ePot.V3 Max hardware manual

This manual is undergoing significant editing. 

Under Construction graphic

About this manual #

This document primarily describes the physical hardware and installation of the ePot.V3 Max (the “V3” or “Max”  ) panel mounted electronic stepped attenuator & preamp controller. The detailed operation and control of the Max will likely be covered in another manual once it’s ready.  

What is the ePot.V3 Max? #

The ePot.V3 Max is a high resolution chassis mounted electronic stepped attenuator for the DIYer, designer or OEM who is looking for exceptional sonic performance in an integrated, software driven, preamp controller that includes input switching, remote control and a menu driven interactive high contrast OLED display interface.

The V3 Max comes with a plug-in LDR (light dependent resistor) attenuation module by default but you can opt for a discrete resistor attenuation module. The different module types are interchangeable.

The graphic OLED Display Module (sold separately) integrates with the V3 to provides an easy and intuitive user control experience through an interactive menu driven control interface designed around  the 7-button Apple remote.

epot V3 Mini layout and dimensions

Physical dimensions #

At 2.7 inches wide by 4.4 inches long the footprint of the Max is ___% smaller than its predecessor,  the V25. The overall depth is slightly greater than 1 inch but we recommend allocating a 1.5 x 1.5 inch volume of space around the length of the Max. 

Ambient conditions #

The ePot.V3 was designed to operate within nominal room temperature conditions that are typical for home stereo equipment. LDRs are known to be temperature sensitive. Therefore large departures from nominal home room temperature conditions  may cause the LDR attenuation module to operate poorly.  Operating the V3 with an LDR attenuator module inside of equipment that gets very warm  may still work but you may have to run calibration when the Mini has been warmed up.  We have not found this to be a problem within our own preamp products but the caution is valid. 

Installing the Max #

The Max is a chassis mounted board that is typically mounted horizontally on 4 standoffs but can also be mounted vertically on its side (mounting hardware not included). In addition to installing the Max itself, the designer will typically also mount the following additional items in a front panel: status LED or OLED display module, IR receiver module, and rotary encoder.  Typical installation steps for the Max are as follows: 

  1. Mount to chassis – The Max board is typically mounted horizontally to a chassis bottom plate via 2-4 standoffs. We recommend minimum 1/2 inch tall standoffs to ensure good clearance and airflow around the power board on the underside of the the Max board. Ideally the audio connection header end of the Max will be oriented towards the rear of chassis to minimize audio signal runs while the other end of the Max is oriented towards the chassis’s front panel. 
  2. Connect to power – The max is equipped with a xxx 2-pin slip on power connector. A mating socket with crimp pins is included with the Max. Care must be taken to ensure proper polarity is maintained since reversing polarity may damage the Max. Power supply voltage can range from 9-30 VDC but 12 VDC is the nominal recommended voltage level. 
  3. Connect audio signals – The Max is a 2 channel (left & right) stereo attenuator/controller. Up to 6 different input sources can be connected to the Max. The Max has built-in analog switches for switching between the different inputs. Inputs/outputs can either be connected via the X pin header or via solder pads.There are separate signal grounds (J2.RG & J2LG) for each channel for convenience so that the user can control where these signals ultimately meet at a common ground point. 
  4. Connect  IR receiver module (optional) – To operate the Max via the Apple remote you must attach the IR receiver module to pins J7.IR, J7.V and J7.G. (see details on the IR receiver module elsewhere herein).  
  5. Connect status LED (optional) – Connect the positive (long) leg of the status LED to J7.? and the negative (short) leg to J7.G. To enable the status LED you also need to place a jumper across pins J7.? and J7.?. The status LED and OLED display are mutually exclusive, i.e. you can install/use either but not both at the same time. 
  6. Connect OLED display (optional) – Connect the OLED display  to the J7 header using the 14 pin ribbon cable. Please note the the red stripe on the ribbon cable must align with the white dot on the J7 header on the Mini. Similarly the red stripe must align with the top edge of the OLED display’s interface board (the edge with the long horizontal row of pins) where the ribbon cable connects to the OLED’s J2 14 pin header. When using the OLED display the IR receiver module mounts/connects to the IR1 solder pads on the OLED interface board which in turn connect through to the Mini via the 14 pin ribbon cable. Please do NOT connect a separate rotary encoder to the OLED J3 header since this encoder will interfere with the Mini’s embedded encoder.  

Power regulator board #

The ePot.V3 Max has a separate dedicated power regulator board mounted to its underside that connects to the main board via a 5 pin header located hear the XX power entry plug. The regulator board is powered externally through the power entry plug. 

