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G8HQP Dave · 4th May 2011, 9:34 pm

The Troughline 2 takes the MPX signal straight from the discriminator, but the stereo version uses V5b as a cathode follower for MPX. It does this by moving the de-emphasis from before this stage to after this stage. In the 2/3 de-emphasis is done by R32 and C50. In the Stereo version mono de-emphasis is done by R42/R43/C50, and stereo de-emphasis by R48/C59 and R49/C60.

I think your best option is to modify your 3 to make it more like the Stereo version. The chip decoder will expect a reasonably low impedance input, so the cathode follower will provide this. MPX is destroyed by de-emphasis so you need to remove these components: replace R32 by a wire link, and simply remove C50.

4th May 2011, 9:34 pm	#5
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: A Stereo decoder for Leak Troughline 3 The Troughline 2 takes the MPX signal straight from the discriminator, but the stereo version uses V5b as a cathode follower for MPX. It does this by moving the de-emphasis from before this stage to after this stage. In the 2/3 de-emphasis is done by R32 and C50. In the Stereo version mono de-emphasis is done by R42/R43/C50, and stereo de-emphasis by R48/C59 and R49/C60. I think your best option is to modify your 3 to make it more like the Stereo version. The chip decoder will expect a reasonably low impedance input, so the cathode follower will provide this. MPX is destroyed by de-emphasis so you need to remove these components: replace R32 by a wire link, and simply remove C50.