What does everyone shoot for on output impedance.  I see a lot of stuff using 50, and 100k volume pots which make up most of the impedance.  When is low too low?

Quote from: Brian MarshallWhat does everyone shoot for on output impedance.  I see a lot of stuff using 50, and 100k volume pots which make up most of the impedance.  When is low too low?

Output impedance and the LOAD that you see at the output of an amp are different things.  What value you should use for a pot at the output of an effect depends upon the output impedance of that amp.

If it's a transistor amp, a common emitter circuit for example, then the pot would have to be at least ten times the value of the collector resistor to prevent significant loading.  Of coarse, whatever resistance follows in the chain will be in parallel to whatever reistance is on the pot and can in turn load this down.

Op-amps tend to have very low output impedance so lower pot values can be used without affecting the performance of the amp.  Same goes for many follower circuits.

PS  Sometimes loading is factored into the equation.

Shouldn't I be looking at the impedance of my amp's input jack when figuring out what impedance would be ideal for an effect's output?


For instance I found Fender and Mesa Boogie have 1meg loads at their input so I would think a 1 meg load at an effects output to be ideal.

Is this wrong?

Wouldn't matching these loads optimize signal to noise ratio and basically make for a better sound?

Now, how does one deal with loads like that of a wah pedal?
I suppose a JFet boost/buffer?

How  about a Tube Screamer and it's 10k output?

Are we now talking buffering all of out true bypass pedals?

schematic, links  or ideas for making mismatched pedals work properly with each other? (Please)


Thanks alot.

http://diystompboxes.com/sboxforum/viewtopic.php?t=499


This is a good link for impedance.

Thankyou BillyJ

Matching impedance generally means huge volume and tone loss I shoot at 100k input Z and 1M or higher output Z. Wrong!

edit: I screwed that up, it's 1M input Z and 100k output. :roll: Oops.

Output impedance can never be too low, except in the very special case where you are feeding an effect that 'expects' to be directly fed from a high impedance pickup or similar.
I usually have a 10K pot driven from an op amp. (which means the output impedance varies from about zero at full vol, to a max of 5k half way down, to zero at zero output.)