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The iRIAA Filter is a two-channel passive inverse RIAA response filter for use in testing phono
preamplifiers. Unlike traditional networks, the iRIAA Filter includes a correctly placed upper 3.18us
(50kHz) corner in its transfer function. Dual inputs accomodate either 50 ohm or 600 ohm sources with
outputs at both -40dB and -60dB. Frequency response is accurate to within +/-0.25dB from 10Hz to 100kHz.
Quality components include 1% metal film resistors, 2% polypropylene capacitors, gold plated connectors,
and a double-sided fiberglass PC board.
Makes a great "break-in" tool for phono preamps, just connect any line level music source as the input
(the FryBaby is even better!).
Read Michael Fremer's positive review in Stereophile.
Many folks wonder how accurate their phono equalization needs to be. I ran a few quick simulations to
show just how sensitive the typical RIAA filter is. I modified nominal capacitor values by +/-5% to get
this dB vs. frequency error plot. The nominal (blue) response uses
closest value 1% components. A full 5% component error leads to a peak 0.4dB amplitude error. This is
far less than what most loudspeakers achieve. However, for best imaging and soundstaging, the left and
right channels should be matched as close as possible.
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