Charge Coupled Crossovers

[BTH K10A]

For some years Greg Timbers the designer of JBL's statement speakers (Everest, K2 etc.) has advocated the use of Charge coupled crossovers in both these new JBL's and as an upgrade to older models. The benefits are supposedly to achieve as near a Class A biased crossover as possible.

http://www.lansingheritage.org/images/jbl/specs/home-speakers/1993-k2-s5500/page10.jpg

http://www.lansingheritage.org/images/jbl/specs/home-speakers/1993-k2-s5500/page11.jpg

http://www.lansingheritage.org/images/jbl/specs/home-speakers/1993-k2-s5500/page12.jpg

http://www.audioheritage.org/vbulletin/showthread.php?3555-Bypassed-and-Biased-Capacitors

Has anyone here on the forum tried this theory on other makes of speakers?

[Reid Malenfant]

The benefits are supposedly to achieve as near a Class A biased crossover as possible.
Apologies but this makes no sense :scratch: Class A biasing is down to the quiescent current dissipated in a power amplifier ;) As any crossover network only deals with AC signals there is no DC standing current (or quiescent current).

What the various pictures appear to show is bypassed capacitors with better quality but lower value components. I can't fault that as they do improve things :)

[BTH K10A]

Apologies but this makes no sense :scratch: Class A biasing is down to the quiescent current dissipated in a power amplifier ;) As any crossover network only deals with AC signals there is no DC standing current (or quiescent current).

What the various pictures appear to show is bypassed capacitors with better quality but lower value components. I can't fault that as they do improve things :)

Yes, but my understanding was that a 9 volt dc battery is used to pre "bias" the cappacitors. I don't know if the analagy with Class A is quite correct but reports from JBL owners who have changed their crossovers to this configuration are alway positive. I have also heard a pair of the new DD66000 everests and they were certainly the most acomplished speaker I've listened to.

Below is a quote from another forum.


"Originally Posted by gtimbers
The capacitor biasing is something that has existed for many years. Tube equipment does it automatically since there is usually a large DC offset between stages. Some early transistor amps/preamps had two polarized caps in series with the center point going to ground through a large resistor.

I personally became aware of this technique for speaker systems through communications with Ed Meitner, currently of EMM Labs. He is a wealth of information regarding these "tricks" to help linearize or improve the sound of passive components.

It turns out that the bias trick actually increases measured IM distortion and the higher the bias voltage, the greater the increase. It is not by a great amount, but it is measureable. The sound imporvement (or change) is very rarely perceived as worse and is never linked with a increase in IM distortion. The sonic effect is one of smoothness, increased spaciallity, detail and stuff like that. IM has a muddling or confusing effect so I doubt that this particular steady state measurement is explaining the sound difference either way.

Simply put, we are striving to create a class A situation but as was just pointed out, depending on the bias voltage with respect to the voltage across the capacitor, we may only have an "A" condition up to a particular drive level. So if it makes you happier, consider the change to be class AB, but heavily biased to A. You must also keep in mind that the voltage across the input terminals of the crossover network does not tell you what voltage or current is applied to any individual component. Some parts block signal and others shunt signal so the loading on a particular part is not obvious. For the most part, the caps are well taken care of with 9 volts, even at healthy drive levels. The obvious choice for 9 volts is the small cheap battery and holders that are available. No current is involved so a smoke detector battery and holder is a natural choice.

We did do one system with 18 v (M9500). Certain of the Japanese reviewers thought it was an improvement. I can't personally tell any difference. I am also told on a regualr basis (again by our Asian customers) that the battery must be changed at least every 90 days and that the sound degrades after that. Once again, I have not been able to "hear" any difference after 90 days and the battery is certainly still good for many years from a voltage standpoint.

What playing around I have done with initial application of a battery to a biased circuit (that has not been previously powered up) is that it takes about 3-5 seconds for the soundstage to change. I have tried to measure the voltage level in that time period and it seems that several volts is all that is necessary to accomplish 90% or more of the improvement. Once a circuit has been energized, it is nearly impossible to return it to zero. You have to individually short out each cap and leave them shorted for a while or else they will creep back up somewhat. If you replace the battery with a short and play the system for a while, the caps will start to bias themselves, although not to anywhere near the same degree.

