There already are a few threads on electrolytic capacitors
This one arises from a discussion in the thread " Dx Blame ST - Builder's thread - post pictures, reviews and comments here please." around the posts #333 to #357
The statement was that electrolytic caps work best for audio when they are operated at a DC Voltage bias of at least 10% of its rating.
Or something like that. The auther of this statement did not yet give a more precise version of what that is actually supposed to mean.
I suggested to spin off this topic to a seperate thread, to keep the other thread clean, and it got approved by one member, so here we go 😉
Feel free to copy the relevant posts of the Blame ST thread and repost them here, or link them, so everyone has the chance to get up to date as easily as possible.
My intention is, to have a fair discussion, and to stick to facts, reality, i.e references to repeatable experiments and results.
This thread is supposed to clear up myths that come across from time to time, like the one mention above. It is not meant to propagate and create new myths, as this is already happening enough anyway.
Have a good time!
krachkiste
This one arises from a discussion in the thread " Dx Blame ST - Builder's thread - post pictures, reviews and comments here please." around the posts #333 to #357
The statement was that electrolytic caps work best for audio when they are operated at a DC Voltage bias of at least 10% of its rating.
Or something like that. The auther of this statement did not yet give a more precise version of what that is actually supposed to mean.
I suggested to spin off this topic to a seperate thread, to keep the other thread clean, and it got approved by one member, so here we go 😉
Feel free to copy the relevant posts of the Blame ST thread and repost them here, or link them, so everyone has the chance to get up to date as easily as possible.
My intention is, to have a fair discussion, and to stick to facts, reality, i.e references to repeatable experiments and results.
This thread is supposed to clear up myths that come across from time to time, like the one mention above. It is not meant to propagate and create new myths, as this is already happening enough anyway.
Have a good time!
krachkiste
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I really know very little about capacitors, which are truly complex as any other part. But I would imagine a polar electrolytic aluminum capacitor has an oxide on only one side of the plates, and to maintain originally specified performance for a long length of time the capacitor should always or often have some voltage on it of proper polarity. If you operate such a capacitor for long with ac loads and no bias there will be all sorts of strange things developing in there, maybe even quickly enough to change an audio signal enough to hear. Also I suppose that keeping the capacitor polarized would help some distortions be more even order. Actually, this effect would probably exist for non-polar capacitors as well. If the bias is very high voltage compared to the signal, voltage dependent characteristic change would certainly be minimized for the signal. (possibly helping tube circuits sound better) What effect voltage bias has on current dependent characteristics is well beyond my knowledge, though it seems to me it would be a larger effect in electrolytic types.
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well if you keep caps at 10% of there max voltage they have a long life.
but i don't know if they perform worse at a really low voltage.
but i don't know if they perform worse at a really low voltage.
I have never heard or read anything like that.
That a capacitor should not work well at low voltage.
When it comes to film capacitors,
they are generally electrically better the higher the voltage rating.
And I think this goes for electrolytics, too.
There might be very big lyts unsuitable for certain things in audio,
but this is mainly because of physical size.
And of course because lyts are several levels below film caps in electrical quality.
That a capacitor should not work well at low voltage.
When it comes to film capacitors,
they are generally electrically better the higher the voltage rating.
And I think this goes for electrolytics, too.
There might be very big lyts unsuitable for certain things in audio,
but this is mainly because of physical size.
And of course because lyts are several levels below film caps in electrical quality.
Now we need the author of that statement to come explain why the 10 percent or how it was arrived at, has anyone else come accross this recommendation.
Interesting to note that my assumptions about 2nd harmonic and increased bias voltage were essentially wrong in an opposite way...
That article is about solid dielectric capacitors, not electrolytic ones. Conclusions CANNOT be extrapolated from one type to another since there is a major difference.
The electrolytic capacitors have the dielectric maintained based on the DC voltage across them. That DC is necessary and I can see why a value close to the nominal rated one could be beneficial, enhancing the electro-chemical oxidation insulation layer.
That is different from a solid dielectric capacitor, that is "stressed" by the DC component and suffer from hysteresis and short-term remnant polarization.
The electrolytic capacitors have the dielectric maintained based on the DC voltage across them. That DC is necessary and I can see why a value close to the nominal rated one could be beneficial, enhancing the electro-chemical oxidation insulation layer.
That is different from a solid dielectric capacitor, that is "stressed" by the DC component and suffer from hysteresis and short-term remnant polarization.
I am happy that many here are reading up on cap problems. They can be a real problem, if you pick the wrong one, and the data sheets will not warn you.
I thought Walt Jung found that electrolytics give lower measured distortion when they have a high DC bias. In addition, avoid using electrolytics to set the LF point of an amplifier as they work best with small signal voltages across them and the bulk of the signal across the resistor or device which loads them.
Design the circuit so that you can use available values of polypropelyne, polystyrene, or others that have very low DA for signal coupling and don't worry about it.😉
do we always have this choice e.g. for the feedback network dc-bypass cap, with respect to noise and offset?
In 1984, I think, Ben DUNCAN ran a very long series of articles in an English magazine "Hi-Fi News and Record Review". It was for an up market pre-amp and I think that at one stage he said he couldn't use a plastic film cap for some reason and so he used two conventional electrolytics wired back to back to make a non-polarised cap. Now the two points that were interesting were that (i) I think he ran a resistor up between them, i.e. where they joined to have a a power supply rail voltage there and (ii) that I recall he argued for the use of a fairly high Working Voltage for the cap'. Have trouble recalling it exactly but I think it may have been over 300v in a s/signal circuit running fairly modest split-rail power supplies of 20 v dc or so.
All Ben's work was pretty well thought out and designed for sonic accuracy but I can't recall the exact rationale for these decisions.
All Ben's work was pretty well thought out and designed for sonic accuracy but I can't recall the exact rationale for these decisions.
"The electrolytic capacitors have the dielectric maintained based on the DC voltage across them. "
really?
really?
I've just finished reading Douglas Selfs latest book 'Small Signal Audio Design'.
Very interesting. Did you know that the average signal, between the microphone and the final mix down just before it goes onto the LP or CD goes through about 100 op-amp stages? mostly NE5532/34 but some TL072. He also says, through 'hundred's of electrolytic capacitors'. He should know.
So, don't agonize over a few electrolytic s in your power or pre-amp. Just build it!
Very interesting. Did you know that the average signal, between the microphone and the final mix down just before it goes onto the LP or CD goes through about 100 op-amp stages? mostly NE5532/34 but some TL072. He also says, through 'hundred's of electrolytic capacitors'. He should know.
So, don't agonize over a few electrolytic s in your power or pre-amp. Just build it!
Not all really good audio CD's or LP's Doug Self does not not know more than I do, and I have made the studio boards and master analog recorders for several major audio recordists, including Mobile Fidelity, Wilson Audio and Crystal Clear Recordings.
A curious statement ???
Caps have already been discussed to death here. http://www.diyaudio.com/forums/solid-state/169833-polypropylene-vs-silver-mica-cdom.html
The topic seems to be like a religious experience to some , who like to TITHE the blackgate god in search of audio nirvana. 😛
Seeing the statement... "maintaining the integrity of the dielectric usually requires the steady application of the correct polarity of direct current else the oxide layer will break down and rupture" , one would assume that more voltage would better maintain that oxide layer. as far as 10% , this would depend on what "voodoo" mixture that the electrolyte was composed of , and the thickness of the dielectric.
This is why I go way overboard in derating my electro's (100v for 60Vdc , etc.)
OS
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