Chaining various effects / impedance matching

[FantomXR]

Hey people,

maybe just a simple question:
When I chain several effects, do I want matching out- and input-impedances?

I guess so. But I wonder:
If I look at the effects on the market I see that many of them have a high input impedance of about 470k and a low output impedance of about 10k. But if I chain them than the next effect would also have a high input impedance of 470k. So the output with 10k sees the input of 470k. Why is it the case? And does it even matter?

Thanks,
Chris

[patrick398]

Impedance. Everybody's favourite topic haha. I'm really no expert but i think the best way to think about input and output impedance is to think about what effects before and after 'see'. So the output of a pedal 'sees' 470K impedance at the input of the next pedal in the chain. Similarly that effect looks back and 'sees' and output impedance of 10k. That's my remedial understanding of it, for what it's worth

[idy]

Here is what you are missing. Input impedence describes how much an effect loads what is feeding it. Low input impedence on a pedal and your pickups are strained and sound weak. Output impedence is a requirement, a figure your pedal would "like" to "see" in the next stage. As long as the output impedence of a box is lower than the input imp. of the next stage things are usually ok.
So designers *generally* seek a high input imp. and a low output imp. The ideal box does not load the thing feeding it and will not burn up or otherwise misbehave if you short circuit the output.
A guitar amp may have 1m input imp. and 8 m(or 4 or 16)ohm output. A pedal may have 400k input imp. and 10k output. A vintage pedal may have an input imp. in the low 10s of kohms.

[ashcat_lt]

Everything useful is a voltage divider.  The output impedance is the "top resistor", and the input is the "bottom".  In order to pass as much voltage as possible, the top resistor wants to be much smaller than the bottom.  It's really about that simple. 

If we cared about ideal power transfer, I think we'd want impedance to be more or less matched, but all we care about in pedal work is voltage. 

A ratio of 1:10 comes out to somewhat less than 1db loss, which is generally considered to be acceptable.  BUT bigger is always better, AND we have to expect that we will at some point be plugging a guitar right into these inputs, and while the DC resistance of a guitar pickup isn't really all that big, the impedance gets real big real fast at higher frequencies, so that we try to fudge the input impedances higher in order to be more likely to get something more like treble out of them.

[PRR]

> When I chain several effects, do I want matching out- and input-impedances?

No.

Also: don't think about it. Those commercial products are rigged for clueless non-geek users so they do not have to think about it.

[FantomXR]

Everything useful is a voltage divider.  The output impedance is the "top resistor", and the input is the "bottom".  In order to pass as much voltage as possible, the top resistor wants to be much smaller than the bottom.  It's really about that simple. 

If we cared about ideal power transfer, I think we'd want impedance to be more or less matched, but all we care about in pedal work is voltage. 

A ratio of 1:10 comes out to somewhat less than 1db loss, which is generally considered to be acceptable.  BUT bigger is always better, AND we have to expect that we will at some point be plugging a guitar right into these inputs, and while the DC resistance of a guitar pickup isn't really all that big, the impedance gets real big real fast at higher frequencies, so that we try to fudge the input impedances higher in order to be more likely to get something more like treble out of them.

Thanks! That totally cleared it for me!

Thanks,
Chris