AC coupling vs. DC coupling

Here's a typical comment about one type of capacitor...

"Electrolytic capacitors have no place in the high fidelity audio chain
anyway.  They are nonlinear and create distortion.  Their only real purpose
is as energy storage devices in power supplies"

This guy has absolutely no idea but to all intents and purposes he looks like an expert and his webpage is well read because it came number one in a search. It comes number one because lots of people go there - sent by others....

So why if "Electrolytic capacitors have no place in the high fidelity audio chain" are they used in decoupling which is actually the return route to supply FOR THE SIGNAL? After all, "they have no place", except they do.

Even a little low power preamp requires something in the order of 1,000uF for a low impedance return to supply - what is the alternative to an electrolytic? There is none!

Therefore all amps must be "nonlinear" and "create distortion".

Well here are the myth busters...

Electrolytics do distort! They distort at their -3dB (or turnover) frequency! A decade or so above and their distortion is no different to most other capacitors - therefore set the turnover frequency a decade or so below the lowest pass frequency and they DO NOT DISTORT. This old timer obviously doesn't know that - he's just being a fashionable cap basher - vigilantes are dangerous...

Electrolytics do not work at high frequencies! Partly right! At frequencies above 10kHz they start to become inductive - it's not a step-change - it happens gradually. BUT THEY'RE STILL A CAPACITOR! Because they are a massive pair of plates miniaturised by being made into rather elongated narrows foils wound up inside a can, they are inductive because they are a winding. Therefore at some high frequency their AC resistance rises, and I tell you now that high frequency isn't audible to the human race. However, it can leave a high gain circuit in trouble (phono preamps are very high gain and that's what I've been making for the last 30 years or so...), and that is the reason for bypassing - a film cap which can handle the highs gets placed across (in parallel) with the electrolytic. The lower inductance of the film cap in parallel with the higher inductance of the electrolytic results in an overall lower inductance.

And that's how the signal is returned to the supply IN "DC COUPLED" AMPLIFIERS.

Yes, I'm still talking about DC coupled - I haven't started talking about cap coupling as such.

Now there are those who will say "but we're talking about power here". Listen, what power are you talking about? A neg 60dB signal from a preamp into a 30k power amp input isn't power! However, the so called "decoupling cap(s)" couple the return back to the power supply and we're talking nano-amps here! That's NOT POWER.

So these "DC COUPLED" amps are superior? As the signal struggles through the "horrible" electrolytic(s) bypassed by a film cap (the bass and mid frequencies taking the electrolytic route)? No, that's not the case - capacitors are as important in audio as everything else is. You cannot serve two masters - if you serve the truth master like I try to, you cannot serve the money master - the money master knows it's best to knock the capacitor because that's where those who have money to spend have been brainwashed - so they all jump on the bandwagon!

So here you have a lone voice? A guy selling cap intensive products that beat DC coupled circuits! But hey, he must have bribed them? Yes, he must have bribed them reviewers because the cap bashers are the multitudes and Graham Slee is all alone in what he says???

So google me! Yes google me. You have my address - I don't hide behind a nickname - I publish who and where I am. Go on - google me and look at my mansion! Oh, that's odd - he doesn't have one....

No, and I don't bribe reviewers - they like what they hear, and it's cap intensive.

So unbrainwash yourself and in the next instalment I'll flesh out how coupling works and how decoupling is actually coupling.

This topic has now been hijacked twice by different writers who wish to "dirty" any attempt of explaining the true purpose of capacitors in an audio amplifier.

They cited no scientifically acceptable facts to support their claims (or rubishing of this topic), but just rode the tidal wave that is sweeping "hi-fi-fo-fum".

I see that as censorship of me and the truth when there is enough of the same on an incredible number of websites elsewhere which members if they so wish can avail of themselves.

The laws of nature stand, and the laws written down by those who discovered them have not yet been scientifically challenged - in fact, everything electronic on earth and floating above it in orbit - your very lives! - depend on these laws.

Those laws include that of Ohms, Faraday, Henry, and Kirchoff. We are being told here that they are wrong. I will not allow such lunacy on this community.

As such the replies have been deleted and the individuals suspended.

Edited by Graham Slee - 24 May 2009 at 4:35am

Hmmm, Graham, if I remember it right (can't read it back now):

Edited by Graham Slee - 31 May 2009 at 7:51am

Hi Han,

I think dvv himself will be thankfull I removed his replies by the time I've finished my explanation/teach-in.

Opinion is fine, but the laws of nature prevail.

The question I was asked is what is best: AC coupling vs. DC coupling.

I don't like to lie to my readers - I didn't want to answer the question in the typical BS arrogant way that has corrupted much of hi-fi.

Therefore I have told the truth - there is no such thing as a DC coupled amplifier. Therefore the question cannot be answered because all amplifiers of music (being an alternating signal) are AC coupled.

As many have commented, the power supply is often not considered part of the amplifier when it obviously is. However, that is where their learning often stops. This is quite convenient when wishing to argue a particular standpoint. On the other hand, the truth derived from the laws of nature removes opinion (what someone imagined and decided to indoctrinate in people for gain).

As for the mandatory, nature's laws mandate. The laws of nature written down by men are not opinion. Kirchoff is not at odds with Faraday - Henry is not at odds with Ohm. But we see in hi-fi many people at odds with one another - don't we? Should not this be a lesson?

Unfortunately man will often side with opinion rather than fact. If you don't believe that, then consider this: Only a few hundred years ago most seafarers believed the earth was flat and if they sailed too far they would fall off the edge of the earth. They put opinion before fact. The fact was that a few thousand years earlier a scribe had recorded in the Old Testament that the earth is like a ball spinning in space. Rather than accepting the Old Testament fact they limited their progress by listening to opinion. Much like people who do the rounds of the hi-fi forums?

EDIT: As for "olde fashioned", we see from the last paragraph that the ancient scribe was bang up to date, and the more modern concept of flat earth was a misconcept...


Edited by Graham Slee - 25 May 2009 at 7:42am