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.
- Basic topology, opamp, RIAA network, opamp, rumble filter, output muting
- MC and MM with 4 different gains
- 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.
- Dual mono power supply with super regulators, much smoothing capacitance, fast recovery diodes or schottky diodes, possibly a Curcio regulator (looks very interesting).
- Transformers on board, both EI-types and toroids. Possibility to have an external transformer
- RIAA network with multiple sizes of caps so you can use almost any type, big, normal and small ones.
- Rumble filter, 18 dB/Octave which can be bypassed or even omitted
- 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.
- First opamp with DC-servo, possibly also the second one (therefore need for muting)
- Maybe circuit for class A biasing of the opamp outputs.
- 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.
- Maybe an option for easily interchangable RIAA network modules for i.e 78 rpm records. (Thanks Udo for the idea)
- Maybe option for balanced output, either with a daughter board or on board.... still maybe
- I will possibly offer super matched parts for the RIAA network in order to get extremely good accurancy.
- Printed circuit board with groundplane, good quality and best possible physical layout
- More wishes?
- If you want additional features please send a message to me.
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.