How to select audio amplifier input decoupling capacitor value

[@gregorydechiaro2407]

Best video I have come across to date. I am visual and he shows you how to use your scope correctly, and explains very clearly the math involved. Excellent!

[@TRONMAGNUM2099]

I watch your videos and think some of these high end audio companies should have you on staff. You blow me away on how well you know amplifiers.

[@redjr16]

John - Have you ever thought about doing a series of videos on the basic functions of using a digital storage scope for audio testing? You have such a great way of simplifying audio topics in a down-to-earth way. This would be of real value for me, and allow me to start using my scope in a more productive way. Thanks so much for these videos, as I am starting to learn more about the basics of audio amps and the theory behind them. Great job!

[@callmejackaroo4723]

John, you're an audio ninja slash wizard! A ninjard! I really appreciate your videos! I got back into electronics just to fabricate amplifiers for fun, gifts, & just occupy my time and brain. I had a really difficult time finding videos that are worth a hoot... Until I stumbled across yours. I may have given it up had I not. So thanks, my friend! Keep it up.. please!!!

[@25830]

Hi John, your videos are just excellent! The information and help you provide is invaluable!!! I'm in the process of building a DIY LM1875 stereo amplifier and am learning so much about how to go about it just from watching your videos! For instance, today I watched another one of your videos in which you advised not to use ceramic caps in the audio path because they add unwanted distortion, so instead, use film caps. You pointed me in the right direction and I ordered four .1uF film caps online today! Every time I watch your videos I learn another valuable tidbit of information! Thank you, Sir and keep up the great work!

[@JohnAudioTech]

I appreciate the positive feedback!

[@TBL_stevennelson]

I heard if we all add a simple comment like Thanks John will get a little boost in pay. He does a great. Job with. Testing. And all, the recommendations he made over the last few years has been great for me as I did use it to buy 15 devices for various projects. That saved me. Money and I really need to penny pinch so If we. Can all give a small comment we. Can repay his hard Work.

[@twotone3070]

Interactions help by suggesting to YT that people are interested in the video and with this information it then recommends the video to more people. More potentials views, more ad rolls and more income.

[@georgejobin1744]

I'm new at this stuff john. I have most of the equipment to use with what your doing.Thanks to you and your methods of teaching I'm learning to do it. Thank you so much John I'm really getting really understanding this

[@markthackray3185]

I just recapped a NAD c352. I used Panasonic FC caps. Amp sounds wonderful! Cool video, most interesting. Thanks!

[@jeremywoods8431]

Most amplifier designers choose an input filter based on the feedback networks lowest pole. The input pole is generally chosen to be 1 decade above the feedback pole to avoid low frequency oscillation or motorboating as some call it.

[@stevelemur6113]

Thank you for a reasonable, practical, understandable presentation. My hat is off to you.

[@jp040759]

Fun exercise. Thanx. Interesting thought on removing the low end for LM386 amps with small speakers.

[@shean-koklim4197]

Thanks for the knowledge John, I learned something today.

[@jasona716]

It always makes me laugh when you mention the FeeeeeeelTech! Thanks for the interesting video!

[@worstuserever]

Thanks for following up with this. It was already on my to-do list of research topics and your last video prompted my curiosity. Also +1 for Snickers' inclusion.

[@northox]

Very interesting. Thanks John! Will test this on the amp I'm building - the DIY Honey Badger.

[@stephenwong9723]

You also need to consider the output capacitor in series.

[@jimdavis5230]

DC coupled class a/b power amplifiers with a split power supply don't have an output capacitor, hence then need for DC offset loudspeaker protection.

[@logotrikes]

Thanks John I now know something about choosing an input cap.....

[@AmazonasBiotop]

Thanks! If the space is to narrow in the cap location. Then I think that you can just remove it and bride it on the PCB and put a cap somewhere on the positive lead on the signal input. Good explanation! My mono block amps has a role of at 40hz when they go to bookshelf's. And I use a sub below that. frequency. When I use 12v then it is unnecessary to pump out juice that just is non beneficial.

[@EngineeringEssentials]

Very informative! Thank you!!

[@Apollo-p1l]

You should record some Snickers snoring or purring audio and use that for bass response test.

[@Gersberms]

If you had an opamp on the input, say you wanted to buffer the signal or something, what resistor value (from opamp input to ground) would you choose after the input cap? You could have a 1 megOhm resistor and a very small cap. Or is it important to match the impedance of whatever the incoming signal is? I heard that line signal devices may have a 10 kOhm output impedance.

[@DasAntiNaziBroetchen]

Omg the Snickers clip is fantastic!

[@dmcbohol]

Hi John, from the Philippines here Would it be safe then to use 2.2uf as input caps? I think the frequency responce would be just about covers the audible frequency range Another thing I noticed when I replaced all the ceramic type capacitors of a mini amp with a Polyester Film (Mylar) of the same value (including the electrolytic input cap) the mini amp sounded much finer & has less distortion.

