polarized vs nonpolar caps in circuit design

[bcarso]

[quote author="buttachunk"]Peter,


I think Jung was commenting on the older BP cap design (2 polar caps, no bias), and in that case is correct. The newer caps, FWIR, are not simply 2 unbiased polar caps, as per his comparison.

IMHO, newer BPs are the way to go. in a lab, with gear designed specifically for the 2 polar caps with a resistor thing, I still heartily doubt that there would be any improvement over good Panasonic or Nichicon BP caps.[/quote]

As I've mentioned from time to time in these discussions, there is some opinion and evidence that the dual foil construction bipolars do indeed outperform biased single 'lytics and biased back-to-back 'lytics. Cyril Bateman has written at length in Electronics World expousing this POV, and I believe a Jensen Tranformers app note mentions a specific bipolar as being very good. Sorry I don't have cites handy. However, a search of this site ought to turn some up.

None that I know of conjectures why this should be the case. My guess is that it pertains to the piezoelectric properties of the construction, perhaps minimizing electrical-to-mechanical conversion and making what there is more symmetrical.

IIRC Greg Timbers of JBL, who designed speakers with internal batteries for 'lytic bias, had someone supposedly demonstrate that bipolar 'lytics had lower distortion than his biased parts. He nonetheless maintained that the biased ones sounded better, so perhaps there was some compensatory overall effect.

 

[Svart]

I'm still convinced of BP caps instead of biased in my experiments. I LOVE the Nichicon Muse BP.. the nice green ones.. pretty and sound good at the same time!

 

[clintrubber]

Hi,

[quote author="buttachunk"]Peter,

:guinness:

sorry, wasn't trying to shoot down your question. [/quote]
All fine, it didn't felt that way :thumb:

just added that because there are some who would read this and may go to the extent of trying to wire 2 caps and a resistor into pre-exsisting designs for the sake of "it may be better".
I think Jung was commenting on the older BP cap design (2 polar caps, no bias), and in that case is correct. The newer caps, FWIR, are not simply 2 unbiased polar caps, as per his comparison.

That's interesting, wasn't aware of new- vs old-style BP's.

[quote author="mikep"]one thing about using 2 back-to-back caps is you could specify 2 different parts to save a little money. for instance, the cap that connects to the outside world could be a 63V part (plus side out) so that a line output stage could withstand a bad patch into a mic input with phantom present. IMO, an important feature for broadcast audio equip.

mike p[/quote]
That's indeed an interesting one :thumb:


[quote author="bcarso"]As I've mentioned from time to time in these discussions, there is some opinion and evidence that the dual foil construction bipolars do indeed outperform biased single 'lytics and biased back-to-back 'lytics. Cyril Bateman has written at length in Electronics World expousing this POV, and I believe a Jensen Tranformers app note mentions a specific bipolar as being very good. Sorry I don't have cites handy. However, a search of this site ought to turn some up.[/quote]
FWIW, here's a list that I had around of the EW+WW-issues with the articles Brad mentioned:
C. Bateman, Capacitor Sounds, Electronics World, July 2002, pp. 12-18
C. Bateman, Capacitor Sounds 2, Electronics World, September 2002, pp. 16-22
C. Bateman, Capacitor Sounds 3, Electronics World, October 2002, pp. 12-18
C. Bateman, Capacitor Sounds 4, Electronics World, November 2002, pp. 40-50
C. Bateman, Capacitor Sounds 5, Electronics World, December 2002, pp. 44-51
C. Bateman, Capacitor Sounds 6, Electronics World, January 2003, pp. 44-51

Bye,

Peter

 

[NewYorkDave]

I have some of those issues of Wireless World, but not the whole series. I'll have to look for them...

I used to buy WW at the local Barnes and Noble, till the magazine became too slim and the price too high.

 

[clintrubber]

[quote author="NewYorkDave"]I have some of those issues of Wireless World, but not the whole series. I'll have to look for them...[/quote]
I believe all those issues are still saved @ work (we had a subscription there). If the paper these articles are printed on is still readable by then, I'll scan them after my retirement :wink:

I used to buy WW at the local Barnes and Noble, till the magazine became too slim and the price too high.

It's not what it's been indeed :?

 

[bcarso]

Reprints of articles are available from a service, but they get the proverbial arm & leg.

 

[NewYorkDave]

Could be time for some discreet sharing via back channels. 'Nuff said.

 

[gnd]

I'm wondering... Bipolar cap is two caps in reversed series, no bias. So why is there a need to bias when connecting two polarised caps?

Is there some internal bias with bipolar caps? They have just two wires, isn't it? So connecting two polarized reversed, without bias voltage, is the identical to one bipolar. So there may be some extra advantage with biased polarized pairs, because of bias voltage, which is absent in bipolar cap.

How is it?

 

[JohnRoberts]

[quote author="gnd"]I'm wondering... Bipolar cap is two caps in reversed series, no bias. So why is there a need to bias when connecting two polarised caps?

Is there some internal bias with bipolar caps? They have just two wires, isn't it? So connecting two polarized reversed, without bias voltage, is the identical to one bipolar. So there may be some extra advantage with biased polarized pairs, because of bias voltage, which is absent in bipolar cap.

