parallel resistors / capacitors in crossover

[jimbo1968]

I'm designing my active filters. Are there any things to consider when paralleling resistors or capacitors to get the wanted values?

I chose // resistors thinking of board layout. Maybe series is better ?

[richie00boy]

I use parallel for both resistors and capacitors. I design for 3 of each, and I don't have to use links if I only use 1 or 2. Plus it's usually caps that give you a hard time on values, and paralleling lowers inductance and raises capacitance.

[jimbo1968]

How accurately do you try to match your filters?

If my 24db LP worked out spot on 200Hz is it OK if the HP stages are say 197Hz and 203Hz ? or does that do something nasty to the signal (phase?)?

ie do I have to match the 2 stages closely to each other or can they be used as above to average out?



PS. Roughly how much is a capacitance meter?

[gfinlayson]

PEAK electronics manufacture a LCR meter, which costs £79.

http://www.peakelec.co.uk/acatalog/jz_lcr40.html

[richie00boy]

A couple of Hz at 200Hz is absolutely nothing, it's 1% error. IMO there's no need to measure caps, but it can't hurt if you want to.

I use 1% resistors and 5% caps and always get perfectly good enough results. Paralleling caps also usually gains you better than 5% tolerance anyway due to stats, according to Doug Self. Whatever you use will be MANY times better than a passive crossover anyway.