A TBC is usually what people start looking to buy when they decide to improve the quality of their recordings, not just accept whatever the tape, VCR and capture card/DVD recorder decide to do on their own. And it is a good first step towards hardware restoration, though often misunderstood...
There's really not much to this.
Here's the quickie, all you really need to know:
Under $50? Good luck, shop eBay
, and cross your fingers. Expect to pay $200-300 for a new TBC, prosumer grade full-frame. Maybe half price used. Maybe. DataVideo TBC-1000 and AVToolbox AVT-8710 are the two most popular models.
- Improve quality?
A TBC corrects the signal. It is not there to "improve quality". It may improve quality, usually seen to remove jitter or odd movements. The visual improvements are often small, but very valuable. Many people observe that it works best to remove jitter.
- Line? Full frame?
Do not confuse a "line" TBC (mostly worthless) with a "full frame" TBC. DVD recorders have worthless line TBCs, do almost nothing. Those line TBCs are better off in cameras, can actually make a difference there.
- Passthrough TBC?
Camera TBCs are not why passthrough "removes" MV. It just digitizes a signal and has no way to interpret MV in the hardware. Simple as that. TBC has zero effect.
- JVC TBC?
The JVC series S-VHS VCRs have DigiPure DNR (digital noise reduction) circuits integrated into the TBC. It is a special kind of TBC, and is why this one can "clean the picture quality". It is NOT only a TBC at work here.
- Audio TBC?
TBCs with audio connections merely passthrough the audio, nothing more.
- TBC makes my tape worse?
No TBC is perfect, so about 1% of the time, it's known to make a tape worse. (Or more often if all of your tapes have the same flaw.)