IMO, trying to get conformance to RIAA to some super-tight value is futile- as others point out, your cartridge, the cutter, and the mastering EQ circuits will introduce greater errors. 0.3-0.5dB is probably better than "good enough," and not too hard to achieve. IME, the more important thing is to have channel-to-channel match be tight as a drum- this affects imaging.
What is the pertinence of testing an RIAA equalized preamp with square waves ?
The cartridge output signal is submitted to a lot of low pass filters in the whole preceding process and can never have a shape resembling the square waves issued from a laboratory signal generator.
The cartridge output signal is submitted to a lot of low pass filters in the whole preceding process and can never have a shape resembling the square waves issued from a laboratory signal generator.
IMO, there's a specified equalization and square wave testing is a fast easy way to check conformance. People do hear <1 dB changes in frequency response, so getting the circuit as close as practical isn't a waste of time. How good is good enough? I don't know, but 0.5 dB seems like a good place to start. Would you be happy with a signal that was 5% low in some range? Well, that's 0.44 dB. We argue about minutia, but a 5% error seems worth some discussion.
Of course the output can have a shape resembling the sig gen waveform, or something's horribly wrong with the circuit!
Of course the output can have a shape resembling the sig gen waveform, or something's horribly wrong with the circuit!
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Actually, you can get a pretty good one, albeit band-limited. Very diagnostic of frequency response errors and cartridge ringing.
A 1KHz square wave into an RIAA equalizer will produce a sort of triangular wave with rounded ramps on both rising and falling sides.
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