Subwoofer Power Supply Problem

[EugeneC]

Signed up to say thanks to all those who contributed to this thread for the past 15+ years. I was experiencing a constant hum with my subwoofer, and while the plate amp was not the one described in here, it appears that the power supply PCB used by the Woofers by Bob Carver Dominator Model D-10 uses the same (or extraordinarily similar) PCB. The board in this case is labelled JUNIOR V1.2 POWER SUPPLY

One of my two caps looked slightly bloated, and it matched the regularly discussed 1000uf 25v ones in this thread. I replaced both on my board, and no more hum!

Including some pictures in case they can help others in the future. Especially for others who have Bob Carver dominator subwoofer amps that might not be aware that this thread could help.

The bloated cap:



The Junior v1.2 PCB with the caps in question circled in blue:



The bottom side of the PCB with the solder points for the caps in question circled in blue:



Replaced caps:


The Woofers by Bob Carver Dominator D-10 Subwoofer Amp

[EricBJN]

Re: Subwoofer Power Supply Problem

Hi to everybody,

This is just to thank you: I replaced the 6 caps that were very bad and my sub is working fine now.
This forum is great !

[thatscappy]

Re: Subwoofer Power Supply Problem

Okay so I got one of these and the guy offhandedly mentioned that there was a bit of a tone when starting it up. I tried it out and it was playing what sounded like a real tone from a synth pretty loud. So I found this forum and bought 2 1000uf 25v capacitors to replace in the unit. They were definitely bad looking. I replaced them and started it up and, well, the tone is now gone. But unfortunately it looks as if it's still not working. So now I am wondering, what's next?

[seabrook]

Re: Subwoofer Power Supply Problem

A quick success story:

I just replaced the six highlighted power supply capacitors (47 microF, 470 microF and 1000 microF) and now the AC hum is gone! After several years of being sidelined and nearly being tossed my ULW-10 has risen from the ashes like a Phoenix!

Thank you all, thank you!

[audiodane]

Re: Subwoofer Power Supply Problem

Greetings. I also have a humming UFW-10 that's been sitting on my kitchen table for the last 4 months waiting for dissection (finally started humming after about 8 years). I finally had some time to look into it this weekend. Just found this thread today. I've submitted to Emotiva Audio (formerly Jade Labs) where the original amp design originated from, for a schematic and ideally a PCB layout as well, if they have it. If I'm allowed to share, I will do so. My hum is also only when certain RCA's are attached. For example, an iPod doesn't exhibit the problem because the iPod doesn't have a fixed ground reference, it's just an electrically-floating battery powered device. Anyway, I digress. My caps do not exhibit any visual signs of damage (no bulging or vented tops), but I'll be interested in removing them to see what their bottoms look like, based on Bob's post. I'll post back when I know more. I have two as well, and while the other is not humming (yet), I'll likely perform the cap replacement on both while I have all the tools out and setup.

In the mean time, I thought I'd reply on a few others' posts.

It's not going from standby to "on", which it should do if it sees a signal on the LFE input.

One of my UFW-10's has developed a bad RCA connection. Resoldering the taps on the inside of the amp didn't help, so it must be some corrosion within the female portion of the connector. These amps are designed to go into "on" mode immediately after turning on (well, there's about a 5-10 second delay between applying power and the amp going "live"), and then going into standby after some amount of time (tens of minutes, not seconds) without a recognized signal. Try all your RCA inputs immediately after applying power. Also make sure you have a known good RCA signal.

I'm a new member with a busted UFW-10. Mine makes no sound at all. Has anyone tried modding one to use an outboard amp with the existing crossover & such? I have an old pro amp that would work well. Thanks!

There are a few fellows that have done this, yes. I can't recall all of them at the moment. A few used to hang out over at Chase Home Theater (formerly Tweak City Audio). There was also talk about an updated woofer at some point, though not enough people were interested to make it reality.

A fellow gave me two of these Onix UFW-10 subwoofers because of the hum.

Man I wish I had your friends...

Thanks for the great pics, Bob!

My thought mehind using the DVOM on the cap was this....On the face of the voltmeter, the cap test happens to be the same knob position as the Ohm check.

I realize your problem is solved now, but can you post a pic of your meter? On many meters, if the ohm-check is one color and the cap-check symbol is another color, there may be a button that swaps between the two functions. That's how my Fluke 189 operates. Turn the dial, hit the button, and boom you're in cap-check mode.

cheers,
..dane

[999999999]

Re: Subwoofer Power Supply Problem

^^ Additionally, while I don't know if it is the problem, if your 2 large caps on that board were bad too it could cause this.

