Capacitor polarity in gyrator

Thread Starter

hrs

Joined Jun 13, 2014
334
Hi,

I'm working on a modified BOSS HM-2 which uses gyrators for tone control. It has an odd capacitor value (C35) of 1.5uF. I happen to have some tantalum caps with this value. Then I noticed the C35 polarity on the BOSS schematic is opposite to some schematics you can find online.

I did an LTSpice simulation which shows the signal polarity reversing.

Assuming my simulation is correct, my question is: Will a tantalum cap stand up to this abuse? Otherwise I have a "normal" 1uF electrolytic that measures 1.2uF and I might use that.
 

Attachments

crutschow

Joined Mar 14, 2008
27,475
Electrolytics (including tantalums) are normally polarized, have a wide tolerance, and are thus not well suited to use as frequency determining components in audio circuits (they are okay for power supply filtering).
Much better to use a film capacitor, even though they are physically large.
 

Thread Starter

hrs

Joined Jun 13, 2014
334
My experience with tantalums is that they are not tolerant to polarity reversal. AVX has this study of the effect of 10% reversed polarity: https://www.avx.com/docs/techinfo/17_Reverse.pdf

I don't see any reversed polarity in your simulation. Could you consider a 2.2 uF and 4.7 uF non-polarized in series (about 1.498 uF)?
Thanks, I kind of expecting that. But I didn't think of the excellent suggestion to use series caps. I've read somewhere that if you put polarized caps back-to-back you get a NP cap. But there was a price to it which I forgot. Anyway, I think I'll be going this route, thanks again.
Electrolytics (including tantalums) are normally polarized, have a wide tolerance, and are thus not well suited to use as frequency determining components in audio circuits (they are okay for power supply filtering).
Much better to use a film capacitor, even though they are physically large.
The biggest film capacitor I have is 1uF and it's indeed large. Since this is just a one-off I can hand pick one that is good. I went through my bag of 1uF elco caps to find the 1.2uF I mentioned earlier and most are actually quite close, within a few %.
 
Top