LM1881 Sync Stripper
A note: Only use this guide if you need a “loose” chip. Using a surface-mount version will be a bit smaller and in most cases be a better solution. You can find more info on that in this guide. Also, if you’d like, you can buy a pre-made sync stripper on 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 skills.
– LM1881 chip (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)
– Start with the chip itself. You’ll want to make sure the circle on the top of the chip is always aligned the way you see in these pictures:
– Straighten all the legs and remove the unused pins as shown below. You can cut or bend the pins off:
– I like to trim the excess off the end of the pins. This is also a good time to add solder to each pin:
– Trim the length of the 680k resister and solder it to the pins as shown below:
– Turn the circuit over (note the orientation of the pins!) and get ready to solder the capacitor. This part is a bit tricky…trim and solder the 0.1uf capacitor to the resister, however you need to get the capacitors legs as close to the actual resister as you can. You need to make sure the capacitor legs aren’t touching anything else except the resister. Then, fold the capacitor over onto the LM1881.
– Here’s an example of both the proper and improper way to install the capacitor, but much more spread out, so it’s easier to see. Please note on the “good” picture the capacitor is only touching the resistor and on the “bad” picture, both the capacitor and resistor are touching the LM1881 chip:
– Next, turn the chip back over to it’s original orientation (note the circle in the upper left). Solder the second 0.1uf capacitor to the middle leg of the LM1881. I trimmed and bent the capacitor’s leg, so it could lay flat on the LM1881. Please note the capacitor’s other leg is above the LM1881, not touching it.
– Solder your wires to the points as shown below. You’ll need power (the chip can handle 5-12 volts, but I always use a 5v source), ground and composite video to the chip, then you can solder composite sync-out to your RGB connector:
– Here are some examples of finished LM1881 circuit’s done slightly different. The one on the left is the exact same as this mod, but both capacitors are on the same side. The one on the right was used inside a console that had lots of extra space, so I was able to spread it out, making it slightly easier to assemble:
– After you’re done, it’s good to cover the circuit with heatshrink tubing, or non-conductive tape, so you won’t risk shorting it out (or anything else around it).
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 offer.