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Re: Impedance matching

>At 7:58 AM -0700 10/4/00, Mike Biffle wrote:
>>Again... watch out trying to recombine outputs from other boxes 
>>with a patchbay. Splitting is fine... (Anyone have a more technical 
>>explanation of this?)
>
>This is sort of a simple view of this issue:

Thank you! Just to complete:

>Outputs are generally quite low impedance (600 ohm or lower),

Still a lot of effect units and built in guitar preamps have 10k ohm 
outputs, meant to connect to a line input. Many OpAmp outputs that 
can drive 600 ohm without loss of volume are not distortion free in 
this situation.

>Inputs are generally quite high impedance (10K ohm or higher, 
>although most modern equipment is in the Meg-ohm range).

Input impedance is not related to modernity. Tubes achieve high 
impedance easily.
The advantage of a lower input impedance is less sensitivity to 
oscilation and less noise/hum, especially in case of being open (not 
used).

Microphone inputs should be at 600 ohm to avoid reflections in case 
of long cables (transmission line). But a mic also works on a higher 
impedance input.

"Line" inputs (also home RCA kind) have 10k...50k ohm.

High impedance in the Megohm range are only needed for pickups, 
especially piezo and guitar magnetics. So only equipment for 
instruments have this high impedance, not mixing desks.

Frequent impedance missmatches are:
guitar - mixer
guitar kind volume pedal (500kOhm) - mixer
guitar - passive DI box
line out - long cable to stage

A too low input imedance cuts treble of a magnetic pickup but bass of 
a piezo pickup.

>  Splitting in a patch bay works pretty well, particularly if the 
>inputs you are splitting to have similar input impedances.


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