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Shadow detail/gamma enhancement for the analog sources - Page 17  

post #481 of 492
PAW,
Right I know that.... the NEC ISS is a great line driver. That's why I was hesitant about putting the gamma card right after it in the signal chain. I didn't want to eliminate the benefit of it's drive circuitry. The only option I could see to get all inputs through the gamma circuit would be to put it at the projector itself.

For now I'll probably just put it at the equipment rack after the switcher and see how it looks for awhile. By doing this I won't be able to use the NEC boosting ability. It's probably not necessary anyway with my line though.
post #482 of 492
zamboniman
So, putting the gamma card AFTER the ISS will niegate any boost the ISS added?
post #483 of 492
Well you wouldn't want to overdrive the card.. If you put it right after the ISS before the long line run and were running the ISS with some boost you could very well be overdriving the card and doing more picture image harm than good. So running the ISS without the boost to match the input of the card which is located right next to it.. The card itself is left to be the buffering interface to the long coax run.

That's why I was thinking about putting it at the projector end of the cable. So I could use the ISS to provide the correct signal levels after the cable run at the proj. But insert the gamma correction on that signal right at the projector.

In the end the differences in picture are probably not enough to worry as long as nothing is overdriven, but that said you have to remember that you can't just boost the signal with the ISS like a crazy man when there is another component right inline with it.

Probably don't even need any boost for the length of the cable I'm using.
post #484 of 492
Quote:
Originally Posted by VideoGrabber
> I already included it into his design, but only as part of the tcoder circuit. <
...
> So moome's transcoder has tse's gamma circuit. That is good to know. <

I'm not sure I understand. Is it in the design (for future implementation), or the currently shipping build versions?

> I have your transcoder and it does not seems to modify the gamma curve like this. <

Sounds like the former.

- Tim
do all th emoome cards have thsi built in?
i wonder if mine has it?
Martin
post #485 of 492
Hi,

None of Moome's cards have it yet.
post #486 of 492
Quote:
Originally Posted by WTS
Hi,

None of Moome's cards have it yet.
Moome's NEC ISS card is suppose to. When it's released.
post #487 of 492
Well that is yet to be finalized.
post #488 of 492
I would be interested in the NEC 6010/20 card if someone were to sell me an extra ISS6010/20 they might have?
I guess I can check on ebay or videogon tonight...

Martin
post #489 of 492
Quote:
Originally Posted by tse
The output should equal the input when the input is 0.7Vpp with some full white content. Small changes to the resistor in R2 spot can adjust for perfect gain = 1.

Change all three with same value. Small changes only.

Pots will probably cause bandwidth problems, not recommended.

Changes should not be attempted unless using scope to monitor results. Use of precise 0.7V video input required.

Etc., ect.

Ile,

Now I understand what the horizontal markers are. I don't know why I didn't see that at first.

Scott
OK i tested that resistor value change to make get output back to 0.7v..(mine was that 1.1 volt also) that 510ohm must be changed to 1.2kohm!! to get that 0.7 volt output ? I tested that with videosignalgen. and digital oscilloscope. and yes i didint forget those 75ohm terminationresistors. Ok this corrector is not"standard" model, i use little more "boost" for correction( instead those R1 2.4kohm i use 1.5kohm to get gammacurve more suitable for my sony 1272)

Bye the way TSE. Can i "move" that bendingpoint (of that correction curve) lower just bye changin those sd101a diodes to sd101c (forward voltage drop for sd101 a is 0.41 and for sd101C it is 0.39volts)?
post #490 of 492
Thread Starter 
1031,

Are there other changes than R1=1.5K? That should not make that big of a difference from original. The attachment shows input vs output with R1=2.4K and R1=1.5K.

Only the peak to peak value is important. This circuit will shift the DC level down where "black" is slightly negative but that doesn't matter as the projector's input is AC coupled and the DC restore takes place internally.

Scott
LL
post #491 of 492
Thread Starter 
If there is going to be experimentation with any discrete circuit I would recommend using the little pin sockets that are part of some IC DIP sockets. They add little parasitics and let you change components easily. Check the attachment.

Scott
post #492 of 492
Quote:
Originally Posted by tse
1031,

Are there other changes than R1=1.5K? That should not make that big of a difference from original. The attachment shows input vs output with R1=2.4K and R1=1.5K.
No. Thats only difference.
I made two correctors and second one is for testing purposes. And that second one was that same that JaniH and ILE tested. And that second was "original desing" they also noticed that outputlevel was little too strong. On my sony that was not problem because there is trimmers at inputcard for signal level correction..
I have nothing to complain, Im very happy with that gammacorrector.. But some others has noticed that "boost"...
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