QSX-03 Phono amplifier with passive RIAA equalization

It's time for me to design a RIAA amp with passive RIAA correction. The name should be QSX-03 since this is the third amp.

About the name

The name is rather much alike the QSXM3 but I have decided to stick to my present way of naming projects. As you can see of the pictures the first amp was called QSX-001 but also with a Mark II. I thought this mark thing was cool. My, at that time, cassette recorder was called JVC CD-1635 Mark II. There was actually a Mark I also but unfortunately too noisy. My rule now is three letters and two numbers so QSX-03 it shall be.



  1. Basic topology, opamp, RIAA network, opamp, rumble filter, output muting
  2. MC and MM with 4 different gains
  3. Adjustable input impedance and capacitance, both for MM and MC cartridge. Are four switches for each capacitance and resistiance enough? Should I use one 8-pole DIP switch or should I use two? Not decided yet.
  4. Dual mono power supply with super regulators, much smoothing capacitance, fast recovery diodes or schottky diodes, possibly a Curcio regulator (looks very interesting).
  5. Transformers on board, both EI-types and toroids. Possibility to have an external transformer
  6. RIAA network with multiple sizes of caps so you can use almost any type, big, normal and small ones.
  7. Rumble filter, 18 dB/Octave which can be bypassed or even omitted
  8. Muting of the output with relays which shorts the output when the relay is deactivated. Since I will be using DC servos there will be startup and shutdown transients at the output which can be nasty if the preamp and power amp are both switched on.
  9. First opamp with DC-servo, possibly also the second one (therefore need for muting)
  10. Maybe circuit for class A biasing of the opamp outputs.
  11. RIAA network with the optional Neumann constant. The parts for the RIAA network can be made of regular caps or with bigger audiophilic caps such as Mundorf and similar.
  12. Maybe an option for easily interchangable RIAA network modules for i.e 78 rpm records. (Thanks Udo for the idea)
  13. Maybe option for balanced output, either with a daughter board or on board.... still maybe
  14. I will possibly offer super matched parts for the RIAA network in order to get extremely good accurancy.
  15. Printed circuit board with groundplane, good quality and best possible physical layout
  16. More wishes?
  17. If you want additional features please send a message to me.

Time plan

This is a long term project and I'll hope I have something at the end of 2018 but I won't promise anything.

More wishes or comments

A thread about it is found here. Feel free to add wishes.