Re: Cap orientation help needed

Posted by induction on May 04, 2015; 8:45am
URL: http://guitar-fx-layouts.238.s1.nabble.com/Cap-orientation-help-needed-tp19761p20120.html

motterpaul wrote

I am trying to understand the phrase "Figure out which side of the cap touches the part of the circuit with a DC shift and put the positive leg there."  Okay - so DC shift means there is a coupling cap which is changing the state of the DC (or eliminating it) for the coupling of sub-circuits within a larger circuit, because one side has different DC requirements from the other side. So, in this case both 100n caps have one side connected to Vref and the other side eventually going to ground. The DC bias on the side of the 100n caps that goes to ground should have 0 bias - is that correct?

That's correct, in this case. There is no source of DC voltage on the side of the cap that touches ground, so the bias must be zero there. In some other cases, it might not be possible to say that the bias is necessarily zero on one side and Vref on the other, but it should be possible to say which side is higher in voltage.

In other words, when you say "Figure out which side of the cap touches the part of the circuit with a DC shift and put the positive leg there" - that means to put the positive side on the side before the bias shift? and that the ground goes to the side after the bias shift? Meaning the "shift" is from a section with a DC+ bias containing the IC, to  audio subsections (the tone stack and the volume pot) where we really do not need DC. Am I on the right track, or completely off base?

You can't really generalize to 'put the positive side on the side before the bias shift' without knowing which way the bias shifts. The general rule always applies: put the positive side where the DC voltage is higher. Beyond that, it's a question of figuring out how the DC voltages sit in the circuit.

I've just written an extensive post on how to read schematics, that touches on the cap orientation issue and may be of interest to you. I put it in a separate thread because it's really long.