Line level to phono input

Posted on Feb 6, 2014

The circuit does two functions: signal level attenuation and inverse RIAA filtering. The signal attenuation is needed to convert the 500 mV signal to 2. 5 mV signal. The inverse-RIAA filtering is needed to make the frequency response of the system flat (same equalization that is used when music is transferred to vinyl in the studio). The picture bl

Line level to phono input
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ow shows the frequency response of the ideal inverse-RIAA filter: The picture below shows the circuit diagram of one channel. The other channel (for stereo) is identical. The circuit is so simple that you can easily build it by just soldering the components together and fit them to small metal box with the RCA audio connectors. This circuit is a simplified version of circuit published in Elektor Electronics (T. Giesberts, Pick-up input becomes line input, Elektor Electronics, December 1995, page 99). The basic circuit idea is same, but my circuit is simpler and it does not use high-precision components. The performance is not the same, but I think that this circuit build even from 5% components is adequate for many purposes. This part list is for the one channels described in the schematic. Usually you want stereo sound, in which case you have make two identical circuits: one for left channel and one for right channel. When you connect this circuit to your amplifier, set the phono input to MM or MD position (if it has a selector). Keep in mind that phono input is much more prone to pick up interference, because signal levels in it are much lower than in line level inputs. Typically almost all receivers, and most integrateds have standard `low-gain` phono preamplifying sections (30dB to 38dB of gain typically). These require the use of either moving magnet cartridges (typically in the 2. 0 to 5. 0mv range) or high output...

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