APOX-1
255 Step relay-based non-constant impedance Volume Controller
Based on lots of great input from the folks over at
www.diyaudio.com the APOX-1 design has been modified. We are finishing
the design work and software.
We have changed from a Aleph like volume control scheme, to a shunt mode scheme
suggested by Petter on www.diyaudio.com This new shunt type volume controller
uses fewer relays as the previous version, has more output levels, and the
audio path is not attached to ground( except if using as single ended ).
| Features |
The Relay board will have the following features:
Uses high quality hermetically sealed signal relays DPST with internal shield.
Two Fully differential inputs and outputs. (L+, L-, LGND, R+, R-,RGND)
30 resistors required for balanced volume control.
Board accommodates axial or radial resistors.
1020 position Relay Controlled Volume Setting. (however, many settings will
sound identical to others and may be removed) At this time 255 settings were
generated in a lookup table for the microcontroller. This gives a fairly linear
volume control of approximately 0.23 dB per step. This allows for very fine
adjustment in volume.
Microchip microcontroller controls all relays indiviudually to try to
accomplish equally spaced decibel output
Microcontroller acts as I2C Slave for simple wiring requirements to APOX-IR
board
Up to eight of these boards may be stacked up with 3 jumpers for address
offsets.
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Pics
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Board Layout
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Note: The shield ground plane on left, and digital ground plane on right has
been ripped up for clarity
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Dimensions
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Schematics
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Download the latest shunt mode APOX-1 version 3.0
schematics here.
The following schematics have been obsoleted
Download the shunt mode APOX-1 version 2.0 schematics
here.
Download the old Aleph like APOX-1 version 1.0 schematics
here.
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Resistor Calculations
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Click here for the new C++ file to calculate the
PIC's lookup table and the programs output files.
Click here for an APOX-1 (rev 3) resistor
calculator Excel spreadsheet to determine acceptable resistor values to
use
This older spreadsheet is now obsolete
Click here for an APOX-1 (rev 2) resistor
calculator Excel spreadsheet to determine acceptable resistor values to
use
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[ Apox Audio ]
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