how much important is a dc coupling output capacitor? - diyAudio
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Old 13th January 2008, 11:05 AM   #1
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Default how much important is a dc coupling output capacitor?

hi..i am a new electronics engineer and love to make diyaudio..i made a single ended circuit and it sounds very good.but it is only 6 watts rms http://diyaudioprojects.com/Solid/ZCA/ZCA.htm here is the circuit.

i have two pairs of wharfedale 8.2 it is 86db .i want to make a plh amplifier.because it is more powerful.

i want to make a single ended class a circuit because it doesnt have crossover distortion

now i ask you which dc coupling capacitor is most reliable? is it important to select 85celcius or 105 celcius or 125 ones?how much important to select low esr capacitor.i want to have purest sound.

thank you
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Old 13th January 2008, 11:55 AM   #2
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With the output capacitor the reliability will be good if the rated voltage is greater than the power supply voltage.

Many years ago Ben Duncan wrote about coupling capacitors for a low level preamp' line stage he designed in an English magazine. I remember that he said that he thought a capacitor with a much higher rated voltage than was strictly necessary sounded better. (I can't remember why.) But they are more expensive. But your amp power supply has a low voltage so you could run a 63v or higher and see what it sounds like. Some people like to keep the capacitor away from heat sinks because generally most components last longer if they are kept cooler.

Other people may know more about the tempreture rating but you are unlikely to need more than an 85 celcius rating.

Generally people like low esr caps and some catalogues (such as RS Components will have section with caps that are designed to have a low esr.

What you might try is to run a few caps in parrallel. (So that for instance you had four 1,000uF together) That way you will tend to minimise the inductance etc. I guess it would lower the esr too.

I would like to hear what you discover.

Edit; I notice the designer has an email address on the website.
He might have some ideas about the best cap'.

Good luck, Jonathan
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Old 13th January 2008, 12:16 PM   #3
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i asked some questions but they dont know much about this subject..i think a few component is better..

is there anyone to prefer something better..i use nichigon capacitor now..i have elna capacitor too..but it is 85 celcius
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Old 14th January 2008, 07:37 AM   #4
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heyy is there anyone knows about single ended class a output capacitors ?
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Old 14th January 2008, 09:40 AM   #5
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Hi,
there is expertise till overflowing in the PASS section of this Forum.
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Old 14th January 2008, 11:59 AM   #6
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Default Re: how much important is a dc coupling output capacitor?

Quote:
Originally posted by umut1001
now i ask you which dc coupling capacitor is most reliable? is it important to select 85celcius or 105 celcius or 125 ones?how much important to select low esr capacitor.i want to have purest sound.
Temperature rating is important if the temperature is reaching 60 deg C. Then the life time may be short but. Not more than 105 deg C is hardly necessary at all but it's no harm to use it. I can't see that ESR is particulary important but if you don't want to think or take a chance, take a high performance cap of some sort. I would use perhaps more than 4700 uF, 10000 uF maybe.
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Old 14th January 2008, 03:31 PM   #7
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i used 85celcius 6800uf elna but later i replaced 105c 10000nichicon . i am not sure what to do.there is a 10uf arcatronics mkp in parallel also..
how big capacitor must be used ? i have no idea..how can i measure it ? is there any calculation method?
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Old 14th January 2008, 03:37 PM   #8
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Yes the higher the capacitance the lower the corner frequency where you cut the bass off. 6800uF is fine.
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Old 14th January 2008, 04:25 PM   #9
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Default hi Andrew

hi andrew..could you give me a link about class a output caps?i couldnt find it.
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Old 14th January 2008, 06:06 PM   #10
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Quote:
Originally posted by umut1001
i used 85celcius 6800uf elna but later i replaced 105c 10000nichicon . i am not sure what to do.there is a 10uf arcatronics mkp in parallel also..
how big capacitor must be used ? i have no idea..how can i measure it ? is there any calculation method?

When the impedance (which rises as the fequency falls) of the series cap is equal to the nominal speaker impedance (eg 8 ohms), half the output power is lost, ie there is 3dB attenuation.

This is known as the corner frequency.

So if you want a corner frequency of 10Hz, calculate the C which is 8ohms at 10Hz using

C = 1/(2*pi*f)

and take it to the nearest available value.

The temperature and ESR ratings of caps are much more relevant to their use in power supplies where ripple current causes losses and local heating.
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