In Reply to: Thanks Kurt but i use the KAB compute for RIAA value posted by lovetube on February 26, 2011 at 20:42:31:
The KAB calculator will get you close but not the right answer.
It assumes the source impedance is very very low and in most valve circuits it isn't. It also assumes the load which is the grid bias resistor of the 2nd stage is 50 times that of the source resistor. If these two conditions aren't met, the calculator will be off. Depends on how accurate you want to get this thing. Say your series R is 330k, then 50 x 330k = 16.5M for the 2nd stage grid. As Kurt days, grid leak bias can be handy and get you close but not all valves like it and that's not your circuit at present.
IME, the best way is to sim it. Don't bother messing around with calculations unless you know all the variables and how they interact. The EQ loads the first stage but not in a linear fashion as it's impedance changes with frequency. With high Z EQ networks, the Miller capacitance of the 2nd stage will affect the values.
You could measure it but you will go nuts trying to dial in an all-in-one EQ this way. A sim can get you there in very little time. I use them all the time to determine EQ values. Before sims were easy, I had a mammoth spreadsheet that would do it but even that was hard work and error prone. A few sums won't get you there very easily.
cheers,
Stephen
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Follow Ups
- RE: Thanks Kurt but i use the KAB compute for RIAA value - Stephen R 11:22:33 02/27/11 (5)
- Hi Stephen can you help me sim my circuit please - lovetube 15:26:36 02/27/11 (4)
- There you go - Stephen R 05:38:03 02/28/11 (3)
- RE: There you go...Thanks for your work and Sim... - Minussss3db 20:22:31 02/28/11 (0)
- Thanks Stephen - lovetube 05:58:31 02/28/11 (1)
- RE: Thanks Stephen - Stephen R 07:26:10 02/28/11 (0)