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Old 17th October 2009, 09:49 AM   #1
Nick_C is offline Nick_C  United Kingdom
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Default Output Capacitors (confused)

Hi all,

I have just finished building an amplifier based on the LM6171 with a Buf634 on the output.

Its all going well & sounds very nice, I have measured for DC offset & there is nothing much at all, however I am concerned about the possibility of something going faulty & destroying my headphones, for example the buffer sending the V+ (15v) through to the output, or anything else going faulty come to that.

I have fitted 470uf electrolytic's as output caps, I have read about the fact they can degrade the sound quality but so far I havent heard anything bad.

I also have a 15-0-15 supply & have read that because my output would essentially be swinging from + to -, that I would require a bi-polar cap.

But here is the thing, everywhere I read on the net says the same thing, that by using a polarised cap in the way I am should sound terrible, as half of the music cycle is causing the cap to work the wrong way, against the polarity, its too short to make it go bang I believe, but everyone says it will sound terrible!!

I have wired up a few caps to test in a way that I can go from, through cap, to no cap, & I have always had good ears but I honestly can not hear even the slightest difference with or without the output caps in place.

It kinda makes a mockery of what ive been reading online about all this subject, it should be sounding terrible, but there honestly is no difference, ive even hooked it up to a scope & then my PC (RMAA) again no visual difference to a square wave or anything else.

Can anyone shed any light onto why im able to use a polarised cap in this way without any sound degradation? ive even tried the done thing of bypassing the caps with 0.22uf polyesters, as I read people saying that it made a big difference to the highs, but again I havent found that do anything either, there is no loss of highs with the electrolytic in place or not.

One last thing, ive also tried several caps, ranging from a cheap 7p SMG brand, to a Nichicon FG, also from 0.22uf up to 1000uf, bass was effected with too lower values as expected (corner frequency I believe its called) but from 220uf onwards it was back to being flat from 10hz to 100khz.

So im puzzled!
Nick :-)
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Old 17th October 2009, 06:33 PM   #2
ratza is offline ratza  Romania
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Quote:
Originally Posted by Nick_C View Post
Can anyone shed any light onto why im able to use a polarised cap in this way without any sound degradation? ive even tried the done thing of bypassing the caps with 0.22uf polyesters, as I read people saying that it made a big difference to the highs, but again I havent found that do anything either, there is no loss of highs with the electrolytic in place or not.
That is because the difference between caps is so small that you can't hear it. This might also mean that you are not filled with all the audiophile crap and you're still able to judge by yourself if it sounds good or not.
See these and have a laugh and/or feel sorry for them:
Matrix HiFi --> Blind testing high end full equipments
ABX Double Blind Comparator Data

BTW, nice option for the buffer.
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Old 17th October 2009, 06:56 PM   #3
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Quote:
Originally Posted by Nick_C View Post

So im puzzled!
Nick :-)

You should be happy, rather than puzzled. Or you can continue experimenting. How about a diode in series with that cap? An LED? There must be something you can hear.

Unrelated question: do you listen long and loud on your cans?


Slightly more seriously: i doubt a reversely biased capacitor becomes a significant distortion generator at very low voltages. It would be a problem at speaker levels but not so much with cans. You mention nothing about your listening acuity or the quality of your system. Do you consider yourself an experienced listener? Per example can you hear absolute phase?
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Old 17th October 2009, 08:34 PM   #4
cbdb is offline cbdb  Canada
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If the cap is going into the negetive you will decrease its life span and it might eventualy explode.
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Old 17th October 2009, 11:11 PM   #5
Nick_C is offline Nick_C  United Kingdom
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Quote:
Originally Posted by ratza View Post
That is because the difference between caps is so small that you can't hear it. This might also mean that you are not filled with all the audiophile crap and you're still able to judge by yourself if it sounds good or not.
See these and have a laugh and/or feel sorry for them:
Matrix HiFi --> Blind testing high end full equipments
ABX Double Blind Comparator Data

BTW, nice option for the buffer.
Yes I do get the feeling that there is a lot of exaggeration going on when I read about the so called differences.

