dc to dc power supply

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I have a pair of 31 band mono eqs for my truck and the problem with them is the power supply. The power supply makes noise that passes through them into my amps. Is there a way to filter the power supply and if not could someone post me a schematic for a 14.4 volt power supply. I dont know much about power supplys but I can follow a schematic. I dun know if this makes a difference but the power supply is 11 to 15 volts dc input and a regulated 14.4 output with positive and negative outputs.If anyone has any suggestions please post them. I couls make a schematic of the power supplys they currently have if it would help to solve my problem. Any help would be appreciated.Thanx.

Noise of the power supply in vehicles is probably caused by the alternator which doesn't supply a very neat DC-voltage. You can simply solve this problem by placing a cap between the positive and negative supply rails. This capacitor should flatten the voltage peaks which causes the noise.
There's maybe one problem left: the value of the cap is depended on the current through the load, but in a car every device (or load) is placed in parallel with each other; so the cap should be huge!!!

So I recommend to use "voltage regulators"; have a look at:
(look under: "Adding an IC Regulator to a Wall Adapter or Battery")

best regards,


Thanx for the advice but the noise isnt caused by the altenator because the noise is present with the vehicle off. I tried a seperate voltage source from my truck thinking it might be a ground problem but the noise was still present. The power supply is cheaply made prolly out of crappy components. Any other help and or suggestions would be appreciated. TIA.
These eqs you're powering, do you know how much current they draw? I assume from what you say that they require a +/- supply. If you could run them from a slightly lower voltage (say +/- 9V) and they don't draw much current (less than say 50 mA) you could use a combination of a linear regulator and a switched-capacitor inverter to produce the negative supply.
Check out the Maxim site for ICs that do this:
There's lots of app notes and stuff there to keep you busy for a while.
Alternatively, you could try to just clean up the supply you've got. If you have access to a scope, check if you can see what the noise looks like.
What might be the best way to clean it up is a capacitance multiplier, see project 15 at:
it's not a steady frequency. kinda a medium pitched hum with a slight poping or clicking sound...I think I need new power supplys for the eqs. I'm having problems finding books on dc to dc power supplys. I think I could make some better than the ones I have now if I could find a schematic or a book or something to go by.
well, given the data you've provided, the current supply is a switching buck/boost regulator with non-inverting output for the +ve supply rail and inverting output for the -ve supply rail. i wouldnt try to change the nominal supply voltage for the device. You'll probably have some degree of difficulty in producing a suitable power supply due to the difficulty in obtaining a suitable high frequency inductor.
I would first try the simplest test with a cap between the + and - rails. If you want further isolation you could put a small resistor before the cap on the + rail which will then decouple the rest of the stuf in the vehicle. If you want you could also place a diode in series with that resistor so that you won't have tha cap supply current to stuf that's not supposed to get it after switching the power off. For the EQs the power consumption shopuld be low which would then call for a resistor somewhere around 2.2 to 4.7 Ohms or so as a first test. Price for this would be anything from 0 to a couple of bucks depending what's in your scrapped eqiupment drawer...

MrUnsocial said:
I think I could make some better than the ones I have now if I could find a schematic or a book or something to go by.
The first thing you'll need to do is find out the voltage and current requirements of the circuit. We can't suggest circuitry for you unless we know the requirements.
You won't find many books. There are lots of application notes, however, read those instead.
Besides the references I gave earlier, also try the Linear Technology website. They have some classic application notes on switching regulators.
Thanx for all the help guys. The voltage of the circuit is 14.4 and current is less than 1 amp. I have tried putting a cap across the input power and it didnt help.. the diode in series with the + seemed to help for a little while but the noise came back. Any comments or suggestions are welcome. thanx again, you guys have been real patient with me and I appreciate it. There are a lot of good suggestions I will try and if you have anything to add feel free.
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