Improving the Coupling Capacitors for Better Tone Sounding

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I never did like the sound of mica caps, now I know why

I always liked the look of the RMC ceramic caps with the green paint. Made them sound better.

I like the Fender 10 pf caps with the diamond logo but don't know who made them.

Polycarbonate caps have good tempco specs. Found this out in a 60 cycle oscillator for a power meter tester. The circuit was right in front of a cooling fan. The fan would make the frequency drift from 59 to 62 cps , polycarb fixed the problem.

FM discriminator coils use those weird dog bone caps for low L.
 
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But is it audible distortion?
I’m not sure if anyone has ever devised a methodology to test this comprehensively

I suspect in the majority of cases the answer would be “no” (or at least “not reliably”), but probably not 100% of all possible use cases

A relevant set of accompanying questions may be:

In which specific applications are very small amounts of distortion likely to be significant?

Does changing dielectric material for every single capacitor in a device yield a different result than changing only one?

Do insignificantly-small amounts of distortion (by percentage) become significant if substantial amounts of gain are later applied (e.g. is the impact greater if the DUT is installed in a microphone before large amounts of preamp gain?)

Might non-objectionable (or even undetectable) amounts of distortion become significant if fed complex program material (of the type that might create intermodulation products)?

Might a listener become, with repeated exposure, sensitive to/aware of small distortion percentages that had been undetectable at first?

Etc.
 
Polystyrene are also good for the pF range, but they tend to cost even more (use them if you need higher V handling - then they may be comparatively cheaper than NP0/CG0). They may be better in tube amps because they are axial vs radial like MLCCs.
I do like the sound of polystyrene caps but their performance can go downhill in high temperature applications like tube guitar amps.
 
I just tested some more 1uF non polar caps with that dielectric absorption test box that I posted a couple of days ago. The Wimas in that post had pretty low residue, but today I tested a 1uF 630V Solen MKP-FC metalized polypropylene, and it flatlined with almost no measurable residue. No wonder people like these. Best I've seen. Fairly small for 630V too. Might be too clean for a bluesy guitar sound, but it would be great in a clean preamp or mic circuit.
 
I had used, for my sins, to be inter alia the repair guy (one of an unending series) at Orange Music in London back in the late '70s, as well as doing hundreds of repairs for my own company, plus design and build stuff for bassists. Orange used to build their amps with whatever caps they could get cheap by the barrowload, just like Marshall, Vox, Sound City, Fender and everyone else AFAICS. ;) The things that make the difference IMHO in a specific amp's sound are valves/tubes, bias, and of course transformers. Of course different caps may change things, but the change might not be an improvement. I had people coming back complaining about changed sound after repairs to factory spec, but usually it was that the valves or transformers had been changed and the bias put to where it should be as per spec not where it had drifted to after being on the road. Consistent valve amp sound is hard. Transistor amps were much easier. Now I use modelling to get where I want to go!

The capacitor thing is much more relevant in studio gear, but not much of it is wrongly or badly chosen. As far as tantalum is concerned, just say no except in timing circuits, and even then - must you? NEVER across rails. Fizz! Bang!
 
I remember some years ago (15 years) when I started to work/service/restore Tube amps, Tube gear and vintage microphones, that many people advised to replace all old PIO caps for new film capacitors, in case there was any PIO in that specific old gear. The reasons were that:
- they didn't age well and are known to deteriorate over time, making them unreliable
- you couldn't depend on then and they can fail in a few different ways
- the dielectric can break down over time
- they can also leak, and once the oil leaks out of them they're useless
- could have corrosion around the edges and pins
- the paper can absorve humidity leading to breakdown

Probably some other reasons, I don't remember all.
But I did as the more experienced people advised, so I always replaced them in old equipment.

It was a surprise to me that in the last years a PIO Hype grew and people started to buy NOS PIO (NOS = OLD) caps to use them in their equipment. It seems they are now popular again for guitars, microphones and other gear.

