads are independent of one another.
>Optical in is using IC621, co-axial is not - this is something I did not
>know. Therefore different loads are being demanded from the power supply
>depending on the input type used, this raises the possibility of effecting
>(in some small way) the power available to the analogue amp.
That IC will be powered up all the time regardless, and even if it wasn't
the difference in load is tiny. Power to the analogue stage is not
affected.
>I suppose differing demands by the MiniDisc spindle motor my also effect
>the
>power available to the analogue circuitry.
Yes they would if it were unregulated. This is a much bigger change in load
than an IC being in use or not. And yet due to the magic of competent power
supply design it makes little difference.
Though some high end CD players go to the extent of having separate supplies
for the transport & audio electronics to completely eliminate electrical
interaction between the two. Kind of a brute force approach. Guess how
they connect the transport to the audio section.
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