NP cap to polarized

[AMK]

Between pin 8 and 9 of the Lm324 there's weird symbol- a 15uf NP cap, since we believe in SMD Versions I'm thinking of using just a polarized one(unless someone gonna prove me other).
Where should the positive placed?
Early versions were using two caps like this:



The newer XO seems to ditch it:

[ElectricDruid]

Pin 9 of the LM324 is basically a virtual ground*, and the output will switch from close to one rail to close to the other.

So that's why they used a non-polarised cap (or the equivalent arrangement of a pair of polarised caps) - because either orientation of a polarised cap is going to be wrong half the time!

HTH

* It's not exactly at the midpoint voltage since 2.4K+820R is not 3.9K, but that doesn't matter here.

[GGBB]

The newer XO seems to ditch it:

Are you sure?

[Rob Strand]

When you see caps marked NP it generally means non-polar electrolytic capacitor.   They have no polarity marking.  These are different to the more common polarized electrolytic capacitors, which have a polarity marking.

Unless you know better you shouldn't replace an NP cap on a circuit with common electrolytic, or visa-versa for that matter.

Using two back-to-back connected polarized electrolytic caps in place of an NP cap is a valid change - as is done on the two examples.

What's on the PCB's is a different matter but the idea still applies.    Check the polarity markings and the value.

[Phend]

Used NP in the AE Tremolo. 1uF, 3 places, probably matched them. They didn't replace polarized electrolics.

[ElectricDruid]

Are you sure?

Good spot, Gord! That does look a lot like it!

[AMK]

Pin 9 of the LM324 is basically a virtual ground*, and the output will switch from close to one rail to close to the other.

So that's why they used a non-polarised cap (or the equivalent arrangement of a pair of polarised caps) - because either orientation of a polarised cap is going to be wrong half the time!

HTH

* It's not exactly at the midpoint voltage since 2.4K+820R is not 3.9K, but that doesn't matter here.

Ohhh I see
 

The newer XO seems to ditch it:

Are you sure?

Nice catch! pin 8 and 9 seems like they're connected together, that got me confused...

[antonis]

pin 8 and 9 seems like they're connected together,

Good for a buffer (voltage follower), like IC4d..

[AMK]

which method is more recommended- two polarized 33uf back-to-back or 15uf np?

[duck_arse]

do you have any 15uF non-polarised on hand? can you source them [do you want to have to?] easy and cheap?
do you have 33uF [or 22uF or 47uF] polarised on hand? space to fit them?

same either way electrically, so comes down to what you've got/can get/will fit.

[ElectricDruid]

which method is more recommended- two polarized 33uf back-to-back or 15uf np?

+1 what Duck said. Same difference. Whichever is easiest, cheapest, fits best.