CurtPalme.com Home Theater Forum

koldby · Posted: Thu Jul 23, 2015 6:24 pm Post subject:

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

There IS information on over-I and I-sense signals, but strange enough they are listed in the VIM's section.

As I am tayloring the VNB in to my NEC, I'm quite up to date in the construction of the VNB Smile

Generally the brightness of the circuit can be set with the ofset of either Q12, Q19 (it driven through Q12 here), ideally the over-I or I-sense should not affect brightness, a different bias/gain setting of the brightness circuit probably would solve that part of the problem.

barclay66 · Posted: Thu Jul 23, 2015 8:35 pm Post subject:

Thanks!

This data will help. Interesting to see that there is indeed a different setting of the potentiometer between the 8" and the 9" neck boards although they share exactly the same schematic...

Regards,
barclay66

koldby · Posted: Thu Jul 23, 2015 10:40 pm Post subject:

Maybe also a difference between the i-max for LUG tubes and LCP tubes?

koldby · Posted: Fri Jul 24, 2015 10:05 am Post subject:

barclay66 · Posted: Fri Jul 24, 2015 11:07 am Post subject:

Hi,

You might want to look up this thread: http://www.avsforum.com/t/1127826/vdc-8-highres-projector#post_16022468

Here Scott explains the following:
"The schematic. 81771-01 is part number. This card is not compatible with original Electrohome style cards. P/N 02-270340-01 is new version but can be mixed with E-home cards."

And later:
"The 81771 cards won't work with the originals because when spotkill is enabled the transistors on the original cards will not allow the voltage to go higher than about +0.7 or 0.8V. That will not go high enough to kick in spotkill on the 81771 cards.
Spotkill has been a problem with different configurations because of the small difference between enabled and not. The 81771 takes more than +1V to kick in spotkill which allows more noise and crap without false enabling.
The 02-270340-01 card has the same thresholds as original Electrohome cards so spotkill works."

This is where my idea of functional similarity between an old style card and a 02-270340-01 comes from...

Regards,
barclay66

koldby · Posted: Fri Jul 24, 2015 1:00 pm Post subject:

I remember now that I actually read that thread.
But if I read Scott correct he is saying that with the new VNB the spotkill will no have so many false trigering as the old, so if you have the new versions in the rest of the PJ, you will only benefit from this.
Problem is with older PJ´s that the spotkill will not work at all...!
But I cannot see it would have any influence on brightnes and contrast???

koldby · Posted: Fri Jul 24, 2015 1:28 pm Post subject:

By the way have you noticed that VDC placed a footprint for a better connection to VIM?
About time... Mini jacks for HighEnd Video signals is not a good idea IMHO!

barclay66 · Posted: Fri Jul 24, 2015 1:55 pm Post subject:

barclay66 · Posted: Fri Jul 24, 2015 2:09 pm Post subject:

koldby · Posted: Fri Jul 24, 2015 3:06 pm Post subject:

No but I am about to change the VIM to a MCX 75 Ohm.
I think it is the same footprint as SMB connector.

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

The input circuit is also different from the old style, that circuit have influence both on contrast (=gain of opamp) and brightness (=bias of opamp).

koldby · Posted: Fri Jul 24, 2015 8:55 pm Post subject:

So what would you suggest?

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

koldby · Posted: Sat Jul 25, 2015 12:47 pm Post subject:

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

koldby · Posted: Sat Jul 25, 2015 1:45 pm Post subject:

Thanks

koldby · Posted: Sat Jul 25, 2015 1:53 pm Post subject:

Unfortunately it is not directly traslateable to the new VNB

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

koldby · Posted: Sat Jul 25, 2015 3:07 pm Post subject:

As the output stage in new and old VNB is very similar (except for the transistors used, one could probably translate the -1,4 to " Q12 to the same in the new VNB.
I don´t think it is just a matter of adjusting G2/Drive. Aparently the outputstage has some issues in linearity and dynamic range.
A couple of questions:
Why did they change the inputstage to HFA1100 and an emmitterfolower? Is the Z-in of 2SC4271 much lower than MRF5943?
Why did they change the I-sense/Over-I stage?
Why did they change the Brightnes driver and spotkill?
VDC had supposedly only simulator customers as their goal, and that calls for LUG tubes. Did they make the changes to be better with very hard driven LUG tubes , beside the fackt that they couldn´t get more Motorola transistors?

Speculations from my side