HDMI to VGA adaptr issues [720p]

[strayan]

I currently have a HDMI to VGA adapter plugged into my video card's HDMI port. It is outputting a 1360x768 signal to a HDTV with a matching resolution. As it is 1:1 pixel mapped the desktop and text etc looks exactly as it should (flawless) and I am very happy with it bar one thing - I have to undervolt my video card or I get a very faint ripple or wave type effect which appears when playing games. Now I suspect that this has something to do with inherent shortcoming in analog VGA signals (read interference) but it still confuses me because I assumed the HDMI port was sending a clean digital signal to the VGA adapter (but why is the issue only present when gaming?). Not being the type of person that can let something like this go I ended up buying 3 completely different VGA adapters in an attempt to isolate the issue. Someone has suggested they mighht be passive adapters rather than active adapters, but how the hell do I tell? All I know is that they are all in-line adapters that don't require an external power supply. Would anyone be able to explain what I'm seeing or recommend a HDMI to VGA adapter that handles things differently to the ones I'm already using or have another suggestion... something bizarre like buying a new PSU?

[Guspaz]

There is no such thing as a passive HDMI to VGA adapter. You'd need to have a DP++ compatible DisplayPort output, and then you could have a passive DisplayPort to VGA adapter, but not HDMI.

[strayan]

There is no such thing as a passive HDMI to VGA adapter. You'd need to have a DP++ compatible DisplayPort output, and then you could have a passive DisplayPort to VGA adapter, but not HDMI.

I did not know about DP++. I will give that a shot.

Any idea where the EMI is coming from or how to address it?

[Nekoi]

It might be of help if you would list what converters you have tried.

If the devices you were using don't have a separate power cable they will take the power through the HDMI cable. So the graphic card will supply the converter with power.

I also recently went shopping for such a converter. And pretty much all of the ones I found came with some sort of power cable, most use USB cables. In most cases it should work without a power cable. But that's not the proper way.

[Guspaz]

HDMI is only required to provide a minescule amount of power (55 milliamps at 5 volts), so if an active converter will work on bus power alone is a crapshoot: the answer is yes only if the HDMI device provides far more power than it is required to.

[strayan]

It might be of help if you would list what converters you have tried.

Sure:

https://www.amazon.com/Ableconn-HDMI2VG ... 783&sr=1-1

https://www.amazon.com/UGREEN-Adapter-C ... ugreen+vga

https://www.aliexpress.com/item/Male-to ... .57.7WC6Jx

HDMI is only required to provide a minescule amount of power (55 milliamps at 5 volts), so if an active converter will work on bus power alone is a crapshoot: the answer is yes only if the HDMI device provides far more power than it is required to.

Is there any way to disable power over HDMI?

Maybe I should try fibre optic hdmi cable: https://www.kogan.com/au/buy/unitek-15m ... ed-unitek/

Tempted to try optical cables but I read that some optical cables still have copper wire running along it for power: https://www.amazon.com/Optical-Cables-C ... OJRF6K#Ask

[Guspaz]

Most devices that need more power than most HDMI devices produce have a supplemental power input (usually in the form of a mini or micro USB jack), using that will cause it to draw power over USB instead of HDMI. Some devices are designed to work within the power that HDMI does provide: Monoprice's optical HDMI cables are designed to work with 250 mW, which is within what HDMI is required to provide.

A 1.5 meter long fibre optic HDMI cable is laughably useless, so I'm going to assume that is intended to be a 15m cable. Either way, that's overpriced: Monoprice will sell you a 100m long fibre optic HDMI cable for US$135, and that appears to be a 15m cable for AU$115 (US$88). So it's not very cost effective, although I don't know what the equivalent to Monoprice is in Australia. Here in Canada, we have local distributors like PrimeCables who carry most Monoprice products by having stuff shipped to them in bulk as freight, presumably there is some equivalent in Australia.

Fibre optic video cables are only useful if you need to run a cable longer than copper is practical, and you're still within the realm of much cheaper ultra-slim HDMI cables at 3m or less. I don't see any point in a fibre optic HDMI cable below maybe 20m (where active HDMI cables top out), and there are cheaper solutions involving cat6/cat6a cable for long distance runs below 100m.

Of course, in your situation, you're looking to use the cable as an optoisolator. I'm speculating, but I don't think that would make a difference: if your HDMI port is putting out dirty power, you're still going to be using that power to convert the signal to optical. I would imagine that they don't have copper running that long down the cable, they probably draw power at both the sink and the source.

The UGREEN adapter you bought supports external power via USB. Try using an external power supply with it to see if that makes a difference.

[strayan]

You'd need to have a DP++ compatible DisplayPort output, and then you could have a passive DisplayPort to VGA adapter, but not HDMI.

Thanks, this solved the issue!

[strayan]

Of course, in your situation, you're looking to use the cable as an optoisolator. I'm speculating, but I don't think that would make a difference: if your HDMI port is putting out dirty power, you're still going to be using that power to convert the signal to optical. I would imagine that they don't have copper running that long down the cable, they probably draw power at both the sink and the source.

I recently bought a 1.5m optical HDMI cable and it eliminated the problem as well. Money well spent.