Hi-Fi Phono Preamplifier with RIAA Specification

Overview

The circuit was designed according to the RIAA implementation of Hi-Fi phono preamplifier for the purpose of reproducing an audio from a moving magnet cartridge.

Terminology

• Recording Industry Association of America (RIAA) – the trade group that represents the recording industry in the United States
• Phono Preamplifier – an electronic circuit that equalizes and amplifies the analog output of the cartridge in a phonograph turntable where the output is increased to intensity equal to other audio sources like CDs and tapes and to restore the original signal, RIAA equalization is required
• NE5534 – a high performance low noise operational amplifier having a combined excellent AC and DC characteristics and features such as capability of external compensation, capability of offset nulling, wide range of voltage supply, low harmonic distortion, with output voltage swing at peak to peak, high slew rate, 100 dB common mode rejection ratio, high gain of DC Voltage, unity gain bandwidth at 10 MHz, and noise voltage of equivalent input
• 7915 – a 3-terminal negative fixed voltage regulator with features such as surface mount package availability, contact factory for other voltage options, availability of voltages -5V, -12V, -15V, fold back current limiting, internal thermal overload protection, compensated output transistor safe area, good load and line regulation, current output to 1.5A, no external components required, internal short circuit, and 1.5% internal output voltage

Circuit Explanation

The hi-fi phono preamp is a technical standard of frequency response during the manufacturing and playback used on vinyl records, which should have an accurate equalization. The RIAA equalization of phono preamps recreates the original analog signal by attenuating the highs and amplifying the lows. The RIAA is responsible for distributing, manufacturing, and creating 85% of all legitimate sound recordings in the U.S. and certifying albums and singles for reaching gold, platinum, multi platinum, and diamond awards.

This circuit is responsible for recovering audio from old turntables with moving magnet even on the rising of CD usage. It is made possible because they contain amplifier that does not remove phone inputs but rather line inputs. The capacitors C1-10 used in the circuit were properly selected to comply with the requirements. The low head voltage is increased in the line level while the essential response adjustment is made relative to the standard of RIAA. The adjustment is done in the 50Hz and 500Hz frequencies. The combination of R4-5 R17-18, C2, and C11, comprise the filter in the feedback of IC1-3. The weak filter is handled by R7-8, R20-21, C3, and C11, with a frequency of 212Hz. The tolerance of capacitors C2-3-11-12 should be 1% to 5%.

The circuit is being supplied by a single power source that may be encased in aluminum to prevent unwanted noise. The whole circuit can be placed in a box with an RCA jack and main power cable at the back part and diode LED D1 in front. A small switch and a fuse may be used for added protection. The line input of amplifier or preamplifier receives the signal from the circuit output. The resistors R9-22 can be varied to obtain the desired level.

Part List

Application

The hi-fi phono preamplifier with RIAA standard is used best in obtaining a signal from old moving magnetic cartridge or turntables and be fed into a mixing board. Some applications are software-based that are used in digital technologies, magnetic tapes, and CDs, where recording and reproduction of music are done. These preamplifiers can also be built in audio or Audio-Video receiver which may come as external device that produces high quality of audio restoration.

Source:users.otenet.gr/~athsam/phono_1.htm