You can take this opinion for what it has cost you. I have been very pleased with biasing for many years. I use it in all applications that involve a capacitor and I have rarely been disappointed. Results may vary so if it doesn't do it for you that is okay too. It cost a bloody fortune to implement as it requires 4 times the capacitance and double the capacitor parts count. The network size gets huge as well. Inspite of this, I have never heard a capacitor type that didn't improve (or change) including the nearly perfect teflon variety."

[Reid Malenfant]

Ah, not class A then but simply applying a DC voltage to the crossover capacitors :scratch:

I'll think on this one, if i remember :lol: I'm bad at things like that :o

Just out of interest did anyone mention the noise floor being lowered? Just a thought :)

ATB ;)

[BTH K10A]

Ah, not class A then but simply applying a DC voltage to the crossover capacitors :scratch:

I'll think on this one, if i remember :lol: I'm bad at things like that :o

Just out of interest did anyone mention the noise floor being lowered? Just a thought :)

ATB ;)

I see, is all new to you then :lol:

I've only heard the one set of speakers that have been charge coupled

http://www.techradar.com/reviews/audio-visual/hi-fi-and-audio/hi-fi-and-av-speakers/jbl-everest-dd66000-673108/review?artc_pg=2

but seeing comments on other forums from those that have tried, I was intriged to see if anyone had tried it on any other brands.

I'm always interested in novel concepts and never worry about sailing off the edge of the world. :sofa:

[Reid Malenfant]

I see, is all new to you then :lol:
Indeed & i can't think of any aspects it could improve :scratch: Except Ever Ready stocks might go up so invest in them :eyebrows:

You can't go round putting DC voltage accross certain capacitors in a crossover as you'll only have an inductor between the DC supply you are supplying & the amplifier itself.... Either the battery or the amplifier won't like it, probably both :eyebrows:

I'd like to see some kind of circuit diagram as well while i'm at it :cool:

[BTH K10A]

Indeed & i can't think of any aspects it could improve :scratch: Except Ever Ready stocks might go up so invest in them :eyebrows:

You can't go round putting DC voltage accross certain capacitors in a crossover as you'll only have an inductor between the DC supply you are supplying & the amplifier itself.... Either the battery or the amplifier won't like it, probably both :eyebrows:

I'd like to see some kind of circuit diagram as well while i'm at it :cool:

Network diagram for the DD66000

http://manuals.harman.com/JBL/HOM/Technical%20Sheet/Everest%20DD66000%20ts.pdf

As far as I'm aware no harm has come to batteries or amps from the above circuits.

Speakers gets good reviews too, but then they should considering the cost. :smoking:

[MartinT]

I see the trick. In each crossover, the 9V is applied to the centre of series capacitors, thus isolated from damaging the driving amplifier. I would love to hear a demonstration of with and without charge.

Come to think of it, I'd just love to hear those speakers. I have a soft spot for big JBLs.

[Barry]

What this technique seems to be doing is trying to compensate for dielectric hysteresis (more often called dielectric relaxation): the momentary delay in changing the molecular polarisation of the dielectric.

However for the dielectrics used in audio capacitors, the dielectric relaxation times are so short that this phenomenon only occurs at very high frequencies (i.e. those corresponding to optical wavelengths).

It's hard to imagine the benefit at audio frequencies warranting the increased component count in the crossover. However one of the strengths of horn-loaded speakers is the rapid attack or preservation of the leading edge of a transient. In that respect such complication might help.

I would be interested to hear a speaker with and without voltage biased capacitors in the crossover.

[lurcher]

I am not convinced you can assume that a battery is not itself capable of affecting the sound. They have a non flat ac impedance, and a noise floor (at least when delivering current). Different types used as cathode bipass certainly have differing sounds.