Altec Lansing 221 Woofer volume control.

[Whosondephone]

The Altec Lansing 221 is a 2.1 (two satellite and one woofer) speaker system. It is one of the best sounding low power speakers I have heard. However it has way to much bass. Most Altec Lansing speaker systems have a bass level adjustment on the sub-woofer. I am going to try either installing one or soldering some 10W resisters in series to the line going to the woofer driver.

They are using the TA8229K:
http://audiolabga.com/pdf/TA8229K.pdf

And the BA5417:
http://rohmfs.rohm.com/en/products/databook/datasheet/ic/audio_video/audio_amplifier/ba5406-e.pdf

It appears to me that the BA5417 is used for the woofer. And they are using a large electrolytic cap to eat up the highs. (purple '>' in pictures)

the through-hole image is flipped.

I'm thinking that it might be best to go with the potentiometer because adding resistance to the crossover may change the crossover frequency. However if it is before the amp it should be fine. (famous last words)

This is quite an ambitious project for me. I'm not sure how to implement a potentiometer right now. I'm beet. Does it sound like I know what I'm doing? Any Ideas or words of encouragement/discouragement? You are wonderful thanks for reading!

 

[Harald Kapp]

Both of the amplifier chips you mention are stereo ones. The BA5417 is probably used in BTL mode (datasheet, figure 7) to output more power to the woofer. In that case pin 11 would be the input pin to the amplifier. As I don't know where teh signal to pin 11 comes from (more specifically what the output impedance of the driving stage is), it is not easy to make a recommendation. The schematic in the datasheet, on the other hand, shows an input resistance of ~30kΩ. Therefore the input voltage can easily be attenuated by a series resistance on the range 0 Ω (zero attenuation) to 30kΩ (50% attenuation) or more attenuation for higher resistances.

Instead of wasting power in a series resistor to the woofer, I suggest you adjust bass level on the amplifier. Try a 10kΩ potentiometer in series with pin 11 of the BA5417. You'll have to de-solder that pin from the PCB and insert the potentiometer between PCB and pin using very short wires, or shielded wires /shield connected to ground). Use the potentiometer as variable resistor only, not as voltage divider, as the pot's resistance together with the input resistance of the amplifier will form a voltage divider.

 

[AnalogKid]

I agree. If you can trace the input back to its source, probably the output of an active filter opamp circuit, then you will get better results and better adjustability if you modify the signal at a low power point rather than at the high power output.

ak

 

[Whosondephone]

You are right on Harald. Sucked the solder off pin 11 and wired in a 500K pot that was lying around. While adjusting the pot it didn't seem to affect the x-over. Unfortunately I was picking up to much 60Hz. This project is going to be a X-mas gift. For the time being I found a 16ohm pot from a speaker in the garbage and wired that in series with the woofer. I won't be able to give it a good listen until tomorrow.


I might just pick up another speaker system for $15 and try the high impedance pot on pin 11 with some shielded cable.


Thank you for the help. I most likely would not have picked up on the BTL configuration.

 

[Blank]

Hey guys, I'm really hoping someone can help me out. I got the system that I'm using for a while now, but when I got it, it wasn't working. after opening it up I realize that the transformer wasn't good so I got a replacement and it started to work. BTW the subwoofer wasn't connected .... So I decided to open it up again an connect them to see if it was work and it is . my problem now is when I connect the sub's I realize that they are very low and there is little bass coming from it ...I tried to connect a different subwoofer to it but got that same results. I also tried the subwoofer on a different system and they work fine ..I wanna know why my subwoofer isnt working properly on my system...side note I'm using a 12v 1.0a adapter instead of a transformer would that have anything to do with why my subs or not working properly...im also thinking of buying a larger watt speaker ...I wanna know what I should do different? Plz help!