CurtPalme.com Home Theater Forum

km987654 · Posted: Sun Jun 01, 2014 9:03 am Post subject:

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

No, The gap in their supply voltage is too much 110V vs. 200V, if you'd lower the supply voltage then you'll limit your maximal contrast, the gain of the chips are also different.

Can you post a 1:1 resolution pattern to see how are VPJ08s doing 1080p60?

One other solution was in my mind when I came up with this push-pull thing: the circuit which was used in the PG xtra and XG..0. A circuit which is push-pull but uses a combination of a VPA13 IC and a discrete transistor amp.

Pros:
-Doesn't require special symmetrical input signal.
-Doesn't require supplemental clamping circuit as dual VPA constructions.
-Probably it could be a "swap in" replacement for VPJ08 boards. With a relative low additional component count, and matching circuit gain.

Cons:
-Still need to locate space for additional 5-6 parts on the board, one transistor must be mounted on the heatsink.
-The supply voltage must be converted from +200V to +110V and -75V (or so)
-Higher than average bandwidth achievable but not top of the hill (still it may be better than the 909's...)
-A modified board has to be recalibrated.

Check for my PG xtra screenshots with 1080P 60-75-85Hz screenshots: here
As you see at 60Hz it seems to be resolved bandwidth wise, but at 75Hz not really, assuming the neckboard is the bottleneck the barco should do this too with a similar circuit, this was a stock NEC neckboard.
The performance probably could be pushed further with this circuit using VPA15Hs and better transistors, but extreme care must be taken for the right ammount of peaking (this is where I stuck with my PG xtra experiment) and then the XG came in the door, so my interest in finishing this mod dropped significantly, there wasn't much interest anyway (well, except for me), but the experimental board is still lying around, have more or less the needed instrumentation already...

I have a friend here who has a VPJ08 neck board, which he can't use because he is missing either a matching RGB driver board or controller board (or whatever is needed to run that fine in his BG808 non s). So if there would be interest in this, maybe I can help, and if it would work would be happy to share the know-how...