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In Reply to: RE: impedence of CCS mu output posted by bobbyj on April 7, 2010 at 18:24:37:
Here's the math for plate resistance. (see link)"The reason I'm asking is that a RIAA filter that follows, seemingly is based on this number, or perhaps is comfortably under a "number"."
The output impedance is part of the filter. In a RIAA filter the first resistor is a series resistor. If the math calls for a 220K ohm resistor and the output impedance is 10K ohm then you would want to use a 210k ohm resistor so that the total resistance the rest of the filter "sees" is 220k ohm.
You would want to keep the 1:10 or 1:20 (Lynn Olsen) ratio when driving a RIAA filter.
If the series resistor is 220k and the shunt resistor is 34K at some frequency the shunt cap will have a reactance of 0 ohms. So the driving tube has to drive 200k plus 34k at those frequencies.
The second cap in a RIAA filter is a shunt cap that's not in series with a shunt resistor. At some frequency the reactance of that cap will approach 0 ohms. So the load the first stage will have to drive is 220K ohm. You wouldn't want to try to drive 220k with a tube stage that has a 50K ohm output impedance.
Hope this helps.
Tre'
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Follow Ups
- RE: impedence of CCS mu output - Tre' 04/7/1018:57:48 04/7/10 (5)
- RE: impedence of CCS mu output - bobbyj 20:18:13 04/7/10 (3)
- RE: impedence of CCS mu output - Tre' 20:40:39 04/7/10 (2)
- RE: impedence of CCS mu output - bobbyj 10:15:02 04/8/10 (1)
- RE: impedence of CCS mu output - Tre' 10:20:13 04/8/10 (0)
- Here's a helpful calculator - Tre' 19:02:17 04/7/10 (0)
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