CurtPalme.com Home Theater Forum

[htguy1]

Hi,

So I am wondering if anyone has discovered any better video opamps than the LMH6702 or El 5166?


Can anyone remind me, as I recall you have to change some resistors to get the 6702 to work right? If so can anyone remind which ones and what values they need to change to?

Thanks

God bless...
mark

[htguy1]

Anyone use/like the THS3201? I found this from Scott: The THS3201 should be a good replacement for the CLC449. It isn't a drop in replacement. With the gain set for +2 and +/- 5V power the feedback resistor for CLC449 is 250 ohms. For THS3201 it needs to be 715 ohms. The gain set resistor will have to change, also.

I am not going to say that the mosfets won't work. They might but I have to question the on resistance. At 300 ohms it is kinda high for the circuit. It will be plenty difficult to make the circuit work as designed by Analog Devices. Good RF circuit board design will be needed.

Scott
______

[htguy1]

Anyone else try this with the ths3201? v

1031 wrote:
No keep those original 100nF caps there but put those 100pF mica´s arcoss them. Those caps on that picture are 15uF low esr tant+470nF cer+ 100nf(that original one) and 47pF cer and that blue one is 100nF and that is between vcc and vdd (+5/-5v)pins. Also i replaced those 4.7ohm resistors with 56uH smd coils. I scoped noise voltage on vcc/vdd pins and that cap combination showed that noise was very low. Much lower than original 4.7ohm+100nF combination.

[redfox001]

I found that you can change a few opamps but the difference is very small. To do it right you need something like 20 years experience and even than there is still things learned.

[Nashou66]

Its a very hard op amp to tame. the Opa 695 is little easier but still has issues. The El5166 is the best drop in replacement I have found. there is other op amps not has high BW but they do not need to be. Look for the ones that have the highest Flat GBW , along with a fairly high peak BW at a gain of +2.

For example the OPA 695 needs a certain value for a gain of 2 but using that will give you way to bright image, so you have to play with resitors to get where you want. it is nice and sharp but adds other problems. There is a lot with op amp testing.


Not for the faint of heart.

Ask MP how much work goes into finding the right cocktail of ingredients to clean up the image, increase bandwidth and not alter the image while doing all that. Not easy !

Save up the $$ and have Mike get your Vim up and runing.


Athanasios

[jbmeyer13]

[htguy1]

Hi,

What is it running to have Mike work his magic on neck cards and an 03p VIM.

Thanks

God bless...
Mark

[jbmeyer13]

PM Mike and he'll tell you. Depends on what exactly (if anything) you are supplying as a donor board, what resolution you are planning to run, etc.

For example, 1920 x 1080p/60 and 1920 x 800p/72 are considerably less stressful on a video chain than full blown 1080p/72. You can't really run the latter unless you have a Radiance because the raster ringing will be pretty severe unless custom timings are used.

In my experience, there's a lot going on when trying to optimize the entire chain with some being very subtle yet crucial changes. The first thing you need to do is identify what your goals are with regards to resolution/refresh and then work around that accordingly.

[htguy1]

quote="Nashou66"]Its a very hard op amp to tame. the Opa 695 is little easier but still has issues. The El5166 is the best drop in replacement I have found. there is other op amps not has high BW but they do not need to be. Look for the ones that have the highest Flat GBW , along with a fairly high peak BW at a gain of +2.

For example the OPA 695 needs a certain value for a gain of 2 but using that will give you way to bright image, so you have to play with resitors to get where you want. it is nice and sharp but adds other problems. There is a lot with op amp testing.


Not for the faint of heart.

Ask MP how much work goes into finding the right cocktail of ingredients to clean up the image, increase bandwidth and not alter the image while doing all that. Not easy !

Save up the $$ and have Mike get your Vim up and runing.


Athanasios[/quote]

I know you are right but I really love the feeling of making mods myself when I can. What other problems does the opa695 add? (And how do I start addressing them?) The 695 is quite bright a g+2 so I have to turn it down a bit for sure...


I'm so excited right now because a hunch I had based on two Youtube video's electronics and theory I watched last week led me to a hunch on how to make my VIM better and tonight I proved to be correct!!! I just love being able to spend a few hours and seeing a difference! So I guess I am brave or foolish enough to keep playing with it until the day I get the money for MP mods...


Thanks

God bless...
Mark

[Nashou66]

Post a link of the you tube videos.

For the opa695 just play with different values of the FB and G resistors.

Also the DC restore resistors some times need tweaking as well. Not only adding caps but some times adding small value caps
or inductors across them and or the main power rails. Like you said its fun to play around and see changes either good or bad.

I use to love it when I had time now I sort of lost the enthusiasm i had a few years ago.

It might come back some day......


Nashou

[htguy1]

[stridsvognen]

https://www.curtpalme.com/forum_archived/viewtopic.php@t=37160.html

It would be nice if you would share your experience, and post some before and after screen shots documenting the difference, using the new pattern ecrabb made.

[htguy1]

[stridsvognen]

You can start with the SMPTE pattern on the HD basic disc.

You should get a test generator who can put out a RGBHV and a HDMI signal.

Its important to have the ability to adjust the bandwidth up and down, so you can check if its linear.

And you should aim for a video chain with no peaking, and a perfect reference point/ DC level.

[htguy1]

Hi,

I'm looking to buy a couple of inexpensive spare VIM. Boards if someone has some to spare. Mine have been model so many times over the years that the traces or getting ready to break.