Harold, I have no experience with the 70, only the 705. I must do the following on my 705 to get adequate volume for me (1) turn the detector volume to 28-30. Max volume is 30 and (2) turn the volume control on my headphones to maximum volume. I have 3 different pairs of quality phones and this scenario is the same for each. I contacted my Minelab dealer, with this concern, who in turn contacted Minelab. One of their techs contacted me telling me basically if I wanted more volume to increase the threshold. I have less than perfect hearing in one ear. I am able to hear well enough but doesn't leave any margin to increase volume.
Dan