electrolytic caps verse ceramic caps - Page 1
Forum section: electronics / beginners

author: ajpetersen
author_rank: Newbie
timestamp: March 15, 2022, 05:49:09 pm
content: I am fixing a old peavy keyboard amp KB 300 from the 80's. And the electrolytic caps need replacing. They used electrolytic in the signal path of the op amps. Now I understand using them as bypass or power rails but are they really necessary in the signal path or can I use ceramics as to not replace them again. My boss says they probably used them back in the day because they were cheaper. but then I read an article about microphonic feedback. Is this true? or can I use ceramics.

author: Zero999
author_rank: Super Contributor
timestamp: March 15, 2022, 05:56:17 pm
content: The answer is it depends on how the capacitor is used and the type of ceramic. If it's in the signal path, then make sure a non-piezoelectric ceramic capacitor is used. A piezoelectric capacitor is microphonic, meaning it generates a small voltage when subject to vibration. This can cause interference and acoustic feedback.

author: magic
author_rank: Super Contributor
timestamp: March 15, 2022, 06:00:17 pm
content: Good ceramics for signal coupling are C0G/NP0 dielectric and only available up to maybe 1µF if you are lucky and willing to pay through your nose.Electrolytics start from 1µF up.No overlap between these technologies. Just use elcos.Watch out for bipolar ones (capable of equal voltage in each polarity).

author: Zero999
author_rank: Super Contributor
timestamp: March 15, 2022, 06:33:10 pm
content: Electrolytic capacitors are available down to 100nF.https://uk.rs-online.com/web/c/passive-components/capacitors/aluminium-capacitors/?applied-dimensions=4292048893,4293330461Another alternative are film capacitors.

author: SeanB
author_rank: Super Contributor
timestamp: March 15, 2022, 06:48:55 pm
content: If you are really wanting to not use electrolytics use film capacitors, though even a 10uF 63V one will be a lot bigger than an electrolytic of same value and voltage rating. No reason not to use the electrolytics there, just use higher voltage ones than the existing, and for things like 10uF use 100V units, or even for all values below 100uF in signal paths, as they will be not much bigger than lower voltage ones, and there likely is room enough to install them as well.

author: magic
author_rank: Super Contributor
timestamp: March 15, 2022, 07:01:15 pm
content: Quote from: Zero999 on March 15, 2022, 06:33:10 pmWell, OK.I don't think I have ever seen an elco less than 1µF in the wild.For power you would just use ceramic.For signal, 100nF film are not too large.

author: bdunham7
author_rank: Super Contributor
timestamp: March 15, 2022, 07:06:34 pm
content: Are the caps bipolar and used in a non-biased (AC) signal path or are the polar and used in a biased (DC + smaller AC signal) signal path? If the former, you can use PP film if they'll fit. If the latter, just put in high-quality el-caps, audio grade if you like. You can go up in voltage to keep the physical size similar. They'll last another 40 years or more. Have you confirmed that any of the audio-path caps are actually bad?Most ceramic capacitors would be a terrible choice for that application.

author: BrokenYugo
author_rank: Super Contributor
timestamp: March 15, 2022, 07:13:38 pm
content: Wouldn't the whole MLCC DC bias problem potentially show up here too?Signal chain electrolytic caps tend to run cool and seem to last until the seals fail and they dry out. I'd just select 105*C and forget about it.

author: TimFox
author_rank: Super Contributor
timestamp: March 15, 2022, 07:25:47 pm
content: The MLCC bias problem is not important for C0G (NP0) capacitors, which are also non-microphonic. However, they are hard to find much above, say, 10 nF. If possible, film capacitors (even PET) are usually a better choice than electrolytic for coupling capacitors, when space allows.

author: SeanB
author_rank: Super Contributor
timestamp: March 15, 2022, 07:26:52 pm
content: Quote from: magic on March 15, 2022, 07:01:15 pmSony for one, along with Matsushita, used 0.47uF and 0.33uF electrolytics in equipment, though the Sony ones were notorious in that they had a 100% failure rate after 5 years, the Matsushita ones you will still find 30 year plus ones in equipment which are still, considering their age, good, with ESR under 50R, which is within spec for them, as they are 85C parts. Use 100V 105C parts, which are likely the same case size as the originals, and which will look similar, and last another 40 years.

author: mariush
author_rank: Super Contributor
timestamp: March 15, 2022, 07:52:09 pm
content: Digikey has nearly 600 capacitors in stock with values between 0.1uF and 1uF and voltages from 25v and up:https://www.digikey.com/short/5q5r78t2No need for ultra low esr series, you can probably even go with 85c rated capacitors for your application.