Increasing Filter Capacitance in Subwoofer Amp

[Monjul]

I have a 20 year old Kinergetics SW200 subwoofer/crossover amplifier that currently uses two 10,000uf 75v storage caps. I wanted to refresh these and was interested in increasing the storage. How high do you think I can increase this? Can I double it to 20,000uf each or should I play it safe and maybe try two 15,000uf caps? I appreciate any advice offered. Thanks.

[event horizon]

You should be able to double it without a problem, if the newer components fit then Bob's your uncle The only thing i'd do is pay attention to the rectifier or bridge feeding the capacitors, possibly upgrading that will pay dividends & might well be needed as the current pulses into bigger caps will be heavier. It'd make things a tad more efficient & possibly prevent the demise of the rectifiers/bridge that is already fitted You probably won't gain a lot as the limiting factor might well be the transformer, but it certainly won't do any harm.

Nothing like building things like a tank

[Monjul]

Originally Posted by event horizon

You should be able to double it without a problem, if the newer components fit then Bob's your uncle The only thing i'd do is pay attention to the rectifier or bridge feeding the capacitors, possibly upgrading that will pay dividends & might well be needed as the current pulses into bigger caps will be heavier. It'd make things a tad more efficient & possibly prevent the demise of the rectifiers/bridge that is already fitted You probably won't gain a lot as the limiting factor might well be the transformer, but it certainly won't do any harm.

Nothing like building things like a tank

Thanks. It's a huge toroidal xformer so I'm thinking it will work well.

Hopefully the rectifier can handle it. I assume that if it can't, it will blow fuses at power up?

Also, I'm new here so I have to ask... who's Bob? Does he sell caps?

[event horizon]

Originally Posted by Monjul

Hopefully the rectifier can handle it. I assume that if it can't, it will blow fuses at power up?

Also, I'm new here so I have to ask... who's Bob? Does he sell caps?

Sorry, "Bob's your uncle" is an old english saying meaning "it's not a problem".

You might pop a fuse at startup but you are more likely to blow the rectifier if it can't handle the pulsed current through it, that's why i mentioned a possible upgrade. The transformer should be ok as it will have a certain primary & secondary resistance so will to a greater extent self limit the output current it can supply. Be careful of the rectifier though, it might well experience peak current pulses that could short the diodes & then the input fuse will definately blow.

[mickeymoose]

"who,s Bob?"
That was funny. A line for Emanuel in Fawlty Towers.
Sorry Monjul, I too once had to negotiate English, you are doing OK.
Modern electrolytics are much smaller and a larger capacity will fit readily into your space available. Make sure the new caps are the 105 Deg. C type.

[Monjul]

LOL. Got it. Uncle Bob is good....

I took a look at the rectifier and it's a Fagor FB2502. The datasheet can be found here.

FB2502 Datasheet pdf - 25 Amp. Glass Passivated Bridge Rectifier - Fagor

So does it look like it should be replaced or is Bob my uncle with this rectifier? ;}

If you think it should be replaced, what would you recommend? Thanks!

[Eva]

Old capacitors should be measured before considering them defective. Typically, large can capacitors have extremely long life, as high as 10.000 hours at 105ºC and many times more at lower temperatures, while the tiny electrolytics are the ones with shorter life. On the other hand, you should think twice before disposing big capacitors in good condition because they contain gentle amounts of toxic substances inside.

To compare the ability of different diode bridges to whitstand inrush current, compare the Ifsm and I2t ratings. There are better bridges than the Fagor with 500A Ifsm and 1100A^2s I2t (GBPC35 from IR).

[Andersonix]

I wouldn't bother unless you use at least twice the capacitance, and 10mF (per rail?) is quite wimpy for the typical amp. I added 60mF per rail to the existing 23mF - so 3.6 times more - in my Acurus 100W amp, and now it SLAMS. Fortunately it already had a thermistor, so the fuse doesn't pop on turn-on. The rectifier bridge will only see more current for the split second it takes to charge the extra caps, so I wouldn't worry there (but you should prob consider a thermistor on the primary).

[h_a]

The rectifier bridge will only see more current for the split second it takes to charge the extra caps

And that's what makes the problems...the pulses are huge currents. One can be glad that not more manufacturers use Schottky bridges which are especially sensitive to overload. If these blow, they straightly short and reversed polarity fed into the amp is when the real fun starts. The usual Si based stuff is more forgiving.

A new and more powerfull bridge is not expensive.

Have fun, Hannes

[Monjul]

Ok guys, give me some examples of what I should buy as I'd like to find a vendor that sells the caps and the rectifier I need. So far Eva (thanks), recommended the GBPC35 which I believe is a Vishay.

Also, the rectifier is heavily soldered in. Should I follow suit or use crimp connectors that some recommend. Thanks.