DIY - LM1881 Sync Stripper
This page will show you how to use an LM1881 chip to "strip" the sync information from composite
video, for use in an RGBs video signal. If you'd like to buy a pre-made sync stripper, please check out this page.
Please note that the LM1881 outputs TTL-level sync. If you're going into a device that's expecting 75 ohm
video-level sync (such as the framemeister), then you'll need to add the 470ohm resistor to the output line.
There's more info at the bottom of the page and for more information on sync, please see the main sync page.
You will need basic tools (more info can be found in the tools section), plus the
following items for this circuit:
- Basic tools, such as pliers, tweezers, etc.
- Soldering iron / solder
- Basic soldering
- LM1881M chip, the SOIC
version (please see the links to the right for the chip) --->
- One 680K resistor
- Two 0.1uf Capacitors
- One 470 ohm, 1/4 watt resistor (if 75 ohm csync output is needed)
This is a fairly easy circuit to build, but there's a few tricks to make it
smaller and easier. Also, this guide assumes you'd like to use a mounting board (thanks to the guys on
the neo-geo forum for the idea). You can use this guide if you'd like to
solder directly to a chip, but this is a "cleaner" way to make the circuit. I'll walk you
through it step-by-step:
- This is the main LM1881M chip you'll be using (surface-mount, SOIC version) and it's relevant
- Start by adding solder to both the chip legs and the pads on the board, by heating the area with your
soldering iron and then touching solder to the metal. I got used to doing this on a desk, but using a
stand and alligator clips will make it easier:
- After applying solder to both, use pliers or tweezers to hold the chip while you mount it to the
board. Once it's lined up, you should be able to just touch your soldering iron to it and they will
- Next, you'll want to use a multimeter to check your solder points. When checking, make sure to touch
the pin where it enters the chip, not near the bottom where you may accidentally be making contact with the
circuit board's pads. Then, touch the other tester to the pad that matches it's input. If a
connection isn't made, you could try adding more solder to the joint between the pad and pin:
- Add a 0.1uf capacitor to the hole that corresponds with pin 2 (composite video in) on the
LM1881M. I suggest using a multimeter to double check that the hole on the board matches the pin on
- Then add a 680K resistor to the holes corresponding to the arrows below (once again, I suggest
using a multimeter to double check the holes to pins between the chip and board). Also, make sure that
the resistor isn't touching any of the pins on the chip, or touching the other holes on the
board. I have mine run above the board to ensure it's not touching, as shown in the bottom-right
- Next, solder a 0.1uf capacitor to the resistor. I like to solder it as close to the resistor itself
as possible, to make sure it's not touching anything else, or touching to board's pads.
- Finally, solder power and ground, as well as composite video in / csync out:
- After you're done, it's good to cover the circuit with heatshrink tubing, so you won't risk shorting
it out (or anything else around it).
- That's it! Overall, it's pretty easy to make and is a bit smaller then soldering it directly to the
chip. I actually fit one of these inside a VGA head and for use with my N64 and RGB dsub switch! Also, it makes for a much cleaner look. That being
said, if you prefer the chip-only solution, you can check out this
75 Ohm csync output
Please note that this guide shows you how to build the sync stripper circuit; It does NOT
talk about use case scenarios. If you're plugging this into a display or video processor (such as the
Framemeister) then you'll need to add one 470 ohm, 1/4 watt resistor to attenuate the output to 75 ohm video
standards. Many RGB monitors accept a wide variety of sync signals, including the TTL sync that this
circuit outputs. If you'd like to be safe, just add the extra resistor; It's literally as easy
as just soldering it to the output pin.
That's it! A pretty easy circuit that can really come in handy!
If you've arrived at this page as part of the RGB Guide, please move along to: what method you'd
like to use to display RGB. If not, feel free to head to the main sync
stripper page, or check out the homepage for everything else we have to