The DÆ v3.0 Stepped Attenuator pictured below is the most recent version and has been in testing for several weeks.

This stepped attenuator has a combination of features that are rarely found in other attenuators. It is motor operated allowing the use of a remote control to adjust the volume level. Each attenuator is a mono unit so two are required for stereo operation. Each attenuator is equipped with a Bluetooth radio that keeps the two attenuators of a stereo pair synchronized and communicates with the remote. The details of each of the subsystems of the attenuator are described below in greater detail.

This features and principle of operation of the attenuator subsystems starting from the knob are described in greater detail here.

Knob Stepper Motor - At the top of the image is the manual input knob attached to a stepper motor. The stepper motor allows that knob position to be adjusted via radio control from the remote control or from the paired attenuator in a stereo setup. When the owner adjusts the volume knob on one attenuator of a stereo pair the other attenuator moves in lock-step. The motor also provides improved tactile feel by applying magnetic damping to the stepper motor shaft during manual operation.

The motor has two shafts. The knob is mounted on the front input shaft and a holder for a magnet is attached to the rear shaft. An AMS AS5600-ASOM Hall Effect Sensor on the Control PCB accurately measures the angle of the stepper motor shaft.

Control PCB - The Control PCB is the heart of the attenuator. The Control PCB has a Laird BL652 module that includes the Bluetooth radio and the microcontroller that runs the embedded logic to control the attenuator. The Control PCB also has the two Trinamic TMC2130 stepper motor controllers with StealthChop that provide ultra quiet motor operation. One of the stepper motor controllers operates the Knob Stepper Motor and the other one operates the Ladder Stepper Motor.

Ladder Stepper Motor - The Ladder Stepper Motor rotates a “yoke” that has arms supporting small cylindrical magnets. The Ladder Stepper Motor positions the magnets next to the small reed switches of the Ladder Sections that select the ladder step for the desired attenuation.

Ladder Sections - Two Ladder Sections are shown with a series of twelve pairs of resistors and associated reed switches arranged around the perimeter of each Ladder Section. A maximum of eight ladder sections are possible for a maximum of 96 steps. This attenuator has a total of 24 steps on two Ladder Sections.

Rear RCA Connector PCB - The Rear RCA Connector PCB provides for inputs for Phono, CD, A1 and A2 inputs as well as an output connector. The Rear RCA Connector PCB also has four reed relays to make the input selection under control of the Laird BL652 module.

I am currently working on an updated battery charger/power supply, differential input PCB and filter/output PCB. Once these system are tested, I will be ready to complete the v3.0 of a complete preamp and phono preamp.