AudioSector / Peter Daniel Moving Coil Phono Preamplifier
Completed 8/2021
This project was originally based on the 47 Labs PhonoCube moving coil phono preamp, (details here) as re-interpreted by Peter Daniel of AudioSector with premium parts and an improved power supply. The best starting point for info on this project is the Peter's website:
https://audiosector.com/docs/phono-stage/details
There is a long thread (over 500 posts) on DIY audio related to the design and construction of this phono preamp:
https://www.diyaudio.com/forums/audio-sector/151938-phono-stage.html
In addition to Peter's interpretation of the 47 Labs PhonoCube, RJM Audio also has done some work on this design that may be of interest:
Full details of the design are in the DIYAudio thread mentioned above, but here's a look at the audio schematic.
And the shunt power supply schematic.
Peter designed a beautiful gold plated PCB for this project, top and bottom shown here. The AC inputs and transformer are at the left, shunt regulated power supply in the middle, and audio circuit on the right, based on OPA627 and OPA637 ICs.
This shows the populated power supply section under test to confirm all was working correctly before connection to the audio circuit.
I built some custom aluminum heatsinks as the shunt regulators generate a bit of heat. These definitely get warm, but not hot, to the touch. Because of the heat, for the main power supply caps between the heatsinks I used Panasonic FC's rated for 105 degrees.
I used Silmic II power supply decoupling caps visible at the right end of the PCB, otherwise pretty much what was suggested by Peter in the power supply.
Measured voltages of the +/-15V supply. Not bad given no adjustments or tweaking.
This is the (mostly) populated audio section of the PCB, separated from the power supply as it will be mounted separately, before installing the ICs.
I used some high quality 1% polystyrene film and foil caps I had on hand for the phono equalization (the white .01 and .047s).
I used all 1/4 watt Dale 1% metal film resistors, and you'll also see another pair of the Silmic II power supply decoupling caps in the center of the PCB.
The red caps are long discontinued Black Gate non-polar Type N, as specified by Peter.
Instead of running wires from the input and output RCA jacks to the PCB, I soldered them directly to the back of the audio board, shown here.
The RCAs are Vampire PCB2F/S gold/teflon connectors.
You can also see the rear panel of the enclosure, drilled for the RCAs in the off-kilter pattern created by the two channels of the PCB being mirror images of each other.
Top view of the assembled preamp after wiring the power supply and AC power connections.
On the left is the IEC inlet, power switch, and an LED to indicate the preamp is powered up.
The fuse is actually mounted below the transformer on the bottom of the PCB.
Closeup view of the assembled preamp. The ground lug is on the lower right, tied to the common ground at the Silmic II filter caps.
As you can see here, the signal path from the input, thru the preamplifier, to the output is just a couple inches in length.
Just visible at the lower left are three ventilation holes below the heatsink. There are matching holes in the same area on the top cover for both heatsinks to allow air movement over the heatsinks.
Photo of the input/output end of the preamp. Not much to see here, just the inputs and outputs, with the ground lug over on the left.
And the power end. Even less of interest here - IEC, power switch and blue LED.