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Battery Biased Passive Crossovers

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Posted on January 20, 2010 at 00:38:02
Synthsayer
Audiophile

Posts: 113
Location: Lexington, KY
Joined: December 20, 2009
 Does anybody have info on how to use battery biasing for passive crossovers?

JBL's Project Everest DD66000 uses this method and I was wondering how it is done and if it really makes a difference.

It appears to use a 9 volt battery connected to capacitors in the mid and tweeter sections of the crossover.
"Ad Astra Per Alia Porci", - To the stars on the wings of a pig: John Steinbeck

 

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RE: Battery Biased Passive Crossovers, posted on January 20, 2010 at 03:11:42
quirck
Audiophile

Posts: 213
Joined: December 23, 2006
 If I apply that to my network the battery will be empty in no time.

 

RE: Battery Biased Passive Crossovers, posted on January 20, 2010 at 06:05:39
SLM
Audiophile

Posts: 321
Joined: March 2, 2002
 Thats why you put a capacitor both sides of the battery.......

The original capacitor is replaced by two capacitors in series of double the value and then a battery with a large value bias resistor connects from the junction of the capacitors to the negative lead on the network .

 

Incorrect..., posted on January 20, 2010 at 06:16:29
JLH
Audiophile

Posts: 742
Joined: June 25, 2000
 The battery is tied between two capacitors and a high value resistor therefore there is no direct current path for the battery to discharge. The capacitors block DC current and the high value resistor raises the AC impedance so attenuation doesn't occur through the battery. The battery will last for years. The only discharge path would be through the capacitors due to leakage current, which will be extremely small.

To install a battery biased network perform the following:
For each series capacitor (high pass) in the network, replace it with two capacitors of twice the value and series wire them together. ( i.e. replace a single 10uF cap with two series wired 20uf caps) Tie the + terminal of the 9V battery between the two capacitors. Next connect a 1 or 2 Meg resistor to the - terminal of the 9V battery. Lastly, connect the other end of the high value resistor to the return leg of the network.

And yes, it will make a difference with high efficiency speakers. The battery biasing lifts the low level single away from the zero crossing point of the capacitor's dielectric, thus increasing detail that would be otherwise lost.

 

RE: Incorrect..., posted on January 20, 2010 at 12:06:19
freddyi
Audiophile

Posts: 3852
Joined: December 6, 2001
 is the important function to keep conditions above that threshold and not worry about the battery voltage being in the range of the amplifier's peak voltage?
Karlson Evangelist

 

RE: Battery Biased Passive Crossovers, posted on January 20, 2010 at 13:46:33
coffee-phil
Audiophile

Posts: 1444
Location: Shingle Springs CA
Joined: January 7, 2010
 I am guessing that what he is doing is replacing the non-polarized electrolytic capacitors (which are in essence back to back polarized capacitors) with back to back polarized caps and biasing them to avoid the possible non-linear effects of the electrolytic capacitors. 9 Volts strikes me as not enough since 9 Volts peak is about 10 Watts in a 4 Ohm system.

If I were going to replace the caps in a crossover I would just use oil filled paper or film caps and not bother with the biasing. The cost of real capacitors for crossover frequencies above 800 Hz should not be enough to bother trying to make electrolytics better behaved. For sub-woofer frequencies I can see why someone might do this.

I am glad you posted this. It had never occurred to me before. The radio in my BMW is getting funky and I am toying with the idea of replacing it. New radios now typically come with 20 W / channel BTL amps which is more than sufficient for my main speakers. I want to cross to my sub at 100 Hz which calls for nearly 400 micro-farads. In a decent capacitor this will be huge and cost a fortune. A couple of 800 microfarad electrolytics back to back with bias is starting to seem like a decent solution.

Phil

 

RE: Incorrect..., posted on January 20, 2010 at 14:02:14
djk
Manufacturer

Posts: 6135
Joined: June 17, 2000
 Idealy the bias voltage would be in excess of what the total signl is, but that is not really practical.

It is enough to shift the zero-crossing point away from 0 in the music. What we are trying do do is keep the discharge of the charge stored in the dielectric fron discharging where there should be silence in the music (nothing to cover up the noise).

 

There is likely to be an optimum bias level for each capacitor., posted on January 20, 2010 at 14:02:55
Al Sekela
Audiophile

Posts: 9169
Location: Northern California
Joined: February 18, 2002
 I've done this with cables but not crossover capacitors.

Too much bias makes the cables microphonic. I expect the same thing would be true of capacitors. You just have to experiment to find the optimum voltage.

Another trick is to isolate the batteries from the circuit with high-value resistors (say, 50K) and bypass with small caps. The battery cases are steel and will interact with the audio signal if connected directly to the circuit. Be sure the batteries are well isolated against acoustic vibration.

