Reply To: OSSC Pro Gain Voltage / ISL51002

[M3Patterns]

I just looked at the ADV7125. While it does offer the ability to output higher voltage with a variable resistor (which would be helpful in analog-land) it does not appear to handle anything beyond exact 8-bit input, which means no superwhite accommodation (which is basically what I meant by not letting the Extra AV Out clip at all, but instead just pass higher voltages.)

That means that you really have to dial in the gain so as not lose 8-bit precision. In digital-land, that’s understandable, but the Extra AV Out could have more flexibility, since analog signals can accommodate voltages over 100IRE.

That also means that certain consoles that generate superwhites over 100IRE (like the NES) are going to be clipped unless the ISL51002 gain is lowered below unity. But if you do that, you do lose 8-bit precision in analog-land. The more the gain needs to be lowered to compensate, the more that reduces the availability of 8-bit values.

For instance, if you had an 120IRE signal that needed gain reduced by a factor of 1.2x, the 255 values of 8-bit would also be reduced by 1.2x to about 212.

That wouldn’t really be an issue with something like the ADV7123, which is 10-bit. Could a future revision use that chip or another higher bit option?

 

Right now the best current option for pure passthrough that handles superwhites would be to:

1. lower input gain, either before input into the ISL51002 or using the adjustable gain in the menu.

2. Increase gain after the ADV7125, using an external VGA to VGA amp.

 

Any thoughts on this?