General overdrive / boost question

[chaz]

I've been playing around with my Fulltone FD-2 lately and it seems as though I can get a pretty substantial amount of boost over my clean channel with this thing (significant volume change).

However when I switch to one of the dirty channels on my amp and activate the boost, it merely tightens up the sound a little bit (classic metal sound).

Can anyone give a technical reason why there is not as large of a volume boost over a distorted channel but a pretty huge boost with the clean channel?

[aron]

Headroom. There's not as much headroom in the overdrive channel.

[chaz]

So is the only way to get a boost on a distorted channel to have a seperate switched volume control between pre-amp and power amp stages?

[PRR]

> boost over my clean channel

Put 8 inches of stuff in a 4 inch pipe. Get pretty dense.

> dirty channels ... merely tightens up

Put that 8"-into-4" stuff into another 4 inch pipe, it can't get much denser.