low-pass RC filter

[yeeshkul]

Does it matter in what order i place the cap in parallel with the load and the series resistor? I thought it didn't but ... it actually played a role when i was building Red Llama. The order had quite an impact on the circuit behaviour. Although the theory only talks about cap in parallel and series resistor, Red Llama was quite picky about the placement.
res -> cap .. OK
cap -> res .. oscillations

[alanlan]

Yes, it does matter.  It won't form a low pass filter otherwise.  Also, caps don't generally like capacitive loads and that probably explains your oscillation assuming it is an op-amp output.

[yeeshkul]

Thank you

[alanlan]

Sorry, should have read "Also, *op-amps* don't generally like capacitive loads". 

[cpm]

i was about to ask about that "capacitive load" issue, but feeling bad for that much lazyness i asked google first 

http://www.analog.com/library/analogdialogue/archives/38-06/capacitive_loading.html

the first paragraphs are enough for a basic explanation

[yeeshkul]

Interesting thing is that the resistor placed after the cap doesn't form the filter. It is still in series with the source and the load, and so is the cap in parallel.

Also, i see that i experienced troubles where i should not have experienced any troubles (talking bout Red Llama) ->  the cap straight on the IO output (= capacitive load) was doing fine fine. The cap decoupled by the resistor was doing things - although along with what you said, the low-pass filter was not formed in this case ...