Thanks for that - if I've understood correctly then changing the voltage x3 (ie. 0.5 to 1.5V) does indeed give a shift of between 9.5 and 10 dB

the other thing I had come across on the dada site was this passage relating to resistor values for 405 gain reduction:

It's stuff like this that makes me hesitant to simply buy a kit of parts on ebay. Does it also vary from one set of boards to another?