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Re: Ping Allen Wright: RIAA trimming

IIRC, Allen wrote his comments in the context of passive EQ split into two parts, one part between the first and second tube stage, and the other between the second and third. Trimming is tricky if you're thinking of the usual 4 component RIAA network, whether passive or active, because changing any one component will affect all the time constants. The definitive paper on this was written by Stanley Lipshitz and published in the Journal of the Audio Engineering Society many years ago. If you're using a 4 component network it's best to just use his equations to design an accurate network.

With a split EQ you can certainly do trimming since the time constants don't interact, however, remember that the best reverse RIAA networks are probably only good to within plus or minus 0.1 dB and Llipshitz equations allow you to design an RIAA network that is as accurate IME. You have to incorporate the output impedance of the preceding tube and the Miller capacitance of the following tube to get that degree of accuracy, however.

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