Repairing B&W AS6 subwoofer with burned plate amp (have schematics)

N

Numex

Audiophyte
I recently inherited a B&W AS6 powered sub (100W 5 ohms) and it doesn't work. When I power on with no other connections, it emits a loud hum. When connected to my receiver, it doesn't respond to any input.

I took off the back panel to look at the amp and there's obvious scorching on the PCB used to connect the transformer and the driver. The other components appear fine (transformer is clean, fuse is intact), so hopefully it's only this circuit that needs fixing. I have no way of knowing if the driver is okay as I don't have any way of testing it.

BW-AS6-3.jpg BW-AS6-4.jpg

I have the schematic for this sub and have marked the components that are within the burned area in the attached image. Visually, none of the components themselves appear obviously bad (resistors aren't burned, capacitors aren't bulging, diodes look clear), but I have no way of confirming their real state without getting some tools. The PCB seems to be the worst off as I can see burning through the layers when held to a bright light.

Bowers_and_Wilkins_AS-6_service_manual_Page_5.png

I have a couple options and hoping some of you can help advise. Should I:
  • diagnose the circuit and replace damaged components? Is it even worth it if the PCB is damaged? What are the chances the printed circuit still being usable? Keep in mind that I don't currently have tools to diagnose but willing to invest a bit as a learning experience.
  • replace the whole plate amp all together with something like the Dayton SPA250? (Note: someone else did a similar modification and it seems to work). It's not too expensive, but will undergo CFO scrutiny.
  • should I look into converting to an external amp instead and keep the cabinet and driver?
In the meantime I've emailed B&W parts to see if they have this circuit available (doubtful after almost 20 years).

Any input appreciated!

Update:
B&W replied and said they don't stock replacement parts for the sub anymore and referred me to Encompass as a possible place to find a part. Searching Encompass comes up with nothing relevant.
 
Last edited:
TLS Guy

TLS Guy

Audioholic Slumlord
I recently inherited a B&W AS6 powered sub (100W 5 ohms) and it doesn't work. When I power on with no other connections, it emits a loud hum. When connected to my receiver, it doesn't respond to any input.

I took off the back panel to look at the amp and there's obvious scorching on the PCB used to connect the transformer and the driver. The other components appear fine (transformer is clean, fuse is intact), so hopefully it's only this circuit that needs fixing. I have no way of knowing if the driver is okay as I don't have any way of testing it.

View attachment 41701 View attachment 41702

I have the schematic for this sub and have marked the components that are within the burned area in the attached image. Visually, none of the components themselves appear obviously bad (resistors aren't burned, capacitors aren't bulging, diodes look clear), but I have no way of confirming their real state without getting some tools. The PCB seems to be the worst off as I can see burning through the layers when held to a bright light.

View attachment 41703

I have a couple options and hoping some of you can help advise. Should I:
  • diagnose the circuit and replace damaged components? Is it even worth it if the PCB is damaged? What are the chances the printed circuit still being usable? Keep in mind that I don't currently have tools to diagnose but willing to invest a bit as a learning experience.
  • replace the whole plate amp all together with something like the Dayton SPA250? (Note: someone else did a similar modification and it seems to work). It's not too expensive, but will undergo CFO scrutiny.
  • should I look into converting to an external amp instead and keep the cabinet and driver?
In the meantime I've emailed B&W parts to see if they have this circuit available (doubtful after almost 20 years).

Any input appreciated!

Update:
B&W replied and said they don't stock replacement parts for the sub anymore and referred me to Encompass as a possible place to find a part. Searching Encompass comes up with nothing relevant.
I had a look at the circuit. As is usually the case those burnt components are effect and NOT the cause of the failure. If you replace them, they will burn right away. Those switching power supplies are a nightmare to diagnose and repair. So my advice is not to try.

Now that is a ported sub and will require no Eq.

So you can buy a different plate amp. Or better leave the current plate amp alone and put speaker terminals on the enclosure, directly connected to the driver, and then buy an external amp to power it.
 
