Maximum Capacitance before Pffffft? - diyAudio
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 18th March 2002, 09:06 PM #1 diyAudio Member   Join Date: Oct 2001 Location: Baton Rouge, La Maximum Capacitance before Pffffft? Excessive capacitance doesn't come up often with regular magnetic coil loudspeakers, but electrostatic panels have quite a bit of it. And in the case of the amp / loudspeaker set I'm hoping to build here, It can be quite a problem. So the question I'm asking is, how do you tell how much capacitance an amplifier design can drive, without building it and going the 'lets try and see' approach? The amp design I'm looking at is basically a scaled-up version of Kevin Gilmore's ES headphone amplifier design at Headwise . The panels are going to be full-range and LARGE; as large as i can make them. It's direct-drive, so there's no transformer in there to load; it's (almost) the same as wiring a capacitor across the output of an amp and letting it rip. Of course, the panels' capacitance is defined by its area and stator spacing, so in order to get as large a panel as possible, I need to know how to determine an amp's maximum capacitance tolerance. So how do you calculate the limit capacitance? What mechanism is at work here that eventually drive the amp to explode? As I understand it, it deals with driving an amp into UHF oscillation. Any experience of pointers on this topic would be great, and of course criticism and commentary are welcome. Thanks. - Jonathan
 19th March 2002, 06:56 AM #2 diyAudio Member     Join Date: Jan 2001 Location: Germany You have to calculate the impedance at high frequencies. The larger the capacitance, the smaller impendance the amp sees at high frequencies. Z = 1/(C*2*pi*f) C : Capacitance pi : 2,1314... f : frequency That´s not the only factor that is important. Even more important is if the amp is stable in the firat place. A capacitance in the output can cause many older design amps to oscilate. This is not at all easy to calculate.
 19th March 2002, 07:15 AM #3 diyAudio Member   Join Date: Jan 2002 Location: nowhere isn't pi more like 3.14?
 19th March 2002, 07:37 AM #4 diyAudio Member   Join Date: Oct 2000 Location: Sweden Yes, pi is 3,14 /Freddie

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