Buffer Impedance Question

[goldenmonkeycolor]

Hey there, long time looker, newb pedal builder.  First time poster.  I'd like to start out by saying the giving of free information with this and a few other forums is just absolutely amazing.  So cool how many people are willing to share so freely.  Thanks for getting me started on this new hobby.

I recently built a stratoblaster buffer to install in my strat per some recommendations from a few other forums.  It sounded great on my breadboard and really brought out the sparkle and fattened up my strat with a nice couple db boost. 

I just installed it into my strat and I plugged it in (with strings off, had to install it under my pickguard) and tapped the pikups with a screwdriver.  I put the blaster on a switch and the blaster side is definitely louder than the non blaster side, but before I put the strings back on I decided to measure the resistance coming out the end of the cable (measuring resistance from tip to ground at the end of a cable connected to my guitars output jack)  I figured I would get a lower resistance with the blaster in the circuit.  I am getting like 5.8k (which is the impedance of my pickups) with the blaster off, but with the blaster on I'm getting about 100k.

Now I did test the circuit on a breadboard and it sounded great, like it was making my volume control wortk a bit better, and it was bringing up some chime and sparkle and punch.  I figured it would lower my output impedance.  Do I just have the wrong understanding of impedance or is there something wrong here?  I installed the blaster on a switch just in between the volume pot and the output jack with a battery on the ground of a stereo jack.  I did change a resistor so that I could get 4.5v on the drain (?) of the jfet (to bias it- might have been the gate?)

Is there something wrong here or am I just understanding impedance incorrectly?

Thanks a bunch again!  I really appreciate what you guys do here!

[teemuk]

The answer is that you are understanding impedance incorrectly.

What you measure is the DC resistance between output and ground, this is not the same thing as output impedance.


19 and a half minutes long, and I haven't watched this yet, but I reckon it should satisfy rest of your curiousity:
http://www.youtube.com/watch?v=Sp2HC47Amgc

[dwmorrin]

If you used the first schematic I found image googling "Stratoblaster Buffer" then you are just reading the 100k resistor (R5) connected to the output capacitor.
Your meter "sees" the output capacitor as a dead end, so the only circuit you are measuring is through the 100k resistor.

Your meter is only good for dc resistance.  ac impedance is not measured this way.
The output impedance is the 22k drain resistor.

[dwmorrin]

I installed the blaster on a switch just in between the volume pot and the output jack with a battery on the ground of a stereo jack.

Is there something wrong here ...?

Possibly...
Does the switch disconnect the +9 volt side of the battery?  If not, you're probably draining the battery all the time.  Move the battery neg terminal to the ring terminal of the stereo jack... unless you're using it in stereo?

[goldenmonkeycolor]

I installed the blaster on a switch just in between the volume pot and the output jack with a battery on the ground of a stereo jack.

Is there something wrong here ...?

Possibly...
Does the switch disconnect the +9 volt side of the battery?  If not, you're probably draining the battery all the time.  Move the battery neg terminal to the ring terminal of the stereo jack... unless you're using it in stereo?

thanks for the help, but that was my mistake- i did connect the ground to the ring of the stereo jack.  my bad!

[GibsonGM]

But other than that, you can't use DC resistance as an indicator of impedance.   Gotta read up on it, it's a pretty neat phenomenon!  All depends what frequency (ies) you are talking about.    Google up, tons of info out there.   

I can tell you, the output impedance of the 'blaster will be plenty low enough to play nicely with all amps/pedals )

[chptunes]

Jack Orman has a great explanation of pedal impedance on his site:  http://www.muzique.com/lab/imp.htm

-Corey

[goldenmonkeycolor]

Jack Orman has a great explanation of pedal impedance on his site:  http://www.muzique.com/lab/imp.htm

-Corey

thank you for that!  I just need to go through that whole site and memorize it