Be careful where you source your components - Page 1
Forum section: electronics / general

author: LektroiD
author_rank: Frequent Contributor
timestamp: March 27, 2015, 09:44:24 am
content: Most of my work is in analogue ausio and synthesizers, and over the years I have discovered through experience that the quality of capacitors is essential. I was not getting good results from the filters I recently built, so I thought I'd have a closer inspection of the MLCC capacitors I was using... I was shocked to find a 0402 hiding away inside the casing.This has nothing to do with audiophool nonsense, there is definitely a marked difference between good through hole capacitors compared to SMD when it comes to analogue filtering. SMDs are fine for decoupling and digital stuff, but not analogue filters.

author: radix
author_rank: Contributor
timestamp: March 27, 2015, 10:16:01 am
content: Quote from: LektroiD on March 27, 2015, 09:44:24 amSo could you explain it to us newbs? Why are SMD caps not good for analog filtering? They don't have enough parasitic inductance?

author: rollatorwieltje
author_rank: Unknown
timestamp: March 27, 2015, 10:19:47 am
content: Don't they all look like that? Other than those big disks I remember through hole ceramics looking like surface mount parts with legs welded on. The capacitor itself is constructed like a stack of thin sheets with end caps on them. I have some early ones that aren't even epoxy dipped.Be aware that the capacitance of MLCC is highly dependant on voltage, some shitty ones are only like a fifth of the capacitance at their rated voltage. It can be tricky to find this information, and some are far worse than others. I've seen the rated capacitance being specified at voltages as low as 0.5V with a tolerance of like +10% -60% over their voltage range (I think it was a TDK 0603 X5R).

author: Monkeh
author_rank: Super Contributor
timestamp: March 27, 2015, 11:06:14 am
content: Quote from: LektroiD on March 27, 2015, 09:44:24 amAnd which SMD parts have you been using for filters?

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: March 27, 2015, 11:36:52 am
content: surely ceramic caps like that are a shitty choice for any audio application because they're really non-linear?

author: Zero999
author_rank: Super Contributor
timestamp: March 27, 2015, 11:51:01 am
content: There's nothing wrong with this. It's normal for through hole ceramic capacitors to be SMT components with leads welded on.Whether it's good for audio or not depends on the dielectric. Generally film is recommended for audio but ceramic can be fine, so long as you choose a decent quality dielectric.

author: TimFox
author_rank: Super Contributor
timestamp: March 27, 2015, 12:55:14 pm
content: All MLCC parts are built for use as SM parts, but they are available with leads, either conformal coating or military-style molded plastic boxes.It is fashionable to say that ceramic capacitors are non-linear, but that is not true of all types. There are many ceramic dielectric types in common use, some of which are linear and some are horribly non-linear (where the capacitance falls dramatically with applied voltage). In general, the higher the dielectric constant, the smaller the capacitor and the worse the non-linearity.Common dielectrics:NP0 or C0G: Q roughly 1000, similar to polypropylene film. Good temperature co-efficient. Linear. Limit to maximum value available due to low dielectric constant.X7R: Q < 50, roughly similar to polyester (Mylar) film. Decent temperature co-efficient. Linear enough for some applications, but NP0 preferred for filters, RIAA circuits, etc. where there is substantial AC voltage across the part.Z5U: I have called these "dog shit with leads". Q roughly 20. Applying full rated DCV reduces capacitance by factor 2:1 or worse. Smallest size due to high dielectric constant of ferroelectric material. Bad variation with temperature.

author: AndyC_772
author_rank: Super Contributor
timestamp: March 27, 2015, 12:58:10 pm
content: Don't forget Y5V... easily loses 80% of its capacitance as soon as you apply the rated DC voltage. I won't use them, ever.

author: TimFox
author_rank: Super Contributor
timestamp: March 27, 2015, 01:38:12 pm
content: In general, the non-linearity of a capacitor only matters if there be a large AC voltage across the capacitance. This can happen in a low-pass or high-pass filter near the corner frequency.

author: tszaboo
author_rank: Super Contributor
timestamp: March 27, 2015, 01:55:16 pm
content: Quote from: Hero999 on March 27, 2015, 11:51:01 amWell it pretty much doesnt matter how linear it is if you put it into the power supply.Quote from: LektroiD on March 27, 2015, 09:44:24 amI was shocked that they still make TH MLCC ceramic caps. I dont know, why would anyone use it?