How is it?[/quote]

With polar caps in the forward direction there is quantifiable leakage current, often specified on data sheets, in the reverse direction AFAIK (in other words I'm guessing here) you will have normal leakage for low voltages and a voltage thresholds where breakdown and higher conduction can occur. This threshold is not well defined and may even change with age. I had one experience with a production part installed backwards and the failures mode was not certain or very predictable.

By applying a DC bias to the intermediate junction you can insure that signal related terminal voltage changes will not reverse bias one of the two capacitors and you experience well defined forward leakage in both parts.

In general I prefer the known to the unknown (or guesses). I like to keep signal related terminal voltages low in all cases when using polar capacitors.

JR

 

[rlaury]

Hi all:
Here's a good article on caps that I refer to time to time.
Start reading at "Capacitors."

http://www.nashaudio.com/CapArticle.pdf

RonL

 

[chrissugar]

Thanks Ron for posting that. :thumb:

chrissugar

 

[gnd]

[quote author="JohnRoberts"]With polar caps in the forward direction there is quantifiable leakage current, often specified on data sheets, in the [/quote]

This leakage is not present in bipolar electrolytic caps?

If bipolar is just two polars in one package, then there is also leakage, is it? Isn't it then, that two polar caps with central bias are better than one bipolar cap, because bipolar cap is two caps in one package, and cannot be biased?

 

[gnd]

[quote author="mediatechnology"]This can be advantageous in phantom blocking circuits. SSL used it here: http://www.ka-electronics.com/images/SSL/ssl_82E149.pdf Pin 1 is tied to 48V unswitched. This particular circuit recovered quickly from phantom switching.

I'm not sure that in general coupling applications there's going to be much sonic difference between different bipolar configurations. Modern bipolars have gotten much better.
[/quote]

SSL used cap biasing also in output stages http://www.ka-electronics.com/images/SSL/ssl_82E195.pdf,
and filter stages http://www.ka-electronics.com/images/SSL/ssl_82E242.pdf,
and mix bus http://www.ka-electronics.com/images/SSL/ssl_82E26.pdf, but not in bus compressor.

Interesting. Why yes in mix bus, but not in bus compessor? Any idea?

 

[JohnRoberts]

[quote author="gnd"][quote author="JohnRoberts"]With polar caps in the forward direction there is quantifiable leakage current, often specified on data sheets, in the [/quote]

This leakage is not present in bipolar electrolytic caps?

If bipolar is just two polars in one package, then there is also leakage, is it? Isn't it then, that two polar caps with central bias are better than one bipolar cap, because bipolar cap is two caps in one package, and cannot be biased?[/quote]

The forward leakage in a polar electrolytic is much smaller than the current flow in the reversed electrolytic if it approaches the breakdown knee. So the reversed cap will act like a rectifier and charge up the forward cap reducing the magnitude of the reverse voltage, effectively protecting it from damaging current flow.

Biasing the mid point so both caps are always forward biased eliminates even that minor interaction. I am not aware of measurable artifacts from that, while there may be some very small transient effect.

JR

 

[clintrubber]

[quote author="NewYorkDave"]Could be time for some discreet sharing via back channels. 'Nuff said.[/quote]
For those interested:
http://www.groupdiy.com/index.php?topic=15803

Just give me a yell when it's not under the radar enough.

Bye,

Peter

 

[bcarso]

How odd. The last reply didn't take.

Thanks for that. There is an amazing amount of information in those articles.

 

[clintrubber]

[quote author="bcarso"]How odd. The last reply didn't take.[/quote]
It may have, in the thread of the link above. Might not what you meant though.

Thanks for that. There is an amazing amount of information in those articles.

My pleasure. With all those scan-meisters here around I'm glad I could do something in return myself one day.

Regards,

Peter

 

[bcarso]

Ah yes it went into the other thread.

 

[gnd]

Peter, great collection of articles on caps. Thank you.

I noticed in section of polar electrolyitics, that biasing them with DC actually increases distortion, actually just 2nd harmonic. Did I get this properly?

It is interesting to see, that SSL biases all dual polar caps from +18V, via 1M resistor. Is this increasing 2nd harmonic distortion? 2nd harmonic is the musical one, is it? So this would give some pleasant coloration to circuit. What do you think on this?

 

[bcarso]

I'm becoming convinced that people have used biased electrolytics* and shunned bipolars based on theory. And the theory is seductive and plausible. It just happens that (probably) with the double-foil integral construction bipolar 'lytics, it is incorrect. At least, based on measurements by the likes of Bateman, it is incorrect for minimizing distortion.

If one prefers the sound anyway in a given case, perhaps it is due to liking some 2nd. Perhaps it is due to the second harmonic at one stage cancelling the opposite polarity second in a later stage. Can't argue with what someone thinks sounds good.




*No one argues of course that allowing significant reverse-polarity bias on a polarized electrolytic is a good thing. That gives one distortions (and d.c. leakage) that are easy to hear and to measure. I'm referring here to the bias at the center point of two series-connected back-to-back polars in a bipolar coupling situation.