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Hi guys

I've been fiddling around with RGB amplifier in my spare time
an Analogue LT6557

At first working externally with both a SNES and Megadrive V1 but I wasn't happy with the output, it was a little dark.

It's currently not working with my various SNES models or Famicom due to trying to perfect it on my Megadrive first. This is through a Master system converter, and obviously applies to this system as well.

This is the sort of quality I am getting, only issue is to get the video standard spot on for proper wide range compatibility with televisions and scalers etc as I want this to work through my OSSC when it arrives.

I read an article about Arcade TV who sort of "pioneered' the whole bypass thing, he states you need to attenuate the the input signal to .7vpp, which a gain of 2 amp then outputs 1.4vpp which then passes through the 75 ohm resistor in series and divides to .7vpp at the television by the 75 ohm to ground terminating resistor.

I sort of reverse engineered the underside of the board, and adjusted the value of some of the resistors until it "looked" right on an RGB hacked television (my Loewe isn't fussy)

I've thrown together a quick PCB of my prototype on oshpark, it does use 1206 footprints on places but 1805 will fit...

any experts here have a bit more knowledge on this stuff and care to help with resistor values. I may fork out for a "real" oscilloscope to help out with this... I mean its almost perfect on my Loewe set with factory RGB scart input. The video is with FACTORY settings and no changes in the OSD.

The data sheet for some reason recommends 75ohm terminating resistors at the input as well...

The quality of output is far too good for me to put this aside as an unfinished project...

I mean some levels on sonic on the MD look 3D and have so much "pop"

https://oshpark.com/shared_projects/xxUPtrbn (board)

BTW I reverse engineered the master system converter that comes with Analogue SG systems and it will be on Oshpark for free once tested... :) I managed to squeeze it onto a dual layer PCB even smaller than their 4 layer board.

Takes only a 4.75k ohm resistor, they used through hole type due to traces on internal layers, but SMD is cheaper and easier to obtain at this value.

0b1a31496cd36accdd5e55a3a1b45c59.png (17.39 KB)

70f6843bfebb63b2de1beeabbd4ae9a4.png (21.47 KB)

Come to think of it I may as well just stick a bunch of 10k trim pots on the board when they arrive and see what I can come up with

but

from what I can see the boards attenuation seems right when compared to a master system CXA1145 doing 1.6vpp at the scart terminal on the TV end. Mine are doing around 1.5 R/B but for some reason my Green channel is half of R/B channel everywhere i check... maybe a dud amp is throwing me off

have confirmed with full white screen on sms test suite

Author	Message
L10N37 Joined: 27 Jun 2020 Posts: 212	New RGB amplifier for SMS/MD/Genesis/SNES/Super Famicom etc Posted: Tue Aug 11, 2020 4:26 am
L10N37 Joined: 27 Jun 2020 Posts: 212	Hi guys I've been fiddling around with RGB amplifier in my spare time an Analogue LT6557 At first working externally with both a SNES and Megadrive V1 but I wasn't happy with the output, it was a little dark. It's currently not working with my various SNES models or Famicom due to trying to perfect it on my Megadrive first. This is through a Master system converter, and obviously applies to this system as well. This is the sort of quality I am getting, only issue is to get the video standard spot on for proper wide range compatibility with televisions and scalers etc as I want this to work through my OSSC when it arrives. I read an article about Arcade TV who sort of "pioneered' the whole bypass thing, he states you need to attenuate the the input signal to .7vpp, which a gain of 2 amp then outputs 1.4vpp which then passes through the 75 ohm resistor in series and divides to .7vpp at the television by the 75 ohm to ground terminating resistor. I sort of reverse engineered the underside of the board, and adjusted the value of some of the resistors until it "looked" right on an RGB hacked television (my Loewe isn't fussy) I've thrown together a quick PCB of my prototype on oshpark, it does use 1206 footprints on places but 1805 will fit... any experts here have a bit more knowledge on this stuff and care to help with resistor values. I may fork out for a "real" oscilloscope to help out with this... I mean its almost perfect on my Loewe set with factory RGB scart input. The video is with FACTORY settings and no changes in the OSD. The data sheet for some reason recommends 75ohm terminating resistors at the input as well... The quality of output is far too good for me to put this aside as an unfinished project... I mean some levels on sonic on the MD look 3D and have so much "pop" https://oshpark.com/shared_projects/xxUPtrbn (board) BTW I reverse engineered the master system converter that comes with Analogue SG systems and it will be on Oshpark for free once tested... :) I managed to squeeze it onto a dual layer PCB even smaller than their 4 layer board. Takes only a 4.75k ohm resistor, they used through hole type due to traces on internal layers, but SMD is cheaper and easier to obtain at this value. 0b1a31496cd36accdd5e55a3a1b45c59.png (17.39 KB) 70f6843bfebb63b2de1beeabbd4ae9a4.png (21.47 KB)

L10N37 Joined: 27 Jun 2020 Posts: 212	Posted: Tue Aug 11, 2020 10:10 am
L10N37 Joined: 27 Jun 2020 Posts: 212	Come to think of it I may as well just stick a bunch of 10k trim pots on the board when they arrive and see what I can come up with but from what I can see the boards attenuation seems right when compared to a master system CXA1145 doing 1.6vpp at the scart terminal on the TV end. Mine are doing around 1.5 R/B but for some reason my Green channel is half of R/B channel everywhere i check... maybe a dud amp is throwing me off have confirmed with full white screen on sms test suite

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