SNES MINI. RGB Amplifier Chip Mod or Standard 3 Wire Mod??

Do you live in the US? I can lend you my SNES Everdrive.

 

Yep I live in NJ.

 

Also just found this link to a forum post: SNS-CPU-RGB-02 Video Circuit (w/ S-RGA A Encoder)

It would be interesting if a similar input circuit for RGB is used in the SNES-mini.

 

This is my SNES Mini, using the amp chip and 75ohm resistors on the R,G, and B lines,



i have the system running through a xrgb-mini. I have test it against another SNES mini with no mod and the brightness level as far as i can tell look exactly the same i cant seen no difference.

 

The input circuit on the mini is a lot simpler than that and is very similar to the early N64. On the mini the RGB signals come from the S-CPUN chip, each signal has a resistor to GND and then goes through a coupling cap to the SRGB amp. On the N64 the RGB signals come from the DAC, each signal has a resistor to GND and then goes through a coupling cap to the encoder chip or in the NUS-001(FRA) case to the SRGB amp.

The only difference between the 1CHIP, mini and early n64s is the values of the resistors and the caps.

On the install diagrams that retrorgb provides on his site in the link below the input to the THS7314 is connected before the resistors and coupling caps on both the mini and the N64.

https://squareup.com/market/retrorg...etrorgb&utm_medium=embed&utm_campaign=menu_v1

 

Good info, thanks. Yeah the components on the little board that he sells is the decoupling cap (between 5V and GND) and the 75 ohm resistors on the RGB output lines, needed for impedance matching.

We need to check the resistor values used on the input side going into the S-RGB encoder, it would be good to know.

 

I didn't mean the cap and resistors on the THS7314 board. I meant that the input to the THS7314 is connected before the resistors and coupling caps on the SNES mini and N64. The resistors and coupling caps on the SNES mini and N64 are there to bring the RGB signals from the S-CPUN (SNES mini) or DAC (N64) down to the correct level and remove the DC offset for the input of the SRGB chip or the Encoder chip.

The resistor values used on the input side going into the S-RGB encoder are slightly different depending on the console, N64, mini or phat 1CHIP.

Try connecting the THS7314 amp here and see if it helps:



PS. Hope you don't mind me using your pictures retrorgb. It was the quickest way to show what I meant.

 

I'm gonna be pretty busy for the next few days, but I'll try to get to it on Sunday. Good idea though!

No, not at all, I'm glad they could help!

 

On Page 1:

Just as a side note:
To my experience, I got a wobbly picture on the screen if I use the decoubling caps given on the SNES mainboard

 

The THS7314 is supposed to support both DC and AC coupled signals. Maybe the value of the decoupling caps on the SNES is a bit high for the THS7314.

To quote the datasheet:

"If more hum rejection is desired or there is a loss of sync occurring, then decrease the 0.1-μF
input coupling capacitor. A decrease form 0.1 μF to 0.047 μF increases the hum rejection by a factor of 2.1.
Alternatively an external pull-down resistor to ground may be added which decreases the overall resistance, and
ultimately increases the discharge current.
To ensure proper stability of the AC STC control loop, the source impedance must be less than 1-kΩ with the
input capacitor in place. Otherwise, there is a possibility of the control loop to ring and this ringing may appear on
the output of the THS7314. Because most DACs or encoders use resistors to establish the voltage, which are
typically less than 300-Ω, then meeting the <1kΩ requirement is easily done. But, if the source impedance
looking from the THS7314 input perspective is high, then add a 1-kΩ resistor to GND to ensure proper operation
of the THS7314."

I'm not sure about the mini or the N64 but the decoupling caps on my phat 1CHIP are at least 0.1uf. Can't say exactly as my meter is not very accurate. Maybe that is the reason for your sync issues when you tried using the decoupling caps on the SNES as I previously suggested..

 

Do R6, R7, and R8 terminate to GND? I'll have to check when I get home on my mini. I'll check the cap values too.

It could be those were values specific for the S-RGB chip. It might be better to grab the raw RGB from the original points and add caps and resistors on the input lines. The resistor should go between the signal and GND. Regardless, the RGB signals need to be checked first before choosing any values.

 

the strangest thing just happened, I have done the DIY RGB amp mod a couple of times now without issue and just came across a snes mini that wont display using my ntsc scart cable, it will only work using the scart cable I use with my pal N64. I went and got another snes mini that I had tucked away that I haven't touched and that one too will only display with my pal scart. and just to make sure the rgb mini that I use wont work on the pal scart so I dunno...weird

 

Did you connect csync to pin 3 on the multi-out?

 

oh yeah..... that will do it, thanks

 

Has anyone tried this on a pre 1-chip SNES, taking the signal from the points right before it goes into the older video amps like the s-enc?
I'm curious to know if there will still be an image quality difference.

 

The signal is already taken from the points before it goes into the video encoder on the early SNES boards because the s-enc chip doesn't output RGB anyway.

 

I knew that, getting old, losing my memory.

Has anyone tried this on a pre 1-CHIP SNES?

 

I'm looking to get two of these amps, one for my Super Famicom (to get rid of the line down the middle and improve the picture) and one for my N64 (to give it rgb output). I thought I'd run the installation process past you guys and see if you have any input.

For the SNES, retrorgb reccomends installing it like so:

http://retrorgb.com/1chiprgb.html

Then installing some 750 ohm resistors to correct the brightness. This is slightly different from his SNES mini install guide, which reccomends 1.1k resistors, which is a value he got from measurements someone oh this forum took. So is 750 ohm the best value to use in the 1chip SFC?

For the N64, I had originally been reccomended to use a PCE amp, but this amp appears to use the same amp, costs a bit less and is a tidier install, so I think I'd go this route instead.

Retrorgb's install guide for the N64 goes like this:

http://retrorgb.com/n64rgbmod.html

As with the SNES 1chip mod, he reccomends installing some resistors to correct the brightness (75 ohms) but again, doesn't have a measurement to base this off, so is 75ohms the best value to use?

I also rember needing to cut the composite sync trace when I rgb modded my pal n64, but you don't need to do anything like that with this mod?

 

The values of the resistors were calculated in https://www.assemblergames.com/forums/showthread.php?53053-SNES-Mini-RGB-Measurements


The 1CHIP has different resistors than the Mini on the circuit board, that's why the values are different. You still need a combination of 75 ohm resistor and 220uF capacitor on the output lines, whether you have them on your little rgb amp board or in the RGB cable.

You don't have to cut the composite sync trace. You need it for RGB syncing. Make sure your cable uses the composite sync pin and not the composite video pin.

 

Cool, thanks for the link! So basically for a 1CHIP SNES, I just need to solder a 75 ohm resistor and a 220uF capacitor to the R, G and B output of the amp? retrorgb's guide says to install the resistors to the input side of the amp, but you're saying it's better to solder them to the output instead? For the sync pins, I'm using an official Nintendo PAL RGB cable that I added some extra components (Some capacitors as I recall) to make it suitable for an NTSC SNES/Super Famicom. Will this be suitable after this mod has been completed? Do you also have measurements for the NTSC N64?