Voyager-1 is currently 3.3 times further away (21.7 billion km vs 6.6 billion km) so the path loss is 10.3dB more. It has an 18W X-band transmitter (NH is 12W) and a larger HGA (3.7 m vs 2.1m). This gives an overall spacecraft EIRP increase of 6.7dB. On the negative side Voyager uses an old FEC code (rate 1/2 concatenated vs rate 1/6 Turbo) which loses around 2.5 dB. Overall the link is around 6 dB worse. I believe that Voyager 1 currently supports TM rates of up to 600 bps to the 70-m DSN stations so this would imply a margin of around 2dB for all losses in that case (it is currently far from solar conjunction).
British Astronomical Association
Supporting amateur astronomers since 1890