The power regulator board produces 3 different voltages each using low noise 2 stage regulation with a  switching 1st stage followed by a linear 2nd stage.  The voltages are as follows:

  • +3.3V – primary voltage for powering the microcontroller, control DAC, encoder and display.
  • +5V – positive split voltage for powering the current control op amps and also analog switches when a discrete attenuator module is installed
  • -5V – complementary negative split voltage. 

Some components on the power regulator board will feel hot to the touch when the Mini is powered up. This is normal. 

Plug-in attenuation modules #

The V3  requires a 2 channel plug-in attenuation module to function. The attenuation module plugs into the J1/J3 female headers on the V3 board. There are two types of plug-in attenuation modules available – LDR and discrete. Both types provide 2 channel stereo attenuation. The LDR type uses light dependent resistors and the discrete type uses pairs of discrete thin film surface mount resistors. Each of these attenuation module types are described in more detail below. 

LDR attenuation module #

The LDR attenuation module uses 2 pairs of LDRs with each pair controlling one channel of volume. Each LDR pair (channel) operates fully independent of the other. The LDR pairs are  configured in a series/shunt arrangement that essentially emulates how a potentiometer controls volume.  The resistance level of each LDR is independently controlled by a precision JFET op amp current controller which gets its set point from  a 16 bit DAC controlled  by a software driven 32 bit ARM microcontroller. 

ePot.V3 LDR Attenuation Module

The performance characteristics (current vs. resistance) of each LDR is stored within an EEPROM memory chip on the attenuation module. The microcontroller reads the stored performance data of each LDR in real-time  in order to set the target resistance level of each LDR as needed to achieve a given volume step. This process happens every time a volume step change occurs. The LDR attenuation module has 100 volume steps over a -60 to 0 dB control range.  Each step change in volume is totally smooth and without any sonic artifacts related to control or step switching. In fact there’s  no actual switching per se between each volume step, only a continuous analog transition from one set of resistance levels to the next. 

The impedance of each LDR attenuation module is nominally fixed and must be specified at the time the Mini or  LDR attenuation module is ordered. The impedance level is marked on the module within a circular  white stick-on label which may be on bottom side of the module. The impedance level of each LDR module can in fact be changed by using an ePot.V3 Max which has built-in on board LDR calibration/programming, a feature not present on the Mini due to its smaller size. 

Discrete attenuation module #

The discrete attenuation module uses 7  pairs (+1)  of discrete thin-film resistors per stereo channel for a total of 30 resistors per module. Thin-film resistors are typically composed of nickel-chromium metal deposited onto a ceramic base. These resistor pairs are arranged as a logarithmic set of individual switchable series/shunt attenuators with values of -0.5 dB, -1 dB, -2 dB, -4 dB, -8 dB, -16 dB and -32 dB.  This is sometimes referred to as an R-2-R or ladder resistor set. This arrangements provides 127 attenuation steps of 0.5 dB per step over a control range of -63.5 to 0 dB. Individual resistor accuracy is typically 1% or better. 

epot,v3 discrete attenuation module

Each of the 14 discrete attenuation resistor pairs (7 per channel) are switched using single pole double throw analog switches that have fast, noiseless break-before-make characteristics. The result is smooth transitions between each of the 127 volume steps with no discernible sonic switching artifacts. The analog switches also have ultra-low distortion specifications of 0.004% THD. 

Switching is controlled directly by V3’s 32 bit ARM microcontroller working through an output port expander chip located on each discrete attenuation module. Use of the expander chip greatly simplifies the control wiring making it possible to drive both types of attenuation modules from a single common control header.  

The impedance of the discrete attenuation module is currently fixed at 60k. In the future we may offer discrete attenuation modules with other fixed impedance levels. 

Changing attenuation module types #

The ePot.V3 checks to determine which type of module is present each time it powers up. Therefore, it’s a simple matter to switch from one attenuation module type to the other. However, you must power down the V3 to swap out a module or change module type. Gently remove the current module and then gently insert the new module. Apply power, wait briefly for the unit to boot up, and then turn it on to use. 

J1/J3 attenuation module headers #

These two female headers accept the plug-in attenuation module. The attenuation module must be plugged into both headers simultaneously. The fit may be a bit tight and necessitate the gentle rocking of the module as it’s pressed in or removed. Care should be taken to ensure that the pins align properly with both headers before applying insertion pressure on the module. Care should also be taken to ensure the pins are not inadvertently offset and missing their respective sockets. 

J1 audio header #

J1 is a 6 position female header that routes the left and right channel input and output to and from the attenuation module. The 6 pins correspond to the same 6 audio input/output/ground pins described under the J2 screw terminal below.  

