Please move as needed. I need a simple technical answer to this question. I have 4 combo units and seperate players and recorders. In order to dub copy protected material between units either tape or dvd to dvd, I need to use a BLACK BOX between them. Same brand/model. I found what appears to be the same box on MCM ELECTRONICS. I found a similar box(s) on another site. The only difference between the two is that one is marked "VHS TO VHS" and the other "DVD TO DVD". My current box is the former. Since the box works in any combination of player and recorder in either direction, that begs the question, is there any electrical difference between the two? I tried one between my player and dvd recorder attempting DVD TO DVD dubbing. "CANNOT RECORD". It DOES work with non protected material as expected. I do not know whether the issue is a bad box, or that two combos work together. I tried using a WORKING box. No go. I ordered one of each on the off chance that the box needs to be dvd to dvd specific which defies logic. A complete answer please. firstname.lastname@example.org.
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You won't get a "complete answer" with so little information. A black box?
There are many variations on the MCM type of CP stabilizer: they became commodity items long before DVD was a blip on the radar. As a general rule, they are optimized to clear VHS protection but don't work well (if at all) with DVD protection: DVDs include the old VHS protection scheme plus newer additional analog and digital protections that usually require either a TBC or a DVD-specific filter to clear.
The MCM box is known to have a trimmer setting on its internal circuit board that can be adjusted to change its filtering action somewhat. Several users have reported success dubbing from both VHS and DVDs after tinkering with this trimmer (a miniature knob you can turn using a jewelers screwdriver). The second version of this box you saw (the one marked as "DVD compatible") either has this adjustment already made at the factory, or uses slightly different filtering firmware.
Anything selling for less than $50 won't be 100% effective. Reliable CP filtering requires a pricier "black box' like the Grex or a TBC like the AVT-8710.
Last edited by orsetto; 22nd Jun 2013 at 03:13.
My memory is a little blurry on the details, but from what I recall the video stabilizers from the VHS days were compensating one of the video timing signals (I think it was the horizontal blanking signal). There were DIY circuits in magazines (that was before the internet); the idea was that the copy protection relied on a weakened signal on the tape, when you copied the tape the signal would get even weaker and the VCR wouldn't be able to play the tape.
Look at the circuit in your black box, you'll notice that the input and output are connected together. That doesn't seem to make any sense as the video signal would just pass right through to the output, but since the box only generates a timing signal to override the tape's weaker one, it works.
The next generation of copy protection used a chip inside the VCR and a code in the video's vertical blanking interval (if you played with your CRT TV vertical adjustment you would see it as white squares). The old black box was useless against that, so they came out with a new box that just "erases" any signal in the VBI.
When DVD came out, the fear of widespread pirating was even worse; they had to get a fool proof copy protection system (CGMS-A). They made it part of the video encoder chip and it works in conjunction with the chip inside the recorder. The copy generation management system works a lot like before only the signal is different. So any box that can clean the VBI will beat it.
All this to say that if your black box doesn't work, it probably is one of the first type. Simple boxes like the Sima and GoDV work. As Orsetto mentionned, a TBC would be an even better option, it buffers the video and is able to condition much more than just the VBI.
SIma or GoDv might work, might not. One thing's for sure, they do a great job of corrupting video and making it look pretty murky. The O.P. needs a full-frame TBC.