CleanRGB Setup
The CleanRGB Universal can be installed in any console that has native RGB signals somewhere on the system.
The purpose of the CleanRGB is to tune those signals into correct IRE levels, removing the DC offset, cleaning and filtering the signal, and setting the gain correctly.
Install the CleanRGB into your desired system by soldering it to ground and 5V (or if the voltage is over 5V to the >5V pad). Then the RGB and Sync inputs to your source signals, and the outputs to your AV port.
Remember to disconnect any existing outputs already going to your AV port.
The output can be used with most RGB cables; however, we test and recommend our own Pure DC CleanRGB SCART cables sold on retrosix.co.uk. These have no magic, no capacitors, resistors, sync strippers or other stuff inside, just good old shielded high-quality pin-to-pin connections.
There are specific install guides for each CleanRGB setup in consoles inside the Wiki pages.
If you have no tools and want to tune the CleanRGB by eye, you can just turn the dials (starting with the Sync dials) until you get at least a black screen (locked onto Sync signal).
Once you get that, you can turn the other dials and visually watch the colors appear.
Below are some photos of a correctly tuned CleanRGB for specific consoles to give you a good reference point.
Note the position of the flat part of the pots.
The simplest way if you don't have an oscilloscope is to tune the pots by the resistance table below. These are known resistance values for specific consoles that should get you close enough to perfect output that you can tune the rest by eye.
Potentiometer | Clockwise | Counterclockwise |
|---|---|---|
DC Offset | More resistance = Removes DC | Less Resistance = Signal Unchanged |
Divide | Less Resistance = Increase | More Resistance = Decrease |
Gain | More Resistance = Increase | Less Resistance = Decrease |
Simply measure the resistance between the two points of each potentiometer as shown here and turn the pot until you get that resistance.
Make sure to measure the values while there is no power applied otherwise the values will not be right.
Console | DC | Divide | Gain |
|---|---|---|---|
Master System | RGB 6.1k SYNC 6.1k | RGB 16.8k SYNC 16.8k | RGB 14.4k SYNC 0R |
SNES / SFC (SNSP-CPU-02) | RGB 0R SYNC 5.45k | RGB 9.67k SYNC 14k | RGB 0R SYNC 0R |
SNES / SFC (SNS-CPU-GPM-02) | RGB 0R SYNC 5.45k | RGB 11.9k SYNC 11.9k | RGB 0R SYNC 0R |
Amiga CD32 | RGB 5.7k SYNC 5.7k | RGB 10k SYNC 10k | RGB 0R SYNC 0R |
As the CleanRGB has been designed to be universal, we have to configure it by turning the potentiometers on the board to remove DC offset, and then divide or gain the final signal to the perfect voltage level.
This can be done visually, using a multimeter, or the most accurate using an oscilloscope.
Each of these steps is repeated for each R, G, B and Sync inputs.
The end goal is the RGB output test pins should be 1.4V (lowest to highest voltage) when pure white is shown, and the Sync should be 0.6V (but is often higher and is generally ok for the sync pin).
As the circuit design offsets the DC base to 0.2V, you will see a 0.2V offset, followed by a 1.4V signal, giving a peak of 1.6V.
Although the Sync on paper should be 0.6V, it is very common for sync to be much higher voltage.
A common voltage is 1.4V just like the RGB values.
The highest some receivers accept the Sync pin is 1V terminated / 2V floating. so ideally do not exceed that.
Before the voltages are set, you must remove the DC Offset from the input signal, then set the final voltage gain.
Start by turning on the console.
Measure the input signal to figure out where we are at. This is the RED IN or BLUE IN pads for example, where the wires were soldered to the CleanRGB. Here is the Red signal coming in.
As we can see, we have a few issues. The voltage should be as close to 0V as possible, without clipping the lower parts of the signal.
Secondly, the voltage level should be set to 1.6V at the final output stage (0.2V offset and 1.4V signal range).
Let's start by removing that 2V DC offset. Probe the DC Offset test point, and turn the DC offset potentiometer.
Turning the pot clockwise removes the DC offset (so lowers the signal). Turn it until its very close to 0V.
The final step is to set the final output voltage. Probe the final stage test pad. This pad ignores the receiver's pull-down so the output regardless of if a receiver is connected or not should be 1.6V when 100% brightness is shown on screen (0.2V offset and 1.4V signal range).
For the Sync signal technically, it should be 0.6V, however almost all receivers are happy that the Sync signal can be anywhere from 0.3V to 5V without issue, so this is much less critical.
A cool fact, if you tune the Sync voltage level it often shifts your final image left or right, so you can use it as a screen horizontal position adjust too.
The goal is to tune the Divide and Gain potentiometers until the voltage is 1.6V peaks.
Turning either the divide or the gain counterclockwise reduces the signal and turning them clockwise increases the signal.
The closer the divide pot is turned to 0 ohm the less affected the signal is, meaning it won't be divided. The larger the resistance (up to the maximum 47k) the more the signal is reduced.
Turn either or both pots until 1.6V is achieved.
Note the final stage output has a 0.2V offset from ground by design to allow any receivers DC restoration circuit to still work.
Notice I am ignoring the capacitive spikes on the signals and going to the actual signal flats for the 1.6V signal.
Once happy, you can do the final tuning visually. If your color tone is off, and you have too much red tint for example you can reduce the red by turning the divide or gain CCW.
The final output should be RGB at 1.6V and Sync at 0.6V to 5V based on final output or screen position.
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