[@JohnAudioTech]

Yes, 2.2uf would provide flatter response but 1uf is good enough. 2.2 uf film caps won't fit in the tight space on this board.

[@HimanshuSharma-dm8ol]

Sir i want to share this with u . When i used transistor writen that it is made for switching applications like 13005 and 4205d in the output stage ,these transistors consumes very less current in biased state compared to normal 3055. Sir why it is so ?

[@Spentelectrons]

Is the dc offset and coupling capacitor an issue if an op amp is used as a buffer?

[@gbaker6478]

Hi, how are you? I'm looking to figure out how to calculate capacitor value for a rca inline cable between the pre-amp and amp using a capacitor to set the signal to 60 Hertz. The input impedance of the amp is said to be crucial in figuring out the value of the capacitor. I want to put a capacitor on the positive side of the rca cable between the input and output on one side and leave the second output to run to a sub. This way the amp only receives 60 Hertz and higher but the sub gets a full range signal. So a 1 in 2 output with the capacitor on 1 output going to the speakers 1 full range going to the sub. I don't know what I'm doing so I'm trying to explain this as best I can. ____ line out to sub Line --[ In __capacitor__speakers Hoping that's clear lol Can you help?

[@1pcfred]

Good stuff. I don't think I'd be hooking that amp up to speakers that can get down to 20 Hz though. 100 Hz maybe?

[@amitghosh6966]

Why do some amplifier boards have reduced values of Input and output coupling capacitors if it affects the overall frequency response ?

[@cezarlixeanu]

higher value capacitors are more expensive, they're trying to save money this way

[@alphabeets]

Saving a few pennies. Seems silly to me to be that cheap.

[@GuilhermeRochaFast]

Always great

[@AmmarH413]

Great vid John . May i ask if the value of the cap shifts the freq response for the high frequencies too ?

[@Spentelectrons]

No, it doesn't. You would need the signal to pass through a resistor and then a cap to ground to accomplish that rather then the signal passing through a capacitor and then a resistance to ground.

[@Helectronics]

Very informative video, good job!

[@nconrad4504]

Thank you John!!

[@MrDunk66]

Thanks John.

[@amitghosh6966]

Can I use 1uF or higher (10uF) capacitor at input for Lm386 and Tda2822 chips if I don't get 0.1 or 0.22 uF ?

[@JohnAudioTech]

1 uf is fine.

[@dargall1]

That is amazing how much that cap on the input improved the response with the solid state amp. Do you know if this also applies to the input stage of a preamp tube like a 12AX7, 12AU7, or 12AT7 ?

[@maker-matt]

Yes is the easy answer, but the input resistance (The R of the RC as John has explained) is an actual resistor from the grid to ground and is typically of much higher value. My 12Ax7 tube preamp the "Grid Leak" resistor is 6.8 meg Ohms so the capacitor can be a much smaller value like a .01...

[@dargall1]

@@maker-matt Interesting. Thanks!

[@uK8cvPAq]

Should a low pass filter for removing RF go before or after the high pass filter (both passive)?

[@AstrosElectronicsLab]

It doesn't really matter. In most cases, I've always seen a fairly low capacitance (330p - 470p) close to the input lead of the IC/first transistor

[@joshuawang5859]

Nice video! will this change cause any earlier drop on high frequency?

[@JohnAudioTech]

No.

[@DasAntiNaziBroetchen]

You seem to try to improve the frequency response by adding bigger caps, however I feel like you're forgetting about power filtering. You're probably better off adding multiple, differently sized caps, to improve frequency response AND filtering, unless you can guarantee your power supply is super clean (none of my PSUs were clean enough to not need any additional filtering). EDIT: Now I see we weren't talking about the same caps... I was talking about the big electrolytics... BTW, how is the frequency response in the higher frequencies now? Doesn't a bigger cap increase ESR and therefore weaken higher frequencies unless you add some small caps in parallel?

[@JohnAudioTech]

The larger film capacitor on the input won't harm the high end of the frequency response. Input impedance is far higher than the cap's ESR anyway.

[@darthbubba866]

Not that this particular amp would be used for this purpose, but turntables and vinyl records get into the rumble and record warp range around he 5Hz mark. Extending the frequency response too low will result in excessive woofer cone travel and lots of amperage being sent to the speaker for no useful reason.

[@maker-matt]

That is true and a very good point! - if you look at the frequency response of a really good amp like my Rotel RX-803 (from 1977) it's 0.5 Hz to 60 khz and, yes you can see (but not hear) the woofer cones move in conjunction of a warped album. So coupling this amp for -3db at 10 Hz is great, as It does not have the power supply "headroom" to spare.