J3 control header #

J3 is a 12 position (2 x 6) female header that provides power and control signals to the attenuation module. 

J2 screw terminal | power & audio #

J2 is an 8 position screw terminal located on the opposite end of the board from the encoder.  Power and audio both connect to the Mini through the J2 screw terminal header. 

The J2 connections are as follows: 

  • J2.V – nominal +12 VDC power although the Mini is able to operate with 9-30 VDC supply. 
  • J2.G – power ground
  • J2.RI – right channel audio input 
  • J2.RO – right channel audio output
  • J2.RG – right channel audio ground
  • J2.LG – left channel audio ground
  • J2.LO – left channel audio output
  • J2.LI – left channel audio input 

The Mini typically draws under 150 ma without the OLED display and upwards of 300 ma with the display.

Each audio channel is entirely independent of the other within the Mini including the audio signal grounds. 

J6 wifi/bluetooth header #

J6 is an 8 position (2 x 4) pin header that’s intended to interface with a 3rd party WiFi or Bluetooth communications module. This feature remains in development and is not currently functional. The V3 will require a firmware update to enable this feature if/when it becomes available. 

J7 OLED header #

J7 is a 14 pin (2 x 7) header that carries the power and control signals for the OLED display, the IR receiver module, and the Status LED. 

The J7  header can either be used for the Status LED & IR receiver or the OLED display but not both at the same time.

When the J7 header is connected to the OLED display via a 14 pin ribbon cable, the IR receiver module can no longer connect directly to the J7 header and must instead mounted directly on the OLED display interface board or otherwise be connected to the same 3 IR solder pads.

J8 programming header #

J8 is a 5 position pin header located parallel with and right above the J7 OLED header. J8 does not have a “J8” label on the PCB. The programming header is exactly what it sounds like – the header through which the Mini gets programmed either in the factory by Tortuga Audio or in the field by users. 

The J8 pins going left to right are as follows:

  • J8.V – +3.3 VDC power  
  • J8.C – programming serial clock
  • J8.D – programming serial data 
  • J8.G – power ground
  • J8.RX – UART #1 receive pin 
  • J2.TX – UART #1 transmit pin  

Pins V.C.D.G are used by Tortuga Audio to install the original applications firmware. Interfacing with these pins requires specialized equipment and software and is not intended for use by the end user.

Pins V.G.RX.TX can be used by the end user to update the firmware using an application provided by Tortuga Audio. Connection to these 4 pins requires a special purpose USB-to-serial cable which are widely available online and typically cost between $10-15 or a USB-to-serial breakout boards that allow the user to accomplish the same thing for around $5 plus the cost of a standard USB Mini cable plus a square pin (4)  jumper cable.  Examples of each are shown below. 

The detailed procedure for updating V3 firmware via the programming header is outside the scope of this document. Please refer to the V3 Firmware Updating documentation elsewhere in this system. 

S1 Rotary encoder & pushbutton #

S1 is an incremental encoder wherein a pair of internal switches open and close in different sequences depending on whether the encoder is rotated clockwise or counterclockwise. The microcontroller decodes these sequences to determine the direction of rotation. In addition, S1 has a 3rd integral pushbutton switch which is activated by pushing in the encoder shaft.

These encoder’s signals are used by the V3 microcontroller to turn the V3 on/off, control volume level, adjust channel balance, switch inputs (not available with the Mini), and mute/unmute the volume.

S2 Reset pushbutton #

The S2 Reset pushbutton will reset the controller as if you cycled the power off  and then on again. It resets the microcontroller. This is NOT a “factory reset” type of reset. It’s provided as a convenience but in practice is unlikely to be used very often. The S2 Reset button has a special purposed when used in conjunction with the S3 Boot pushbutton described below. 

S3 Boot pushbutton #

The S3 Boot pushbutton is used in conjunction with the S2 Reset  pushbutton in order to place the V3 into “bootloader mode” for purposes of updating the V3’s firmware. By pressing the Boot pushbutton, then briefly also pressing/releasing the Reset pushbutton, and then  finally releasing the Boot pushbutton as well, this places the V3 microcontroller into bootloader mode. When this is done with the V3 connected to a PC or a MAC equipped with the  appropriate software, the software can then establish communication with the V3 via the J8 header and then update the V3’s firmware. 

Firmware updating procedure  #

This documentation is still being developed. The detailed procedure for updating V3 firmware via the J8 programming header will either be added here or there will be a link to a separate V3 Firmware Updating document. 

Operation and control  #

This documentation is still being developed. The detailed procedures for operating and controlling the ePot.V3 models will be added as soon as they become available. 

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