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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Bypass Capacitors posted by David_toatley on June 17, 2000 at 07:22:41:
[ Is polyproprelene still the cap of choice for this application or is metallized polypropelene just as good or better?
Can metallized be substituted for polypropelene and visa-versa? ]There are two different types of capacitor contruction: metallized film, and foil and film. The foil and film are generally conceeded to be a better cap, and they cost more. However, since many of the caps that you will be bypassing or replacing are either much worse (electrolytics, mylars) or no better than metalized PP, they can be used with great results. How much better than met. PP you want to go is going to be dictated by the sophistication of your equipment and system, and how readily you hear subtle things such as cable differences, etc.
The PP film and foil caps ar ethe next step up, polystyrenes are better still, and the teflon caps are the best, albeit incredibly expensive.
[ Do you still need to bypass in pairs to optimize performance?
Do you need caps of the values specified or this because of the type used? ]It is not the pairing, but the relative amounts of inductance and the value of the cap. Say for instance, you have a 100 uF cap you want to by-pass. The rule of thumb is to use values in one tenth increment steps to bypass it. This would mean a 10 uF, then a 1 uF, then a 0.1 uF, and even in extreme cases, adding a 0.01 uF. In most cases, the first two steps will buy the most improvement, and adding still smaller caps might not be as apparent as the addition of the first two. If the ratio between the caps becomes too large, then there will be a gap in the impedance minimum between the large main cap and the bypass/es. The values do not have to be exactly one tenth, the range of about 2 to 1 for the bypass value will work just fine. In the above example of a 100 uF main cap,. a bypass of 5 uF would also be OK, as would the second bypass at 0.22 uF. This kind of stretches out the range a little but would tend to obviate the need for additional bypasses, except for critical points in the circuit, where the ratios should be closer, not further, and the correct number of bypasses should be used. A good example of a critical location would be a feedback cap or main signal cap, a cap in a loudspeaker crossover (all your music passes through the loudspeaker).
One further note: The smallest value bypass should have the shortest signal path, and should be soldered as close to the two circuit points as possible. Minimum lead length should be used, and the part should be affixed in place rather than left to hang or dangle, a dab of hot melt or some double sided tape is good.
For an explanation of how bypass caps work, see:
http://www.AudioAsylum.com/audio/general/messages/8137.htmlJon Risch
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Follow Ups
- Re: Bypass Capacitors - Jon Risch 10:14:45 06/17/00 (3)
- Multicaps - Tgrossi 21:02:39 06/17/00 (2)
- Re: Multicaps - Mark Kaepplein 11:41:53 06/19/00 (0)
- Re: Multicaps - Jon Risch 08:55:23 06/18/00 (0)
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