Impedance pls help to understant it

[arma61]

Hi

I saw this word showing up several time in this forum, could anybody explain a little bit which problems arise if this is either high or low and how do i misure it and , if need change it. I'm building an FX from an old schematic (could be end of '70s), and I couldn't get it works properly so before to post the 'problem' i would like to go through it myself. The main problem (but there are other) I have at the moment is that when I play a note on my guitar the FX gives what it's supposed to give but then suddenly the sound weak (like it's tired! so it didn't sustain, while I can still see the string vibrate) and I cannot hear anymore the effects sound but the guitar sound (very low and distorted).

thx 4 help, at least with impedance.
Armando

[R.G.]

Give this a read:
"Impedance - - what is it and why does it do all those terrible things to you?"
http://www.geofex.com/Article_Folders/impednc.htm

[foxfire]

the early note decay/no sustain could be a bias issue. check your transistor voltages.

[arma61]

Thx u both.
Fox fire, shall I check the transitors voltage when the Fx is quiet or playing guitar, or both. I never understand this!

they are 4 - 2N914, it looks like they are there to amplify the signal; emitters to the next base and collector to gnd (sorry I cannot yet post the schematic) .The FX is powered with 9V (from a leaded battery 12V and a TL709 or something like that!), any idea what voltage should I get, with sound and withou sound.

thx 4 help
Armando

[foxfire]

i'm barely good at diagnosing problems much less fixing them, but read this, http://www.diystompboxes.com/wiki/index.php?title=Debugging if you haven't already.

[soulsonic]

You should check voltages with nothing plugged in and with the input shorted to earth. This way is very accurate.

[QSQCaito]

It'd be much better to know what circuit are we talking about.

BTW; take a look at the debugging thread

[aron]

Did you check out the FAQ in the Wiki? I'm serious? I added a number of entries on this very subject.

[arma61]

thx again to all

as it seems this post is overtaking the Subject I thought to open a new post with a different subject (I will use the word "minisynth" in the subject so if you want to you can continue to read it.
Armando