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Question on capacitor replacement... higher value vs original value?

post #1 of 10
Thread Starter 
I am in the process of recapping my 30 year old Harman Kardon 430 Twin Powered Solid State Receiver.

According to the service manual, several caps in the power filtering section have a +100% -10% tolerance level. Does that mean that it is ok to substitute values that are up to double the capacitance value? Is there exactly any benefit to replacing the caps with a higher value, or should I just stick to the original values? The replacement caps I am using are Panasonic FCs and NHGs from Digikey with +-20% tolerance.

Thanks
post #2 of 10
Power supply electrolytic capacitors have a tolerance of up to 100% higher, so yes you can replace another capacitor as long the replacment is equal or higher in uFs and voltage..... Be sure to check physical size..
post #3 of 10
Thread Starter 
Is there any benefit to using a larger value then?

I am hesitant to do so even if its ok, since I figure there has to be a reason why the designers chose that specific value. I doubt cost savings would be the main reason...
post #4 of 10
This may help if you know electronics:

http://sound.westhost.com/power-supplies.htm
post #5 of 10
My understanding is that physical size and cost are the two largest limitations on capacitor choice.
post #6 of 10
Quote:
Originally Posted by Miwo View Post

I am in the process of recapping my 30 year old Harman Kardon 430 Twin Powered Solid State Receiver.

Back in the day's when I had hair, there was a popular hack folks made to Dynaco power amps that involved replacing the power supply filter caps with much larger value parts. I tried this myself and you really could hear a substantial improvement in the sound quality. The caps I had were so large they wouldn't fit in the enclosure so I put them in an external box and connected them with heavy wires. Yeah, it was ugly - but I thought it was worth it.

In general, you can't go wrong increasing the value as long as you maintain the same or higher voltage rating.

Remember these caps can be dangerous if connected wrong. Hook them up backwards or exceed the voltage rating and you can be building a bomb. I've seen some big 22,000 MFD caps explode with enough force to bend heavy sheet metal - no joke.
post #7 of 10
Probably a DIY audio forum is a better place for this type of question.
Try http://www.diyaudio.com/forums/
Remember bigger capacitors will place greater demands on the power supply input section. Bridge rectifiers sometimes fail when more capacitance is added. But up to 100% more should be OK.
post #8 of 10
Thread Starter 
I think I will compromise and use replacement caps that are 50% higher. That way, it is not too much more, and will still be within the tolerance level of the original cap values. I have already replaced the Main Amp and Preamp cards with equal value Panasonic FCs, so all i have left are the Rectifiers and main power filtering caps

Originals: 30 year old Elna caps (some look to be leaking)
2x - 1000uF 35v +100% -10%
2x - 2200uF 35v +100% -10%
4x - 4700uF 35v +50% -10%
1x - 470uF 25v +100% - 10%

Replacements ordered:
2x - 1500uF 35v +-20% Panasonic FC
2x - 3300uF 35v +-20% Panasonic FC
4x - 4700uF 35v Panasonic NHG (Digikey didnt have higher Panasonic values)
1x - 560uF 25v +-20% Panasonic FC
post #9 of 10
Quote:
Originally Posted by Miwo View Post

I think I will compromise and use replacement caps that are 50% higher. That way, it is not too much more, and will still be within the tolerance level of the original cap values.

The value of electrolytic caps in general tends not to be very accurate. Just the nature of the beast. I've seen references to the fact that they can vary as much as 50% from the rated value.

As for the load placed on the power supply by larger caps, this only holds for the brief time the caps are charging on power up. Once they are charged, the load would be about the same. The additional load can stress rectifier diodes and the transformer. Transformers are tough so I wouldn't worry about that. The diodes are usually very robust as well, but that can vary with the quality and type of parts selected. I've seen over loaded silicon diodes get so hot they melted the solder holding them in the PC board and they fell out - and they still worked just fine! That's not to say that all diodes will handle that much stress however.

There is some possibility that larger caps could increase the line inrush current, blowing the input fuse. Switching to a time delay fuse or slightly increasing the fuse value would fix that.
post #10 of 10
I have replaced many capacitors in all kinds of circuit boards and have given them a new lease of life. Many are simply thrown away when they can be repaired very cheaply. Electrolytic caps for most pcbs are only a few pence, so it makes it worth while. Computer monitors are a common example and you can replace them all for a couple of pounds. Just stick to values as close as possible, slightly higher but never lower.
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