how do you convert a passive subwoofer to an active one ?

i have a sony reciever, and it has an active (externally powered) subwoofer output. i recently acquired a set of sony speakers to replace the old ones i accidentaly blew. all speakers connect normaly, except the subwoofer, which uses two bare wires. i need a way to convert this subwoofer, which uses an outboard amplifier, to one with an onboard one. oh, and it has to be for less than $35 , because for that money, i could buy a new one, at goodwill. many thanks !

The most expensive part of any amp is the power supply. If you can find a good used one (preferably 2) to use then you have a great shot at building a decent amp for cheap. Try that Goodwill store for miscellaneous power supplies, maybe even something from a printer. My local Goodwill has a bin for unknown supplies, dirt cheap.

Here's a couple of links to start:
My pertinent thread with link at the Nuts n Volts Forum
Another answer here at Instructables

The amp in question is called a Losmandy amplifier and it is stable from 2 ohms up and flat from 0 Hz to 70 kHz at 0.5% distortion (THD). This particular version (on the right side) will output about 10 watts with the plus/minus 16 volt supply listed.  Here's the fun part: Build 2 of them, wire the inputs normally on the first one and reverse them on the second one, put the speaker between the outputs of them and you now have a 40 watt bridged amp! Bridging gives you 4 times the power, so you have to make sure the power supply(ies) can keep up. Just make sure they can give over 40 watts (apiece, 60-80 would be better).

To make it even cheaper, use a TL082 or a LF353 instead of 2 TL081's. Use side A for the first amp and side B for the second amp (always read the data sheets, they are online).

Hope it helps,
Qa

what you need is any amplifier that matches specs for your subwoofer (Ω ohm resistance)
all you need to do, is plug the subwoofer output of the sony receiver into any input of your outboard amplifier R or L.
then plug your subwoofer into the regular speaker output of your outboard amp, if you plugged the input into a R plug, put your speaker on a R output vice versa
orksecurity6 years ago
The way you convert it to active is to put an amplifier with suitable frequency response and power between it and the receiver.

If you have the outboard amplifier, you've already got what you're gonna get.

If the amplifier is missing, that's the part you need to find or replace.
Buy one, you ain't going to do it for 35 USD

Steve