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Old 9th Dec 2017, 1:17 pm   #1
stevehertz
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Default Capacitor types for best audio performance

Now that's a can of worms opened - sorry.. For all of my life - that's as an electronics engineer, audio enthusiast and musician - I have been sceptical that capacitors in a signal path can sound different. Actually, that not quite true, I strongly believed that it was all poppycock, untrue, lies, stupidity, audiophoolery, etc etc.

In recent years, trying to be more open minded on the subject, and having read bits and pieces here and there that there is scientific, measurable evidence that capacitors can sound different in a signal path, I'd like to know more. But I'm still to be convinced at the present moment - I'm just more open minded!

I invite the more level headed, sound of mind, physics/electronics based, non-audiophool forum members to put forward their science based understanding and views on the subject. May I add, I am not to be convinced by any amount of "I can definitely hear the difference" type answers. And there's the dichotomy, to be able to hear the difference is the goal (!), but given that what someone claims to hear is purely subjective, it is open to a million and one psycho acoustic effects, and therefore such remarks, as a matter of fact, can never be viewed as 'proof'.
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Old 9th Dec 2017, 2:00 pm   #2
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Default Re: Capacitor types for best audio performance

It is a can of worms because it is largely the old subjectivity vs objectivity dilemma. But there are a lot of poor quality or age damaged parts out there too.

My view on this is that once "most" interstage coupling capacitors in valve amps are such that they are in good physical condition, with no electrical leakage in the dielectric and they are of a design where there is a good low resistance connection from the lead in wires to the foils, then I think you would be hard pressed to detect any difference in the sound quality/tone in an audio application.

In RF applications the construction of the capacitor is far more important though and its a whole other story.

Having said that, aged waxies can have severe dielectric issues. I have a classic one that acts as a network of 4 components, the original value, a leakage resistance in parallel, an combined capacitor of 10 times the value in series with a resistor, all in parallel with the terminals. I call it "the capacitor with two exponentials" as two time constants can be seen with it, in a pulse circuit.

In valve gear, old capacitors can cause severe frequency response and distortion issues, especially because they couple into high impedance grid circuits and as everyone knows "that cap" can throw off DC bias levels too.

In transistor gear, I'm afraid electrolytic caps are notoriously poor, their ESR increases with age and they electrically and physically leak with age. But again you might be hard pressed to detect any difference between two new similarly rated electros in an audio circuit, but if they are over 20 to 30 years old, its another story.

So it seems to me that like all good fairy tales, there is an element of truth that capacitors will "affect the sound" but for the most part I think it applies to aged/damaged capacitors, not most new ones.

Where capacitors are in places in amplifiers where the ripple currents might be high, say in valve output stage cathode bypass applications or as output coupling caps in transistor amps it obviously makes sense to use the lowest ESR cap available if you are forced, as one often is, to use electrolytic caps.

Electrolytic caps will never be as good for all important parameters of capacitor performance as non electrolytics, they are just smaller & cheaper for the same voltage and capacity, that is all. I have learnt this the hard way over the years.

If people are claiming they can hear the difference between two new leakage free 0.1uF 630 V poly caps, of different brands, in perfect condition in a valve amplifier signal coupling application, most likely that is the psycho-acoustics at work or just a suggestible listener to put it another way.

I'm not suggesting that a lab test of one kind or another couldn't prove that these two capacitors had subtle differences in their physical properties (such as inductance that could be important at radio frequencies) but I think at audio frequencies and in the nature of the circuits they are used in, in audio amps, that those differences are too small to be audible.
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Old 9th Dec 2017, 2:04 pm   #3
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Default Re: Capacitor types for best audio performance

Oh no not again....All done to death...If you like what you buy then fair enough, if you don't then go buy something else.

Lawrence.
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Old 9th Dec 2017, 2:11 pm   #4
stevehertz
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Default Re: Capacitor types for best audio performance

Just to clarify, I'm not 'investigating' old, perhaps leaky caps etc, I'm talking about modern caps of different dielectrics and the measured performance differences that they exhibit in modern solid state equipment.
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Old 9th Dec 2017, 2:22 pm   #5
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Default Re: Capacitor types for best audio performance

Capacitors do have slightly different characteristics but the audible effects will be very small if they exist at all. Lab test gear can measure all sorts of exotic stuff, most of which will have no impact on performance at audio frequencies.

As far as I'm concerned, the only test that matters is a double blind A/B listening test. These are relatively easy to conduct, but the fact that they are so rare in the hifi world speaks volumes.

