car subwoofer filter 48 db/octave

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which one is better?

v11.png


or

v21.png


... tkx
 
Both of them will not work. There are 2-5 volts ripples of charging current present in car power. Relatively to the source ground this virtual ground will consist half of potential of those ripples. Shortly, it will be equal to applying 1-2 volt noise to the input of your crossover.
To avoid power supply noise the only option is the switching supply with both voltages taken from same transformer and ground galvanically isolated from car power.
If you don’t mind to tweak with it, you can build your own PS. There is pretty much of controllers to do it. Someone already did similar work.
http://powersupply88.com/bipolar-15-v-and-5v-from-car-battery-supply.html
Or you can use manufactured DC/DC converter with bipolar output voltage.
3-5 watt will be sufficient. On cars with old and sulfated battery, the charging voltage can achieve 20-25 volts and you need in converter with max input voltage rated higher those numbers.
 
You are moving in right direction. Look in simulator how much of current consumes your circuit with applied 50 and 1000 Hz signal of maximal amplitude. I think it should be no more than 50mA. Of course you don’t need in such powerful switches and thick wire. The 0.8mm wire is overkill.
One more project http://sound.westhost.com/project69.htm
Number of turns for primary winding depends on frequency, voltage, core cross-section area and ferrite permeability.
Taking into account that there can be more than 12 volts, for this core and 30kHz frecuency , I’d put 50-80 (the more the better) turns of primary winding
Minimal wire diameter 0.3-0.4 mm for primary winding, and 0.25mm for secondaries
 
Do check how much takes every single amp.
Something is strange here.
The maximum I expected is 2.5mA DC + 1-1.5 mA(AC) per one amplifier.
12 mA are taken by R1,R4.

Quite conservative equation to determine wire diameter is
D=0.7*sqrt (I) .
For 150mA secondary coil you need in 0.28-0.3 mm wire,
Primary with central tap can be wound by same wire diameter.
 
Typical dc consumption is 1.4 mA per amp.
I think it is just wrong numbers in model for LTSpice.

By the way, in order to get best noise performance R22 R34 resistors must be excluded.
Source impedance is unknown, but being assumed 600ohm,the feedback loop for U1 U2 U9 U15 must include resistor with nominal which is equal to the input resistor (you use in series with capacitor) plus 1.2kOhm.
 
Yes, exists model for almost same chip( except audio ratings) -Motorola MC33001 and it has this value corrected.

The knowledge you are getting while building own converter is valuable thing but it will take time and resources before you can build reliable and efficient device.
You must know, disrelec.com they are represented in your country, and possible you have access to others suppliers.
DC/DC converters are not too expensive and very compact. There remains risk for 9 - 18volt converters because of the possibility of higher voltages in charging system.
I can suggest TMR 3-2422 WI, it is most efficient at 24V but still stable at 10-12V too.
17.5 EUR + taxes aren’t too much for such cute piece of electronics.
 
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