Re: Valve preamp.
I've just run a passive RIAA through TINA, allowing 0.1% tolerance to perfect value resistors, and 1% to capacitors.
The maximum error, with all tolerances stacking up worst case, is +/-0.094dB.
Picking the nearest E192 value resistors in 0.1%, and two standard value caps in parallel for one of the caps (all 1%), gives +/-0.11dB worst case stack up, which is perfectly acceptible.
That is for the passive RIAA that I use, so series R of 22k, then 3.2k in series with 100n, then 33n//1n across that.
Craig
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