I will have a look at those links next up..
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Old 17th October 2009, 11:18 PM   #6
Nick_C is offline Nick_C  United Kingdom
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Originally Posted by analog_sa View Post
You should be happy, rather than puzzled. Or you can continue experimenting. How about a diode in series with that cap? An LED? There must be something you can hear.

Unrelated question: do you listen long and loud on your cans?


Slightly more seriously: i doubt a reversely biased capacitor becomes a significant distortion generator at very low voltages. It would be a problem at speaker levels but not so much with cans. You mention nothing about your listening acuity or the quality of your system. Do you consider yourself an experienced listener? Per example can you hear absolute phase?
Yes I am very happy with the circuit, as for a diode or an led, im not exactly trying to add components until I can hear an audible difference, im really only after protecting my cans against DC, the cap being a good blocker of DC.

Well I dont really buy into all that "Experienced Listener" title, I just know what I like when I hear it, but I am very good at hearing subtle differences, which is why im puzzled why I cant hear ANY changes to the sound by introducing an output cap, especially when I read online from others about how bad they are & that they seriously degrade the signal, but im wondering if its been blown out of all proportion, or maybe more the case it could be circuit dependant, maybe some circuits may put the cap under more stress & reveal any weaknesses, the output cap in my circuit isnt actually working all that hard at all, its basically a DC blocker.
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Old 17th October 2009, 11:24 PM   #7
Nick_C is offline Nick_C  United Kingdom
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Originally Posted by cbdb View Post
If the cap is going into the negetive you will decrease its life span and it might eventualy explode.
Im more concerned about the actual sound of the whole idea of adding such caps, it would never actually explode at such miniscule AC voltages, but yes it could lower the life of the cap I guess.
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Old 17th October 2009, 11:32 PM   #8
Nick_C is offline Nick_C  United Kingdom
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Originally Posted by ratza View Post
That is because the difference between caps is so small that you can't hear it. This might also mean that you are not filled with all the audiophile crap and you're still able to judge by yourself if it sounds good or not.
See these and have a laugh and/or feel sorry for them:
Matrix HiFi --> Blind testing high end full equipments
ABX Double Blind Comparator Data

BTW, nice option for the buffer.
I thought about what you said about not being filled with all the audiophile crap especially when I saw just now a website selling (wait for it) oxygen free audiophile grade mains lead for an insane price, they actually said there was a noticeable difference to the sound by using this lead, what? how about when they plug it into the wall socket which has behind it metres & metres of standard cheap twin & earth mains cable throughout the house

Its a world I am getting drawn into, but im trying to stay subjective about it all, I trust my ears more than what ive read, im slowly coming to the theory that it might be how you implement parts in a circuit whether or not they will sound good or bad or hear no difference, maybe in a tube amp where the output caps have 100v fed to them perhaps then they might start to have their own sound signature, being as they are actually working harder, I dont know, im clutching at straws here...
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Old 17th October 2009, 11:53 PM   #9
kaos is offline kaos  United States
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I canít hear crap with headphones (maybe because Iím not used to them). With real room speakers though I can hear some fairly subtle changes. Not sure what that says about me, or the importance of the outer ear in hearing (headphones send the sound straight down the ear canal while speakers use the outer ear in a more normal way). You may want to try a good power amp with some decent speakers before making very many generalizations based on your finite experiences so far.
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Old 18th October 2009, 04:07 AM   #10
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One thing I will say is that there is a big difference between a capacitor on the output of an amp compared to on the input. Distortions that capacitors will introduce will be small... if that distortion is on the output it will quite likely not be audible. If however it is on the input (before amplification) then depending on the gain of the amplifier, the distortions may be amplified many times over, and can become audible.

If for no other reason, you should change the caps to non-polars for safety reasons... Exploding electrolytics are not nice, and I would hazard a guess that if one exploded whilst you were wearing your headphones, that it would not be a pleasant experience.

Tony.
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