author: TimFox
author_rank: Super Contributor
timestamp: March 27, 2015, 01:59:47 pm
content: Quote from: NANDBlog on March 27, 2015, 01:55:16 pmBecause it's still a free country.

author: tszaboo
author_rank: Super Contributor
timestamp: March 27, 2015, 02:22:24 pm
content: Quote from: TimFox on March 27, 2015, 01:59:47 pmGotta love the out of the blue no reason brainwash merikan propaganda.

author: TimFox
author_rank: Super Contributor
timestamp: March 27, 2015, 02:33:42 pm
content: Quote from: NANDBlog on March 27, 2015, 02:22:24 pmSorry for my excessive subtlety. In American English, "it's still a free country" means "because I want to".Some of us prefer TH construction, but the world is trending towards SM construction.Some (including you?) would probably prefer we stop using TH, but I shall continue.

author: tszaboo
author_rank: Super Contributor
timestamp: March 27, 2015, 02:51:55 pm
content: Quote from: TimFox on March 27, 2015, 02:33:42 pmSo, my problem with TH MLCC is the following:I dont know why do you expect manufacturers to keep supporting and making obsolete technology? Surely 98% of every new component is made SMD.So for manufacturers if is certanly not viable to run their old equipment, producing TH components. I'm surprised that this was found, probably it was cheaper to produce it this way than using the old capacitor production line.If the datasheet specification is met, they are fine. Also, if you were using their components, and you were registered with proper supply chain, they sent an email if they changed the manufacturing process.

author: TimFox
author_rank: Super Contributor
timestamp: March 27, 2015, 03:13:19 pm
content: I have used TH capacitors that contained MLCC "chips" inside for years. They are a sensible package for TH applications, and the fact that the MLCC chips are standard SM sizes makes it easy for the manufacturer. If nobody bought them, they would stop producing them. MLCC is not a panacea: The smaller internal dimensions improve parasitic inductance, but can result in other problems. For example, seehttp://electronicsbus.com/failure-modes-and-reliability-design-guidelines-of-ceramic-capacitors/for practical problems with failures. The older disc ceramic capacitors, now hard to find, were probably more reliable, but not available in large capacitance NP0 units due to having only one layer.

author: SeanB
author_rank: Super Contributor
timestamp: March 27, 2015, 04:32:31 pm
content: Those have been around since the 1970's, though you generally got them as a glass body with the capacitor visible inside. Used for decoupling on digital boards, and favoured by IBM a lot. Good as they could fit into a DIP footprint inside the socket so no extra space needed on the board. What you get depends on the manufacturer, as the capacitor inside can range as described above from pretty good to utterly abysmal, depending on the manufacturer and the little block of ceramic they use.

author: Tim F
author_rank: Regular Contributor
timestamp: March 27, 2015, 05:26:21 pm
content: Quote from: TimFox on March 27, 2015, 01:38:12 pmThis x1000. Lots of situations you can get away with dog shit capacitors in audio circuits because the corner frequency is ultra/sub sonic.

author: TimFox
author_rank: Super Contributor
timestamp: March 27, 2015, 06:22:27 pm
content: I am now retired, but in my previous day job we used technology appropriate to the task. Our digitizing x-ray detector boards used SMT for the amplifiers, ADCs, and FPGAs in order to achieve the required density. The same system had high-power motor and safety controls assembled on DIN rails with point-to-point wiring and leaded components inserted into the terminals where required (for example, protection diodes on the relay coils). Not everything need be built to the density of a cell phone.

author: VK3DRB
author_rank: Super Contributor
timestamp: March 28, 2015, 03:08:34 am
content: Quote from: blueskull on March 27, 2015, 01:06:03 pmLike most ICs.I remember a few years ago we had to design a RS-232 converter using discrete transistors in an instrument cluster for a popular GM car, because the easy to use RS-232 converter chips cost too much. If we saved 50 cents on a board we saved the company $100,000 per year.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 28, 2015, 04:41:44 am
content: Quote from: blueskull on March 27, 2015, 01:06:03 pmAmen and ditto. If you are drawing pay associated with doing engineering work you need to use that high price shoulder mounted accessory. If you use it right your employer (or you, if you are self employed) will come out ahead even after paying the high rate for you. If not they will quickly discover that they can get a thoughtless approach to the problem at a much lower cost. Of course if you are self employed the process of firing yourself is even more painful.

author: John Coloccia
author_rank: Super Contributor
timestamp: March 28, 2015, 10:52:46 am
content: Quote from: Tim F on March 27, 2015, 05:26:21 pmNo you can't, because:a) you can't tune a circuit to sound good when the cap is constantly changing values...look up cap aging and heat during solderingb) you can't tune a circuit when your tolerances are garbage. Crappy tolerances are OK for decoupling networks, not high quality audioc) crappy capacitors can be significantly microphonic...so when you bump into the unit, or rub your hand on it, you hear it through the speakers. That would be acceptable?re: though hole vs surface mount.On products which might see some board flex, and that need to last a long time and be serviceable for 20+ years, through-hole wins for reliability and service life. When you design consumer garbage that you know will end up in a land fill in 2 years, it doesn't matter. When your products come with lifetime warranties and are expected to work, nigh after night, in some pretty unfriendly environments, you worry about stuff like this.

author: rs20
author_rank: Super Contributor
timestamp: March 28, 2015, 11:10:28 am
content: Quote from: John Coloccia on March 28, 2015, 10:52:46 amCrappy tolerances are just fine for both decoupling AND AC coupling, as long as your AC coupling is very ultra/sub sonic, which it should be. Also, decoupling/coupling networks and high quality audio are orthogonal things, you're presenting a false dichotomy there. Specifically, crappy tolerances are just fine for decoupling and coupling in high quality audio. Filters for your treble and bass control, sure, use NP0, because you never needed large values anyway.Fair point on the microphonics; except engineering is an exercise in compromise. So saying that "you can't" because of microphonics is a bit strong when these things are often sitting in a very still/sturdy cabinet.

author: John Coloccia
author_rank: Super Contributor
timestamp: March 28, 2015, 11:32:34 am
content: When you AC couple, you're usually high pass filtering as well, so Radio Shack Y5Vs aren't going to cut it. Most of my filtering caps are in the 33n to 1u range. The only time I use NP0 is when I need small values, like 100pF.With any sort of high gain, microphonic coupling can be so bad that you can sometimes run your hand just on the enclosure, or tap on it lightly, and you'll get loud noise through the speakers. If you've never played with it, you'll be shocked how bad it can be. It took me a good hour to figure out where that thump was coming from the first time I ran into it!But I don't have any problem with surface mount components in a through hole package. I know some people say they can hear the difference, but personally I can't and I simply have to trust my own ears.

author: dannyf
author_rank: Super Contributor
timestamp: March 28, 2015, 11:59:32 am
content: QuoteHas been like that for years. The standard manufacturing process now.

author: TimFox
author_rank: Super Contributor
timestamp: March 28, 2015, 04:31:33 pm
content: Piezoelectric effect in high-dielectric-constant ceramic capacitors is important. I have seen no mention of piezoelectricity in NP0/C0G low-dielectric-constant ceramics.One material used in these capacitors is barium titanate, which used to be common in "on-purpose" piezoelectric transducers, but now mostly replaced by PZT for transducers. This effect is mentioned in ceramic capacitor data sheets, but apparently there is no practicable way to specify the effect quantitatively. One of my colleagues had a problem with a microphonic circuit board (flexing) and successfully followed my advice to replace a ceramic capacitor with a film capacitor (0.1 uF if I remember correctly). As several contributors mentioned, choosing a component for a specific application should be done with data sheet or manufacturer consultation, since the "other stuff" between the leads can be important.

author: wraper
author_rank: Unknown
timestamp: March 28, 2015, 04:58:00 pm
content: Quote from: LektroiD on March 27, 2015, 09:44:24 amThrough hole MLCC except NP0 (very small capacitance) were never good for audio/passing any signal through them. They always had Y5V or similar crappiest ceramic for any capacitance more than few nanofarads.

author: wraper
author_rank: Unknown
timestamp: March 28, 2015, 05:09:24 pm
content: Some are talking that technology had changed to using SMD capacitors inside but AFAIK through hole MLCCs always had such construction. I just cracked open 30 year old Soviet MLCC cap and it is exactly the same. Just capacitor inside is bigger, seem like 0805. Now they can make the same rating Y5V capacitor in smaller package, so put smaller cap inside the through hole part too.

author: wraper
author_rank: Unknown
timestamp: March 28, 2015, 05:19:55 pm
content: Quote from: NANDBlog on March 27, 2015, 01:55:16 pmTake some modern SMPS used in various equipment. Unless it is ultra small, likely you will find all through hole design on the one layer PCB.