N

Numex

Audiophyte
I had a look at the circuit. As is usually the case those burnt components are effect and NOT the cause of the failure. If you replace them, they will burn right away. Those switching power supplies are a nightmare to diagnose and repair. So my advice is not to try.

Now that is a ported sub and will require no Eq.

So you can buy a different plate amp. Or better leave the current plate amp alone and put speaker terminals on the enclosure, directly connected to the driver, and then buy an external amp to power it.
Thanks so much for your reply!

There are so many external amps to choose from which is really nice. It gives me a bit more flexibility in terms of budget and availability compared to plate amps.

Thanks again.
 
N

Numex

Audiophyte
I thought I'd follow up on my original post and share what I did in case it helps others in a similar situation.

After determining the plate amp was blown, I went down a long rabbit hole into amp replacements.

I started at looking at Dayton (APA150, SA100), OSD SMP100, and Behringer (KM750, A500). My research lead me to car amps and using a computer power supply. Finally I settled on looking into cheap Class-D amps widely available on Amazon.

I went with a cheap "100W" TPA3116D2 amp board by Douk Audio / Nobsound for $11 (Amazon link). This amp doesn't have crossover, but my Yamaha receiver handle that for me.

I also got a Monoprice RCA to 3.5mm adapter for $5. I already have an unused 19V laptop power supply for it.

AS6-amp-01.jpg AS6-amp-02.jpg
AS6-amp-03.jpg


I'm in a bit of a 3D printing kick right now, so I ended up making a custom case for the board that used the existing B&W AS6 amp screw holes.

While I was at it, I also decided to plug the ports with some custom printed caps. :)

AS6-amp-04.jpg
AS6-amp-05.jpg


For $11, the amp works surprisingly well. It's definitely good enough for movies and video games, and is a step up from my previous 10" powered sub. I have the volume dial on the amp dialed to 1/4 and I find it blends nicely without being too obvious.

All-in it cost me about $20 total for the parts and materials. The Nobsound amp won't be as capable as more expensive amps, but for fixing a sub on the cheap, it definitely works.

Hope this helps someone in the future.
 
TLS Guy

TLS Guy

Audioholic Slumlord
I thought I'd follow up on my original post and share what I did in case it helps others in a similar situation.

After determining the plate amp was blown, I went down a long rabbit hole into amp replacements.

I started at looking at Dayton (APA150, SA100), OSD SMP100, and Behringer (KM750, A500). My research lead me to car amps and using a computer power supply. Finally I settled on looking into cheap Class-D amps widely available on Amazon.

I went with a cheap "100W" TPA3116D2 amp board by Douk Audio / Nobsound for $11 (Amazon link). This amp doesn't have crossover, but my Yamaha receiver handle that for me.

I also got a Monoprice RCA to 3.5mm adapter for $5. I already have an unused 19V laptop power supply for it.

View attachment 42296 View attachment 42297 View attachment 42298

I'm in a bit of a 3D printing kick right now, so I ended up making a custom case for the board that used the existing B&W AS6 amp screw holes.

While I was at it, I also decided to plug the ports with some custom printed caps. :)

View attachment 42299 View attachment 42300

For $11, the amp works surprisingly well. It's definitely good enough for movies and video games, and is a step up from my previous 10" powered sub. I have the volume dial on the amp dialed to 1/4 and I find it blends nicely without being too obvious.

All-in it cost me about $20 total for the parts and materials. The Nobsound amp won't be as capable as more expensive amps, but for fixing a sub on the cheap, it definitely works.

Hope this helps someone in the future.
Very creative! Well done.

As a matter of interest, why did you plug the ports?
 
N

Numex

Audiophyte
Very creative! Well done.

As a matter of interest, why did you plug the ports?
Thanks! Your feedback on my initial post was very helpful.

I plugged the ports based on the idea that it can tighten the sound but honestly I can't really tell much of a difference plugged or unplugged. So it's mostly cosmetic at this point, but does help keep the dust and Nerf darts out of the housing.
 

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