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Made my Own VGA to Scart cable, audio buzzing!!
Posted: Mon Mar 22, 2021 6:54 pm
by BlockABoots
So i have built my own scart to vga cable to use along with a HDMI to VGA adapter. I followed the diagram from here,
https://github.com/mist-devel/mist-boar ... ScartCable
- scart.jpg (55.63 KiB) Viewed 8706 times
the only alteration i did was to add a 470k resistor to the sync line on the scart end (Pin 20).
But i noticed im getting a slight audio buzz from the left speaker of my TV when using the Mister!!
Should i be soldering a small wire from Pin 2 (right audio) to Pin 4 (Ground) and Pin 6 (left audio) to Pin 4 (ground) on the scart plug???
I take it thats what this symbol means on the diagram right??....
- scart 2.jpg (2.66 KiB) Viewed 8706 times
to join the audio line to the ground line right???
Re: Made my Own VGA to Scart cable, audio buzzing!!
Posted: Mon Mar 22, 2021 7:13 pm
by jca
BlockABoots wrote: ↑Mon Mar 22, 2021 6:54 pm
Should i be soldering a small wire from Pin 2 (right audio) to Pin 4 (Ground) and Pin 6 (left audio) to Pin 4 (ground) on the scart plug???
I take it thats what this symbol means on the diagram right??....
to join the audio line to the ground line right???
No, what it means is that you should use a shielded audio cable with the shield connected at both ends one at the 3.5mm plug and the other at pin 4 of your SCART connector. If you use a 3.5mm audio pig tail you just have to connect pin4 of SCART to the shield.
Re: Made my Own VGA to Scart cable, audio buzzing!!
Posted: Mon Mar 22, 2021 7:22 pm
by BlockABoots
jca wrote: ↑Mon Mar 22, 2021 7:13 pm
BlockABoots wrote: ↑Mon Mar 22, 2021 6:54 pm
Should i be soldering a small wire from Pin 2 (right audio) to Pin 4 (Ground) and Pin 6 (left audio) to Pin 4 (ground) on the scart plug???
I take it thats what this symbol means on the diagram right??....
to join the audio line to the ground line right???
No, what it means is that you should use a shielded audio cable with the shield connected at both ends one at the 3.5mm plug and the other at pin 4 of your SCART connector. If you use a 3.5mm audio pig tail you just have to connect pin4 of SCART to the shield.
'3.5mm audio pig tail' ?, is that where you have 3 dedicated wires inside the cable housing, (left, right and ground)?
Thats what i had yes, so i did connect up the 3rd black wire to Pin 4 of the scart cable, but that didnt seem to help with the slight audio buzz.
Is the buzzing just due to a poor quality audio cable do you think and no way to remedy it?. I should say that the VGA cable i bought and copped one end off didnt have wires for R,G B ground BUT the picture looks super clear anyways
Re: Made my Own VGA to Scart cable, audio buzzing!!
Posted: Mon Mar 22, 2021 7:45 pm
by jca
3.5mm audio pigtail is a 3.5mm plug already connected to a short piece of audio cable like this:
- 31t5cR5f-RL._SX385_.jpg (9.7 KiB) Viewed 5744 times
By using one you don't have to deal with the nasty nickel plated connections on the plug - I hate soldering those. The cable has 2 wires (left and rigth) and a shield. If you used only 3 wires without shield it could be the cause of your buzz. Where did you connect the audio on MISTer?
Re: Made my Own VGA to Scart cable, audio buzzing!!
Posted: Mon Mar 22, 2021 8:02 pm
by BlockABoots
jca wrote: ↑Mon Mar 22, 2021 7:45 pm
3.5mm audio pigtail is a 3.5mm plug already connected to a short piece of audio cable like this:
By using one you don't have to deal with the nasty nickel plated connections on the plug - I hate soldering those. The cable has 2 wires (left and rigth) and a shield. If you used only 3 wires without shield it could be the cause of your buzz. Where did you connect the audio on MISTer?
Ah i bought a generic 3.5mm extender cable, male on one end and female on the other and just chopped the female end off. The cable had 3 wires inside red, white and black no shielding foil just the black ground wire.
My HDMI to VGA adapter also had a 3.5mm jack on it so thats where i got the audio from the mister
Re: Made my Own VGA to Scart cable, audio buzzing!!
Posted: Mon Mar 22, 2021 8:32 pm
by jca
I guess the non presence of the shield could be the cause of the buzz. It seems that shielded cable are becoming rarer: the pic I linked to seems to be similar to yours - blanc, red and black wire without any visible shield.
Re: Made my Own VGA to Scart cable, audio buzzing!!
