Looking for more amp distortion out of my Lab Series L5

[leftu2]

Morning gents!!
I've re-created the early Ty Tabor rig (early 80s elite strat, lab series amp/ midiverb 2 *patch62*/ and celestion g12k-85 speakers)
I need more distortion.....from the amp (channel 2).....every pedal I've tried changes the tone severely.
On a side note, I get more distortion from the low input than from the high input?? I'm a noob about how solid state amps work if someone can
tell me why that is please?
Can someone please look at the schematic and tell me how to add more distortion to this amp? 
Here's a link to the board layout and schematic :
http://www.rru.com/~meo/Guitar/Amps/Lab/schem.html

[vampwizzard]

youre going to be stuck here.. theres a ton of circuitry to wade through. Ive always known these as clean amps. Mods would be closer to pedal mods than amp mods.

[leftu2]

youre going to be stuck here.. theres a ton of circuitry to wade through. Ive always known these as clean amps. Mods would be closer to pedal mods than amp mods.

You're right, a lot going on in there. I was just hoping someone could point out a value of a resistor, cap  etc I could change to get where I wanna be.
I definitely don't want to do major surgery on it. 

[pdf64]

Not sure if the distortion trimmer r171 adjusts bias or gain; maybe mark where it is and give it a tweak?
Also consider increasing the value of r197 (eg 22k would give a 6dB boost) or reducing the value of r156 (eg 10k would give 12dB boost).

The simplest thing would surely just use a flat gain pedal though, no less valid than tinkering with the amp.

The Lo inputs are more sensitive (and lower impedance) than the Hi inputs. The input stages are a simple inverting opamp circuit, the theory behind them is pretty simple.

[thetragichero]

make sure to setup the compressor (limiter), distortion, output bias, and dc offset trimmers as instructed in the schematic/service notes. setting up the bias was a weird process (removing fuse and measuring current across fuse socket) but works
just had one of these that i poured some love into to get it running factory fresh. using my les paul with fairly low wind pickups into the second channel with volumes cranked along with deft use of the mid control/multi filter i was able to get about as much crunchy/chunky distortion as one would want out of one of these
if you have a scope with a test signal to through making sure all the semiconductors are passing signal. i had to replace a few of the 1458s (i used 4558s). the ca3080 always seems to need replacing but that's only used in the limiter circuit, which shouldn't be on if you're trying to get drive out of this
also make sure some dingbat didn't replace the ca3094 with a 3080 as i have done... twice. will still pass sound but not nearly as loud as when you have the right chip in 🙃