wdrazek Posted January 14, 2012 Share Posted January 14, 2012 I have a pair of Forte I's that date back to 1986. They sound good powered by a mid 70's Marantz 2226 receiver. I'd like to get better sound from the setup, and a lot of research has turned up capacitors as a potential way to improve things. So, my question is: what causes capacitor failure? I know age is a factor, and the 20 year mark is when caps are often said to need replacing. Is that due to their age alone, or to additional factors, such as amount of use, humidity, or other factors? Also, what are the indicators of bad caps? Quote Link to comment Share on other sites More sharing options...
Guest " " Posted January 14, 2012 Share Posted January 14, 2012 they type of capacitor has a lot to do with it's break down. electrolytic's break down, but can be reformed. oil caps dry out and are jsut done gambling once they go down hill. of course, the papar and wax caps are a done deal once they start to dry out. sealed film caps do better and seem to last longer. The oldest caps I kept in service was from an amp built in 1977. Once powered up on a variac, the amp ran fine 45+ years later. On the speaker caps scene, there are improvements based on they type of caps, aside from the concept of restoring aged caps. Quote Link to comment Share on other sites More sharing options...
jacksonbart Posted January 14, 2012 Share Posted January 14, 2012 its due to a poor up bringing Quote Link to comment Share on other sites More sharing options...
mustang guy Posted January 14, 2012 Share Posted January 14, 2012 I thought it was because they didn't study. Quote Link to comment Share on other sites More sharing options...
jacksonbart Posted January 15, 2012 Share Posted January 15, 2012 I thought it was because they didn't study. What comes first the chicken or the egg? Its always someone else's fault. Quote Link to comment Share on other sites More sharing options...
Groomlakearea51 Posted January 15, 2012 Share Posted January 15, 2012 The laws of thermodynamics and entropy. ....and Murphy's Laws of general failure...... Quote Link to comment Share on other sites More sharing options...
Quiet_Hollow Posted January 15, 2012 Share Posted January 15, 2012 Barring signs of physical defect, the next question is, "does this capacitor still meet spec?" Either case is a mode of failure from a functional POV. The only way to know for certain is to measure its capacitance and its ESR. Quote Link to comment Share on other sites More sharing options...
wdrazek Posted January 15, 2012 Author Share Posted January 15, 2012 Thanks for the information. I don't have the tools to measure, unfortunately. The prior original owner did not use the Forte's much for several years so I wondered if the caps were bad for sure. Guess I'll never know. My Forte plan now is to get a Crites network, either cap replacement or all new. Suggestions on which to do are welcome. I do not want to go the ALK route as I don't want to substantially alter the basic design, just improve on it where possible. I also want to replace the mid/ tweet diaphragms with Klipsch ti, assuming they are still available. The website has nothing on them from what I can find. For the Marantz, frankly I am surprised it sounds as good as it does, considering it was last produced in 1979. Just wondering if it's worth dropping $200 or so into caps knowing that other components are probably out of spec, too. Maybe, as others have suggested, a low powered tube amp is a better route. Quote Link to comment Share on other sites More sharing options...
JJkizak Posted January 15, 2012 Share Posted January 15, 2012 To keep your brain at a minimum stress level if they are 20 years old just replace them. Otherise as you try to go to sleep you will be thinking about those capacitors, maybe a couple are marginal. The new ones will have way better ESR's than the old ones ever dreamed of. JJK Quote Link to comment Share on other sites More sharing options...
Quiet_Hollow Posted January 15, 2012 Share Posted January 15, 2012 The new ones will have way better ESR's than the old ones ever dreamed of. Got data to back that up? Think about what your telling him to do. [:|] "Spend $200 bucks so you can sleep at night.." [bs] If it bothers the OP that much, pull the caps and take them to the local technical college or university EE department. That or a local electronics repair shop. They have the equipment to check 'em out, and either way is cheaper than new caps if they spec out good. Quote Link to comment Share on other sites More sharing options...
djk Posted January 16, 2012 Share Posted January 16, 2012 Most failure in crossover caps are an increase in ESR. The main problem is the lead attachment. Solens had a problem with the metalization on the film. Plastic films in general get brittle and may develop fractures after about 20 years or so. Most of the newer film caps sound better than the inexpensive film types used 20+ years ago. Quote Link to comment Share on other sites More sharing options...
Don Richard Posted January 16, 2012 Share Posted January 16, 2012 Plastic films in general get brittle and may develop fractures after about 20 years or so. Specifically, pthalate-based plastics outgas their plasticizers over time, leading to brittleness. Polypropylene does not use them and should last indefinitely. Quote Link to comment Share on other sites More sharing options...
BEC Posted January 16, 2012 Share Posted January 16, 2012 As others have mentioned, high ESR is the normal failure mode for crossover caps. I can show a picture to illustrate this. In the picture is a 2uF motor run cap from a Klipsch crossover. Notice that it is still in spec for capacitance. But, the ESR has increased to 68.32 ohms. Almost no signal was going to get through that cap. Bob Crites Quote Link to comment Share on other sites More sharing options...
BEC Posted January 16, 2012 Share Posted January 16, 2012 So, what is a good reading for ESR? I would say that anything above 1/2 ohm, I can typically hear in comparison with a truly low ESR cap. A new polypropylene cap should have ESR at around a few hundredths of an ohm. Most of the crossover caps will be at or above 1/2 ohm ESR by the age of 20 years and most will still be in spec for capacitance. Measuring capacitance alone without measuring ESR means almost nothing. Here is a good polypropylene motor run cap. Bob Crites Quote Link to comment Share on other sites More sharing options...
wdrazek Posted January 17, 2012 Author Share Posted January 17, 2012 Thank you. This is very helpful. From what I am reading it is a matter of aging, not so much use, non-use or other factors. And that holding the capacitance alone means next to nothing. How vulnerable are the other crossover components (resisters, autotransformers, etc.) to degrade due to aging? Thanks again to all of the helpful posters. Quote Link to comment Share on other sites More sharing options...
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