MM cartridge preamplifier - open project
Please feel free to download documentation of OPENAMP1, MM preamplifier open project.
can be found in the links below the photo of the assembled board
Assembly instructions and board manual
Bill of materials
Gerber PCB files
Noise, Signal to noise ratio
Special emphasis was put on reduction of disturbing noises, hum and buzz.
New set of calibrated noise and spectral density measurement was done in October 2020. Input of the phono preamp was terminated by 50 ohm resistor, to see the preamp noise limit, and then by Shure M35X cartridge, to see the real life noise behavior. It has to be mentioned that preamp gain is 40dB at 1kHz. Noise level measured is -90.6dBV, A weighted, with 50 ohm input and -85.7dBV, A weighted, with the Shure cartridge.
Noise with input terminated by 50 ohm resistor
Noise with input terminated by Shure M35X cartridge - this shows "real life" conditions
Output voltage swing
Max. output voltage swing is 30Vp-p with 2 x 17V power supply. This assures immunity vs. transient overvoltages at the input. Next measurement shows output voltage swing at 20kHz.
Pavel Macura 12/2012