[999999999]

Re: Subwoofer Power Supply Problem

^ Use a multimeter to probe the power supply board, checking that the voltages are doing what is expected/tolerable ranges. Also check that all your solder joints are good and no caps are in backwards. Do you feel this problem is one that is persisting, even if it were overshadowed by the prior problem, or is it an entirely "new" problem?

[nutty08]

Re: Subwoofer Power Supply Problem

Nevermind, I figured it out from the pics above. I have a new problem after replacing the 6 caps mentioned above though. I started with the very loud hum problem that started suddenly in the middle of the night. Now, after replacing the caps, I just get a "popping" sound, maybe ~120hz or so, with mild in/out movement of the woofer. Putting signal on the inputs does not change this and I get no music/sound from the woofer. Any ideas?

[nutty08]

Re: Subwoofer Power Supply Problem

This is an admittedly embarrassing question, but I just replaced all the caps on the PS as described here, but since I took it apart 3 weeks ago, I can't remember where the subwoofer posts go! Dumb mistake I know, but does anyone have a picture with the sub still wired in, or can described where they go. Thanks
-josh

[pcrx]

Re: Subwoofer Power Supply Problem

Hey, New to the forum - an AVS regular though... I just ordered up a new Dayton amp for this same sub with the same problem... I am going to dig open my amp and see if I can replicate the successes others have had here before installing a new amp.

[Bob in St. Louis]

Re: Subwoofer Power Supply Problem

Done.

Number Two is finished, and works perfectly.
Looking at the time since my last post, that's how long it takes to fix one of these. Of course it's always faster the second time you do something, but in reality it's an easy repair.

$6 to fix two subs with an MSRP of $1200.

Rock on dudes.
Great thread. Thanks to ALL who have posted.

Bob

[Bob in St. Louis]

Re: Subwoofer Power Supply Problem

SUCCESS!

I removed the old caps and found the bottom of one of them was a little discolored. Looks like some "juice" had leaked out and corroded the metal electrical lead.
In the picture, are four caps, it's the one on the far right.

I replaced them with the two on the left. Note the temp ratings.

The sub is dead quiet with no hum, no buzz. In fact, it's so quiet that I thought I left something disconnected, as it was almost "too" quiet.....

....until you feed it some music, then it ROCKS!

So there's one subwoofer fixed, I've got one more to go. Not bad for $5.76.

[Bob in St. Louis]

Re: Subwoofer Power Supply Problem

OK, gotcha.
Of what I understood of your post, I am incapable of performing.
What I didn't understand.....well......there we have it. haha

Thanks Mr. Nines.
I do believe I'll replace the caps this weekend and post the results.
Good point about the POTs. I've got some of this stuff to clean all of them.

Thanks!
Bob

[999999999]

Re: Subwoofer Power Supply Problem

Yes as the cap charges it should appear as a rising resistance until it reaches the peak voltage the meter uses, but even a defective cap that isn't shorted could reach a peak resistance value. Your meter's manual may describe a test involving the timing of charge to determine the capacitance for a large value cap (but I don't know if it includes one this large) but I would not be comfortable assuming anything about ESR without an ESR meter or test jig meant to measure that.

If the severe movement of the driver is while a signal is applied it could be some kind of interaction from unstable power. 60/120Hz hum isn't a steady signal, it does sound harsh but fairly repetitive.

I don't know what the rest of the sub looks like. Other things that can cause noise include a leaky transistor, it could be a mere TO92 sized, 6 cent part causing this. Without an amp schematic it may be beyond the scope of a forum post to try to guesstimate that, but briefly with no signal to the amp if a transistor isn't being biased much if any and the output is higher than it should be per the hFE spec on its datasheet, it is suspect.

Basically you just probe all around the amp looking for signal or power irregularities, if the power amp stage is a chipamp IC instead of discrete, or at least a transistor driver IC with transistor output pairs it becomes more easy to troubleshoot. The other option is to just start replacing anything inexpensive, since a lot of parts can be replaced for a few cents each. The adjustment dials (POTs) on the back complicate things a bit, I'd also turn all those back and forth several times to see if there is a POT wiper contact issue, after a while the springiness of the wiper may decrease and/or the grease can harden effecting the contact.

