Single supply sub filter

Car amplifiers have a DC / DC converter which generates symmetrical positive and negative rail voltages for the amplifier and symmetrical positive and negative rail voltages for the lower level op-amps in the signal path. You're not trying to build a single supply sub filter but a sub filter black box which has a 12V input. Inside this box you will need a DC/DC converter. This could be as simple as a switched capacitor filter circuit which can take 12V and give you 12V and -12V. This is only possible here because you are not going to need more than a few milliamps of current. The filter itself can be a Linkwitz-Riley 24dB/ octave filter. It is quite commonly found on the web. has some examples listed there. Try that first.



2002-04-12 4:41 am
An DC to DC converter is a swithing power supply, so it is hard to design. Switching power supplies has a higher ripple than linear power supplies. Op-amps can handle 12 volts in single supply mode, but the ground level rises half the power supply or 6 volts. palesha, you could use two linear voltage regulators for a voltage of +/-9 volts.


2002-04-12 4:41 am
BeanZ, gave little bit of information such as filter order and web site address.

I forgot to post

Bill Fitzpatrick:
Don't listen to BeanZ unless you want to waste your time.
No offense, but this sounds like a **** who said this. Next time try skipping, "Don't listen to ______ unless you want to waste your time." Nobody likes to read those sentences.;)
Electro is right that a true DC/DC converter with a high frequency transformer and assciated magnetics and feedback loops is difficult to design but that is not necessary in your case. The converters I refered to were some of the switched capacitor types from LinearTech and Maxim. They use charge pumps to generate a negative voltage from a positive one. So you will end up with a positive and negative voltages. These ARE a DC-DC converter because you are turning a DC voltage into a different one . No magnetic components are needed though, just a few external components to an IC and it is easy. This will give you the benefit of keeping your true car ground reference and the benefit of using good dual rail op-amps for the filter. But for $30 the Soundstream sounds like a true deal. Look up the types of power parts that I was referring to, they are called "Charge Pump Inverters" or "Charge Pump Regulators" for future reference
I am curious and I would like to see how you to take a 12V supply and get +/- 9V out with linear regulators...? It's not going to happen. If you use single supply op-amps, the signal will be clipped on the negative sides because the input signal swings lower that your ground.
I'm very surprised!!!

Palesha, do this:
- open your poweramp and find the + and - rail.
- depending on the power, you will find voltages from 12 to >60V.:att'n:
- get 2 wires (one for each rail), and use the cheap 7812 and 7912 to stabilise the voltage.
- Here you have an 12-0-12 volt supply.

Now use a simple low pass filter as Bill Fitzpatrick said.

A NE5534 with 2 caps and 2 resistances will make an excellent subwoofer filter circuit.

This did help?


Pedro Martins :cool:
That is one way to do it but there is one major issue here. If the voltage input rails are going to be 20V-60V then the linear regulators are going to dissipate a huge amount of heat. The NE5534 will draw a comparatively large amount of current for an op-amp, something like 150mA or so. If the voltage rail input is 30V then: You will be dissipating 2.7W in each of the linear regulators. A good size heatsink is required. Not huge but a good size. It will get warm. However, it is probably undesirable for Palesha to open the amplifier and dig into the innards. It can be done but go for it if you are up for it. It could be fun!!!

Well, you need a 4 section pot for a single channel 4th order SallenKey filter. But why do you need to vary F3? Just pick the correct F3 in the first place and use fixed resistors.

As a side note, we were faced with the problem of an 8 section pot to change F3 for 2 channels simultaneously. The distributors for Bournes won't sell the parts for ModPots separately but they will put one together for you if you want to pay almost $80. In other words, they have you by the balls. I was so irate I emailed them back and asked why they wanted to screw me. No reply, of course.

We solved the problem by building our own 8 section pots for a cost of less than $2.
I have got one IC BA 15218 which is single & dual supply and also low noise. TI claims that their TLC O7x series is also very much suitable for single supply operation. Comments about the above two IC's is welcome. Herewith attached specs. of BA 15218 for reference.
Mahendra Palesha


    40.6 KB · Views: 32