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#290575 - 12/12/11 10:37 PM
Re: Capacitors
[Re: Ape09090]
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DaveBass
Old Timer
Registered: 30/10/02
Posts: 6462
Loc: The wilds of Surrey
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Well, that's as maybe, but you're not going to be using electrolytic capacitors in a guitar. Non-polarised capacitors hand over to electrolytics somewhere around the 1uF region, although personally I've used plastic film capacitors up to 20uF or more in specialised applications. Anyway, below 1uF you're not going to be using electrolytics.
A simple model of a real capacitor has four elements, the most important of which is the capacitance C. In series with that is a low inductance, caused by the wound construction of many capacitors, plus leadouts; and a low resistance, which represents losses, most due to dielectric imperfections. This equivalent series resistance (ESR) determines the ripple current rating of the capacitor, i.e. how much it heats up when high currents pass through it. The final element is a high parallel resistance, representing dielectric leakage, i.e. the fact that a capacitor won't hold its charge forever.
In smoothing applications such as in switched mode power supplies, the ESR and ESL (equivalent series inductance) are important as they dominate the performance at ripple frequencies (which are usually well above 20kHz in a SMPS). The ESL resonates with the capacitance C, and above the resonant frequency the component looks more like an inductor than a capacitor. A common design trick is to use a lot of small electrolytics in parallel rather than one big one, as this raises the resonant frequency.
Non-electrolytic capacitors, even of wound construction, have a resonant frequency usually well into the radio frequency range and this will have no effect at audio frequencies.
Dave
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#290580 - 12/12/11 11:23 PM
Re: Capacitors
[Re: DaveBass]
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Ape09090
Old Timer
Registered: 01/12/11
Posts: 1188
Loc: South Wales
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I just read about Allen Bradley carbon composite resistors,apparently they have zero inductance and that's a good thing.
Do you build your own amps as well then Dave?
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#290602 - 13/12/11 11:51 AM
Re: Capacitors
[Re: DaveBass]
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Ape09090
Old Timer
Registered: 01/12/11
Posts: 1188
Loc: South Wales
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Well,I spent 7 quid on those allen bradley resistors last night,lol
It will have worked out cheaper just buying a new guitar soon.
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