Sub help!

[adie]

When I switched on my old B&W ASW1000 sub last night there was a not so lovely hum. Checked plug- ok. Hum at speaker inputs (which is how I've been running it). Hum when I ran fingers over the inputs, except 1 of the black ones.
What to do? With exceptionally humid conditions of late I thought that may be an issue. Having noticed that the hum had decreased  the longer I fiddled, I left sub in middle of the room at full volume with music playing softly,as I had some other urgent stuff to take care of . When I moved it back to its usual spot at usual setting (+-1/4 vol, crossed over +-45Hz),  I noticed that the sub's output had decreased along with the hum, so that even at full volume it was still not performing much.

Have taken the electrics out and  my more tech proficient colleague has cast his eye over it and unplugged bits so that I can attempt reflowing the board with his soldering equipment. Before I start tho, does anybody have any sound advice (pun intended). Everything looks well intact, though he wants to examine the volume first.

You may gather I'm somewhat technically challenged. Warwick isn't so fire away please!

[JimGore]

Hi Adie,

The is very strange.  When last did you use the sub?

I am wondering whether the power supply filter caps are not causing this - they may be dry.

Regards,
Ian.

[adie]

Thanks Ian,

I use the sub almost daily.I've never had a hiccup, never driven it hard for more than a few seconds.
 I had moved it the previous day to another plug outlet, since I felt I had too many components running where it was (new plasma tv).
Warwick is pleased with your deduction as that was his thinking. I've shown him some of your work so he's happy to be keeping such exalted company. He still wants me to check for dry joints first.
Bugger!
Newbie with a soldering iron- dangerous... Best I get cracking. Got friends around on Sat for movies. Got to give them a good show.
I'll let you know how things go.

[JimGore]

Just out of interest - what happens when you put the sub back into the old power socket?

Good luck with the soldering - I know how you feel over there.  Replaced most of the caps in my DAC some time ago, and it took alot longer than I was expecting it to.

Ian.

[adie]

It's the same in the old socket.
Best I solder on then.
 Been tempted to buy another sub in the classifieds with money I don't have. You snapped up the B&W ASW600 tho.The B&W's fine for movies but a tad tardy with music.
There's an old AR 12" for sale here in Durbs but I doubt that would offer any improvement.
 If I knew what i was looking at on the circuit boards etc., I'd probably be modifying as we speak. Why are my tech friends so busy when I need them??

[adie]

So...
Piqued Warwick's interest and the plan of action now is to get bigger caps and bigger triacs-he showed me what/where they are- in the hope that it will improve performance. He said it worked a treat on his car amp.
Question. He's not sure if it's worth getting bigger triacs as the performance (when its performing) may be an acoustic design issue. Any suggestions?

[---------]

Been tempted to buy another sub in the classifieds with money I don't have. You snapped up the B&W ASW600 tho.

He is using that sub for his bedside radio when many of us had far better uses for it!!

[JimGore]

Yip, that is correct.

I will post some pictures later this evening 

Ian.

[adie]

Question. He's not sure if it's worth getting bigger triacs as the performance (when its performing) may be an acoustic design issue. Any suggestions?
[/quote]

JimGore (anybody)- any advice? Apart from slightly bigger caps, what about the triacs?

[JimGore]

I would be careful of changing anything in the amplifier circuit without knowing exactly what is currently in there, and why.  Not everything can be swopped out directly - you may be opening a can of worms.

Rather just check that everything is still working well, and change out the big electrolytic caps in the power supply.  That may very well improve the overall sound of the subwoofer on its own.

Regards,
Ian.

[adie]

Thank you Ian.
Won't open that can!

Regards,
Adrian

[ludo]

There are preciously few amps that have triacs in them at all. Cartainly no car amps that I know of. If you suck equivalent/improved parts out of your thumb you will most likely have a fire soon.

Click through the links here , the service manual is in there. Warwick should have a look at it.

[adie]

Thanks so much Ludo.
Loving this forum.

[adie]

  Happy to report all systems working hundreds. reflowed the power circuit board (didn't get round to the pre-amp board) and replaced those caps- at a mere R30 each. Thanks for all the help.

 I run my home theatre system using the VA amp via pre-outs from the AV receiver for the front speakers and sub. My cd player runs directly to the VA amp. I've been running speaker cable from my Valve Audio amp to the sub and have felt it to be a bit slow.
If I send signal from my cd source via RCA to the amp and via coaxial to the AV receiver and then from the AV receiver via sub out, then signal from the sub back to the Valve Audio amp, would I get a faster/better response?

[JimGore]

Glad you have everything up and running again!

If you use an RCA cable for the signal, the quality may be slightly better but it won't do much if you feel the sub is slow - that will be a characteristic of the driver and cabinet combination.

Regards,
Ian.