The resulting frequency response and the difference to the ideal frequency response is shown in the plot. In the table you find ideal and practical values for all components. It must be approximated and in this case the approximation is improved by paralleling two capacitors each as required.
The ideal frequency response cannot directly be achieved by standard components. Source resistances up to 1k will also have little effect, and this fits well to low resistance RCA or headphone outputs. With R3 = 1.5k the reduction is less than 0.1dB 20kHz, with 10k it's about 3dB.Īny capacitance on the RIAA input up to 50pF or more is negligible. If R3 becomes too high, high frequencies are reduced. R3 influences the frequency response at the upper end. I selected it so that with my amplifier the standard (DIN) inputs show the same sensitivity as the phono input with this adapter. This resistor determines the output voltage or the overall voltage gain. The current produces a proportional voltage across the operating resistor R3. The frequency response of the current through the network formed by R1, R2, C1 - C4 corresponds to the inverse of the standard RIAA curve, so these components determine the frequency response of the circuit. So I designed a miniature passive network to convert a normal audio signal into the signal that phono inputs require.Īs the amplification of a phono input is quite high, this pre-equaliser network can be made completely passive. I was missing another input for a standard audio signal at this amplifier.I had an amplifier with an unused RIAA input and.I came up with this idea when I was in a situation where.
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