Linear Audio Vol 12 contains an article by Hans Polak on the design of a 'non-plus ultra' phono preamp. Hans has kindly agreed to make the PCB layout Gerber files available for interested readers.
Update: after several requests for an MM-version, Hans has worked out some changes to the original design to make it a better fit for MM cartridges. Here are the changes, which only affect the input stage:
- 2x AD797 to be replaced by 2x OPA1641, matching these op-amps is not necessary;
- R3 becomes 165 Ohm instead of 15 Ohm;
- R4 becomes 47K instead of 1K;
- R8 becomes 47pF instead of 111Ohm, which may be a better value for optimum damping of your cartridge, but you may have to adjust it to your cartridge;
- R7 becomes 100pF, for the same reason as above;
- C32 and C33 change from 220pF to 120pF, or possibly lower depending on the required capacity for your MM cartridge and the tonearm cable;
- C21 & C22 (both 47pF) are no longer required.
With these changes, the SNR figures are:
- Input shorted: 80.7 dBA ref 5mv @5cm/sec;
- With cartridge connected: 76.5 dBA ref 5mv @5cm/sec.