Posted: Tue Mar 23, 2021 10:44 am
by hiddenbyleaves
Maybe you have heard of this already but you could try google "ground loop" and try out the known steps for addressing this issue. A friend of mine is a sound engineer and it seemed to me that alot of time was spent hunting the dreaded buzz known as the "ground loop".
I followed the advice of others in these forums and got a mini toslink to toslink cable and a cheap audio DAC. Then I connected the 3.5mm jack from my scart cable to the DAC and the sound out of my CRT tv's speakers was much cleaner and better, however in between sounds I could hear the dreaded ground loop buzz. I tried many different things that articles on the internet suggest and eventually found that when I touched the red and white audio out on my tv it disappeared. I ended up plugging a rca male to male cable into those outputs and the buzz completely disappeared.
Re: Made my Own VGA to Scart cable, audio buzzing!!
Posted: Wed Mar 24, 2021 9:15 pm
by BlockABoots
hiddenbyleaves wrote: ↑Tue Mar 23, 2021 10:44 amI tried many different things that articles on the internet suggest and eventually found that when I touched the red and white audio out on my tv it disappeared. I ended up plugging a rca male to male cable into those outputs and the buzz completely disappeared.
Guess ill give that a good, despite how stranger it sounds lol
Re: Made my Own VGA to Scart cable, audio buzzing!!
Posted: Mon Apr 12, 2021 9:41 pm
by BlockABoots
So i made another cable today am still getting the same audio buzzing from the TV speaker.
I have been be soldering the bare copper wire from the VGA cable to the metal shell of the Scart cable. Am i right in thinking this bare copper wire is ground? as touching one end of my MultiMeter to this bare copper wire than then any metal part of the VGA plug gives continuity.
I notice in the few guides I've seen for the VGA to Scart cable for the MiSTer none of them say to do this, could this be causing the audio buzzing possibly??
Re: Made my Own VGA to Scart cable, audio buzzing!!
Posted: Sun May 02, 2021 1:14 pm
by C-R-T
The audio ground (pin 4 on the scart end) should not be connected to the other ground pins, it should only be connected to the ground shield on your audio cable.
You shouldn’t use a 470K resistor on the composite sync (scart pin 20) either, it should be 470-1000 ohm.
Re: Made my Own VGA to Scart cable, audio buzzing!!
Posted: Mon May 10, 2021 9:36 am
by akeley
C-R-T wrote: ↑Sun May 02, 2021 1:14 pm
You shouldn’t use a 470K resistor on the composite sync (scart pin 20) either, it should be 470-1000 ohm.
Can the resistor not go over 1000 ohm? I'm about to try and add 2K potentiometer to the sync line, to remedy washed out colours on a Trinitron,
as per this thread. I understand "2K" means "2000" in this case (I know nothing about electronics)?
Re: Made my Own VGA to Scart cable, audio buzzing!!
Posted: Mon May 10, 2021 9:49 am
by Blitzwing
hiddenbyleaves wrote: ↑Tue Mar 23, 2021 10:44 am
Maybe you have heard of this already but you could try google "ground loop" and try out the known steps for addressing this issue. A friend of mine is a sound engineer and it seemed to me that alot of time was spent hunting the dreaded buzz known as the "ground loop".
I followed the advice of others in these forums and got a mini toslink to toslink cable and a cheap audio DAC. Then I connected the 3.5mm jack from my scart cable to the DAC and the sound out of my CRT tv's speakers was much cleaner and better, however in between sounds I could hear the dreaded ground loop buzz. I tried many different things that articles on the internet suggest and eventually found that when I touched the red and white audio out on my tv it disappeared. I ended up plugging a rca male to male cable into those outputs and the buzz completely disappeared.
I ended up going the hdmi splitter route to split out the audio even though I'm using VGA to scart. The clicks and pops that come when changing cores as the FPGA "resets" were not bad but definitely the constant ground loop hum was distracting.
Re: Made my Own VGA to Scart cable, audio buzzing!!
Posted: Mon May 10, 2021 10:02 am
by hiddenbyleaves
I might do that also eventually. I would guess that Audio over HDMI is the best the mister outputs. I have my MiSTer in an arcade cabinet and have been looking for a small soundbar with HDMI in to use instead of my crt tv's speakers.
Re: Made my Own VGA to Scart cable, audio buzzing!!
Posted: Tue Nov 23, 2021 1:27 pm
by pacoarcade
For CSYNC line the adequate resistor in series is 470Ω. This is the voltage using a Rankie HDMI to VGA converter and a consumer TV set, ~400mV, being 1V the maximum acceptable:
- rankie-csync-470.jpg (547.53 KiB) Viewed 5884 times
It would be fine even for TTL CSYNC assuming your TV set is 75Ω terminated.