Modifications
This is a cross-wiki maintained doc.
CX Cards are very cheep and flexible ADC chips as they can be modified for more sampling ability, signal filtering and connectors can be replaced and so on not only do they use standard parts but standard footprints for connectors and are also low cost enough to the point of not a high loss if mods fail badly.
CX White Card With C31 Removal Mod / BNC Mod / Crystal Mod
CX White Card With Cooling Mod / C31 Removal Mod / BNC Mod / External Clock Mod
- Software Defined Crystal Rate
- Improved Signal to Noise
- Hardware Synchronised Multi-Card Capture
- Hardware Synchronised Linear/Baseband Audio Capture
The most advanced mod available today, using an external crystal timing source we can have drift free capture with 2-4 CX Cards and audio feeds.
This allows duel channel video formats such as Betacam to be captured, or Video FM + HiFi FM + Linear for many other formats like VHS or Betamax.
Possible thanks to cxadc-clock-generator-audio-adc By Rene Wolf
External crystal timing via 2 additional PCB boards, a Jig with an SMA and Mainboard has allowed for under 50USD multi card sync, using 2 or more CX Cards alongside a extra input for synchronised Linear/Reference audio capture also has a extra input for headswiching timing signals.
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Raspberry Pi Pico as the interface and control board.
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Adafruit Si5351A for generating the shared clock source with 5 potential inputs.
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PCM1802 ADC for L/R input Linear/HiFi audio capture.
Audio Inputs and Head switch Input is on a dedicated bracket you can 3D print or modify a off shelf one.
USB Connection to Pi Pico provides control and audio feed.
The Analog Devices AD8367 is todays go-to option as its small and low power enough to run internally inside a VCR for example.
AD8367 Datasheet / AliExpress Link / 4.5v AA Battery Holder / Wiki Setup Link
This is primary a soft mod as your just connecting an external amplifier, however you can adjust the physical board components for better handling this is a tinker and see thing.
- Improved Signal to Noise
C31 is a capacitor that bridges the VUMX0 / VMUX1 inputs this causes more issues then anything else and so should be removed by soldering iron or plyers
- Faster Sampling Rate
- Improved Signal to Noise
This is the act of replacing the stock crystal with a faster rate crystal, note this crystal needs to be a fundamental type 3rd overtone will sometimes work but at lower rates.
At stock the CX Cards use a 28.63636 Mhz Crystal, this can be replaced with 40 Mhz fairly easily.
The max the CX chips support is 48Mhz to 54Mhz (according to the datasheet and testing) though this is rare to work outside the CX23881 version of the chip.
The 40Mhz Crystal: Generic 40mhz Fundamental or ABRACON ABLS2-40.000MHZ-D4YF-T Digikey / Farnell (can be sorced from most vendors)
With higher sample rates or just long duration capture more cooling to keep the CX chip at a stable temperature is required in some cases but best practice in all cases for heat generating silicon hardware.
Installation: Clean top of CX Chip with 99.9% IPA, then apply thermal pad or thermal paste, ensure the heatsinks does not contact with any electronic components its best to capton tape the heatsinks and or surrounding components.
Requirements: 40mm heat sync & fan / Thermal Pad / Thermal Paste / Silicone Glue / Kapton Tape
Blue cards come with BNCs but are not the most optimal cards, white cards come with RCA (both have S-Video or Y/C as well) as there is drop-in replacements available.
This requires de-soldering wicking & flush cutters,
The stock metal bracket will also need expanding by 1-2mm.
A Dremel with an small sanding bit or and a cutting wheel, or fine metal file is required for this.
Conformal coating is a layer of insulation this can provide light signal proofing and water/corrision and debris protection.
By adjusting low pass filtering you can, get a softer or sharper look to images, this mainly applys to LD or LaserDiscs for capture however so tape users can mostly ignore this segment.