[Bob in St. Louis]

Re: Subwoofer Power Supply Problem

I thin I see where you're going with the headphone test, however I don't have a pair I could use, much less cannibalize. neat sounding test though.

My thought mehind using the DVOM on the cap was this....On the face of the voltmeter, the cap test happens to be the same knob position as the Ohm check. knowing that, also tells me that as soon as I drop the leads across the cap, the 9volt battery inside the Fluke would be charging the cap. So the digital bard graph on the Fluke that races from near zero ohm into the Mega ohms would be the cap charging
-- am I wrong on that? --
So then, if I'm correct, the cap now hold a DC charge. That's when I could switch the meter to the DCV setting.....and that's when I'd get the .3volt reading.

Although, I could be damaging caps and my meter based on my cockeyed lack of real intellegence.

Since I bought the two caps, and have a long weekend ahead of me, I may install them, put it all back together and see what happens.
If I do, I'll let you know the result.

Bob

p.s. I feel this was a great thread until I came along and derailed it with my lack of basic eletrical knowledge.

p.s.s. By the way, I'm not hearing a 60Hz, or even a 120Hz noise. This is a harsh buzz, with intermittant severe movement of the driver involved. At times (on a bad day) the driver can move what loooks like nearly an inch.

[999999999]

Re: Subwoofer Power Supply Problem

^ I was under the impression all that meter could test was small value uF capacitance, or charge time for an estimate of higher value capacitance. I'm otherwise unfamiliar with ESR testing on that meter. That it held the voltage tells you it isn't shorted or extremely leaky electrically, but I don't think the resistance test is valid (I could be wrong)... also, replacing with a high quality, low ESR 105C capacitor, the ESR should measure lower than the cheapy caps they used even if the originals were functionally within specs still. I wrote a bit more in my prior reply after your subsequent one, it seems my posts are never really final drafts...

[Bob in St. Louis]

Re: Subwoofer Power Supply Problem

Thanks Nines!
So was my little DVOM test a valid one?

I've love to perform a A/B test of a mod such as the one you describe, but lack the finances. As it is, I'd just like to get these working so my son can rattle the house and I have an excuse to yell at him. haha

Bob

[999999999]

Re: Subwoofer Power Supply Problem

^ I'd go ahead and replace all those electrolytic caps (besides the largest higher voltage ones, for now), especially if your hum sounds like the typical 120Hz double line frequency type which does tend to indicate insufficient power supply smoothing... actually, knowing others have them failing and having the board out already I might replace them even if there wasn't any noise present yet.

lol, then again being a tweaker, I'd probably reverse engineer the PSU board subcircuit for that zener/transistor regulated portion and replace it with +/- linear regulator ICs... idealizing, not knowing if there'd be an audible difference which is hard to know unless someone has two units like you do so they can A/B test one after the other, with and without any modifications.

If you have a headphone you don't mind cannibalizing, you could take the drivers and wire them to probe-like tips and listen to the preamp stage output on the sub's amp board to determine if you hear this hum. If it's already present it is probably due to the caps we're discussing, but if there is no hum yet, not until after the power amp stage (through the sub speaker NOT the headphones since it's too high a level for headphones) then it would probably be the largest high voltage capacitors to blame.

Another option is setting multimeter to AC and measuring ripple on the rails of both the low and high voltage subcircuits but I don't know what threshold values would constitute pass or fail for this.

[Bob in St. Louis]

Re: Subwoofer Power Supply Problem

999999999,
Thank you (and all) for the replies.
I did not check the caps. I blindly chose these two to purchase based soley on the information I found on the net (here included).
Granted, there's nothing better than a solid working knowledge about what your'e working on, but hey.... <insert nervous laugh here>

Now you have me worried I'm about to do all this for no reason.
I grabbed my Fluke83 and selected the 'cap' setting. With the leads on the caps terminals, the ohms went from near zero to into the Mega ohms.
Then I selected the DCV range and checked the cap and it reads about 0.3 volt DC.....steady and holding.

I did the same with the new cap, and the results were the same.
If what I did was a valid test, then you are indeed correct and these caps are good.

None of the caps have visual signs of defect, yet the symptom I have is the same all of these units exibit.

Thanks all! Happy Thanksgiving!
Bob

[avanilla]

Re: Subwoofer Power Supply Problem

I replace all six of these for posterity (not including the two large ones). All is well and I am enjoying my "new" old sub.