I don't know if it's just hype and Snake oil or if they really sound better/different,
but I find it really funny that old caps once considered unreliable are now considered the holy grail for some duties.
Please listen to this video at 7:29 about the changing caps in that mics :)

https://www.facebook.com/share/r/oMBmfAvEwGmHKBPU/?mibextid=UalRPS

opacheco
 
(I don't see a scrolling thing for the time in the Facebook video, so here is what appears to be the same video on Youtube FFed to the point he starts talking about the paper in oil caps and experimenting with changing them to mylar ones and "losing the magic": )

 
I haven't seen any replies about this, so I'd like to bring some attention to two characteristics of capacitors that actually can affect their audible and electrical performance.
1. The first is actual impedance versus theoretical impedance. Any passive or active component only operates properly within its expected frequency range, and if it is used at frequencies beyond that range they won't perform in the expected way. RF engineers are painfully aware of the fact that standard diodes and transistors just don't work when you get into the microwave range. Both resistors and capacitors however, can exhibit undesired performance at an eventual high frequency too, where their parasitic inductance becomes significant. Since a lot of capacitors are actually rolled up like cinnamon rolls to cram the two plates into that small space, there is indeed a frequency where the parasitic inductance takes over. If you plot the measured impedance of say, a large electrolytic capacitor, you will eventually find there is a frequency where this inductance kicks in, and it will look more like an inductor instead of a cap. Hopefully that happens well above the audio range so it doesn't screw with your beautifully designed crossover networks, and amplifier feedback loops. This is the real reason that some folks put small value parallel capacitors across those big electrolytic caps, and the rule of thumb often used is to choose a value that is 1/20th the value of the big cap. If you want to get it just right, go ahead and measure the actual impedance performance of those big electrolytic caps in the power supply and those used as coupling caps in the signal path. and choose the correct cap to put in parallel to allow the impedance to continue to drop like it's supposed to.
2. The other capacitor defects are dialectric absorption (DA), and dissipation factor. In simple terms, DA is when a cap that had a charge on it is expected to allow you to suddenly remove that charge. This happens thousands of time a second with audio signals, but caps that aren't so good can have a tendency to hang onto that charge instead of letting it go. This can be audible if it is significant enough, and you will find that very high quality caps will have low DA. Now its quite possible that some guitar amp users may like this sloppy cap performance and that's fine if it make the sound you're looking for. Measuring DA with actual signal sources is not often discussed, but there was an article in Audio Amateur issue 4/1985 page 22, that describes a circuit that you can build to see the effect right on your oscilloscope. I believe there is still a copyright holder on the articles from Audio Amateur, so I can't reprint it, but I will show you the schematic and photos of the one I made, and oscilloscope pictures of some of my measurements using it. Interestingly, John Roberts, one of our regular forum contributors is mentioned at the end of the article as someone who wrote a letter to Audio Amateur about this test.
This circuit uses a reference cap, and has a bridge network that allows you to compare a second cap to it, and display the residue difference on the oscilloscope. I used a Kemet metalized polypropylene 1 uF/630V cap for the reference, and compared it to an old tubular Wima, a new stacked Wima MKS, and finally an old Sprague tubular, probably mylar. The two Wimas are almost identical, but the Sprague has MUCH more residue, especially when you notice that the 'scope's vertical sensitivity is set at 8V/div instead of 500 mV/div. The signal source is a pulse generator with a pulse width of 10 ms, and a period of 30 ms. The source amplitude is about 12Vpp.
When I first built it, I used tiny trimmers for the pots, but that made it really annoying to use, so this version used regular pots and knobs, which made it much easier to adjust. The Radj2 is to compensate for the ESR, while the other 3 pots adjust for the time constant. C1 band limits the input signal. The differential instrumentation amp with precision gain shifting is pretty expensive at $59.29 from Mouser, but the rest of the parts are pretty cheap, and it makes a hell of a cap tester. It will tell you which caps are really really good, but it will also tell you what to look for in a weird cap that you have decided you really like in your guitar amp. Have fun.
CalavoBob,
I would like to do some measurements and see what I actually get between different capacitors and their sonic changes (if any!), but I have some doubts with your schematic:
1- What do you connect in the Rload/Rload terminals?
2- Do you have any instructions in order to use this DA tester?

