Impedance Matching

[maxzimum]

How important is it to match impedance when choosing a Preamp / Power Amp combination? What is the ideal match?

Also, does input/output impedance have any bearing with overall gain?

Thanks.

 

[AndrewT]

it depends.

Sorry, but it depends on how the receiver stage has been designed.
A non inverting stage usually likes to see a low source impedance/resistance. It also usually expects the source resistance to be nearly constant.

The gain of the non inverting receiver is independant of the source resistance/impedance. However there is an interaction between Rs and Zin which attenuates the input voltage slightly.

An inverting amplifier uses the series input resistance/impedance to set the gain of the NFB loop.
Any added resistance at the input will affect the amplifier gain.

Using a ratio of 1:10 for Rs:Rin attenuates most of the errors, but 1:20 is very slightly better.

eg.
Rin=100k allows Rs <=5k. This allows a <=20k passive pot to work effectively.

Watch for capacitance. It will interact with these higher impedances to act as a low pass filter.

A low Rs (<=200r) usually indicates universal compatibility, but do check that the source can drive low impedances.

 

[darkfenriz]

It's a completely non-issue as far as the proportion is more than 1:100.
Order of 1:10 000 is not uncommon at all, so just forget it.