Hi...I am thinking about building a small active full-range single driver monitor for mono checking etc. Can anyone point me in the direction of a schematic for a simple line-in amplifier with volume control?
Not sure what you mean. Does the active speaker already have a power amp in it? If that is the case you just need a volume pot in the feed. Maybe there is not enough gain in the setup? That can be addressed with a simple op amp and again a pot.
Maplin carry a kit for a low noise pre amp module based on the NE5534 (used in about 95% of mixers regardless of what the "tweaks" would have you believe!). Should it be a PA you need Maps again have kits from 1watt to 200watts (bloody isn't! but I have 2 and they chuck out a fair 80W apiece).
'Twere me and it being a "low fi" venture I would seek out a cheap s/h amp from a junk shop.