Subwoofer Power Supply Problem

[Longbow]

Re: Subwoofer Power Supply Problem

Don't understand what you mean by "linear". I call this a conventional power supply. AC Input --> Power transformer --> Bridge rectifier --> Big filter caps. The big caps are the main filters for the 120 Hz ripple output from the bridge.

[PCBONEZ]

Re: Subwoofer Power Supply Problem

That would be a Linear PS.

[lti]

Re: Subwoofer Power Supply Problem

I still don't see why 160V caps are needed or what the tiny circuit board that the bad cap was on is used for. I also don't see how such small caps were able to filter the power supply for a 350W amp.
I only took high school electronics. The only power supply we built consisted of a transformer, rectifier, and a filter cap (the same design as an unregulated "wall wart" power supply).

[PCBONEZ]

Re: Subwoofer Power Supply Problem

I think you are spinning over a typo.
160v should have been 16v.

Such small as what?
It would really help if you referenced what you are asking about..
.

[PCBONEZ]

Re: Subwoofer Power Supply Problem

It is not at all uncommon to use a higher voltage cap to get better specs for some other parameter.

Mobo voltages are 3.3v, 5v, and 12v.
There is no need for a 10v cap on a mobo - for voltage concerns.
But 10v caps are very common on mobos because 10v caps [for a given uF] tend to have larger cans and the larger cans result in lower ESR [at the given uF].
.

[lti]

Re: Subwoofer Power Supply Problem

Look at the pictures. There are two 2200uF 160V caps. The caps that failed were 1000uF.
I didn't think caps with such low capacitance could filter a linear power supply for a 350W amp.

[PCBONEZ]

Re: Subwoofer Power Supply Problem

Oh I see, you just pulled some random caps no one has talked about of a photo posted a year and 1/3 ago...
No wonder I didn't know what you were talking about.

The 1000uF have nothing to do with the 2200uF.
The 2200uF seem to be on the AC side.

As to 1000uF being enough filtering that depends on the value of the inductor, how many caps there are in parallel, and how many other filters are in the thing.

In something audio it makes more sense to locate additional filters close to the amp circuits on the other boards after all the connections and wire runs than to try to do all the filtering on the power board.
.

[999999999]

Re: Subwoofer Power Supply Problem

From what I see on the picture it is that there are two separate PSU circuits on the board, being fed by different transformer windings for different voltage.

You have a large SIP style diode bridge feeding the two big 2200uF/160V caps a high(er) DC voltage, these are filtering the power rails for the output stage of the amp.

You also have a smaller bridge rectifier right behind the first one, it's the little black round button that has "+ - and HY and RB1" visible. Then you have a couple of filter caps C18/C19, then it looks like a basic zener shunt regulation circuit which charges up C16/C17.

I wrote two separate circuits instead of three because I suspect the two low voltage regulated circuits are actually just positive and negative rails for an opamp or opamp-like circuit on the amp board.

There are lots of ways to improve this power board. The best one is probably to get rid of it and make your own. By making your own you could use linear regulators for the two low voltage rails, use higher capacitance for the high voltage rails, BUT you start running into more and more work since this uses connectors and probably just fits in a certain spot in the cabinet.

[avanilla]

Re: Subwoofer Power Supply Problem

My Rocket ULW-10 has been sidelined for over a year because of a dreadful hum/buzz. Now, thanks to this forum, at least I understand the problem. What I don't have is the knowledge and experience for working on circuit boards. Can you give me a "step by step" procedure? At the moment, the only step I don't need help on is the removal of the screws that hold the plate to the back of the enclosure. Thanks!

[lti]

Re: Subwoofer Power Supply Problem

From what I see on the picture it is that there are two separate PSU circuits on the board, being fed by different transformer windings for different voltage.

You have a large SIP style diode bridge feeding the two big 2200uF/160V caps a high(er) DC voltage, these are filtering the power rails for the output stage of the amp.

