CurtPalme.com Home Theater Forum

[beun]

If people are interested I can create a small box with just the adjustable gamma portion of the RTC2200, I am willing to open up the schematics as well, no secrets here.

[papalek]

[Tom.W]

Now there is a match. Scott and Kim together with a bit of collaboration could make this the best gamma card ever !

[jask]

I know that a d.i.y. job of this sort is not for everyone here but the fact that people like Scott and Kim are around (and so generous!) and willing to share the knowlege they have and results of all that work.......
You guys are a couple of Class acts!

Thank you.

[tse]

[jcmccorm]

Thank you very much Scott! That clears it up. I'm still trying to figure out exactly how that DC restore works (particularly the opamp with the series cap in the feedback path. I think I'll Spice it...)

One question though, the output of the comparator in your sync circuit swings to both +5 and -5 and drives a 74HC86. I wouldn't think the HC input would like that (or I'm wrong and the comparator only swings between +5 and 0).

Thanks again Scott. Really clever circuit.

Cary

[tse]

Pin 1 of the comparator sets the most negative excursion. It's at ground so the output swings from 0V to near +5V. The XOR gate is happy. When the /Sample input to the mux is at ground the RED and RED_SW nodes are connected together. If, for instance, at that time the video signal is slightly positive (in respect to U7-5 or ground) the output of U7 will move toward -5V which brings the video signal back to 0V. The DC restore works pretty good, as it needs to, for the circuit to work right. It's actually more complex than the gamma part of the circuit. If your video source had it's video restored to 0V that part of the circuit would be unecessary and could be connected directly to the gamma circuit.

Scott

[v_erich]

@beun:

That would be great, so it would be also a buffer for the non-buffered outputs of the HDFury.
VGA input from the fury to plug it in directly and BNC outputs for the "old" installed cables, so you can use a short HDMI cable to the fury and everythng is fine.

Would be really a great upgrade for thr fury.

Erich

[beun]

I just finished a new schematic, I will post tomorrow.


Kim

[beun]

Attached the PDF with the proposed schematic based heavily on the RTC2200 gamma backend.


Kim

[v_erich]

Hi,

looks good and simple, I like that.


Some comments:

- the power supply is very simple, why are you using so poor 7805 regulators?
- Please at least add some 100n caps between I-G-O of the LM7xxx regulators.
- I would use seperate opamps for each color, 300MHz opamp are to less for HDTV because you
don't have the right slew rates what are needed for this signals, min. 1GHz would be recommended.
I use for cheap things the AD8058 (SO8).
- a lot of supply names are wrong
- output connector should be 5x BNC (not VGA like now)
- the name on the VGA input should be in not out?

Regards,
Erich

[beun]

Erich,

The 7805 regulators aren't actually that bad, the output electrolytic capacitors take care of all the low frequency noise (if there) while the 100nF caps across the supply close to the opamps take care of the high frequency noise.

The AD8058 opamp you recommend doesn't seem to be that much better than the LT1399 (325MHz vs 300MHz and 1000V/us vs 800V/us) while the 1dB flatness is actually worse 28MHz vs 150MHz, but I will look for another convenient video amp.

You are right about the supply names, I just copied it from another schematic and forgot to change the names.

I know some of you would like BNC's at the output but when I keep it as VGA I can put this in a very small dongle format instead of a large case.

I just named it OUT, it is just a name to tie the signals together in the schematic, the actual name is of no importance.


Kim

[v_erich]

Hi Kim,

thanks for your answer.
I know, that the AD OP is not much faster, but you can stuff other better opamp in the same case on the position, thats the improvement

I use very often regulators from linear technology for better power supplies, normally they make a big imporvement in the viewable performance.

If you use VGA out, the people have to buy a expensive vga2bnc cable.
I have installed a very good bnc2bnc cable, I don't want to buy a new one for that, therefore a bnc out would be great, but if not I will install it in a bigger case and make bnc connectors for me only on it
Maybe you can foreseen some holes and via's to solder real cables on the pcb directly for the pimpers out there...

Erich

[stefuel]

Just bumping this back to the front page. I got a tse board from Tom and will try it this weekend. My weekend will be spent pre-wiring a new rack location. My home office is being turned back into a bedroom. I'm getting booted to the garage. A little extra work and a lot of peace and quiet

[tse]

You'll get your best performance if R1, R2, & R99 are as shown.

Scott

[Tom.W]

Scott do you know if Buttsplice used your revised circuit in the large batch made over at the ET ?

[AnalogRocks]

Hey Kim, could you make one of these boxes with a MP 1.4 circuit on it and a VGA HD-15 in and VGA HD-15 out?

Think HD-Fury add on. Gama and a driver stage for long cables.

[AnalogRocks]

Hey Kim, could you make one of these boxes with a MP 1.4 circuit on it and a VGA HD-15 in and VGA HD-15 out?

Think HD-Fury add on. Gama and a driver stage for long cables.

[beun]

I am already working on a gamma dongle, but what is a MP 1.4 circuit if I may ask?

Edit:

I found it, I don't think that anyone complained about the output driver on the RTC2200.


Kim

[AnalogRocks]

[AnalogRocks]

[beun]

As I understand the MP 1.4 circuit is more of a replacement for the cheap video card antialiasing filter, but I have to defer to MP as the actual authority on it.


Kim