SMD capacitors in audio path

[patrick398]

It seems like most SMD capacitors are MLCC (ceramic), are these the same or similar in composition to the common orange through hole caps and is it similarly advisable to keep them out of the audio path?
The only other SMD caps i think i've seen are tantalum but i've always tried to avoid using them because of environmental/ethical issues

[phasetrans]

I've commented on this before, at some length, but here are articles I came across recently that have useful details on this:
https://www.edn.com/signal-distortion-from-high-k-ceramic-capacitors/
https://www.edn.com/more-about-understanding-the-distortion-mechanism-of-high-k-mlccs/

Practical example from one of my designs that is complete, except for KiCAD layout:

22uF Filter capacitors - low ESR 20% electrolytic SMD (Panasonic FK)
1uF bypass / LDO capacitors - 0603 10% X7R MLCC SMD (TDK CGA)
1uF signal capacitors - Film capacitor 5% 5mm lead spacing (hand placed) (EPCOS/TDK)
0.1uF signal capacitors - Film capacitor 5% 5mm lead spacing (hand placed) (EPCOS/TDK)
4.7nF signal capacitors - 0603 5% C0G MLCC SMD (TDK CGA)
180pF signal capacitor - 0402 5% C0G MLCC SMD (TDK CGA)

Edit: Added brands

I personally prefer TDK capacitors because they are reasonably priced (but not the cheapest) from the distributors I use, and include all the voltage coefficient details.

If anyone is interested in the physics of high K MLCC dielectrics, let me know and I can talk about that for a bit. Long, long ago I worked in a research lab that characterized the domain polarization behavior of ferroelectric materials, which is the same class of material that is used for high K dielectric MLCC capacitors.

Edit 2: I should explicitly mention that C0G dielectric is typically a paraelectric material like calcium zirconate. While true High K dielectric material is usually barium titanate, which is ferroelectric, and has the voltage coefficient behavior.

[patrick398]

Thanks, I'll have a read of those. I did think of hand placing them as the fan house I use only offers mlcc but if I'm hand placing them I'll probably just use through hole ones...plus they're pretty and blue

[garcho]

Check out this article, I appreciate his pragmatic view on audio electronics:

https://sound-au.com/articles/capacitors.htm

If something doesn't alter the sound in a way you can hear, it doesn't matter *in terms of the output audio*. There are other concerns, of course. One good thing about SMT is getting rid of the leads, for inductance and that kind of thing, as well as preventing the leads from cracking the cap while you populate the board. Are you designing a high-powered (high fidelity) amplifier or 48-channel console? Or a guitar pedal? That changes things as well.

[Rob Strand]

The problems with smd capacitors has been discussed many times on the forum.

https://www.diystompboxes.com/smfforum/index.php?topic=111219.msg1022128#msg1022128
https://www.diystompboxes.com/smfforum/index.php?topic=124118.0
https://www.diystompboxes.com/smfforum/index.php?topic=116266.0

There are non-ceramic caps more suited for the job and they are becoming more available as time goes on.

For ceramics the degree of the problem boils down to voltage across the cap, the value of the cap and the size of the package.  All discussed in those other threads.

A large DC can cause a decrease in capacitance.   For small values this usually isn't a problem but for larger values say over 1uF it can be quite extreme.    If your 10uF cap is only really 1uF it's not doing what it is expected to do.

A large AC voltage across the cap causes distortion.    If you have a cap used in a filter at 1kHz then it will often see large AC voltages *across the cap*.    That's where the Elliot sound article comes in.
- An easy example is an RC high-pass filter at 1kHz with a 100Hz input.   The cap is blocking the 100Hz and to do that the AC voltage across the cap is high.   
- If however you have an RC high-pass filter at 2Hz, basically just AC coupling, the cap doesn't block a 100Hz and the voltage across the cap is low.      In practice the 2Hz filter is going to need a larger cap, which going to be more subject to the distortion if you use a small package device.

[vigilante397]

The problems with smd capacitors has been discussed many times on the forum.

^THIS.

I'll say the same thing I say every time it comes up: I use C0G/NP0 MLCC where possible, X7R everywhere else, and my ears (and the ears of my handful of customers) can't tell the difference.

[R.G.]

Some SMD caps are film types. Just sayin'.

Just when you think you have a clear, simple rule to follow, somebody changes the rule.   

[vigilante397]

Some SMD caps are film types. Just sayin'.

It's true, but they're generally bigger and more expensive. I've been doing PCB design for a friend that builds but doesn't know how to lay out boards and he's insisting on SMD film caps. The ones he chose are only available in 1812 package (I use 0805 almost exclusively) for values up to 680nF, then 1uF are even bigger. Also the caps are like $0.60 a piece, which is absurdly expensive compared to C0G or X7R.

[merlinb]

It seems like most SMD capacitors are MLCC (ceramic), are these the same or similar in composition to the common orange through hole caps and is it similarly advisable to keep them out of the audio path?

In hi-fi yes, in a guitar pedal no, you won't notice the difference. Ceramic caps are fine for guitar.

[R.G.]

Some SMD caps are film types. Just sayin'.

It's true, but they're generally bigger and more expensive. I've been doing PCB design for a friend that builds but doesn't know how to lay out boards and he's insisting on SMD film caps. The ones he chose are only available in 1812 package (I use 0805 almost exclusively) for values up to 680nF, then 1uF are even bigger. Also the caps are like $0.60 a piece, which is absurdly expensive compared to C0G or X7R.

Yes, they are bigger and more expensive. They are, on average, smaller than the equivalent through-hole cap, value for value, and they do allow an all SMD board for manufacturing reasons.

I'm just doing my "devil is in the details" thing. The idea that SMD caps are all bad because they're ceramic is a poor oversimplifaication.  They're not all ceramic. And some ceramic is not prone to the various quirks of high dielectric factor ceramic. The best rule of thumb is to keep learning about components as hard as you can. Things change.

[patrick398]

Thanks for all the replies folks, lots for me to get stuck into. Apologies for not covering old ground, I assumed this was something that hadn't come up too often.

[Kevin Mitchell]

The capacitor war is never over 
So long as you keep the words hifi and mojo out of the design it can be all ceramic and any person with decent sensibilities wouldn't hear the difference.

Of course that doesn't stop me from doing unnecessary cap jobs. But I do it for the mojo 

-KM

[vigilante397]

Yeah my pedals have zero mojo

[patrick398]

The capacitor war is never over 
So long as you keep the words hifi and mojo out of the design it can be all ceramic and any person with decent sensibilities wouldn't hear the difference.

Of course that doesn't stop me from doing unnecessary cap jobs. But I do it for the mojo 

-KM

Do orange drop caps come in SMD?

Yeah my pedals have zero mojo

I dunno man, i think that's got heaps of mojo...just a different flavour

[Rob Strand]

Do orange drop caps come in SMD?

Only in color

[11-90-an]

I dunno man, i think that's got heaps of mojo...just a different flavour

joMo

[vigilante397]

I dunno man, i think that's got heaps of mojo...just a different flavour

Thanks, I have a friend that builds pedals with all "audiophile" components and he makes fun of me for building "computer" pedals

Do orange drop caps come in SMD?

Only in color

I used some of those for a design at work once, they were like $18 per cap

[Rob Strand]

I used some of those for a design at work once, they were like $18 per cap

You can only hope some of this specialized stuff comes down in price over time.