Hi Everybody!
You may remember the M4 amplifier designed by j4cbo. You can find it http://www.head-fi.org/t/449462/the-m4-a-fully-differential-single-pcb-amplifier-with-relay-attenuator. This was a nice prototype, but since then, there were no developement in the project, no documentation, no nothing, but a circuit diagram.
I always thought, that it is a really great project, and since there were high interest I started to design basically the same. However I made some modifications:
- the design is through hole, no SMD is used
- no built in power supply
- no built in stepped attenuator
The aim of my project is different from j4cbo's, because I would like to design something which can be built by everybody.
In this design one could use the 2SJ76V and 2SK213V lateral MOSFET combo by eliminating the capacitors near the MOSFET and by putting 1K resistors to R3 and R13.
I have enclosed the schematic and the pcb design. Please don't let the name of the transistors confuse you, everything is exactly the same as in the M3 design. The PCB is only for one +/- channel of course.
Followup:
I have figured out the volume control and imput impedance problem. I attached the circuit and the PCB. The design need a 4 gang ALPS RK27 potentiometer, but one could use other too, like you can wire two delta1 like this one. If I am right, the imput impedance will be a constant 20K if I use 10K per gang RK27. Of course one could use a simple design like this http://www.raleighaudio.com/figure_17.htm. Eg. one could use two 5K resistors and one 10K potentiometer, but the input impedance would be changing between 10K and 20K.
If this attenuation seems OK, and nobody will correct me in the design, then I think I will build a prototype. Fortunatelly most of the wiring is on the bottom, so the through hole plating won't be a big problem during DIY PCB.
Please feel free to comment the design. Any recommendation is welcome!
The PCB of the amp:
Schematic of the amp:
PCB of the volume control:
Schematic of the volume control:
