From: zekfrivo@zekfrivolous.com   
      
   In article <0001HW.C7E8AAB70005E1C4F01846D8@news.giganews.com>,    
   udio_empire@comcast.net wrote:   
   >On Mon, 12 Apr 2010 05:47:14 -0700, Arny Krueger wrote   
   >(in article ):   
   >   
   >> "cjt"  wrote in message   
   >> news:4BC289A0.3070103@invalid.invalid   
   >>> Spica wrote:   
   >>   
   >>>> I'd like to increase the filter capacitance of a 21 year   
   >>>> old subwoofer amp from the current two 10,000uf 75v caps   
   >>>> to a pair of 20,000uf 75v caps.  The current rectifier   
   >>>> is a Fagor FB2502.  Do you think this rectifier can   
   >>>> handle the increase or should I upgrade it?  Also, for   
   >>>> reference, the amp uses a single power chip per side as  opposed to   
   >>>> discrete xistors if that matters.  Thanks.   
   >>   
   >>> Why?   
   >>   
   >> Good question.   
   >>   
   >> Just about the only reasonable justification I can think of is that the   
   >> existing caps have lost significant capacitance. This may or may not happen.   
   >> I've seen electrolytics that were still well over 100% of nameplate   
   >> capacitance after over 40 years, and others that were under 10% after 3   
   >> years.   
   >>   
   >> YMMV!   
   >>   
   >> 10,000 uF is actually quite a bit of overkill - a minimum number might be   
   >> 2,500 uF - 3,300 uF.   
   >>   
   >> The real question is "what sounds bad"? I suspect that most "capacitor   
   >> upgrades" satisfy psychological and social needs, not technical needs.   
   >>   
   >>   
   >   
   >My experience is that MOST of the time, second-guessing a piece of   
   >equipment's designer(s) results in retrograde performance. SOMETIMES in some   
   >(admittedly rare) instances, so-called upgrades and tweaks are worthwhile,   
   >but not usually. I replaced some crossover caps in a speaker system with   
   >'Wondercaps' of the same value once and speakers immediately sounded cleaner,   
   >more transparent. I replaced the LM301 op-amp in an old Crown IC150 preamp   
   >with a higher-slew rate pin-for-pin compatible J-Fet op-amp once and got   
   >measurably lower distortion (using a borrowed high-end distortion analyzer),   
   >but I couldn't actually HEAR any difference. It's a crap shoot. And honestly,   
   >the designer generally knows what he's doing and has chosen the values for   
   >his filter caps for a reason. It might be something as simple as the   
   >determination that a larger value adds only expense to the final product,   
   >without adding any measurable or discernible improvement in performance, or   
   >something more critical, like the values chosen matched the rectifier diodes   
   >and a significantly larger value will over stress them. It's best to leave   
   >things alone. If you have determined that the current caps are leaking, or   
   >have failed in some other way (resulting in hum), I suggest that you replace   
   >them with caps of the same value. Most likely "more" will not equate to   
   >"better".   
      
      
   I had also considered replacing the Crown op-amp but I didn't think it would   
   be worth it. Seems like there are many wanting to fool with the filter caps,   
   and I   
   have never arbitrarily replaced any after working on dozens and dozens of amps   
   and receivers.   
      
   As for amps, a cheap transformer and big caps owe more to peak music power,   
   and good transformers and moderate caps tend to work out best. Upgrade the caps   
   if you like. The peak current of the diodes is going to be the peak of the   
   transformer,   
   not so much the actual capacitance. Of course I make amplifiers with   
   a soft start, with a relay and resistance.   
      
   greg   
      
   the diodes   
      
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