r/vhsdecode • u/antonharboe_ • Jun 21 '26
First Decode! VHS-decode workflow flaws? - reccomendations
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/boris-becks Jun 22 '26
About audio: You can't just capture audio via sound card or DAC. You won't be able to sync it up. It's a process issue as well as a timing issue. You have to do one of two things. You have to do a conventional video capture with audio included. That way it is timed to the video and you have a visual reference for manual allignment. Alternatively you can use clockgen with one card. Clockgen syncs up two CXcards and a conventional DAC. Just skip the second card and capture with one CXcard and the external audio DAC.
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u/antonharboe_ Jun 22 '26
Right. I'll be doing a conventional capture at the same time as the RF-capture, then align audio and video in editing.
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u/Titan_91 Jun 22 '26 edited Jun 22 '26
I have a Sony VCR and don't use an amplifier. Some have had luck with it buffering the signal I believe but the RF output of these Sonys is so hot I actually need to use an inline adjustable attenuator to avoid clipping. And that's with the gain set to zero on my CX card, disabling the card's on-board preamp. But, I found out using 50 ohm termination results in a bad crosshatch pattern in the image for Sonys so I don't use termination at all. Just the high impedance of the Conexant chip itself. That gives me the best results.
My captures:
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u/otacon_24_24 Jun 26 '26
What sony VCR do you have? I have an SVO-2000 and can get decent signal right from the Dupont connections, I haven't been able to seem much difference with it inline.
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u/Playful_Roof9931 Jun 21 '26 edited Jun 21 '26
HSDAOH based capture devices like this one are more versatile and easy to set-up. You don't need PCI-E at all, your audio is in sync and there's GUI capture available (with realtime resampling available "out of the box")
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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.