[@johncoops6897]

@@maker-matt - back in the day, many audiophiles would buy or build a "rumble filter" box to allow adjustment of the input frequency roll-off. Rather than a simple RC filter like shown in this video, it was better to have a 2nd Order or even a 3rd Order filter. The more complex filter allowed the curve to be much sharper and thus would have less effect on the low frequency audio.

[@manFromPeterborough]

The TC 750 phono sounds better with 1uF in/out poly film coupling caps, replacing crap electrolytics that were bit high in value for the design orig as following input 4.7uf and out 10uf, the phonostage sounds more transparent and punchy

[@bobking7347]

The only issue with these amplifiers is that they don't have any thermal paste on the back of the amplifier chip, luckily I caught this and some on. Otherwise I could see this amplifier not being to reliable without it. No way it would be efficiently conducting heat to it's heat sink.

[@AstrosElectronicsLab]

Second. Turn on the circuit, John! lol

[@Dazzwidd]

turn on the flames, James

[@jimdavis5230]

Many discrete class a/b power amplifiers have an electrolytic input capacitor which I find very strange. There is no dc across the input capacitor on the power amplifiers I've tested so an electrolytic would be operating with reverse polarity on negative half cycles of the input signal. On several commercial and home built power amplifiers I have strapped out the input capacitor which has had no effect on the DC output offset voltage even with the input shorted to ground. I designed a stereo preamplifier using ultra low dc offset OP27GN operational amplifier IC's. My preamplifier output is DC coupled to the power amplifiers with no problem with dc offset. The dc offset at the power amplifier output is around 8mV with or without the preamplifier connected. I have built fast acting dc offset loudspeaker protection into the power amplifiers. Anyway, strapping out the input capacitor has vastly improved sound quality and extended the bass response.

[@maker-matt]

They are probably "Non Polar" electrolytic caps.

[@jimdavis5230]

@@maker-matt Yes they should be the non-polar types, but they aren't.

[@uK8cvPAq]

I think electrolytics can actually take about 1.5v DC in reverse before they start breaking down and letting more and more DC pass. The relatively high input impedance of an audio amp input stage probably helps limit reverse current damage too.

[@jimdavis5230]

@@uK8cvPAq You are correct however the capacitor should never be subjected to reverse voltage.

[@johnyang799]

The current flows in and out of the capacitor same as charge and discharge because usually it's ac signal. The other end of the capacitor is not directly short to ground so there won't be any damage to the cap even when there's significant DC. Also electrolytic are much larger caps. It's easily over 100uF hence pushing the cut off frequency way lower. With film cap you need to select correct values.

[@technixbul]

All Snickerses like milk :D

[@laxr5rs]

Cool.

[@DasAntiNaziBroetchen]

Coupling or decoupling? You say "coupling" but the title says "decoupling".

[@JohnAudioTech]

Technically, they are for decoupling the DC so should be called decoupling.

[@createinvent]

Feeeeeel the quality! Hahha, nice.

[@johnnytoobad7785]

Most mfgr's of these pre-fab circuits select a cap so that your (1st order) response down by 3db at 20 hz. Not exactly an audiophile response. For a typical bookshelf speaker this is fine. Not so good for floor standing. I built a Velleman Power amp (back in 2003) that utilizes the 7293 amp-on-a-chip. It was down 1db at 20hz.

[@paulb4661]

Sure, keep in mind though that even large floorstanders are usually 10dB down at 30Hz, no matter what their manufacturers declare, and that real in room response is dominated by internal resonances and reflections of a magnitude far exceeding 3dB.

[@johnyang799]

It says decoupling in the title. Pls fix. : )

[@BlankBrain]

That would be an open capacitor.

[@grumss9248]

did i hear you say 20Hz! riducilous, very few speaker systems can produce that low and general rule of thumb is we cant hear below 40hz (professional sound guys say we are just hearing harmonics)... Professional sound systems are normally set up with a low cut filter at 40/50hz

[@grumss9248]

Most of the people watching this would be horrified to learn that their speakers are likely useless below 60hz- and often 100hz.. Low frequency comes at a price and normally means huge boxes and wasted power

[@grumss9248]

ported boxes create an even bigger issue- below their tuned frequency there is nothing to dampen the movement of the drivers causes over exertion of the cone and produces basically stuff all sound while still using big power...

[@Wolfgang3418]

You're right. Two things could improve this, firstly an amp with high damping factor and secondly a type of "boxes" where the cone moves only a bit even at lowest frequencies, a horn speaker! Here you find a great DIY projekt which I'm aming at once my amp is fixed, please look at link #2 in the description. kzbin.info/www/bejne/bqK5gKqNi8Sgjas

[@foxfyre3600]

What about how important is the type of dielectric? When I built my headphone amp I used CYC and polystyrene capacitors because I heard they were the best. Obviously they are larger but I had the room. I wish I owned an oscilloscope so I don't know if my implementation was correct. Still sounds good!