LDR Stepped Attenuator | ePot.V4 Max
$275.00
Available on backorder
An LDR stepped attenuator | preamp controller
The ePot.V4 Max (the “V4”) is a chassis mounted electronic LDR stepped attenuator and preamp controller board for the DIYer, designer or OEM.
The V4 Max provides 2-channel, 100 step stereo volume control, input switching for up to 4 sources, with remote control via infrared remote, plus local control via rotary encoder, and a sporty high contrast OLED display with a menu driven interactive user interface.
The V4 Max is an analog volume control device run by a software driven 32 bit ARM microcontroller. While digitally controlled, the V4 is inherently an analog attenuator and as such does NOT manipulate any audio signals in the digital domain. Analog audio signals passing through the V4 are optically isolated from any power source. There is no active gain stage and there is no active output/buffer stage. Each audio channel sees only 2 resistors (light dependent resistors – LDRs). The LDRs control volume by reducing the voltage of the incoming audio signal. By this definition the V4 is inherently a passive volume controller.
By itself, the V4 can be used as a passive preamp. When mated with the optional buffer board or any downstream gain and/or buffer stage the ePot.V4 becomes the attenuator/controller of a high performance active preamp.
The V4 is the successor product to Tortuga Audio’s popular V3 model preamp controller. The V4 series represents Tortuga Audio’s 5th generation of of audio attenuation technology designed around light dependent resistors (LDRs).
Specifications
| Topic | Description |
|---|---|
| Preamp type | Passive preamp (no no active manipulation of the audio signal by a power supply) |
| Application | 2-channel single-ended or balanced audio (balanced audio requires additional expansion board) |
| Signal isolation | All audio signals are optically isolated from control power |
| Attenuation method | L-pad resistive voltage divider network using light dependent resistors (LDRs) in lieu of potentiometer or fixed discrete resistors |
| Attenuation perception | Smooth, quiet, continuous transitions between each discrete attenuation step |
| Attenuation range | 100 discrete attenuation steps of ~0.6 dB per step over a 0 to 60 dB range. |
| Attenuation control | Precision closed loop LDR current control with 16 bit resolution pulse width modulated command signal |
| Attenuation module | Replaceable plug-in LDR attenuation module each with 4 LDRs (2 LDRs per channel). |
| Muting | Fully muted output at step 0 using dedicated muting relay |
| Volume ramping | User selectable volume ramping behavior (down and up) during muting/unmuting |
| LDR calibration | User-initiated calibration of each LDR against a 100 step resistance schedule that varies with impedance setting with results stored in an EEPROM memory. Measuerment during calibration uses 16 bit ADC resolution. |
| Gain | Unity (1x) gain passive – no amplification |
| Input coupling | Direct coupling with no passive coupling capacitors or active buffering |
| Input switching | Switching between 4 input devices using miniature electro-mechanical relays |
| Input impedance | 50k default input impedance with up to 9 other impedance settings each adjustable between 1k and 99k and the ability switch between impedance levels with live music to optimize input impedance for their system |
| Channel balance | Adjustable channel balance up to 20 steps (12 dB) left or right while maintaining overall volume level |
| Signal interconnection | Pin header or individual solder lugs for connecting inputs, outputs and signal ground |
| Signal ground | Audio signal grounds are isolated from power ground within controller, however, audio signal ground must share common ground with power supply via an external star ground point in order for LDR calibration feature to function properly |
| Remote control | Fully controlled via inputs from 2 different handheld infrared remotes. |
| Encoder control | Partially controlled via inputs from a rotary encoder with integral pushbutton |
| OLED display | 8 bit grayscale high contrast white-on-black 256×64 pixel graphic OLED display with an intuitive, easy to use, menu based control scheme. OLED display assembly integrates the display, an infrared receiver and an encoder into a single assembly with single 14 pin ribbon connection to the V4 board. |
| Auxilliary controls | Optional (via customized firmware) monitoring and control interfaces including trigger out, status LED, serial UART, serial I2C, and 4 digital/analog GPIO pins. |
| Total harmonic distortion | Typically less than 0.5% | essentially inaudible |
| Power requirements | ~5 volts regulated DC rated at or above 0.5 amps |
| Microcontroller | ARM based STM32G4 32 bit microcontroller running at 144 MHz |
| Firmware | Object oriented C++ firmware running under a lean real time operating system (FreeRTOS). Firmware updating via USB connection using a vendor based updating application that runs on a PC, Mac, or Linux machine |
| Printed circuit board | 2 layer FR4 board with high quality gold plated nickel immersion solder pads |
| Optional buffer board | Custom designed plug-in daughter buffer board converts the passive V4 into an active preamp with adjustable gain |
| Optional power supply | Custom linear power supply provides a very low noise source of primary 5 volt power plus split +/- 12 volts for the optional buffer board |
V4 manuals
Tortuga Audio’s online product documentation system (“Docs”) for the V4 includes both a hardware manual and an operations and control manual.
We highly recommend that you explore these 2 manuals via the links below.
This manual describes the design basis, hardware features and interfaces of the ePot.V4 Max (“V4” or “Max” ) LDR stepped attenuator & preamp controller.
(button link does not work yet)
This manual describes the how to operate the V4 via infrared remote, local rotary encoder, together with its menu driven OLED display .
What’s included?
The following items are included by default with each V4.
- The ePot.V3 board itself with a 90 degree 12 pin J4 audio signal pin header installed
- Power supply plug with 4-6 inches of wiring for connecting 5 volt power to the V3 board
- Female faston lug for connecting power ground to the faston ground tab
What’s not included that you’ll definitely also need?
You will have to supply the following additional items some of which can be purchased from Tortuga Audio along with the V4:
- An LDR module if not purchased along with the V4 board
- An OLED assembly if not purchased along with the V4 board
- An approved remote if not purchased along with the V4 board
- Nominal 5 volt DC power supply rated at 0.5 amp or greater.
- Audio signal input/output jacks
- Preamp enclosure
Optional items
The following optional items are offered by Tortuga Audio for the V4 for those who want to explore an active preamp and/or the benefits of a low noise linear power supply
- An optional plug-in solid state preamp buffer board converts the passive V4 board into a true active preamp with adjustable gain.
- An optional low noise linear power supply gives the V4 board plus optional buffer board raises the performance bar for V4
