What's the advantage of having a high (+-200R) output impedance?

Bricolo · 8th February 2004, 12:28 AM

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?

tiroth · 8th February 2004, 12:31 AM

It prevents oscillation of the output stage.

Pedja · 8th February 2004, 12:35 AM

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.

Pedja

Bricolo · 8th February 2004, 12:39 AM

capacitive load? are you refering to the interconnects?

Pedja · 8th February 2004, 12:41 AM

To the interconnects and the (pre)amp's input.

Bricolo · 8th February 2004, 12:56 AM

can some pF cause problems for an opamp output stage?

Pedja · 8th February 2004, 01:08 AM

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.

Pedja

Cobra2 · 8th February 2004, 01:34 AM

It also protects the op-amp....for preventing them shortcircuit if output-wires become damaged...

Arne K

Tube_Dude · 8th February 2004, 01:36 AM

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.

Pedja · 8th February 2004, 01:56 AM

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.

Pedja

8th February 2004, 12:28 AM	#1
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	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?

8th February 2004, 01:34 AM	#8
Cobra2 DIY ! diyAudio Member Join Date: Apr 2002 Location: Stavanger, Norway	It also protects the op-amp....for preventing them shortcircuit if output-wires become damaged... Arne K __________________ Ars longa, vita brevis

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8th February 2004, 12:31 AM	#2
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	It prevents oscillation of the output stage.

8th February 2004, 12:35 AM	#3
Pedja diyAudio Member Join Date: Jun 2002 Location: Serbia	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. Pedja

8th February 2004, 12:39 AM	#4
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	capacitive load? are you refering to the interconnects?

8th February 2004, 12:41 AM	#5
Pedja diyAudio Member Join Date: Jun 2002 Location: Serbia	To the interconnects and the (pre)amp's input.

8th February 2004, 12:56 AM	#6
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	can some pF cause problems for an opamp output stage?

8th February 2004, 01:08 AM	#7
Pedja diyAudio Member Join Date: Jun 2002 Location: Serbia	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. Pedja

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