Understanding DC blocking capacitors in audio

[@TorgeirFredriksen]

Thank you for answering my question Paul. I had to pause the video and go grab a beer as soon as I heard it was my question being answered :) So DC servo circuitry is the trick here. I have always thought that a feedback loop like that still makes the signal pass through a cap on its way back. Which it still does I believe. But as you tell that servo circuit has a much higher time constant, so the amount of signal (AC) being fed back to the input (and through that cap) is probably negligible...

[@petesmith2234]

Ultimately it would make no difference if you used a cap to provide low pass filtering at 0.1Hz in the dc feedback path or to provide high pass filtering at 0.1Hz in the audio path. If, for instance, the cap was poor at passing high frequencies in the audio path, it’ll also be poor at shunting high frequencies in the feedback loop resulting in increased negative feedback and reduced gain at high frequencies. As you say, it would be negligible in the feedback path, but it would be equally negligible in the the signal path too.

[@audiorick841]

Love the tech talk Paul. More of these please 🙂

[@dokukarmagad12578]

Awesome video and channel. There is so much to learn. Thanks.

[@KenTeel]

Good job, Paul. I'd add that the DC in an amp provides kind of an equivalent to an idling speed in a car. DC current sits at a certain level, averagely, but the DC is varied, turning it a bit off, then a bit on to resemble a sine wave (on top of the DC.) So, it's a varying DC voltage. The lowest point of the DC voltage, to the highest DC voltage (the distance between these two) is the peak to peak sine wave. This sine wave is stipped off by a capacitor, in a capacitor coupled amp. And the sine wave "passes through" the capacitor to the next stage of amplification. However, remember that capacitor pass high frequencies better than low frequencies, and so not all AC frequencies (riding on top of the DC) are passed throuigh the capacitor, equally. Some frequencies will get through better than others, and that is part of the coloration that a capacitor adds to the sound. Also there is a phase shift through a capacitor, in terms of the current leading the voltage across it, so that would play into the coloration of the sound, caused by a capacitor, too (also remember that a speaker is kind of an inductor, and theoretically, might color the sound because the voltage leads the current, AKA a phase shift between them.) Someone with more knowledge on this subject of phase shift can add more to what I'm saying or tweek it a bit to make it more accurate.

[@dans550]

Hi Paul, when you explain plus to minus and minus to plus it totally reminds me of a brilliant scene from Young Frankenstein, I'm sure you know the one. Have a great day.

[@Jorge-Fernandez-Lopez]

Great question and answer. Thank you

[@pierpa_76pierpaolo]

I had already been advised to watch this video but I didn't understand it (since I am Italian and don't speak English), only when there are technical examples I get passionate about it and then try to gather ideas by reasoning about it and so on. :)

[@user-od9iz9cv1w]

Great answer. Spending a little extra paya a big dividend. I use a 1uF copper film cap on the output of my streamer tube buffer. Sounds great. Miflex is a good choice for value. Deulund or Vcap for SOTA. Also worked almost as well with a 4uF Russian NOS PIO bypassed with a .1uF silver mica.

[@ford1546]

Norway here It is still very common to use an input capacitor on line in or line out since it is the cheapest solution. The problem is that you often have both an output or input capacitor on the preamplifier and an input on the amplifier. 2 pcs. Nowadays, electrolyte is rarely used, as dc blocking capasitor but instead polyester or polypropylene of good quality such as Wisma is often used. Before, you use the smallest possible capacitor value to reduce the size of the capacitor so that it does not become too large. I think you hear bigger differences on different op amp ic. than what you do with different good capacitors.

[@tomasdub7382]

Mr Paul. Where any specification or picture or some about power supply cable in to this video?

[@psycheopera]

Thank you so much for this video! 🙏

[@garganega]

Household current is AC so where is the DC ripple coming from, the processor?