Of course, as Lawrence says, if people want to spend lots of their money on exotic boutique capacitor brands then that's their choice. If they believe they sound better then they do - to them.
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Old 9th Dec 2017, 2:24 pm   #6
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Default Re: Capacitor types for best audio performance

The attitude I take is that capacitors don't have "sound", but old ones may introduce distortion due to leakage. In some cases this distortion may be desirable.

I just fit yellow polypropylene types and never give them another thought.
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Old 9th Dec 2017, 2:47 pm   #7
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Default Re: Capacitor types for best audio performance

Quote:
Originally Posted by Station X View Post
I just fit yellow polypropylene types and never give them another thought.
That's exactly what I do, but only when needed, of course
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Old 9th Dec 2017, 2:50 pm   #8
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Default Re: Capacitor types for best audio performance

I do of course use the correct 57/43 solder. None of that 60/40 rubbish. You really can hear the difference.
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Old 9th Dec 2017, 2:56 pm   #9
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Default Re: Capacitor types for best audio performance

There are four factors at work.

1) What effects other than simple capacitance do different types of capacitor exhibit

2) The susceptibilities of different circuits to those secondary effects

3) The limits of human hearing

4) Psychological factors.

Number 4 is the can with the most worms in it. Many of those worms are seriously irrational and therefore outside the scope of a rational discussion.

Number 3 is a function which can't be accessed in isolation from number 4. We're all getting older, our hearing is degrading, but we have our own opinions about how good/bad our hearing is. Anyway, whatever you have, you're pretty much stuck with it.

Having summarily disposed of the human factors, we can now attack 1 and 2 with honest to goodness scientific method.

1) Are there any capacitors which ought to sound different in typical applications... Yup! There are some very nasty capacitors around. Nasty from new, not turned nasty through age. Soe plastic film dielectrics exhibit 'dielectric absorption' sometimes called 'soakage' and these can look like there is a second capacitor (or more!) ghosting the first one. You can discharge the thing with a short, remove the short, and watch the terminal voltage from zero begin to climb back to a significant fraction of the original charged voltage. This makes a mockery of citcuits using them for time constants ot integrators. Many is the tale of someone making a a dual-slope ADC and discovering this. Some high voltage capacitors can be rather nasty once they've partially re-charged themselves.

Some ceramic materials are highly non-linear, their capacitance changing with voltage.

Some ceramics and some plastic films are piezo electric and act as unintentional microphones. They can sing and chatter in SMPSs, or introduce noise into sensitive circuitry.

Some wound foil types have dramatic self-resonance modes due to distributed inductance. You can get echoes of pulses and wobbly frequency responses. I have a 1uf polystyrene film capacitor somewhere. It has only one wire going into each foil in one place. It has resonances down into the audio region. I can't imagine why anyone would want one!

But mostly, capacitors have to be fairly extreme to be one of the nasties. The snag is certain dielectric foils or ceramics look just like normal ones. You need to know which does what and just which the one in your hand is.

2) Of course certain circuit places are fussier than others. You could design circuitry with absolutely NO capacitors in the signal path. You can fix DC levels by adding or removing offsets, possibly by feedback using a filterto extract the DC component of a signal and to feed it back. The filter capacitors are out of the signal path.

I don't have any difficulty believing that some capacitors in some places will affect the sound in audio systems. But I do think you have to commit a known and understandable no-no before you get a hearable difference.

Knowing the foibles and failings of components and how to evade them with circuit design is part and parcel of good engineering.

No fairies have to be killed for their dust. Once you've got a grade of component which doesn't have the known failings, then you are on a plateau.

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Old 9th Dec 2017, 2:59 pm   #10
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Default Re: Capacitor types for best audio performance

Might be a few folks on here that worked ( more likely were employed by GEC) on various bits of kit. GEC had a ( or rather the bean counters did ) a policy of buying components till the supplier bill got to "overdrawn", and then move on. I only worked in the Telecomms division, so it might just apply to that division. But we found that it paid to stock certain makes of components to remedy certain "failures to meet " customer specs. Change a component from firm "x" for a similar one from firm "y" and specs were achieved.
And the problem we had with yellow metal metalistic caps was with ladies with a long hand on the iron. The legs came off.
RW- Your mention of human hearing, takes me back to a conversation I had with an oppo in MSDS ( FIFE place) about the prices vs person listening to the kit. And then there was an experiment I did with some TTA (GPO slang for Apprentices) with a studio amplifier and an audio generator. TTA were 18 years old, I was 30. I prided myself on a good hearing range, but the TTA range was a lot higher.
But then, how high( Hz wise ) do you need to go before the harmonics make the individual enjoyment of music a topic for debate?
THAT is a topic for more debate.

