Outsmarting Sony (or, Stupid U-Matic Tricks!)

[captain18]

So, part of the reconfiguration of my edit suite/man cave has been to recable everything to use S-Video instead of composite video for the highest quality video I can get from my collection of professional and prosumer gear. This was pretty easy on the S-VHS front since that's where S-Video was developed to begin with, and my Betacam deck does S-

Comments

BVU-950 board location to get Chroma? / baking tapes?

[turnkit]

THANK YOU FOR POSTING THIS! I am pretty amazed.

I've been fighting for six+ months with now four different DPS-295's to try to get the DUB out to work and give me better quality. One of them has a bad p.s. and the other three are all outputting black-and-white. I am beginning to think I've got a LO-BAND/HI-BAND tape/player mismatch but am not sure. The PALsite mentions -- http://umatic.palsite.com/features.html -- that "Low and Hi-band formats are not interchangeable. Whilst they use the same size tapes a Hi-band recording will play back in black & white on a Lo-band machine." But it doesn't say what happens when you play a Lo-band tape in a Hi-band machine. Will it also display in B&W? Also, how can I tell if I have a lo-band or hi-band BVU-950? And does this B&W display issue only effect the dub-output and not composite? Composite output for my deck is fine: it's in color. Any advice appreciated.

At any rate I like your solution much better. I'd like to come out of the deck with S-VIDEO (unless there is a poor reason to do this) and then go into the DPS-295 via S-VIDEO.

But the dilemma: where do I find Chroma on the BVU-950 deck board sets? Here are the larger of boards I can see inside the deck:
- TBC
- DM
- SV
- AU
- BC
- AU (yes - a 2nd board with the same label although it looks different)
- there is also an MD-44 board that sits above the head

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Also, am curious if anyone reading this has had to "bake" their tapes to get them to play well. I've got to clean the heads every single pass to keep them playing smoothly. I think my tape(s) are shredding/shedding. The easiest way I've heard recently to "bake" is to but in a normal oven and replace the light bulb with something like a 150 watt and let it stay in there for four hours or so... and provide some air circulation via a little box fan. Anyone know of tape brands that really do need this or is it all voodoo?

Re: BVU-950 board location to get Chroma? / baking tapes?

[captain18]

Here's the breakdown of what most of those boards are based on the BVU-870 descriptions:

TBC - (Time Base Corrector)
DM - (Demodulator)
SV - Servo control
AU - Audio rec/playback
BC - Control timing generator
MD - Y/C modulator

The BVU-870 has a YD (Luma Decode) and CD (Chroma Decode) boards, based on the nomenclature, DM is almost certainly a combined Demodulator board. So that'd be a place to start.

I can only see two reasons not to do this (apart from already having a DPS-210). For one, you have to adjust your chroma timing at the TBC. For two, based on the CD-32A schematic, the spot I'm stealing the signal from is before the noise reduction circuit so the chroma may not be as smooth as it otherwise would be. This may or may not be an issue for the BVU-950.

Re: BVU-950 board location to get Chroma? / baking tapes?

[turnkit]

But when you say "you have to adjust your chroma timing at the TBC" how would I go about adjust that to fix the problem that the "horizontal timing on the Chroma will be a little off from the Luma"?

If I am using a DPS-295, for instance, is there a way to adjust the chroma timing to put it back in sync with the luma signal?

Stephan, the fellow who posted the instructions for getting S-VIDEO off the VO-9800 board said he'd try to look through his BVU-950 book to find the signal points there. Hoping he can...

But what's your prediction? In (signal) theory-land, would the DUB YC688 chroma have greater bandwidth over the S-VHS signal?

Do you think the superior signal would come from the pre-TBC'd signal transported via DUB+NTSC2 or via S-VIDEO soldered hack?

I almost want to create both signal paths now just to test.

I've got hundreds of tapes I'm going to be digitizing so I'd like to do it once and know I did it the best way possible.

Re: BVU-950 board location to get Chroma? / baking tapes?

[turnkit]

Do you think the extra wavy lines shown in your checkerboard (in the S-VIDEO signal path) are due to bypassing the noise reduction circuit?

Re: BVU-950 board location to get Chroma? / baking tapes?

[captain18]

The DPS-295 will let you adjust the timing using the "YC HORZ" function, so no worries there.

Looking through the schematics and doing some Googling, I finally pinned down that 688 kHz is the frequency used to encode the chroma portion of the signal on the tape. That would certainly explain why Sony would use it for the dub connector. (And here I thought Sony was just being Sony and being proprietary for its own sake!)

In which case, the signal has to undergo a carrier oscillation modification somewhere to become S-Video compliant. It's just a question then of whether it's at the VTR or at the TBC. With that in mind, then, the decoder board hack is really only useful if you want S-Video without buying additional gear and you're handy with a soldering iron.

Lastly, the additional grain in the checkerboard likely isn't due to stealing the chroma signal before the noise reduction circuit. Since it's a monochrome image any color decoding is going to be spurious to begin with (and I'm 99% certain the recording was a dub from an EIAJ format tape on a Sony AV-3600).

Re: BVU-950 board location to get Chroma? / baking tapes?

[captain18]

I've tried to read up on tape baking, and while I've heard about some great success stories (including a Doctor Who from 1972) so far I have not found anything that really satisfies me in terms of doing this sort of thing at home.

And while there's a lot of talk about '80s Ampex being bad, someone always comes out of the woodwork with a tale of woe from another tape stock. My takeaway is that it's probably very dependent upon storage conditions and the batch the tape came from.

A handful of people talk about using carefully tested toaster ovens, others swear by food dehydrators. What I found most interesting is the point made about having good, even tape winds so everything heats evenly. Also, the possible concern that the heat could cause some amount of stretch or warping that could manifest itself due to modern videotape being written as helical rather than linear with audio tapes.

Much as I'd like to have a monolithic workflow for handling tapes, I'm not convinced I want to automatically bake every tape before capture. Most of the descriptions of sticky shed I've heard suggest a visible clumping of the residue, so I'm not sure whether that's what you're actually experiencing.

[jvraines]

I have had success removing reels from the U-matic cassette and baking them in a Nesco food dehydrator--the same one I use for open-reel audio and videotapes. I give them about 8 hours at 130 degrees F. Then they play fine (after the substantial hassle of reassembling the cassette!) 3M/Scotch brand is the big offender, Sony infrequently, and I've never had a problem with Fuji. I never bake tapes automatically--only after I find them clogging the heads.

[captain18]

I've been meaning to post an update -- I picked up a Nesco FD-61 last fall and used it with great success on EIAJ open reel tapes. Agreed on the timeframe too, 8-10 hours at 130F usually does the trick.

Thanks for posting!

[jvraines]

That's pretty lucky with EIAJs. The tapes I have been converting, from the mid-1970s, require 16 hours of incubation or they still gunk up the deck. Fortunately I like the smell of acetone, though it makes me a little weird . . . LOL