Should I use Polymer Capacitors for replacement?

[pinoy]

I'm replacing the electrolytic capacitors on my 15" Klipsch KSW-300 subwoofer amplifier. The capacitor brand is Soundia and I have not been able to find specs for it. I was thinking of using polymer capacitors as a replacement because they are all around superior to regular capacitors except they have 50x higher leakage current. The best regular capacitor would have 3uA leakage current while a polymer capacitor can go up to 400uA and higher. Should I be concerned to use polymer capacitors on circuits originally designed with regular capacitors?

 

[Matthew Kane]

Use the right capacitors for the right applications is the 1st ground rule you should be taking when doing cap replacements (i.e. don't use a snubber cap for a in path signal circuit or output stage). I'm throwing in a rough guess that you're planning to replace the filter capacitors? Any PSU section capacitors on the plate amp should have a high thermal temperature rating 105'C and above, low ESR at various frequency breaks/leakage specs and high ripple. Klipsch subwoofers are notorious (as well as other big mainstream hifi brands such as Cambridge Audio, Wharfedale or NAD) use cheap Chinese or Taiwan generic capacitors and resistors which eventually break down and cause all sorts of troubleshooting issues.

Drop in a good CDE, Vishay BC (former Philips BC) or any other reputable and suitable electrolytic cap from a reputable source such as mouser or RS components. I wouldn't bother with dropping in a polymer aka solid state capacitor.

 

[pinoy]

What's an acceptable leakage current for a capacitor?

 

[GiGaBiTe]

Pretty much any quality electrolytic capacitor from a reputable manufacturer is going to be better than what was in it originally. Any general purpose electrolytic cap should be fine, but some manufacturers like Nichicon have audio grade caps which are slightly more expensive but have lower noise/ripple.

You'll want to keep the ESR as low as possible, though this becomes increasingly difficult the smaller the capacitor is.

 

[Matthew Kane]

What's an acceptable leakage current for a capacitor?

As low as you can find in the relevant capacitor datasheet. There are always trade-offs so you can need to search for a right balance within the specs.

You'll want to keep the ESR as low as possible, though this becomes increasingly difficult the smaller the capacitor is.

Not really, Cornell Dublier (CDE), Panasonic and Vishay all have low ESR high ripple and high temp rated capacitors as low as 1uf 6.3v for specific ranges. Panasonic NHG, FL, FC and FM ranges are designed for circuit positions where low ESR is required (a'la PSU or switching section of a power supply or decoupling). These come in low capacitance and power rating.

 

[i7Baby]

What size?

 

[GiGaBiTe]

Not really, Cornell Dublier (CDE), Panasonic and Vishay all have low ESR high ripple and high temp rated capacitors as low as 1uf 6.3v for specific ranges. Panasonic NHG, FL, FC and FM ranges are designed for circuit positions where low ESR is required (a'la PSU or switching section of a power supply or decoupling). These come in low capacitance and power rating.

I'm referring to physical dimensions of the capacitor, not the capacitance rating. The smaller the dimension of the cap, the higher the ESR will be.

 

[Matthew Kane]

I'm referring to physical dimensions of the capacitor, not the capacitance rating. The smaller the dimension of the cap, the higher the ESR will be.

Erh compared to what? I was talking exactly about small physical sized capacitors that have low esr. Capacitor size is mostly determined by the capacitance and voltage rating. If you're saying in general that small physical sized capacitors have higher esr compared to a capacitor that is the same rating but physically bigger then you're wrong. Look up the datasheets for Sanyo Oscon SEPC and the mentioned Panasonic series capacitors, comes in small sizes with low ESR as they are specifically designed to have low ESR.