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Old 9th Dec 2017, 3:08 pm   #11
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Default Re: Capacitor types for best audio performance

Quote:
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And the problem we had with yellow metal metalistic caps................
What exactly is a "yellow metal metalistic cap"? Has a subtle joke gone over my head?
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Old 9th Dec 2017, 3:21 pm   #12
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Default Re: Capacitor types for best audio performance

Subjectivity?

Hmmmmm - the Editor of 'Valve & Vinyl' is on record [and print] stating "The best monaural Hi Fi I have ever heard came out of a Bush VHF 94".

Well - when I recovered my [suddenly non-working] example from extended loan, I re-capped it using components from our Canadian friends .... and thought: "this set doesn't sound as good as it used to!

However - after repairing a speaker cone tear and re-building the [doubtless the long vacationing] electrostatic tweeter ...... I just sit back and think: "this thing sounds ****** superb"!!!
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Old 9th Dec 2017, 5:02 pm   #13
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Default Re: Capacitor types for best audio performance

Hi Gents, the definitive work on "component sound" was published in Wireless World in the 70's or 80's by Cyril Bateman, the engineering director of a components company. I'm afraid I don't have the details to hand at present.

His bridge circuit and sound card analysis system did show some distortion in various component types, but most of it in good quality components was at very low levels.
If you can trace the reference it is well worth a read and possibly even building his test equipment.

Ed
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Old 9th Dec 2017, 5:46 pm   #14
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Default Re: Capacitor types for best audio performance

You may be interested in this, thrown up by Google:

http://conradhoffman.com/cap_measurements_100606.html
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Old 9th Dec 2017, 6:10 pm   #15
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Default Re: Capacitor types for best audio performance

Interesting. The results suggest to me that differences will be inaudible in audio applications. I repeat, only double blind testing is meaningful, and very little of that takes place.
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Old 9th Dec 2017, 7:27 pm   #16
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Default Re: Capacitor types for best audio performance

RW, thanks so much for that long, interesting and (as ever) informative response. For those who teetered on taking this thread into the audiophool, smoke and mirrors arena, I did say at the very beginning, I was (am?) the biggest sceptic in the world that capacitors sound different. But, if it's measurable, it may be audible, especially in high end circuits - I don't know. I too subscribe to the ABX testing school of thought, but as already said by Paul, it is rarely practised in hifi circles because the industry would collapse overnight if people did it big time and accepted the results.

So, RW, anyone, what type (not make) of capacitor is a good one for high quality audio use then? That is, to avoid the potential negative issues with some caps that RW highlighted.
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Old 9th Dec 2017, 7:47 pm   #17
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Default Re: Capacitor types for best audio performance

Exactly.

If you have good enough measuring gear you will eventually see differences in all parameters between all things, and without a sense of proportion all sorts of effects can be ascribed to these differences.

The crucial thing is being able to decide when enough is enough.

As the purpose of the whole thing is to consider the mechanisms behind audible differences, then only, as Paul says, proper double-blind testing with a statistically valid number of tests can show whether anything is audible. Anything else is just guessing and leaves the door open to self-delusion and snake oil.

(Wonder how he measured capacitors with seven seven digits in their results. Wonder how many are valid...)

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Old 9th Dec 2017, 8:24 pm   #18
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Default Re: Capacitor types for best audio performance

57/43
In post 8, StationX states he only uses 57/43 Solder, was he taking the ....?
Cheers
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Old 9th Dec 2017, 8:25 pm   #19
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Default Re: Capacitor types for best audio performance

Dielectric absorption is unlikely to have an audio effect as it happens at too low a frequency. At most it will make a small adjustment to the LF rolloff, which is anyway subject to capacitor tolerance.

Polyester caps are very slightly nonlinear, and may introduce small amounts of second order distortion if two conditions are true:
1. the cap acts as part of the LF rolloff (or some other filter) so that it has significant signal voltage across it;
2. the cap has a significant standing DC voltage
It has been suggested that this might possibly explain the popularity of Mullard 'mustards' for guitar amps - but fashion is an equally likely explanation. 'Tropical fish' would give the same electrical effect, but are less popular - so cheaper for us to use in old radios.
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Old 9th Dec 2017, 9:02 pm   #20
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Default Re: Capacitor types for best audio performance

What capacitors would I use?

