An Accurate Inverse RIAA Network
Designing and engineering RIAA equalizers demands a clear understanding of the signal chain requirements during the development process. Once components have been committed to a prototype PCB however, testing is required. Presented here is a simple Inverse RIAA Network, or IRN, that allows testing to be quickly and effectively done.
It is important that the RIAA equalizer response is not only accurate across the audio band (20 Hz to 20 kHz), but also well behaved beyond that. The usefulness of this simple tool can be gauged by the fact that, after building an RIAA EQ amp based on a design published by one of the foremost exponents of the art, testing revealed that, whilst its sine wave response conformity from 20 Hz to 20 kHz was exemplary, the gain at 500 kHz was 8 dB higher that at 20 kHz, which manifest as overshoot on the square wave tests. Some simple mods to the RIAA network resolved the problem, and the response was then flat out to ~100 kHz, after which it dropped off at 20 dB/decade.
Here is the article: Accurate Inverse RIAA
Here are the Gerbers for the Network (you will need TWO PCB’s for a stereo version of the IRM): invesr-riaa