[@NiclasMardfelt]

A normal power line usually have got a few volts of DC traveling alongside the AC. The source of DC-pollution are mostly industrial engines, washing machines and minor pollution form switch mode ac plugs (computers, routers, chargers etc). Worst of them all are the increasing amount of solar panels and electrical car chargers. A bit of pollution is traveling via ground into the electronics. The very few that duties to direct pollution (at the ground cable) from the electronics towards the wall, sounds usually vastly better than power cleaning without that tech. Then you have the RFI and common mode issues, then the need for an extra grounding and things gets complicated. However, in the future when better high performing power cells or batteries becomes available at lower cost, all people interested in hiring or high end will get an off the grid power source feeding the whole stereo, problem solved, late night magic around the clock

[@ford1546]

Finally a question from Norway ✅

[@Veeger]

Couldn't you use a 1:1 audio transformer? It would block dc and pass ac.

[@merakrut]

Marantz are using electrolytic capacitors in their cd-players without any problems, they sound really good. (Elna 220µF 16V Silmic 1)

[@josephvanalstyne4049]

DC died with Malcolm AC still survives with Angus that's the answer

[@robertt6430]

My thoughts exactly. !!

[@philipw7058]

Ifi DC blocker it works great 👍🏼

[@DutchShaggy]

Those are for the power source. Great device to have. The part this question is in the signal path, inside an amp.

[@slode1693]

Paul, you need a white board to sketch on or other visuals prepared to explain this kind of stuff in these types of videos.

[@Mikexception]

It is interesting how everything has it's ups and downs. In solid amplifiers we deal with low voltages and low circuit resistances For that reason it is necessary to use coupling capcitors with low reactances means their values are sagnificant - usualy 1 - 50 uF and wet- It's nothing new. But it may be source of troubles with age - corrosion of plates and ageing electrolyte - like in some 30 years video camcorders. . Seemed in tube amplifiers it was easier - needed rectances are high in compare and capcitances much smaller - 0,01 - 0,05uF. For them may be used dry and durable delecric - ... . hmmm.... not so easy - there are much higer voltages and they in time are exposed to dielectric short cut or micro current leakage . Strangely to me to see that in "ancient times" were used noble materials like mica, masive coper plates which made them bulky but working eternal . Worst moment came in 60ties when all was meant to be portable and capcitors had to be as little as it was possible while production was still not mature . I experienced it in vintage japanese tube gear. And in Bell Sound too I found some 60 years old with bad insulation but still some 80% of dry capcitors and 95% resistors are originals working. Thank you Bell . Hopefully replacement could be called pleasure due to point to point connections. . Now is like new era - technology alows to produce ubelievely small surface mount capcitors - of course only for low voltages. Are they applicable for decent audio? I see that in video cameras SMD mounted audio is truly excellent But for expensive units future service plays important role. I can diagnosesimple circiuts myself and my wish is to have units which I could diagnose and repair all time when I enjoy them.

[@kramerdesign9443]

Damn I want Paul to read me a bedtime story

[@mikecoackley6852]

Blocking capacitors will protect the circuits downstream if something catastrophic happens. I'm thinking a direct coupled servo stuck high or low would cremate whatever is in its way.

[@budgetaudiophilelife-long5461]

🤔 technically ,over my head, but … showing it’s the best time to be an audiophile 🤗👍😎💚💚💚

[@janinapalmer8368]

That not quite right.... dc servo circuits are used mainly in power amplifiers to keep output dc offset voltage at 0v. The way to eliminate dc in series signal paths is to use symmetrical complementary balanced drivers where the output is at 0v .

[@petesmith2234]

Totally agree, however, in practical terms it’s still very difficult as any small DC offset at the input will be amplified along with the audio and if left unchecked would result in DC across the speaker.

[@dans550]

"It could work" !!

[@johnsenchak1428]

Another capacitor video

[@knutarneaakra6013]

Thinking of a comment but guess no just a tiny one.We, most peoples in norway can eacaly spend 1 mill + if we want.

[@bernardwarr4187]

If we can’t here DC why block it lol

[@AN-ce1nd]

Snake oil, smoke and mirrors