Thanks in advence
opacheco
 
(I don't see a scrolling thing for the time in the Facebook video, so here is what appears to be the same video on Youtube FFed to the point he starts talking about the paper in oil caps and experimenting with changing them to mylar ones and "losing the magic": )


dai h,

Sorry, you are right! that is the video.

Thanks for your notes!
opacheco
 
I had used, for my sins, to be inter alia the repair guy (one of an unending series) at Orange Music in London back in the late '70s, as well as doing hundreds of repairs for my own company, plus design and build stuff for bassists. Orange used to build their amps with whatever caps they could get cheap by the barrowload, just like Marshall, Vox, Sound City, Fender and everyone else AFAICS. ;) The things that make the difference IMHO in a specific amp's sound are valves/tubes, bias, and of course transformers. Of course different caps may change things, but the change might not be an improvement. I had people coming back complaining about changed sound after repairs to factory spec, but usually it was that the valves or transformers had been changed and the bias put to where it should be as per spec not where it had drifted to after being on the road. Consistent valve amp sound is hard. Transistor amps were much easier. Now I use modelling to get where I want to go!

The capacitor thing is much more relevant in studio gear, but not much of it is wrongly or badly chosen. As far as tantalum is concerned, just say no except in timing circuits, and even then - must you? NEVER across rails. Fizz! Bang!
AFAICS????....what mean that?
opacheco
 
Please listen to this video at 7:29 about the changing caps in that mics :)

https://www.facebook.com/share/r/oMBmfAvEwGmHKBPU/?mibextid=UalRPS

opacheco

I listened to it, there's no demonstration at all of what he's claiming.
It's just a claim from a guy that likes to post a lot and glamorize himself in gearslutz, a place where the general crowd consists mainly of recording amateurs and enthusiasts.
He is actually a very disrespectful person at times, and I actually seen posts of him in the past spreading his opinions and wrong statements like they were facts.

I truly don't know if PIO caps used as a coupling capacitor make any difference. And if it actually makes a difference if it's for the best or for the worst, or even if that difference is subjective and some people like it with PIO and other people prefer it with another cap type.
I'm just a professional sound engineer that is always working and unfortunately (or fortunately) I never have time to perform these kind of tests. Or maybe I'm also not interested in going that deep into microcosm obsession, I was able to make a career by being a very practical engineer, if a mic doesn't work for that task I will change it for another one and move on with session, the recording and my life.
People seem to hire me and like my work because I provide a sound that they like (or that works fine for them) very fast, they couldn't care less about possibly marginal (subjective) diferences in cap types, they are looking for efficiency.

But if I had the time I think I would like to do some tests with the company of a fellow engineer that might be enthusiastic about this kind of tests and discoveries.

What I enjoyed the most in this video, was this claim:

"Anybody who really know what they're doing in electronics will tell you that that that the coupling capacitors definitely are one of the more audible parts of any circuit"


I would love to know the opinion of people "that really know what they're doing in electronics" about this statement,
people that are very experienced and we can trust, even if just a few.

So Ian, JR, Abbey, Jakob and Kingkorg, could you please comment this and share your thoughts on this subject with us?
 
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I would like to share this article named “The Sound of Capacitors”, I got from (https://diyaudioprojects.com/mirror/members.aol.com/sbench102/). Very interesting article about the linearity point of view of different capacitors types (dielectric types).

According to the autor we have options which we could have a range of sound possibilities vs dielectric types and bias polarization….The author implies that this depends on our experimentation and testing to get the sonic response we are looking for.

I hope this can generate new perspectives and point of views.

Any comments will be appreciate.
opacheco
 

Attachments

  • The Sound of Capacitors, Capacitor Linearity.pdf
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But in your personal experience did you find that coupling capacitors are one of the more audible parts of any circuit?
No, just another component with non-ideal behaviors that need to be considered and managed in competent designs.

Any component can be audible if mismanaged. The one that is more mismanaged can be more audible.

JR
 

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