Understand DC amplifier coupling

[@sebastianpolcyn6358]

Paul, can you please fade in a "to be continued..." at the end of this and make a part two? I mean, you just expertly explained everything around Antonio's question, then left the poor guy hanging XD Also: I think many of us would really like to have this explained to us, me definitely included!

[@Shrek_Holmes]

you get rid of it by having another amplifier, and having the other amplifier basically output the inverted signal, so basically the signals add up because while its inverted, its opposite to it. so that means they superimpose and double in magnitude forming a single signal, what happens to the DC? the DC simply is canceled out because the DC would flow into the speaker from both terminals regardless of where the signal is going. obviously the latter part depends on the topology of the amplifiers, differential output.

[@brandonburr4900]

That one left us hanging Paul! That needs a follow up! Thanks for the whiteboard!

[@antonio1681]

Thank you Paul, as I was the one sending you the message. Happy holidays.

[@QoraxAudio]

After 6 minutes: nope, I'm not going to answer your question! Lol Paul, you little joker! 😂

[@vulcangunner58]

Your "14 yr. old" comment at the beginning of this video is priceless (and so true for some of us)....Thanks Paul, for a little comedy to lead off!

[@jaisongabriel4308]

Wishing a happy Christmas and a very happy new year to you and your family sir.

[@AnalogueGround]

Some of those 1970s Japanese DC coupled amplifiers were a nightmare when a faulty transistor would cause a chain reaction and blow several others. Using substitute transistors without attention to critical gain matching was a no no. AC coupled stages were a dream to work with by comparison.

[@hugobloemers4425]

I think just owning and using such amplifier probably already requires some electronic prowess. I would also not feel happy leaving it on at night.

[@AnalogueGround]

@@Spock105 The 1122 has a DC coupled power amp and all the switch does is connect the preamp section directly or via a 10uF capacitor. I'm not sure why that would be an option but, depending on the spec of the preamp, using AC coupling may offer some useful bass rolloff at the extremely low end, say less than 20Hz. Does the owners manual say what Marantz suggests that it's for?

[@gino3286]

hi very fundamental issue and thank you so much for your great explanation considering what you say about caps I have the feeling that only DC coupled amplifier have the potential to be really transparent to the signal I wonder if a square wave test could be useful to show the impact of the capacitors in series with the signal i have a great faith in square wave test It is very telling about the quality of a circuit imho

[@joshua43214]

Best white board talk yet. You should always do these in this detail level. And you should always preface it with what you where doing when you where 14...

[@lazzer408]

DC-coupled means it will pass both the DC and AC component of the signal into the next stage/circuit. AC coupled means it will only pass the AC component of the signal. The DC component is typically isolated using a series capacitor. The capacitor can color the sound. So if your source output doesn't have any DC present, use DC coupling for best tonality. Use a DMM and find out. It's that simple.

[@2233sc]

I feel robbed of 7 minutes... Hopefully there's a follow up someday.

[@janbill79]

VERY NICE, I know know what my dc coupled 1967 scott model 348b receiver is now . Right away it tells me to check to see if any dc is getting thru. If so. From what. I've learned the dc coupled amp would have bad capicitor before the amp acording to this lesson. But did you say at the end there, DC coupled amps sound worse?

[@janbill79]

I RE-WATCHED THE 2ND HALF. I "GOT "DC" COUPLED AMP". (I got MIXED UP) THE DC COUPLED AMP IS WITH OUT THE CAPICIATOR . SO again I have an dc coupled amp and I shouldn't see any caps before the amp or after. SO THERE IS NO CAPICITORS. (NO CAP BLOCKING ANYTHING) but they still use the coupled name for DC COUPLED AMP. so there must be a diff way they remove the unwanted dc? I learning usally takes about 3x to get something figured out, with help from watching these types instructional videos thanks fro the lesson so it's the AC COUPLED amps thatb sound worse maybe you can erase my first comment so it doesn't mix anybody up I'm just learning.

[@janinapalmer8368]

Yesss..!! DC offset servos in audio power amplifiers !! Make this a new subject ... it might have to be several "Ask Paul's" but it would be of great interest ...

[@janinapalmer8368]

I wish you a very Merry and Happy Christmas to you Paul and your family and all at PS Audio ... keep up the great work ! And also a safe and prosperous New Year ....😀

[@wilcalint]

Quite some years ago I had an interesting conversation with Nelson Pass ( Threshold at the time ) over his extensive use of DC coupling in his products. There is a danger to doing this. He jokingly referred to the following. Given a big enough Threshold Class A DC coupled amplifier if you raise the tone arm/cartridge off the record enough, lets say 4in, and let it drop and it falls fast enough, you run the risk of blowing the cones out of your low frequency speakers. Speaker cones in the middle of the living room floor.

[@paullazarro4295]

200watt Pass designed GFA555, AR TT spinning, my cloths washer starts to spin with an unbalanced load, tone arm bounces a few times and voila 4 10inch subwoofers blown with fried voice coils.

[@wilcalint]

@@paullazarro4295 You should mount them for everyone too see. :-))

[@wilcalint]

@@paullazarro4295 Pass Amps basically look like unlimited current amps with microsecord rise times.

[@plumcharlie]

Hi Paul, So... modular synthesizers are putting out control voltage and the new interplay with a computer digital audio workstations is to use DC coupled audio interfaces that send signal and clock information through devices like (expert sleepers es-8 / es-9) to be converted to CV and then back to computer to be managed in other ways. My question is... where is the danger with the signal to the speakers? Is it just in the amount of volume or is there something else happening with the electronic signal that I'm not aware of. Thanks!

