Dead subwoofer? Don’t pitch it, convert it to passive!

[Wayne A. Pflughaupt]

When I picked up a used 60” Pioneer plasma TV a couple of months ago, the seller threw in an Energy 8” sub he didn’t need. Worked out well, as I was short a sub. The Paradigm sub we had in our bedroom system had been temporarily promoted to our living room system until we can hopefully get a Monolith sub later this year, so the Energy took its place in the bedroom system.

Well, low and behold, the little sucker up and quit working a week or so ago. I really didn’t want to waste any money replacing a temporary sub, so, I decided to “passive-ize” it. I had everything I needed on hand – banana binding posts I could install in the amplifier panel, and a spare Carvin amp with one channel dead that I had retired from my bass guitar rack. (Every Carvin amp I’ve ever owned blew the “A” channel with light-duty usage. Maybe that’s one reason they’ve gone out of business.)

The biggest pain was taking out the eighteen metric socket-head screws (8 for the speaker, 10 (!) for the amp panel). It took more time to get the screws in and out than it did to do the actual internal modification!

The driver showed 5 ohms on my VOM, which verified that it was good. It certainly looks beefy, but it has a plastic frame. That’s probably sufficient for an 8” speaker, though…

Once I got the amp panel out, I could see this was going to be an easy fix. All I did was cut the speaker-level input wires at the amplifier board, and spliced them into the two wires that connect from the board to the speaker. Thus, either speaker-level input is now a direct connection to the original driver. Didn’t even need to install a binding post!

Voila, we now have a passive subwoofer! Dropped the little amp into my bedroom rack, rated for 75 watts RMS, and we’re in business again. (The Energy specs say its amp was rated for 60 watts RMS).

I used to think that speaker-level inputs on a sub were cheesy. I’ll never think that way again! They’re quite handy if you ever find the need to “passive-ize” a dead active sub.

Here’s the little dude hard at work.

Regards,
Wayne

 

[Matthew J Poes]

That’s a nice little writeup.

I actually have a sub with a working amp I want to convert to passive. It’s a DIY job that I want to power off one of my DSP pro amps rather than its built in amp.

 

[flat4]

Good work and nice way to repurpose a sub and amp that would have been sent to the graveyard.

Thanks for the write up!

 

[1_sufferin_mind]

What a creative fix! You may just have helped save a paper-weight Velodyne. Thank you for sharing.

 

[Tonto]

Great little project Wayne, thanks for sharing.

 

[PGS4038]

I've just replaced the faulty amplifier in my B&W ASW750 12" 1000W sub with a Hypex Fusion FA501 plate amp. After setting up the amps built-in DSP eq to suite the room with REW and Hypex's own software, its as good if not better than the original amp. Setting up was a little time consuming and I'm awaiting an aluminium mounting panel to adapt the new amp onto the cabinet, but I'll get there . (anchoring it to a plank is only temporary so no complaints about aesthetics please )

 

[Travis Ballstadt]

I attempted this with a 15" AR sub I had picked up for free that someone was throwing out. I didn't have a home amp capable of driving it worth squat, so it went back into the garage for another year. Then it spent a year or so in the back of my old BMW X5 when I put a new amp into that system, and it worked great. Then I hit a deer and I took it as a sign. That sub was hauled away with the X5 and never came back.

I miss that X5.

 

[1_sufferin_mind]

Now that’s what I call “subdued”

 

[Wayne A. Pflughaupt]

Well, it happened again – the Velodyne SPL-10RGB subwoofer I’m using for my computer audio system bit the dust. A little checking around I determined it was not going to be easy or cheap to replace it with something comparable. Thus, I decided to do another conversion.

This one was a little more of challenge to “passivize” than the little Energy sub was.

Removing the back panel revealed that the banana plug connections were underneath a “second story” circuit board, as shown by the yellow arrow in the picture below, which was held in place by a number of nuts and threaded studs, shown by the orange arrow.

Removing the upper board showed that these banana plugs were soldered directly to the circuit board, unlike the Energy which had wiring from the plugs to the circuit board that was easy to splice into. You can see the banana plugs’ four solder points in the picture below, indicated by the yellow arrows. The two inner ones are the negative terminals, the outer two the positive terminals.

I soldered the wires from the driver directly to those points on the board. I also used a razor-blade box cutter knife to cut through the circuit board traces, thus fully isolating the banana plug terminals from any other circuitry, as seen by the orange arrows pointing to the white hash marks.

Lastly, I snagged a little RAMSA WP-9055 amplifier off eBay to power the sub for a measly $100 shipped. So, that was the entire expense of the conversion – way less than the $3-500 it would have cost for something of comparable (small) size and quality, even going with something used.

The RAMSA only puts out maybe 100 watts @ 4-ohms, far less than the 1000 or so watts the Velodyne amp generated. However, I only use my computer system for music and YouTube videos played at moderate volumes, so the RAMSA is more than enough.

So, I’m back in business on the cheap with another “passivized” subwoofer!

Regards,
Wayne A. Pflughaupt

 

[Wayne A. Pflughaupt]

It should be noted for those wishing to convert a good-quality sub for home theater use, I originally went with a more-powerful pro-audio Crest Audio FA901 amplifier. Ultimately, I couldn’t live with it. Its cooling fan was quiet from a wind-velocity standpoint, but it emitted a high-frequency whine that just drove me nuts. Granted, I was really close to the amp, which is under my desk with the sub.

That was when I re-evaluated my use and decided a low-powered amp would serve my low-demand music needs just fine. The benefit there is that the little RAMSA does not have, or need, a fan.

The moral of the story: A serious HT sub conversion will require a suitable pro-audio amp. Choose your amp carefully and make sure there is a generous return policy, as it may take some “trial and error” to find one that’s quiet enough.

One really quiet yet powerful amp I can recommend from personal use is the Crest Pro xx00 series. I have one in my bass guitar rig, and it is super-quiet, fan-wise.

Regards,
Wayne A. Pflughaupt