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Old 26th February 2013, 02:09 AM   #1
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Default Polypropelene Cap Help!!!

Hi Guy's

I am a newbie here and this is my first post.

I recently decided to recap an old preamp of mine and the service manual indicates all the ceramic, electros and MF which I believe to be mylar/polyester film caps.

I was able to locate all the replacement MF caps at Mouser but they did not have all voltage ranges in stock.

Some of the replacement caps that they did have in stock had voltage ratings 8-10 times higher than the stock caps and are 3-4 times bigger in size.
There is ample room in the preamp for the larger size caps, but, here is my question........

Is there a ratio limit between cap voltage and applied voltage before it causes some audio quality issues?
In other words, if I was to replace a 100 volt 3900pf cap with a 1000 volt 3900 cap, will there be any negative effect in sound quality due to plate size and spacing?

Thanks!

Roland
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Old 26th February 2013, 11:49 AM   #2
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No harm in using a higher voltage rating. Physically larger caps can sometimes create problems of hum and interference pickup, or feedback via stray capacitance, but it depends on exactly how they are used in the circuit. Just be aware that 'upgrading' all caps to 'better' caps may not automatically lead to 'better' sound.
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Old 26th February 2013, 12:34 PM   #3
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Thanks for the reply!

The preamp is over 25 years old so I decided it was time to recap all the electros with audio grade. I did find some of the electros had degraded and that their capacitance were not up to spec......starting to dry out.
All of those caps are being replaced with Elna SilmicII and I'm using the exact voltage replacements.

The problem is the MF caps and I assume that from the service manual that these are all Mylar/Polyester film caps and definintly not Poly's.
The Poly's tend to be bigger in size and I was not able to obtain all the correct voltages from Mouser due to not a stocked item. So therefore I had to buy the higher voltage ones which also mean bigger in size as well. Like I said in my first post, I have the room to install the bigger ones but I have some concerns that if the circuit...for example..... only has 20volts and I use a 1000volt cap, that there would be some other factors that woulld come in to play that I'm not aware of.
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Old 26th February 2013, 01:42 PM   #4
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Oftentimes the higher voltage cap will have lower THD than it's lower-voltage cousin. I would suspect that the higher voltage cap would also be less susceptible to ringing from mechanical disturbance. Sounds like a project.
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Old 26th February 2013, 01:48 PM   #5
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If you use a Tantalum Bead type of capacitor rated at 25volts and only put 4volts across it, in time it will go short circuit due to the chemical format of the Tantalum type capacitor. Paper, polythene, ceramic and electrolytic capacitors are not affected in this way.
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Old 26th February 2013, 03:03 PM   #6
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Quote:
Originally Posted by jackinnj View Post
Oftentimes the higher voltage cap will have lower THD than it's lower-voltage cousin. I would suspect that the higher voltage cap would also be less susceptible to ringing from mechanical disturbance. Sounds like a project.

So I guess from that response that's a good thing!

Just finished up recapping and upgrading my amp so now it's the preamp's turn for a tune-up!
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