You also have a smaller bridge rectifier right behind the first one, it's the little black round button that has "+ - and HY and RB1" visible. Then you have a couple of filter caps C18/C19, then it looks like a basic zener shunt regulation circuit which charges up C16/C17.

I wrote two separate circuits instead of three because I suspect the two low voltage regulated circuits are actually just positive and negative rails for an opamp or opamp-like circuit on the amp board.

There are lots of ways to improve this power board. The best one is probably to get rid of it and make your own. By making your own you could use linear regulators for the two low voltage rails, use higher capacitance for the high voltage rails, BUT you start running into more and more work since this uses connectors and probably just fits in a certain spot in the cabinet.

That makes sense.

[avanilla]

Re: Subwoofer Power Supply Problem

Do you happen to have the part number?

[avanilla]

Re: Subwoofer Power Supply Problem

Oh! I also replaced the 2, 2200uf 160V 85 C with 2200uf 160V 105C Panasonic caps as well.

Would you happen to have the part number for the 2200uf 160V 105c, that is. Thanks.

[al walwala]

Re: Subwoofer Power Supply Problem

Avanilla, I'm sorry the caps were Panasonic caps not Mullard. The big black round cylinders are the caps. They are radial caps, that means they have two lead protruding out the bottom. Look on the side of the cap there will be a color bar which forms an arrow near the bottom. That indicates the lead next to it is the negative lead. make sure when you replace the new cap with the same orientation as the old one (note where the old cap arrow/bar is located). Unsolder the old cap use solder wick or a solder sucker. heat up the solder joint and either wick the solder off or used the solder sucker as you heat the joint. Resolder a new cap into place (note the proper orientation) make sure the solder flows like a liquid around the joint before you stop heating it.

Digi Key P/N: 565-2946 ND

Good luck!

[avanilla]

Re: Subwoofer Power Supply Problem

Panasonic it is. Thank you!

[jski04]

Re: Subwoofer Power Supply Problem

Just fixed mine! Thanks a lot for the information guys!

[Chubber]

Re: Subwoofer Power Supply Problem

I did the dirty deed too, swapped out all 6 caps and fired it back up. The hum was gone!

Unfortunately, it's still not working, but I don't know if it's because something else is broken or I'm not feeding it the right signal. It's not going from standby to "on", which it should do if it sees a signal on the LFE input. It also won't kick off into "calibrate mode" or generally make any sound at all. But that's a topic for another thread.

[sfox]

Re: Subwoofer Power Supply Problem

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!

[999999999]

Re: Subwoofer Power Supply Problem

sfox, being a different amp and possibly different problem you should probably post a new forum topic.

If it has a passive crossover, yes you could just substitute a different amp. If active, you'd need that portion of the circuit and the supply for that portion of the circuit to still work, then take the (input to the amp stage) output from that to your external amp.

Personally, I think I'd try to fix the amp in it instead... you didn't mention what is wrong but if it can be fixed with reasonable effort it seems a waste not to do so, unless it wasn't performing to your requirements and you feel the separate amp will do so.

[sfox]

Re: Subwoofer Power Supply Problem

My bad, thanks for the help, many nines!

[Bob in St. Louis]

Re: Subwoofer Power Supply Problem

Hey all.

A fellow gave me two of these Onix UFW-10 subwoofers because of the hum.
Lucky me.
Didn't take long to find this very helpful forum, and thread. Thanks to all for posting. I'll be ordering the talked about replacement caps very soon.

The one item I thought was interesting, was that even though it's the same model number subwoofer (UFW-10), and the same model number power supply (ULW-10), and the same (apparent visual) circuit topology, I find it very interesting our "bells and whistles" are much different.
Plus, the large red wire shown in a previous post is in a different location than mine is.

Here's a few photo's of the back (outside) of my amp, the (inside) of the amp, the power supply (with model # showing) and a close-up of the power supply itself.
Note; the location of large red wire.

I think I'll only be replacing the two blown caps (C78 and C66)
I'll order two of each cap, obviously, one set for each subwoofer.

I'll keep in touch and let you know what happens.
Bob

p.s. "sfox", contact me. What are you going to do?