what's the best way to tighten up dirty channels on Roadster

[Pontius2000]

I can get good sounds out of channel 1 and 2. but on 3 and 4, I either get not enough distortion or too much. and it all comes out sounding flabby. I want to get a good TIGHT and CRISP distortion sound. kind of like Alice in Chains, TAD, or old Metallica. I've got a Les Paul w/ 490/498 pickups and an S-S-H Stratocaster.

Do I need to add some kind of distortion or compression pedal into the mix?

 

[endless_mike03]

I am able to dial in a good "And Justice For All" type tone on my Roadster without a boost (but using a boost WILL tighten it up) using these settings:

Channel 3. Vintage. Bold Power. Diode Rectifier. Gain 3:00, Treble 3:00, Mid 9:30, Bass 2:00, Presence (depends on how loud you have it set. I have mine at 3:00), Master 10:30.

This setting, for me, is tight, heavy, articulate, and has a pretty fast attack.
That said, I have recently added a clean boost, which has really made my amp come to life.
Most people will use a Tube Screamer or something similar, but I'm actually using a Boss Metal Zone with the distortion turned completely down on the pedal and the volume at around 3/4. This has made it super tight and expressive.

 

[thejay]

Using the amp on BOLD vs SPONGY and Diode vs Rectifier really changes the sound of the amp. Starting there should give you a lot more. Also 50w vs 100w for headroom should be taken into account.

It took me awhile to figure out the sounds I was looking for with the Roadster but when I did I was very pleased. Every once in a while if I have time I will mess with the knobs and see where I can go with it since the amp has so much.

 

[GD_NC]

I say change your pickups. I think 490/498 are muddy sounding. Try something that will give better string definition and sounds a little brighter. A Duncan JB or Dimarzio Super Distorition in the bridge would be a good place to start.

Also try rolling back the volume on the guitar to find the middle ground on your amp.

 

[Tekneek]

Throw a Maxon OD808 in front of it with gain off, volume max. It will tighten things up. Also, there are strong opinions on this one, but you can consider using a Sonic Maximizer. Just use very low settings, or it sounds like ***.