Electrolytic capacitors in series + to  + makes bipolar electrolytic - Page 1
Forum section: electronics / general

author: ngneer9
author_rank: Newbie
timestamp: August 15, 2016, 01:55:59 pm
content: I'm repairing a Samson Servo 4120 quad audio amp and have found the problem to be two capacitors in series +terminal to +terminal. This is part of an opamp control where they are making a very low pass filter from the amplifier output and then using this as an indication of DC output. The two caps (22uf) are both showing open. I have no LCR meter. I've ordered new 10uf ceramic caps from Digikey (two 22uf in series) but am not sure if the "capacitors in series" calculations are appropriate since one of the electrolytics may act as a diode and the circuit would then see only one capacitor. If I had an LCR meter, I'd breadboard test this, but I don't. They did this to save a few cents on the parts list. I'm replacing these caps on all channels.

author: madires
author_rank: Super Contributor
timestamp: August 15, 2016, 02:13:39 pm
content: Two electrolytic caps in series with the plus or minus terminals tied together are a replacement for a non-polarized electrolytic. In some cases diodes are added in parallel to the electrolytics. And yes, it's done to save a few cents.

author: ngneer9
author_rank: Newbie
timestamp: August 15, 2016, 02:26:14 pm
content: As this is my first time using a forum, I was unclear about my question; Is the single ceramic capacitor replacement of the two 22uf electrolytic caps in series + to + calculated to be 11uf or 22uf. If a reverse biased electrolytic cap acts as a diode, would the circuit see only one diode?

author: ngneer9
author_rank: Newbie
timestamp: August 15, 2016, 02:32:50 pm
content: Sorry, I meant one capacitor at end of previous message

author: wraper
author_rank: Unknown
timestamp: August 15, 2016, 02:43:35 pm
content: Never use ceramic capacitors in audio path unless they are with NP0/COG dielectric (only low capacitance). Z5U,Y5V and similar will give especially horrible results. X7R and X5R are better but still awful. Their capacitance is not stable with time, temperature, and applied voltage (can change as much as by 80%). Such capacitors are especially horrible if used in pass filters because they will cause harmonics/distortion, and not stable frequency response. They have microphonic effect too. If this is just for protection circuit, then probably ceramic is fine, but be aware of not stable capacitance.If you connect 2 equal capacitors in series, then total capacitance will be halved.

author: madires
author_rank: Super Contributor
timestamp: August 15, 2016, 02:45:53 pm
content: 11µF is correct, and the circuit would see a cap in case of two back-to-back electrolytics in series. Since both caps are back-to-back, only one is reverse biased. So it's more like a cap and a diode in series. I'm not sure if a MLCC would be a suitable replacement in an audio circuit. Maybe someone else has more insight into this.

author: ngneer9
author_rank: Newbie
timestamp: August 15, 2016, 02:59:29 pm
content: I thought I was doing a good thing by changing from electrolytic to ceramic caps. My other options would be original configuration (2 X 22uf electrolytic) or a single 10uf bipolar electrolytic which now I think would be the best idea.