C1, 4.7uF cap [message #30221] |
Sat, 22 January 2005 18:49 ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
colinhester
Messages: 1349 Registered: May 2009 Location: NE Arkansas
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Illuminati (3rd Degree) |
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Is there a minimum voltage rating? Can someone please make a little friendly suggestion as to what might possibly sound best?
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C1, 7.5 uF/440VAC [message #30229 is a reply to message #30224] |
Sat, 22 January 2005 20:21 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
PakProtector
Messages: 935 Registered: May 2009
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Illuminati (2nd Degree) |
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it is indeed the output coupling cap. Since the impedance of a cap is 1/j-omega-C, we want the cap as large as is sonicaly reasonable. Forget about j and root negative 1. It is the real part of this we will look at. At 20 cps, omega is 2*Pi*20 radians per second and C is 7.5 * 10^-6. this yeilds 1061.03295 Ohms. At 40 cps, it is half that, and at 80 cps, half of that. This is close enough to the 10:1 ratio of input impedance to output impedance which keeps us from rolling off too early, even with a 10kOhm SS amp. For a 100kOhm Valve amp and several tens of pF of cabling capacitance, we're still good. regards, Douglas
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