Attenuation modules for ePot.V3 Mini & Max
The ePot.V3 Mini and the ePot.V3 Max electronic stepped attenuator models both use plug-in attenuation modules. There are two types of attenuation modules – LDR (light dependent resistors) and Discrete (switched surface mount resistors). While one or both types are typically included when purchasing either a Mini or a Max board, these modules can be purchased separately here.
The two attenuation module types are shown side by side in the photo below along with a typical credit card to visualize their relative size. A Discrete module is shown plugged into a V3.Mini. The LDR module is shown by itself below the V3.Mini. Both plug directly into the ePot.V3 Mini and ePot.V3 Max boards via identical mating pin sockets.
Each LDR module has 4 embedded LDRs plus an EEPROM memory chip which contains the attenuation/calibration data tables for each LDR at one or more impedance settings. The LDR Module provides 100 steps of attenuation between -60 to 0 dB. Each channel uses 2 LDRs in a series/shunt configuration. Each LDR is individually controlled via a programmable microcontroller which uses stored calibration data to change the resistance value of each LDR to achieve each volume step. LDRs are not pre-matched because the calibration process normalizes the behavior of each LDR around a 100 step table of target resistance values.
When used in an ePot.V3 Max, an LDR Module can be re-calibrated as needed and can be re-configured for any impedance setting from 1k to 99k with 20k being the typical fixed default impedance level for setting #1.
When used in an ePot.V3 Mini, the LDR Module impedance and associated calibration data is fixed. The Mini is not capable of re-calibrating an LDR Module. To change the impedance or calibrate an LDR Module requires an ePot.V3 Max. Absent the availability of an ePot.V3 Max, you must specify the fixed impedance of the LDR Module when purchasing one for an ePot.V3 Mini.
The Discrete Module uses low noise precision thin film resistors made from nickel-chromium metal deposited on to a ceramic substrate. Referred to as stepped logarithmic attenuation, 7 fixed resistor pairs per channel provide stepped attenuation in increments of 0.5 dB, 1 dB, 2 dB, 4 dB, 8 dB, 16 db, and 32 dB. These 7 stages provide 127 steps of super smooth attenuation in ~0.47 dB increments over a -63.5 to 0 dB attenuation range.
While each step is truly discrete requiring one or more resistor pairs to connect and/or disconnect from the attenuation circuit this switching is done via ultra-fast, and ultra low-distortion, break-before-make analog switches. The result is super smooth switching with no audible artifacts. Left and right channel switching is done independently as well so that channel balance adjustments are also possible; something unheard of with discrete mechanical stepped attenuators.
The Discrete Module impedance is fixed at 60k. There’s no calibration required or even possible for the Discrete Module since its characteristics are permanently set by the resistor set used during manufacture.
The Discrete Module can be used in either the ePot.V3 Mini or Max.
Hardware, operation and control manuals
A more comprehensive description of the epot.V3 Mini and Max hardware, installation, operation, and controls can be found in the following online documentation: