i did the 'resistor added to power board' what they show in the link below as an extra, i found that it reduced the overall volume available (which is what i wanted, as i didnt want to always just be using like the lower 20% of the volume pot before suddenly it is really loud, but instead adding a resistor like they do (can experiment with values) now i use the whole sweep of the volume pot. and when im at maximum volume it is not crazy loud and noisy/buzzy anymore) ... its better for the pot itself also, using the whole sweep of the pot now rather than before where i was always moving it right at the lower end only, wearing that bit out only..
http://console5.com/wiki/Vectrex_PreAmp_Buzz_Reduction
EDIT: i had a check inside my vectrex and wanted to add, i used a 2.2k resistor personally as opposed to the 1k they recommended (the higher the resistor, the more overall volume available is reduced on the volume pot) .. 2.2k is what suited me as now my volume goes up to a level which at maximum is a good 'bedroom level loudness' for me. as for the resistor type, a regular 1/4 watt resistor is fine.