is this true about capacitors????

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#25
gtforme00 said:
Tantalum capacitors have measurably high distortion products in the audio range when used as coupling capacitors.

An externally hosted image should be here but it was not working when we last tested it.
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To measure harmonic distorsion introduced by a capacitor, a voltage must develop across it, which implies not having a negligible amount of impedance at the frequency of measurement. This is the case in filters but not in wide bandwidth coupling.

A recent study :
http://uk.geocities.com/cyrilb2@btinternet.com/
 
#26
Wide bandwidth coupling ALWAYS means that SOMEWHERE the cap does some work. If not WHY is the cap there? IF you must, measure at the coupling frequency. Some caps distort, other caps don't. Would you not prefer a low distortion cap over a high distortion cap? Might make the same difference as between a 4558 and an OPA 2134. You never know, but if you can't tell the difference, then what is the point of talking about audio in general?
 
#28
Gtforme00's diagram shows harmonic distorsion with caps of 220 µF with a 16 Ohm load. I'd prefer to see 2200 µF in this position
I remember the DB preamp which had tantalum coupling caps : its distorsion was extremly low by the standards of the time.
Maybe harmonic distorsion measurements does not tell all, but it tells a lot. See Cyril Bateman's extended investigations, most of them with a 1 kHz sine signal. He show showed that COG ceramic caps are very good and that DC polarisation does not necessarily lowers distorsion of electrolytics. He also patented the use of twin bipolar electrolytics in series.
 
#30
Mr Curl, You said;

john curl said:
Elna's are OK, Muse is my fave, Panasonic is problematic.
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Why is that ?
Is it mechanical failure (leaking electrolite) ?
Or is it the sonic side that you are refering too ?

Would std low esr caps do as replacements for these 'specialised audio' caps ?
And finally, what are your thoughts on bipolar electros and there possible replacements ?

Thanks...
 
#32
electrolytic caps are actually a spin-off of another device that was used in the very early days of radio, the electrolytic rectifier. in fact the materials are almost identical. the big difference is in the assembly of those materials. an electrolytic cap actually uses an oxide layer on one of the aluminum plates as the dielectric. it is actually possible to change the working voltage of a lytic. this is done by a forming process, where a higher voltage than the cap's working voltage is applied through a very high resistance. at first the cap will operate similar to a zener, because above it's rated voltage it conducts. once the oxide layer gets thicker, the current goes down, until eventually the cap stops conducting. the cap has an increased working voltage, but it's capacitance is reduced by a proportional amount. this is because the oxide layer is thicker, and the "plates" are now further apart. lytics kept in storage for long periods of time (5 yrs or more) sometimes lose their oxide layer and need to be re-formed before use. considering this, i tend to wonder about whether it's wise to bias a nonpolar cap for any extended period of time. with any lytic there is always a small leakage current, and this could eventually play havoc with the cap's nonpolar characteristics
 
#33
A rule of thumb I always use when selecting audio capacitors that have to be electrolytic, is to use the longest foil (read:tallest) and the highest voltage available (within reason) for that can space size that exists to work in. For example, if it can be no more than a 22uf 16Vcap, but space allows for a 50V 22uf cap..and that given brand and series has a long version and a shorter (height) version..always go for the taller cap. I've played with that aspect for the past 25 years and the long foil has always sounded better. There are a few reason for this to be a noticeable point.

Some of the slit foil electrolytic capacitors to emerge as of recent are a very good step in the correct direction, with respect to helping electrolytics 'sound better'.
 
#34
KBK said:
A rule of thumb I always use when selecting audio capacitors that have to be electrolytic, is to use the longest foil (read:tallest) and the highest voltage available (within reason) for that can space size that exists to work in.
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Are you referring here to capacitor inductivity? The taller one vs shorter one (assuming same capacity) means less turns of the foil inside and thus less inductive bihaviour 😕
 
#40
I have measured the ESR of a great number of electrolytics, most very old (up to 30 years), a few of them being big ones of photographic flashes (Balcar) which had been very intensively used. The amount of faulty caps was surprising low, I would say an average of 1%.

If you find that output electrolytics introduce too much harmonic distorsion at the ouput of amps, a solution consists in including them in the feedback loop.
 
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