Subsonic filter options

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Jimmy154

Jimmy154

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Joined 2002
#1
Here are links to three different subsonic filters:

SUBSONIC FILTER - Circuit Diagram - Forum - SeekIC.com

Subsonic / Rumble Filter for Phono preamps and Sub-Woofers

Subsonic Filter

I would want for the -3 db point to start at around 18 Hz, I think, and I'm not sure the last one does. But then again the last one does say that it operates between 12-15 Volts, are they all like this? It is important to me since I will want to wire this probably where my head unit is in my car. Will the "safety" resistor the second link recommends be sufficient to send the right amount of current to this circuit? Also I looked on digikey.com (not sure if this is the best place to get these parts) and they had 113 different kinds of TL082 OP amps and I don't know which one to get. Now that I think about it I don't know what resistors or capacitors to get either lol 😀

If the second one can run from 12-15 Volts I would like to make that one, I suppose. Only thing I don't know is what the downward "hashed" arrow means under the 100k resistor. I think it means ground, but the circuit already has a ground, so I guess it's meant to be grounded to something else?
 
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#3
I have been trying to figure out what a split supply for the past hour, but it's not going well for me.

Is there anything that will work that I can do myself? I have noticed that Fmod sells some subsonic filters that plug into RCAs, can I make ones like this myself?

Guess I found it: http://www.t-linespeakers.org/tech/filters/passiveHLxo.html

Looks like it won't achieve the slopes I was looking for though (24-48 db/octave).
 
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#7
I don't know if this will help your situation, but its worth a mention. The TC962 chip, from Microchip, will create a +/- supply from a single supply. Yamaha uses it in one of their bass guitars to get +/- 9volts from a single 9-volt battery. You could use it to create your bipolar supply.

website

TC962.pdf

An externally hosted image should be here but it was not working when we last tested it.


Note: The above schematic is derived from the Yamaha schematic which actually uses the older version chip. (TC7662, or some-such.)
 
#8
I don't know enough about electronics to know if that Yamaha schematic would work the way it is at 12-15V. I actually don't even know why I need it, to create a split supply whatever that is, right?

The 12 db/octave passive low level cross-over looks like a simpler (but less effective) solution, if only I knew what my amps input impedance is or how to measure it.
 
#9
To summarize, I would like to build this subsonic filter, for my friend's car: Subsonic / Rumble Filter for Phono preamps and Sub-Woofers or a similar one. But I don't know what if the circuit two posts above is all I need to make this work. The input voltage would be 12-15 volts from the car battery. I would just tap the radio (head unit) power supply, I suppose. Will this work?

I can read most schematics, but that's about it. My knowledge of electronics is fairly limited, as you probably can tell. I think I could make this work with some help, but should I just give up and go with the simpler passive low level subsonic filter?
 
#12
The chip data sheet says its good up to 18-volt output, but you'ld need to up a couple of those cap values. Honestly, I don't think I'd mess with this method if you don't have a little more electronics experience. I haven't even tried it myself yet.

If you can live with a simple 1st order filter, why not just do as they show here:High-pass filter - Wikipedia, the free encyclopedia

That will give you -6db / oct.
 
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#13
Yes, I read the chip specs, that it had an output of 3-18V. I thought, with my limited electrical knowledge, that I need higher Cap values for higher output, but didn't know what value and what else needed to be changed.

I guess I will go with this 12 db/octave filter: Passive Line-Level Crossover once I figure out my amp's input impedance. I am waiting from a response from Boston Acoustics, since I don't know of an easy way to measure this spec.
 
#15
richie00boy said:
A split supply is one that has positive and negative power rails as well as ground/0V. You could look at project95 on the ESP website.
Click to expand...

Project95 creates a -12V and ground and the +12V input to this circuit would also act as an input to the project99 circuit? Then all I would have to do is limit the current to this circuit (or both circuits?) from my car wiring with some resistor(s)?
 
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