Solid State Guitar Amp Forum | DIY Guitar Amplifiers

I did an experiment to try to prove a point to myself or a forum member or a complete stranger  :loco

The point I wanted to make was an open circuit can be constructed and as long as it's open the voltage will remain the same.

Unfortunately I have failed in that endeavor but fortunately succeeded in learning or affirming stuff I have read about.

I plugged in a constant dc power supply 13.8 v and tested voltage  xP

IMG_20250324_125109320_HDR.jpg

Next I grabbed a resistor added it to the open circuit and got some good results  :loco

IMG_20250324_125346094_HDR.jpg

So life is good yeah I'm intrigued and fascinated and life is good

But then I got greedy by grabbing a large value resistor and that's when everything fell apart  :grr  :lmao:
IMG_20250324_125402456_HDR.jpg

And no I don't understand it but I'm thinking it has something to do with my meter's (internal resistance?)

So yeah I'm off to try and learn about that  :tu:

Ok I have a plan  :grr

I'm gonna go back and increase the resistance in series with (+) and try to discern where voltage begins to drop.

I presume my meter has a 10 megaohm resistance so possibly it's gonna change at the 1 megaohm stage.

 xP

Quote from: saturated on March 24, 2025, 02:10:57 PMI'm thinking it has something to do with my meter's (internal resistance?) 

Yes.  You could look it up, or you could solve for X: 
8.76/12.80 = x/(x+6)

edit:  my mistake, should have read 13.8, not 12.8, see below.

Ok I'm back with some results
It dawned on me that I had a decade resistor box so I was like hey that's pretty rad I can just dial in where voltage starts to roll off  :dbtu:

Unfortunately I looked at it and it only goes to 1000k (which I presume is one megaohm)  :grr

Anyhow I started looking around and quickly found a 1M ohm resistor
IMG_20250325_181122406_HDR (1).jpg

Ok cool so let's try 2M ohm
IMG_20250325_181535321_HDR.jpg

Ok....there we go

I needed something in between so I looked around and found I think a 220k ohm resistor and added it to the 1M ohm 
IMG_20250325_182309314 (1).jpg

And the multimeter is already taking notice of the increased resistance...I think  :loco

Yes.  You could look it up, or you could solve for X: 
8.76/12.80 = x/(x+6)
[/quote]

More homework from G1  :tu:

I tried it with the original equation and got a 13 so I looked it up and it said 10 so I retried it using a different denominator and got closer

IMG_20250326_141025907.jpg

IMG_20250326_141642497.jpg

 xP