Question about Altec Lansing FX4021 Computer Speakers

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Altec Lansing FX4021 Control Pad

There is a control pad that inputs through a microphone jack on the subwoofer. It allows me to control volume, bass, treble and turn the system on and off. The control pad is malfunctioning and will turn the system back on after being turned off, will set all the bass/treble/volume levels back to midrange after being turned up. All I need is a replacement part or a similar device from a different manufacturer.

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Posted on Jan 12, 2008


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Is there a way to use the Altec Lansing VS4121 Subwoofer as a stand alone?

Normally these low end systems components that depend on each other and cannot be interchangeable from other system. So if one of the components (sub woofer or right control satellite speaker) breaks or gets lost the whole system is unusable...
I was in the same situation. Got a sub woofer from VS4121 without original satellite speakers. I acquired satellite speakers from Altec Lansing 251 which used same connectors but the internal wiring was different and incompatible out of the box. Speakers are also glued together so it is impossible to open without damaging it. Not to mention there is no service documentation anywhere..
But if you like electronics you can try to make something based on the information bellow:
Altec Lansing VS4121 connector pinout
If you take the male connector (from right satellite speaker) and look at the pins and number them first row from left to right pins 1-3, second row pins 4-7, the bottom row pins 8-9 and the circle enclosure as 0
0 - Ground
1 - Speaker Right
2 - Treble (seems just like voltage control but may need to be confirmed: Min=0V; Max=voltage from Volume control Pin 9)
3 - Head Set Right
4 - Bass signal (not sure what the exact original design is as I have not opened the speaker) But seems like they use 50K potentiometer and some sort of RC low pass filter configuration. When potentiometer is set to Min it is shorted with ground. When set to Max it is taking signal from Right and Left Head Set (pins 3 and 5) combined through some larger resistors and low pass filter.
5 - Head Set Left
6 - Ground for Head set (grounds 0 and 6 seems to be connected in the subwofer but within the right satelite speaker they seem to be isolated with separate leads to sub)
7 - Power ON/OFF. When OFF or head set jack plugged = 0V; When ON and head set jack unplugged = 5V
8 - 5V Power in
9 - Volume (min=0V; max=5V). It seems they use 50K potentiometer but probably anything >10k should work.
At minimum for standalone sub woofer you will need to implement:
- Power On.Off (switch between pins 8,7)
- Volume control (50k potentiometer (probably anything beteen 10k and 50k will do)between pin 7 and 0 with variable output to pin 9
- Bass control - join two resistors R (I used 7k) and lets call this join point A. Attach other ends of the resistors to pins 3 and 5 respectively. Attach 50k potentiometer (I used 10k) between point A and ground 0. Attach Variable pin of the potentiometer to pin 4 (Bass input signal). Attach capacitor C between Pin 4 and Ground pin 0 (I used Electrolytic 1uF with negative end to ground) . Resistor R and capacitor C should make simple passive low pass filter (Google for formula) that should bypass anf frequency higher than 80-120Hz to ground and feed frequencies lower than 80-120Hz to pin 4.
PS: I managed to hack 251 control satellite speaker to somewhat work with VS 4121 Subwoofer but that is another subject. All electronic parts were salvaged from old broken TV so total cost was $0 but took several days of tinkering for speakers that I could buy used for $10-20 :)

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My left import wont work. How can i fix this?

Make sure your plug is inserted all the way and that there is no dirt or residue on it. Also you can open the volume panel by double clicking on the volume logo in the bottom right of the start menu. Make sure the balance slider is in the middle for the main volume control.
If this helps, please rank me.

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Just match the color of the male and female on each end. Plug the audio cable (mini stereo phone plugs) to the PC audio line out (green miniphone jack) to the Powered speaker mini stereo phone audio line input jack (green color jack). You will have to set the volume controls of the speaker control knob and at the PC on screen volume control panel.

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I have this exact Altec Lansing speaker system and I'm currently just using it with my Dell computer. But, I know you don't have to install these speakers to any high powered receiver for good sound quality. The subwoofer has two separate 200 watt RMS combined amplifiers built in for it's single knob controlled dual 6.5" bass drivers and 2-way magnetically shielded satellites, which are amplified together by any source that has an analog or digital volume control. The speakers act as a preamp receiver to any volume or frequency tone level controlled audio source. These input sources can also equalize the speakers receiving input signal for bass, treble or mid-range adjustments. You only need to obtain the proper adapter to hook up all the speakers to your desired component or device. Besides a computer, for example a TV with a variable audio out function or a mp3 player will work. The adapter that i am referring to is similar to what is included with certain 5.1 Logitech brand computer and multimedia speakers specifying gaming console and TV connecting. It has all three color coded 1/8" connector inputs on one end and RCA jack outputs on the other. This can be purchased more easily online then offline at stores such as Ebay for a fairly inexpensive price. However this adapter will not decode true 5.1 surround, but instead give a 5 channel stereo effect. I guess if one was looking for an inexpensive alternative solution to purchasing traditional high end home entertainment audio equipment, the ADA 995s are one of few computer speaker models in my book that can do a decent job.

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I am trying to hookup my AL subwoofer to my existing comp system.Inserting a wire jack into one of the comp spkrs and subwoofer shuts the sound off.?? It is a FMC0034326 Altec Lansings Subwoofer.Thanks.

You can't just do that. Your sound card needs to have a specific jack just for subwoofers. If you plug it into the speakers, the computer recognizes the subwoofer as a pair of headphones and routes all sound through it. Remember, a subwoofer is not a normal speaker. It only allows a frequency of extremely low sounds (a.k.a. BASS) and won't play anything that you would need a tweeter for.

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Control pad broke

Try at ebay, amazon etc...

Thanks Good Luck
Appreciate to rate as "Fixya"

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Need wiring and 9pin connector diagram

Dell (Altec Lansing) A425 Subwoofer Pinouts

This is a standard female DB-9 serial port.
Here are the pinouts.

Pin 1 = Left Speaker Out +

Pin 2 = Left Speaker Out - (Common Ground)

Pin 3 = Left Line In +

Pin 4 = Right Line In +

Pin 5 = Left/Right line In - (Common Ground)

Pin 6 = Right Speaker Out +

Pin 7 = Right Speaker Out - (Common Ground)

Pin 8 = Power A

Pin 9 = Power B

Jumper (short) Power A to B to turn on.
If you want a volume control you need to put one on the inputs. You will buy buy a stereo volume control or potentiometer.
Here is some info on how to do this.


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