 

RE: Incorrect..., posted on January 20, 2010 at 14:10:01
freddyi
Audiophile

Posts: 3852
Joined: December 6, 2001
 is it sometimes worth trying two (or more) 9v batteries in series? - does R remain at ~2meg with stacked battery? Is one battery for two - three nodes ok? are regular clip on leads adequate for this application?
Karlson Evangelist

 

Yes to everything, posted on January 20, 2010 at 14:12:46
badman
Reviewer

Posts: 8801
Location: Tustin, CA (Orange County)
Joined: March 10, 2001
 And, 9V is usually much more than you need to avoid the zero crossing.



Bass is supposed to sound big. 6.5" is not a woofer size.


 

This is high efficiency!, posted on January 20, 2010 at 14:14:15
badman
Reviewer

Posts: 8801
Location: Tustin, CA (Orange County)
Joined: March 10, 2001
 If 9V isn't LOUD you're in the wrong place!



Bass is supposed to sound big. 6.5" is not a woofer size.


 

RE: Yes to everything, posted on January 20, 2010 at 14:25:49
freddyi
Audiophile

Posts: 3852
Joined: December 6, 2001
 how about film bypass cap(s) at the battery to lower end of 2Meg junctions? - if this is good, what value?
Karlson Evangelist

 

RE: This is high efficiency!, posted on January 20, 2010 at 14:46:27
coffee-phil
Audiophile

Posts: 1444
Location: Shingle Springs CA
Joined: January 7, 2010
 You are quite correct. 9 Volts peak into a high efficiency speaker will be loud. Still staying away from the zero bias point of each cap seems like a good idea. I would use at least 18 volts.

Actually your high efficiency reminder brings up another issue. I'm guessing that most of the high efficiency folks would even consider pentode amplifiers as a tiny step above transistors. How can electrolytic capacitors in the signal path even be considered by someone at that level? No sarcasm intended, here but I might even consider solid state devices in my amps but electrolytic caps give me heartburn.
I will use them for coupling and bypass where the impedance of the cap is low relative to the circuit it is in at any audio frequency applied to it. Using them even for the sub crossover in my car is a big step for me and without this biasing approach I would not consider it.

Phil

 

RE: Incorrect..., posted on January 20, 2010 at 16:49:54
PakProtector
Audiophile

Posts: 12363
Joined: May 14, 2002
 -----To install a battery biased network perform the following:
For each series capacitor (high pass) in the network, replace it with two capacitors of twice the value and series wire them together. ( i.e. replace a single 10uF cap with two series wired 20uf caps) Tie the + terminal of the 9V battery between the two capacitors. Next connect a 1 or 2 Meg resistor to the - terminal of the 9V battery. Lastly, connect the other end of the high value resistor to the return leg of the network.

If you put the battery on the return leg I think you can use one to bias multiple capacitor pairs( for example across two channels ).
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

I hear ya!, posted on January 20, 2010 at 19:36:09
twystd
Audiophile

Posts: 2723
Location: Austin,Texas
Joined: December 9, 2000
 The only place I use the "evil" electrolytic is when I'm forced to make a DC filament supply.

twystd

 

Schematic Diagram, posted on January 20, 2010 at 22:49:25
djk
Manufacturer

Posts: 6135
Joined: June 17, 2000
 .

 

Caps with and without bias voltage, posted on January 20, 2010 at 23:04:38
djk
Manufacturer

Posts: 6135
Joined: June 17, 2000
 Without:

Photobucket

Tantalum with two different voltages:

Photobucket

 

RE: Battery Biased Passive Crossovers, posted on January 21, 2010 at 06:09:55
Synthsayer
Audiophile

Posts: 113
Location: Lexington, KY
Joined: December 20, 2009
 WOW!!!

I have been following this thread since posting it the other day.

The responses are nothing less than amazing.

Thanks again DJK. You are THE MAN!!!

Thanks to you too, PakMaster.

Thankfully, I have enough high quality, 1% tolerance caps on hand to do this. It looks like a trip to the nearest Radio Shack for some 2.2 Meg Ohm resistors and a handful of 9 volt battery connectors/holders will get me started on this experiment.

It should cost me less than 5 dollars U.S. and I'll be able to get to work.

As far as isolating the batteries because of their metal casings, would it suffice to wrap them in something as simple as good quality electrical tape or dip the metal portion in something like PlastiDip which is used for applying rubberized grips for hand tools? http://www.plastidip.com/home_solutions/Plasti_Dip

Thanks again everybody. If I had the chance I'd buy all of you guys a few rounds of beers.

Have a great day :-)

Synthsayer
"Ad Astra Per Alia Porci", - To the stars on the wings of a pig: John Steinbeck

 

I wouldn't bother, posted on January 21, 2010 at 13:35:27
badman
Reviewer

Posts: 8801
Location: Tustin, CA (Orange County)
Joined: March 10, 2001
 There's not a lot of upside to be had. You certainly shouldn't bypass the resistor with the cap, as it'll create a high-pass filter, which in most of these instances, will roll off the top end acting as a shunt.



Bass is supposed to sound big. 6.5" is not a woofer size.


