[McGuyver]

Good morning everyone! I stumbled upon this forum looking into possible options for my DIY subwoofer retrofit I was working on, and found it very useful, so I joined! As my first post I pose a question to those audio / electronics gurus out there.

I have picked up an older Acoustic Research AR 108PS 8" Subwoofer and replaced the amplifier board with a Velleman Discrete 200W mono amp as the existing one was toast. After switching out the Amp, the sub played only as a loudspeaker, so I added a PASSIVE low pass filter rated for 50Hz. Since I had installed said items, I get alot of woofer extension / movement, but very little sound. The amp board gets really hot after about an hour of use... Does anyone have some ideas to how to get my Sub thumping properly? I can provide pictures and whatnot soon. Thanks for the help in advanced!

-Nick

 

[McGuyver]

Interesting, well as far as I know, there is no high pass built into the amp. It is not a plate amp btw, it was an amp board with heatsink only. I reused the existing power supply & speaker / enclosure.

Its a real frankenstein subwoofer right now, but I was using it as a project to try seeing as it didn't work before anyhow. If I add the high pass, how do I adjust it? Sorry for the noob question(s) I still new to this and learning as I go.

Also, the low pass filter has a 188uF filter cap with a coil inducer. I do not know the h rating of the coil but the filter wasn't rolling off at thte freq. I wanted, so I changed the 188uF to 3300uF and thats when I got the huge speaker extension but almost no sound.

 

[McGuyver]

I understand using such a high filter cap without knowing the results can be bad, I can change it back without issue, but the sub still plays like a loudspeaker only slightly muffled with the 188uF cap in place. Will this high pass filter aid in making this speaker work the way it is supposed to? I will post a few pics shortly to show what it is like now, to help paint the picture.

 

[McGuyver]

I do not have any specs for the existing speaker other than it is 4ohm rated for 220Wrms. The enclosure is small, ported down firing.

 

[McGuyver]

I can probly get a Mic, would a PC mic work?

Edit: I got a few pics to show you my citcuit.

http://img507.imageshack.us/my.php?image=wiringscheme.pdf

Note that the wiring scheme is not accurate, the LFP is inline with the speaker.

 

[McGuyver]

Alright, I will have to take it apart and measure it, good suggestion, thanks.

 

[McGuyver]

New Input

First off, thank you everyone for all your help and ideas thus far, they have been helpful.

So far, I got the subwoofer frankenstien working! yay2 I swaped the 3300uF filter cap with the original 188uF NP cap, and hooked the sub back up matching the polarity of the wires... low and behold, the sub played sound!

The only problem is, the amp get really hot still after about 30 minutes of play, and the sub isn't nearly as loud as I was hoping it to be... The speaker is rated at 4ohm, which would make the amp output rated for 100W. I do have a 47k variable potentiometer on the board for volume adjusting, could that be limiting the input to the speaker? Or do I need something else in there?!

Please any input is greatly appreciated and welcome!

-Nick