MM cartridge preamplifier - open project

Please feel free to download documentation of OPENAMP1, MM preamplifier open project.

 

Documentation files

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.

 

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Pavel Macura 12/2012

macura@centrum.cz