Very Simple, Accurate RIAA Phono EQ Amp
Here is a simple no-nonsense, accurate RIAA equalizer amp you can easily build. The design uses an all-active topology and is based around an NE5534A low noise opamp. I make no claims for originality but you wont find any voodoo engineering, fairy tales or outrageous claims: It simply does what it says it does in the specification.
A complete stereo board can be built for about £25 ($35), but probably less.
The article provides some background information on the RIAA EQ standard, launched in 1954, and why it came to be the de facto industry standard after about 1960.
To use the PDF PCB layouts below, you must print the documents out on A4. Measure the reference line lengths to make sure they match. You printer should be 600 DPI resolution or better. However, I strongly recommend you just buy the PCB’s from Jim’s Audio – link above. These are very high quality boards, silk screened and gold flashed.
Overlay and 1:1 PDF negative and positive for the EQ board: Hifisonix Phono EQ Amp for Doc114
Optional PSU Overlay and 1:1 PDF positive and negative: Hifisonix Phono EQ PSU106
Any questions, feel free to email me.
Can I use other op-amps with the Hifisonix RIAA?
Yes, you can. I recommend that you use unity gain stable devices with will not require an external compensation capacitor, unlike the NE5534 used here. You must first REMOVE C2 and C21 – these are the 10pF compensation capacitors. The number of good opamps in 8 pin plastic DIP packages (PDIP or mini-DIP) is unfortunately not what it used to be, so you may have to use a SMD to PDIP adaptor if you want to go down this route.
The plots below are for HIGH gain.
The plot below is of the RIAA noise and distortion at 500mV output at 1 kHz A weighted. This was with board on the workbench, no screening or special precautions and the power supply located about 15cm away. In a metal housing, you can expect about a 30 dB reduction in the 50/60Hz noise. There is quite a bit of noise being picked up from the surrounding CFL lamps etc, but the distortion is almost entirely 3rd harmonic (at -70 dB), with a bit of 5th at about -85 dB.
The plot below is the frequency response after the source signal is passed through a very accurate inverse-RIAA network. The white noise frequency response measurement technique used eliminates extraneous noise sources and is therefore extremely useful. It works by looking at the power spectral density of the amplifier output, which for a white noise source, is constant per octave. If the amplifier response (after passing through the inverse RIAA) is indeed flat, then the overall response will be flat. The A-D was set to 24bits /192 samples per second and the response display set to 30Hz to 100kHz. The RIAA conformity is excellent with no HF peaking and starts dropping off cleanly beyond about 30 kHz.