1.) this is just impedance converting low to high? transistor (common base) can do this right?

2.) reamp box for isolation?
what does isolation for?
a capacitor can do this right?

3.)what does reamp box do?

 

Google ReAmp; the manufacturer's website, and many others, describe the purpose, it isn't a secret. And no, you wouldn't use a common-base transistor circuit for this application.

And if you google ReAmp schematics you will see lots of circuits similar to this:

 

is that a low impedance to high impedance?
i borrow some reamp box, and try "Soundcard line out>reamp>guitar amp" and compare to "Soundcard line out>guitar amp" and they sound the same.
direct line to guitar is just so loud that i have to lower the line volume,
sounds like gimmick to me

 

As I said before, you don't need to convert low impedance to high impedance so why do you keep asking about it? However, the signal will require attenuation.

 

the schemtaic you post above is "balance to unbalanced converter"

im want to record the sound of my guitar speaker, so the chain would be "computer line out unbalanced> guitar amp" but is some "audio forum" said i need reamp box to match impedance of guitar amp. they said i would need a low impedance to high impedance tranformer because guitar pickup impedance is around 100k

im confuse because some of guitar amp/pedal have "buffer" converting high impedance to low impedance

 

That's because most musicians are not electronic engineers and so music forums are awash with myths and hearsay regarding electronic equipment.

The sound card output impedance is probably less than 100Ω and the guitar amp input impedance will be greater than 100kΩ. This is an ideal condition for efficiently transferring the sound card signal into the guitar amp but you will need to attenuate the signal. A 10k pot on the output of the sound card will suffice.

I should add that it is necessary to add a some sort of impedance converter if going the other way i.e. from a high impedance output to a relatively low impedance input.

 

thanks blocco for clearing up my mind, a 10k series? or 10k to ground? or voltage divider to maintain my signal to noise ratio?

 

Like this:

 

That looks quite a bit like the loudness pot on the guitar.
Couldn't she simply turn down the loudness control on the guitar to attenuate the signal?

 

That looks quite a bit like the loudness pot on the guitar.
Couldn't she simply turn down the loudness control on the guitar to attenuate the signal?

There is no guitar.