This document primarily describes the physical hardware and installation of the ePot.V3 Mini (the “Mini” ) panel mounted electronic stepped attenuator. The detailed operation and control of the Mini will likely be covered in another manual once it’s ready.
The ePot.V3 Mini (the “Mini” ) is a panel mounted electronic stepped attenuator that offers exceptional sonic performance with advantages that no mechanical attenuator can match.
The “Mini” is literally a direct physical replacement for any volume potentiometer or mechanical stepped attenuator that through-hole mounts directly into a typical front panel, is secured by a nut and washer, to which you then attach a conventional volume control knob.
The ePot.V3 Mini is intended for any DIYer, designer or OEM who is looking for a high performance volume control alternative to conventional potentiometers or mechanical stepped attenuators.
The Mini 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 to shift/left right or operate louder or quieter than usual at a given volume setting. Operating the Mini with an LDR attenuator module inside of equipment that gets very warm can still work but you may have to run calibration when the Mini has been warmed up and stabilized. We have not found this to be a problem within our own preamp products but the caution is valid.
The Mini is intended for panel mounted via the threaded bushing on the embedded encoder similar to a potentiometer or mechanical stepped attenuator. It’s also possible to chassis mount the Mini via the 2 mounting holes located in the opposite corners of the PCB using standoffs. You can also augment the panel mounting by adding a standoff to just the one PCB mounting hole in the rear of the board giving it additional rear support.
The installation steps for the Mini are as follows:
The Mini has a separate dedicated power regulator board mounted to its underside that connects to the main board via a 5 pin header that runs parallel to the J3 audio socket. The regulator board is powered externally through the J2.V and J2.G screw terminals.
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:
Some components on the power regulator board will feel hot to the touch when the Mini is powered up. This is normal.
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.
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.
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.
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.
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.
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.
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 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 is a 12 position (2 x 6) female header that provides power and control signals to the attenuation module.
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:
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 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 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.
The header pins on the V3.Mini 14 pin OLED header are NOT labeled on the circuit board due to space constraints. Note the white dot as a visual key reference which is present on the Mini. The header with labels is shown above. Each pin is described briefly in the below going counter clockwise.
When the OLED display is used the OLED display comes with the IR receiver module already mounted directly to the OLED display interface board.
Without the OLED display the IR receiver module must be connected to the following J7 pins. A 6 inch 3-wire square-pin cable is provided.
When the OLED display is used there is no way to also connect a status LED to the Mini. Without the OLED display you have the option of connecting a status LED to the J7 header with the 6 inch 2-wire square-pin cable is provided.
The LED provided with the V3.Mini is a typical 3 mm size blue LED with typical dimensions shown below. You may wish to add a resistor to this circuit to tone down the brightness (limit the current) of the LED to suit your needs. This resistor is NOT included.
To enable operation with only a status LED, place a jumper across pin J7.DC and the adjacent J7.G pin. Then connect the status LED to the J7 header as follows:
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:
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 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.
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.
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.
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.
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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