 

RE: I wouldn't bother, posted on January 21, 2010 at 14:46:46
freddyi
Audiophile

Posts: 3852
Joined: December 6, 2001
 didn't mean short - just bypass battery leads - probably not needed
Karlson Evangelist

 

RE: Battery Biased Passive Crossovers, posted on January 21, 2010 at 15:57:29
Alpha Al
Industry Professional

Posts: 2958
Location: N. Carolina
Joined: February 16, 2004
Contributor
  Since: December 3, 2015
 This may be a little off-topic here, but I remember that technique was used in some high-end recording consoles (Midas and Amek, specifically).

They used back-to-back electrolytic caps for coupling.

In most of these, the opamps operate from +/- 18V supplies. The bias voltage was about half of the rail voltage, and was applied through a high value resistor to the mid point of the two caps.

If the bias supply stopped working, the console would still work, but sounded noticibly more distorted.



 

Typically referred to as Charge Coupling...*, posted on January 21, 2010 at 21:52:15
eso
Manufacturer

Posts: 7842
Location: Long Beach, CA, USA
Joined: March 15, 2001







They were a carnival of American decay on parade, and they had no idea of the atrocity they had inflicted upon themselves." Henry Chinaski

 

RE: Battery Biased Passive Crossovers, posted on January 22, 2010 at 02:15:26
Duomike
Audiophile

Posts: 223
Joined: November 14, 2003
 Avantgarde is charging the tweeter cap in their omega models with dc but they transform the amp voltage up and then convert to dc. they have told me that they have experimented with various voltages and found voltages much higher than 9 volts to sound best. the cap they are using is a special version of mundorf silver gold with 3 leads, one for the battery charge.
I can't say how much improvement the caps biasing brings to the sound. all I can say that a teflon v-cap in my omega duos sounds a LOT better than a charged mundorf cap.
Duomike

 

RE: Battery Biased Passive Crossovers, posted on January 22, 2010 at 03:56:46
quirck
Audiophile

Posts: 213
Joined: December 23, 2006
 As I see it this makes sense for polarized electrolytics.
For film caps I suspect the effect being very subtle. Besides that you need the double amount of caps and double the value as with two caps in series the net value is halved.
I would rather use a better caps like Russian PIO or Clarity Caps.

 

Thank you!, posted on January 22, 2010 at 14:34:09
Craiger56
Audiophile

Posts: 5571
Location: San Jose CA
Joined: April 3, 2002
Contributor
  Since: December 29, 2003
 I'd like to assemble some battery-biased high-pass crossovers for use with subs, could you say where I might find more on this? A schematic would be a huge help.

Thanks, Craig

 

A special skill, posted on January 23, 2010 at 18:13:38
SLM
Audiophile

Posts: 321
Joined: March 2, 2002
Being able to tell what something will sound like without hearing it is indeed a special skill but fortunately common enough around the asylum.

The battery biased crossovers improve detail and tone dramatically. Even with better quality caps

later

S

 

RE: A special skill, posted on January 29, 2010 at 04:23:35
Synthsayer
Audiophile

Posts: 113
Location: Lexington, KY
Joined: December 20, 2009
 Battery Biased Crossover; Project completed.

This was really easy to do and after a week of listening here are my observations:

At low volume level detail in mids and highs is definitely improved. Chimes, Bells, Cymbals; all have a much improved quality. You can here the difference between the types of cymbals. Big crash, small crash, china's, splash. Bells and chimes are extra clear. Hi end out of mids and tweeters every bit as defined as with Dynaudio/Focal project I had used in the past.

Environment sounds are especially improved. Rain, crickets, birds chirping; all dramatically improved. I was watching a TV program on the History Channel about 'Bigfoot in KY'. I live about 15 minutes from where the program was filmed. My pet's ears were really perking up with some of the 'nature sounds' material these guys from Texas A&M were using to lure the alleged creature. BTW: I have lived in the Bluegrass area of Central KY all my life and never heard of any 'Sasquatch' here until that program:-) Other people I know say they have heard of it, but...

Back to topic: Overall I would consider the Battery Biased Passive Crossover a success. I would be interested to see what it would do with a crossover made with ordinary electrolytic caps. I'm not going to the trouble to find out, but it's just a thought.

Thanks again to everybody that helped me with this project.

Have a great day.




"Ad Astra Per Alia Porci", - To the stars on the wings of a pig: John Steinbeck

 

VCapTFTF, posted on February 4, 2010 at 06:55:44
smart845
Audiophile

Posts: 668
Location: East london
Joined: May 24, 2000
 Hi Duomike,

you replaced the 2.7uf Mundorf with a Vcap? and left the battery bias off?

What size Vcap did you use? The 2.0uf is $450!

Smart

 

RE: Caps with and without bias voltage, posted on February 5, 2010 at 21:32:22
A9X
Audiophile

Posts: 36
Joined: September 4, 2006
 Do you have shots of the PP and PS with bias to compare to without?

 

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