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THE MOD
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gjaky



Joined: 05 Jun 2010
Posts: 2647
Location: Budapest, Hungary


PostLink    Posted: Thu Apr 19, 2018 8:38 pm    Post subject: Reply with quote


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Some crappy screenshots this time...

All of them are blurry due to camera settings, and also because the projector was not set up properly. the source was HTPC (HDMI) and a slightly modified version of the $20 white chinese HDMI converter (that only supposed to accept up to 1080P 60Hz signals, ahem...).

Ultimate VNB-DB:
It is built upon a ~'97 Rev. 5 "classic" VNB, Only FB3 was removed, and the entire input section was bypassed, so the ULTIMATE VNB-DB board directly drives Q19.
Although there is no intentional peaking in the setup, the system peaks around the 1080P 72Hz clock rate, bandwidth both at lower and higher clock rates look less.
1080P 72Hz:


Regular VNB-DB:

It is built upon a similar ~'97 built Rev.5 classic VNB, it has some performance modifications too: changed R22 to 130Ohm, added extra (2u2) ceramic capacitors to the CLC449's rails, removed R90, FB3 and C53.
The board seems to loose some bandwidth from very low clock rates, ie. 1080P 60Hz is not fully resolved (but 1080i 60Hz does), the effect is not dramatic however, what is more interesting this does not worsen, not even a tiny bit, even at 1080P 95Hz (mind the chinese HDMI converter too)

1080P 60Hz:




1080P 72Hz:




1080P 85Hz:




1080P 95Hz:



_________________
projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB
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gjaky



Joined: 05 Jun 2010
Posts: 2647
Location: Budapest, Hungary


PostLink    Posted: Thu Apr 26, 2018 9:19 pm    Post subject: Reply with quote

mp20748 wrote:
IC77 replaced 5 times = I say BS. But don't feel bad, Kurt consistently claims he has a stock set of neck boards that he's getting to do up to 200MHZ (1920X1080P) by simply replacing one resistor..Shocked I asked Gjaky about this some post back and he later posted on his "The Mod" thread a bunch of smpte patterns showing what a stock neck board look like and goes on here: http://www.curtpalme.com/forum/viewtopic.php?p=480515#480515

Keep in mind, he would be directly putting the test signal into the tested neck board. But what I want you to look at is the pattern he said is 1920X1080P /60hz and also look at the 1920X1080P /72hz. Do note that he also replaced that same magic resistor (R22). What those patterns are showing is proof as have always known, the boards cannot even do 1920X1080P /60hz. What he was also showing was an Ultimate neck board that he does much like what I've been doing (replace way more than 1 resistor). Not sure why some people outrageous claims, knowing some stuff will never fly beyond those hwo know better.


This was posted in the other thread, because it is somewhat unrelevant in that context, I rather give my insights here.
For sure the neckboard is the bottle neck in the bandwidth. But I would be careful with the statement that "stock neckboard can't do 1080P 60Hz" Because if that would be true then the 1080P 95Hz pattern would not look as it does. Please note that signal there has 240MHz pixel clock, and the 1080P 60Hz signal has 148MHz, yet the difference in the presented picture is not that dramatic at all.
Also I have posted earlier that the rise time of the (stock) VNB -based on my own measurements- is around 3.5ns for -3dB bandwidth this would translate to ~100MHz for a sine wave. Now it is known that the pixel clock is twice of the signal change rate so 100MHz sine bandwidth equals to 200MHz pixel clock capability. Some roll off will happen, yes, at 200MHz pixel, but the term "fully resolved" is not well definied anyway, as what does the "fully" mean: 0.1dB flat? 1dB flat? To me the 95Hz shot look good enough still...

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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB
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mp20748



Joined: 12 Sep 2006
Posts: 5358
Location: Maryland

TV/Projector: 9500LC Ultra / Super 02 and 03 VIM


PostLink    Posted: Fri Apr 27, 2018 12:36 pm    Post subject: Reply with quote

gjaky wrote:
This was posted in the other thread, because it is somewhat unrelevant in that context, I rather give my insights here. For sure the neckboard is the bottle neck in the bandwidth


That was my point as well.


Quote:
But I would be careful with the statement that "stock neckboard can't do 1080P 60Hz" Because if that would be true then the 1080P 95Hz pattern would not look as it does


They can't have a known bandwidth bottleneck and still be able to do 1080P /60hz at the same time. It was 1080P /60 that created that bottleneck.

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gjaky



Joined: 05 Jun 2010
Posts: 2647
Location: Budapest, Hungary


PostLink    Posted: Fri Jun 07, 2019 3:05 pm    Post subject: Reply with quote

I was polishing a little bit on the AD834 ULTIMATE VNB-DB my concern with the original solution was that it had a dip (-1.5dB) in the frequency response around 100MHz which is the most important frequency for 1080P 72Hz. Now I changed some component values and added a special compensating network, now at 100MHz the gain is positive (+0.5dB), with a peak at about 300MHz (where there is the first harmonic of a squarwave of 100MHz frequency). But overall the response is smoother than before, it almost fits in an 1dB window from 300kHz to 400MHz, the -3dB point is beyond 500MHz... Wink


AD834_MOD1B.png
 Description:
Modified ULTIMATE VNB-DB, frequency response
 Filesize:  9.39 KB
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AD834_MOD1B.png



_________________
projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB
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