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Old 7th February 2004, 11:28 PM   #1
Bricolo is online now Bricolo  France
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Default What's the advantage of having a high (+-200R) output impedance?

A hundred of ohms seems to be a typical output impedance for a cd player, but why?

Isn't a low output impedance better?

And this impedance isn't even due to the I/V itself, but by adding series resistors in the signal. Wha'ts the need for this?
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Old 7th February 2004, 11:31 PM   #2
tiroth is offline tiroth  United States
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It prevents oscillation of the output stage.
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Old 7th February 2004, 11:35 PM   #3
Pedja is offline Pedja  Serbia
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CDP output stages almost always use feedback. Such stages are usually not stable on the capacitive loads. Series resistor decouples this load. Other than this resistor, output impedance is often notably under 1 Ohm. In the absolute terms, output impedance is not in any specific relation with the sound qualities.

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Old 7th February 2004, 11:39 PM   #4
Bricolo is online now Bricolo  France
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capacitive load? are you refering to the interconnects?
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Old 7th February 2004, 11:41 PM   #5
Pedja is offline Pedja  Serbia
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To the interconnects and the (pre)amp's input.
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Old 7th February 2004, 11:56 PM   #6
Bricolo is online now Bricolo  France
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can some pF cause problems for an opamp output stage?
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Old 8th February 2004, 12:08 AM   #7
Pedja is offline Pedja  Serbia
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Depends on the actual opamp used. Some could drive a few nF, some will have problems even with a 10pF (mainly current feedback ones). Datasheets usually offer good info about this.

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Old 8th February 2004, 12:34 AM   #8
Cobra2 is offline Cobra2  Norway
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It also protects the op-amp....for preventing them shortcircuit if output-wires become damaged...

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Old 8th February 2004, 12:36 AM   #9
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Default Re: What's the advantage of having a high (+-200R) output impedance?

Quote:
Originally posted by Bricolo
A hundred of ohms seems to be a typical output impedance for a cd player, but why?

Isn't a low output impedance better?
But a hundred ohms output inpedance...is a low output impedance!!!

Specialy feeding a pre amp or a power amp.
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Old 8th February 2004, 12:56 AM   #10
Pedja is offline Pedja  Serbia
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Quote:
Originally posted by Cobra2
It also protects the op-amp....for preventing them shortcircuit if output-wires become damaged...
Yes, this might be the reason as well, though the opamps without short circuit current limiting are rather scarce these days.

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