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I think this will be a quick question, and the answer is likely buried in the forum, but I can't seem to find it exactly.

I have a Mark III system I'll be adding a THS7314 amp to in order to amplify the RGB signal up to proper levels. I see plenty of posts about this working and then using a SMS/Model 1 RGB cable.

However, I want to clarify some of the resistors.

Most schematics and pictures I find show 75ohm resistors on the RGB signal coming out of the THS amp. However, I know the SMS/Model 1 cable already has 75 ohm resistors in line on these pins (as well as some 220uf caps).

My question is - Do I add 75 ohm resistors to the amp for this mod, or do the ones in the cable take their place? or do I need both for a combined 150ohm resistance?

Thanks!

asdfqwer426 wrote

I think this will be a quick question, and the answer is likely buried in the forum, but I can't seem to find it exactly.

I have a Mark III system I'll be adding a THS7314 amp to in order to amplify the RGB signal up to proper levels. I see plenty of posts about this working and then using a SMS/Model 1 RGB cable.

However, I want to clarify some of the resistors.

Most schematics and pictures I find show 75ohm resistors on the RGB signal coming out of the THS amp. However, I know the SMS/Model 1 cable already has 75 ohm resistors in line on these pins (as well as some 220uf caps).

My question is - Do I add 75 ohm resistors to the amp for this mod, or do the ones in the cable take their place? or do I need both for a combined 150ohm resistance?

Thanks!

Those 75ohm resistor must be in only one place. Board OR cable, not both.

Usually, if I have a schematic or already printed PCB, I change the board 75 ohm resistors with 0 ohm resistors (or a tin bridge) because I use a cable with 75 ohm (+ 220 uF caps) in it.

Look at this board for example (RGB for TMS99xx VDP): https://tms-rgb.com/

It ends with zero ohm resistors as default.

Author	Message
asdfqwer426 Joined: 22 Feb 2016 Posts: 37	Clarification about using SMS/Model 1 genesis RGB cable with a modded Mark III using THS7314 Amp Posted: Mon Dec 12, 2022 7:07 pm
asdfqwer426 Joined: 22 Feb 2016 Posts: 37	I think this will be a quick question, and the answer is likely buried in the forum, but I can't seem to find it exactly. I have a Mark III system I'll be adding a THS7314 amp to in order to amplify the RGB signal up to proper levels. I see plenty of posts about this working and then using a SMS/Model 1 RGB cable. However, I want to clarify some of the resistors. Most schematics and pictures I find show 75ohm resistors on the RGB signal coming out of the THS amp. However, I know the SMS/Model 1 cable already has 75 ohm resistors in line on these pins (as well as some 220uf caps). My question is - Do I add 75 ohm resistors to the amp for this mod, or do the ones in the cable take their place? or do I need both for a combined 150ohm resistance? Thanks!

siriokds Joined: 10 Dec 2009 Posts: 114	Posted: Sun Dec 18, 2022 7:36 am
siriokds Joined: 10 Dec 2009 Posts: 114	asdfqwer426 wrote I think this will be a quick question, and the answer is likely buried in the forum, but I can't seem to find it exactly. I have a Mark III system I'll be adding a THS7314 amp to in order to amplify the RGB signal up to proper levels. I see plenty of posts about this working and then using a SMS/Model 1 RGB cable. However, I want to clarify some of the resistors. Most schematics and pictures I find show 75ohm resistors on the RGB signal coming out of the THS amp. However, I know the SMS/Model 1 cable already has 75 ohm resistors in line on these pins (as well as some 220uf caps). My question is - Do I add 75 ohm resistors to the amp for this mod, or do the ones in the cable take their place? or do I need both for a combined 150ohm resistance? Thanks! Those 75ohm resistor must be in only one place. Board OR cable, not both. Usually, if I have a schematic or already printed PCB, I change the board 75 ohm resistors with 0 ohm resistors (or a tin bridge) because I use a cable with 75 ohm (+ 220 uF caps) in it. Look at this board for example (RGB for TMS99xx VDP): https://tms-rgb.com/ It ends with zero ohm resistors as default.

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