gscartsw LPF Toggle Switch

This page shows you how to add a switch to toggle the low-pass filter on a gscartsw, using the THS7374.  This is for the gscartsw only, not the 'lite', as the lite doesn't use a chip with a filter.

Introduction:

This mod toggles the low-pass filter on the THS7374 amp that's inside the gscartsw.  When going from analog to digital, you'll always want one LPF in your chain, or you can get interference on the screen.  The only "problem" with LPF's is when more then one are in the same chain;  The end effect results in a slightly blurred image.  As a result, I find the LPF in the gscart extremely handy, but like the option to turn it off. 

Quick reference chart:

LPF On:
Framemeister
Direct into a flat-screen
Direct into a capture card

LPF Off:
OSSC (use it's LPF instead)
RGB Monitors
Any time another device already has one built in (including in the above scenarios), such as a console with a THS7314 mod. 

 

LPF Mod:

Start by unscrewing everything, but make sure to save every single spacer and screw!!!!!  Then flip it over and look for this spot (notice the VGA port on the top for orientation):

Next, carefully desolder and move the "R39" resistor over, as this is the spot on the board that goes directly to the LPF toggle pin.  You'll want to move it over, so it's covering the "R39" lettering and make sure the pads aren't connected at all.  Then solder a wire to the other side of the resistor.  I like to tack the wire down with a tiny bit of glue (seriously, those are SMALL dabs....remember this is a close-up!), so that the wire isn't flopping around.  I then run it through the unused pin 3 of the EXT port out to the top.  DO NOT SOLDER THE WIRE TO PIN 3, just use it as a way to route the wire through to the top of the board.  Click for full-sized:

Next solder wires to pin 1 (ground) and pin 4 (5v) on the Ext port:

Then solder the three wires to a 2-position, 3-pole switch.  Make sure that the wire coming from the pad & resistor is in the middle position.  The orientation of the other two don't matter, but note that Ground = LPF On and 5v = LPF Off.

 

Switch mounting and reassembly

Fair warning:  Drilling through thick acrylic is a pain!  If I didn't have someone helping me, I'd just have epoxy'd it underneath the top portion of the switch and not even attempted to drill.  Also, there are so many screws and washers holding this together, so be careful not to lose any!

 

Results

I actually found that there's still some kind of filtering happening in the gscartsw, even with the LPF turned off!  It's really only noticeable when you zoom in, but it's definitely a hair softer:

In comparison, here's the gscartsw_lite:


 

Summary:

If you want more control over the filtering in your SCART chain, then I highly recommend this mod.  If not, the switch is totally fine, just the way it is! 

 

If you came here while reading the RGB Guide, please move on to the section that shows how to get RGB from each game system! That section also has info on audio enhancements, which versions of each system output the best quality, plus some other helpful info! Alternatively, head back to the main page to see what other retro-awesomeness is available on this site!