Well there is a two-dimensional array of capacitance values and voltage ratings needed for audio and radio reasons. And in addition to the 'might be audible' parameters there are nasty mundane considerations like reliability. Now compound all of the above by the matter of where in a circuit a particular part goes, and life has become pretty complicated. Add in the good makers and the bad makers and your head ought to be at exploding point. The capacitive version of the Total Perspective Vortex!

To sort our way through this jungle, let's order things by the types available and what they're good or bad for.

Ceramics

From a fraction of a pF up to about 4700pF you can get NP0 and C0G types. They have low enough temperature coefficients for RF tuned circuits and are generally pretty linear. I use them in receiver front ends which get tested for intermodulation problems. Availability is rapidly focusing on small surface mount parts and lower voltages than you'd need if valves are your thing.

From a pF to over 100pF there are some fancy and very expensive porcelain ones. Porcelain sounds good and smacks of the Antiques Roadshow (does it have a pottery mark on the underside?) and the price would appeal to the golden ear crowd. But they have a use. I shove 300W pulses at 1000MHz through tiny 0805 surface mount ones, and they survive reliably. RS sell them in singles, some values are a tenner each, so they must sound good.

If you need over 2200pF and it's not going to see any signal voltage across it, then X7R ceramic packs in the Farads more efficiently. It's a bit non-linear with voltage, and a bit microphonic, so use them only in places where it doesn't matter.

When you get over 220nF, then there are more extreme ceramics which will take you to tens of microfarads. Beware, they change capacitance a LOT with voltage and can sing their little heads off. They are being pushed as replacements for electrolytics Achtung! (I wanted a word much stronger-sounding than beware) They have appreciable less effective series resistance than electrolytics and therefore they don't damp ringing on power supply lines. This can cause trouble that is a right devil to track - until you know.

Polystyrene

Well-made ones are good for RF tuned circuits. Poor ones can be unreliable. Watch out for an irreversible shift in value if they ever go above about 75 centigrade. Non-zero tempco which nicely compensates Siemens N28 ferrite cores. The Suflex ones are fragile and the wires too thin to survive vibration. The ones in plastic cases with radial pins are OK. I'd consider them OK at audio but they wouldn't be my first choice.

Mylar

Cheap, I've used loads of them in HP gear. Reliable. Bad dielectric absorption can ruin timing circuits and ADCs. Worked OK for me in loop compensation networks of PLLs. I'll happily use large high voltage ones in valve radio power supplies to avoid electrolytics. EG in place of paper reservoirs and bathtubs in an AR88

Silver-Mica

Lovely old classic parts. I used the Sangamo epoxy dipped ones in loads of RF stuff with never a problem and good linearity in RF tests. Some dielectric absorption, but it hasn't manifested as any problems. Mica reserves are running low so prices are climbing.

Polycarbonate

I've used lots of these in precision filters where values needed were too big for NPO/mica. Somewhat of a premium price, but no probs.

Polypropylene

A fix for the dielectric Absorption of Mylar. A happy choice for audio and crossovers

Aluminium Electrolytic

The energy density forces you into them. Modern Japanese parts are very reliable indeed compared to old ones if you don't get fakes. ESR has dropped as well, but note that some circuits rely on the ESR of electrolytics to damp resonances in power supply distribution networks. I try to keep them out of signal paths as much as possible.

Tantalum Electrolytics

I avoid them like the plague. Advice was circulated in HP to always use them with current-surge limiting series resistance... enough ohms to wipe out their advantage in low ESR/ESL! I've replaced too many that have failed of mundane types, and the metal cased ones I used to have in labstock at $0.45 a go are now 80 quid from Farnell.

Paper

Well, it isn't the paper which really does the work, it just holds the plates apart. It's what it's impregnated with that does the business. Wax based ones didn't last. Hermetic sealing is needed to keep H2O out. Plastic cased ones haven't lasted. Do they have a magical sound? Well that might depend on the impregnating material. I've never heard of listening tests to choose the best oil Within their life expectancy they're OK, they have strays and imperfections that don't show anything special. I think any acoustic superiority only manifests itself to those who already know that those capacitors are in that amplifier.

Some odd thoughts to end with....

Some people believe that the acuity of their hearing is limitless, but they are also prepared to behave as if their financial resources are also limitless and can pay for where the former leads them.

No-one ever complained about the sound of a little brown Hunts paper capacitor.

A Rifa capacitor will definitely offend your nose, no one knows what it does to your ear if put in a signal circuit.

David
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