[@sean_heisler]

Clear as mud.

[@graxjpg]

Close the blinds next time! LOL

[@cornwallonline]

I once bought an AC coupled flashlight. It wasn't very bright, in fact it gave out no light at all. However, I saved a fortune on batteries....

[@mysock351C]

The easy way is to roll the gain off using a cap in the lower leg of the feedback network on the op-amp. Assuming its unity gain stable, the cap will turn the op-amp into a unity gain follower at DC. Im horrifically lazy and impatient and cant wait for a relay to click, so I usually leave it out in my stuff and arrange things so the DC offsets aren't as much of an issue. Although that's not the swiftest thing to do with something like a turn table or another audio device that can have large DC offsets, tho.

[@bjrnhee1646]

This is perhaps one of the reasons why the brand EXPOSURE´'s preamplifiers and power amplifiers are so well-sounding because they are all DC-coupled

[@AudioElectronicsChicago]

Thank you Paul!

[@mgregory22]

So does "DC Coupling" refer to the output that contains the DC signal or without it?

[@Paulmcgowanpsaudio]

DC coupling (despite the name) hopefully has no DC on it. It is better referred to as direct coupling: connecting stages together without the need for a DC blocking capacitor.

[@mgregory22]

@@Paulmcgowanpsaudio Thank you! I really don't know enough about electronics. I didn't know a capacitor could filter out DC from a circuit, or a current, or however you put it :)

[@digitalampco7640]

Not one mention of phase shift, Paul? All Cherry Amps made after 2012 and all Cherry DACs are DC coupled. So, we can make an end-to-end DC coupled system. Here’s more information, including a bit on phase shift, with simulation plots: www.audiocircle.com/index.php?topic=167261.0

[@laurentzduba1298]

A power amp designed to be direct coupled to the loudspeakers - i.e. without output transformers and / or output capacitors doesn't always guarantee good sound quality. Back during the 1996 Las Vegas CES, a now defunct audio company exhibited a "Krell inspired" monoblock amp that doubles its power output everytime the impedance of the connected speaker is halved. While I was later underwhelmed with the sluggish sound quality, I later found our why when the exhibitor opened their amp up to show-off the amp's neat layout. Sadly, whoever designed it didn't have Dan D'Agostino's attention to detail when it comes to power supply design. The amp just sports a couple of gigantic filter caps - instead of banks of smaller ones - and woefully inadequate power supply decoupling capacitor use in the intermediate stage and output transistors; Thus the sluggish sound despite of having a lot of watts on tap.

[@prateeksamuel8603]

How do you get 0 dc with dc-Coupled amplifiers?

[@stefanschneider5624]

10 times is 10dB, 20dB is amplification by factor 100 😊

[@markthomas1225]

10 times in voltage is 100 times in power, which is 20 dB. Paul is correct.

[@JerryRutten]

Voltage amplification is in terms of voltage gain, 20 x log(voltage gain). A voltage gain of 10 gives +20 dB, a voltage gain of 30 gives +29.5 dB, a voltage gain of 100 gives +40 dB. When it is about power gain or attenuation it is 10 x log(power ratio), then 10 times gives +10 dB, 30 times gives +14.8 dB, 100 times gives +20 dB.

[@joeythedime1838]

.19 mark - a little to much personal information.....

[@hugobloemers4425]

It's only 99% true any way ;)

[@JerryRutten]

The sun gives some crosstalk, interference and distortion… Nice expression: “potential DC”.

[@benjaminjoeBF3]

how to get rid of dc offset without the use of caps, thats an interesting topic!

[@hugobloemers4425]

Use a transformer or just add an opposing voltage, both that and the signal are resister coupled.

[@benjaminjoeBF3]

@@hugobloemers4425 Yep thank you, I was just learning that. I also discovered dc servos circuits: sound-au.com/articles/dc-servo.htm Love the internet

[@JerryRutten]

@@benjaminjoeBF3 A big hooray for negative feedback!

[@benjaminjoeBF3]

@@JerryRutten why is that Jerry? Would you be so kind to explain?

[@JerryRutten]

@@benjaminjoeBF3 You didn't read the article? A servo system is actually a system with negative feedback... You feed back the DC part of the signal.

[@scottyo64]

Wow way over my head....lol

[@frankgyure3154]

Off topic. But why does PSAudio just not support multichannel audio. Guess what. We are in a multichannel world. It’s time to drop the word “stereo” and to call it two channel.

[@JerryRutten]

Why do you need 8, 10 or 14 channels when 2 (or 4 with subs) can do it, and can do it better? Setting up two speakers well is an art, setting up 8, 10 or 14 speakers is an impossibility...

[@ThinkingBetter]

My ears are AC coupled...

[@QoraxAudio]

My living room is AC heated and cooled...

[@tactileslut]

So you never have to swallow during ascent on the plane (analogous to re-zeroing the DC offset)? Must be nice.

[@ThinkingBetter]

@@tactileslut Yeah, the DC equivalent of a constant air pressure on our ear drums is sort of bad. It’s interesting how our hearing can be severely impacted by such pressure and how swallowing can clear it up. It’s sort of like a speaker with a DC offset signal moving the cone near the limit where it can’t move much mechanically and will yield much compression and distortion.