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Topic: Replace a polyester cap with an electrolytic in a pinch? (Read 8 times) previous topic - next topic

gonzogeek

If I get the polarity correct can I replace a cap that a project specifies as polyester film with an electrolytic? It's a 1uF cap. I do have some 1uF poly caps on order, I'm just being impatient. I'd like to finish my build this evening. The cap is part of an LFO circuit in an audio related project.

Thanks
Jim

pwillard

Can you show the circuit?

Normally you should be able to do this... but the circuit might mandate that the cap be non-polar.

gonzogeek

http://www.magicmess.co.uk/DSA/dsa_schematic.php

It's C3 which is at the top left of the LFO circuit which is at the bottom right of the entire schematic

pwillard

Ok, here is how *I* would do it.

Get (2)  2uF Electrolytics and connect them  ---+||----||+----   <-----like that in series.  That will give you a 1uF Non-Polar cap.

You need 2uF since you get HALF the rated value when used like this.   IF you used (2) 1uF back to back, you would get .5uF.

But... it you MUST use the single 1uF electrolytic, I would connect the + side  of your 'lytic to R36  (only saying that due to the inverted configuration of the OP AMP)

Pete

gonzogeek

Thanks Pete I'll give it a go and I didn't know you could do that with electrolytic caps. Cool tip!

pwillard

Well, you can't really get away from the fact that it is a bit of a "Kludge"... but if you a really just tying to quickly test the concept... you should have OK results.

MarkT


Well, you can't really get away from the fact that it is a bit of a "Kludge"... but if you a really just tying to quickly test the concept... you should have OK results.


Indeed - electrolytics have very poor specs compared to 'proper' dielectrics - significant leakage and losses, high variability in value, lots of noise, deterioration with age - they are mainly used where this doesn't matter, such as decoupling.  There are 'audio grade' electrolytics which have much better specs for this kind of use.  If you do the kludge, fix it when the proper capacitor(s) arrive(s)!.
[ I won't respond to messages, use the forum please ]

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