Bottlehead Forum

Bottlehead Kits => Crack => Topic started by: tdonnellyem on December 13, 2015, 08:20:27 AM

Title: rca center pin resistance check
Post by: tdonnellyem on December 13, 2015, 08:20:27 AM

hey now,
so i finished building my amp and went through the resistance checks.  all were fine until the last two, the center pins on the rca jacks.  the values i am getting are  107.4K ohms for the left jack and 109.2K ohms for the right jack.  it says the reading should be between 90K - 100K ohms.  the amp is slightly above that.  i have not gone onto the voltage check since i want to make sure that my resistances are ok.  if they are too high what can be the cause for it?  I've gone through the amp twice and can't find any loose wires and all of the other resistances checked out.  any ideas?

thanks

tim

Title: Re: rca center pin resistance check
Post by: Paul Joppa on December 13, 2015, 10:17:51 AM

If correctly wired, this measures the end to end resistance of the level control. Typical potentiometers like these are usually rated +/-20% for resistance precision, so technically the pot meets spec if it is between 80K and 120K - meaning that your measurement is fine.

The resistive trace is basically graphite, like pencil lead. IIRC, a slurry of paste is formed and then baked. This is not a precision process! Fortunately the absolute value is not important, only the proportion of the total as a function of setting matters.

Title: Re: rca center pin resistance check (resolved)
Post by: tdonnellyem on December 14, 2015, 05:50:09 AM

cool...thanks for the heads up.  i figured the 90k - 100k was the range but knowing i can go 15-20% higher/lower is good to know