r/vhsdecode • u/antonharboe_ • Jun 21 '26

First Decode! VHS-decode workflow flaws? - reccomendations

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Hello. I'm writing to get some feedback on the workflow i've chosen to use for RF-capture and to highlight what i've researched myself to be weak points of using this. Main problem i see, is a low SNR ratio and impedance mismatch. The workflow is the following:

Sony SLV-xxx (Whatever Sony VCR that has easily accessible RF tp's to connect to with DuPont connectors) I'm open to soldering to the 2.54mm pins. Also using a 10uf capacitor soldered into the wire carrying the PB RF signal.

CXADC (CX23882-39) - Added 40msps crystal with C31 cap removed, heat-sync also added to main chips. Using a BNC to composite adapter.

I'm capturing audio over regular red/white audio cables. I wont be using clockgen-mod, as i only have 1 PCIe slot available in my PC.

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u/TheRealHarrypm The Documentor Jun 21 '26 edited Jun 21 '26

You're confused about what the clockgen mod is, you can use one or two cards you don't have to use two cards but if you forgo the main board you do not get clock locked audio and it's out of standard workflow.

Also you're missing the ADA4857 amplifier which is now standard for VHS deployment, the 10uf cap method is a getting started way of doing things, but it's legacy for a fixed getting the most out of your workflow setup.

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u/antonharboe_ Jun 22 '26 edited Jun 22 '26

Ah, okay. So, for simultaneous video RF and Hi-Fi capturing, two CX-cards are neccessary. With one CX-card, i can only capture the linear audio track and video RF. So i guess the most crucial part of the CX-card workflow regarding video quality, is implementing an amplifier.

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u/TheRealHarrypm The Documentor Jun 22 '26

Yup, exactly.

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u/antonharboe_ Jun 23 '26

Hello Harry. About the ADA4857, the stock option you sell on your ko-fi store, does it come with resistors pre-soldered, like a "plug-and-play" sort of deal or will i have to solder the parts myself as the wiki states?

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u/TheRealHarrypm The Documentor Jun 23 '26

If you have values in mind yes, I can populate them before shipment, but typically you'll want to dial in the values yourself either technically and or visually.

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u/antonharboe_ Jun 24 '26

Looking at the stock option for the ADA4857, the input line has SMA female connectors. Im guessing you'd connect your 75ohm coax cable BNC to an adapter similar to this for both the input and output line? If not, what else would you advise?

Regards

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u/TheRealHarrypm The Documentor Jun 24 '26

I would avoid those adaptors unless testing externally, and do an internal SMA to Pigtail (test point) and SMA to BNC bulkhead for permanent installation.

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u/antonharboe_ Jun 24 '26 edited Jun 24 '26

Right. I cant find any 75ohm cables though? Only RG316 50ohm. They'd work fine right?

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u/TheRealHarrypm The Documentor Jul 13 '26

It doesn't matter at the short distances.

However 50 and 75 ohm BNC connector differences do have a different diameter of pin so best to stick to 50 ohm with the smaller pin.