DC-Biased Capacitors: Fact or Fiction

[luvdunhill]

Has anyone played with biasing capacitors that normally only see AC with a small amount of DC? I know some commercial speaker manufacturers have been doing this for a while (Vandersteen, Infinity, JBL, etc. comes to mind) usually using a battery and often accompanied by fancy marketing speak ("Charge-Coupled Linear Definition Dividing Network"). There is a lot of ink spilled on the subject, but what do you say?

[nattonrice]

I had a search around and found a couple of papers but nothing specific...

What properties of the capacitor is dc bias meant to enhance?

[mypasswordis]

Wow, I never thought about DC "biasing" a capacitor before. I looked up and found an original document from JBL on it and there seems to be at least a little bit of horseshit/random audio voodoo mixed in there but I guess could potentially work.

http://forums.klipsch.com/forums/storage/3/860249/page10.jpg

http://forums.klipsch.com/forums/storage/3/860250/page11.jpg

http://forums.klipsch.com/forums/storage/3/860252/page12.jpg

He's comparing it to biasing transistors into Class A but it doesn't seem like a good analogy, since the transistor is an active device that needs to switch on if it isn't biased into class A whereas a cap is, well, passive, and "biasing" pretty much just means charging it all the way up with DC unless I'm missing something here. The piezoelectric effect seems to me like random horseshit/voodoo unless you're using ferroelectric dielectric caps, and even then I don't know how much the capacitor would actually "move". Who knows though, I haven't done the measurements, but neither has he.

Needing double the capacitance and double the caps (which means double the ESR?) seems like a bad trade-off for supposedly getting rid of whatever effects dielectric absorption has, though I think I saw some other design with just a 2.2M resistor? Have you thought about implementing a Zobel network or altering phase?

[Looser101]

I had a search around and found a couple of papers but nothing specific...

What properties of the capacitor is dc bias meant to enhance?

Linearity?

The Sound of Capacitors

This in particular...

The Sound of Capacitors - Electrolytics

[Bidoux]

Is this the point of C1, C2 and R8 ? BF862 Preamp - diyAudio

[kevin gilmore]

mikhail used this technique in the squarewave...

all poly/teflon caps exhibit some piezo electric effect.

and electrolytics just don't belong in the audio chain.

[mypasswordis]

mikhail used this technique in the squarewave...

all poly/teflon caps exhibit some piezo electric effect.

and electrolytics just don't belong in the audio chain.

Mikhail was a genius!

That's cool to know, so I guess it wasn't BS. Anybody with poly/teflon caps want to play around with this?

[Nebby]

Mikhail was a genius!

But the question remains.....is he at a MarkL level of genius?

[guzziguy]

I'm sure that Mikhail brought in a lot more money than Markl has dreamed of. So you have the question backwards IMO.

[Nebby]

You are absolutely correct, though I was just trying to link that "genius" comment to the one made here. My attempt at humor simply fell flat, that's all

[guzziguy]

That's OK, I think that he has it backwards too.

[kevin gilmore]

Mikhail was a genius!

That's cool to know, so I guess it wasn't BS. Anybody with poly/teflon caps want to play around with this?

Not exactly.

In fact mikhails amplifier was a fully dc coupled amplifer

with a HUGE amount of dc drift over time and temperature. And the drift was not necessarily positive or negative,

and it was well over 1 volt or more. So mikhail had to put in an output cap, and since he did not know the direction

of the drift, he had to put in 2 caps back to back in series. But then because of the caps he picked, and the

time it took them to actually charge up, he biased up the center pin, so that it did not suck so bad

(meaning no bass for the first hour or so) and then told people to keep it turned on all the time.

Serious clusterfuck, every part of the amp.

http://gilmore.chem.northwestern.edu/dinglepower2.jpg

Edited July 14, 2010 by kevin gilmore

[jcx]

biasing back-to-back electros is a very old recommendation - past its "use by" date

Bateman's "Capacitor Sound" articles showed lower measured distortion from bi-polar Al electros which have full thickness oxide grown on both foils

ploarizing V will increase microphonics - just like a condenser microphone