LINE 6 MM4/DL4 Volume Fix (from 2008)
According a post on The Gear Page, these are the mods for the DL4/MM4 Volume fix:
1) Replace all the input/output buffer components with high quality parts for clarity of signal. Remove the electrolytic caps (C4 and C8), replace with
Nichicon and WIMA; Remove TL072 op-amps (U3 and U22) and replace with Burr Brown hi-fi OPA2134UA.
2) Removing RF filter caps from pre-relay inputs and post-relay outputs (C1,
C36, C23, C24) in order to make the pedal TRULY true bypass and eliminate tone sucking.
3) Reduce R36 and R37 from 36k to roughly 22k (24k according to Jeorge Tripps) for increased gain of output buffers. This will fix the “volume-drop” problem some people experience.
#2 and #3 are crucial to do. #1 is just for tone snobs. Furthermore, #2 was caught pretty early in the revision history so pedals built after 2001 already have this implemented.
I did step 3 only, and I was satifsfied with the results. This is how I did it.
STEP 1: Take your pedal apart!
Here is my road beaten MM4. Actually, I bought it used (aka pre-beaten) off of EB*Y.
After taking the screws off the back, your pedal should look like this. Slide the battery clips out. Then remove the 4 black screws. Then remove the silver retaining screw/nut in center. Remove nuts from input/output jacks.
This is what you should have left. This is the part you have to work on. Now turn it over!
STEP 2: SMT FUN or “How the hell do I remove these small components?”
This is when things start to get interesting. R36/37 are indicated in the picture. Pretty freakin small, huh? A steady hand with your soldering iron is mandatory! If you have had 4 or more cups of coffee, I do not recommend attempting this. Go for a swim. Read through a Mouser catalog. Come back in 4 hours…
Desolder the resistors by heating up one end and quickly shoveling it off the PC board WITHOUT damaging the copper pads.
STEP 3: Installing 22k resistors or “So this is how a square peg fits in a round hole.”
At this point, you notice there are no nice holes to run your resistor leads through. Some of you might get discouraged at this point, but you can make it work! Take your resistor, make a small ‘L’ at the end of the lead, and solder the ‘L’ to the pad.
Make another L fold over the resistor. I used some heat shrink to prevent contact with the next resistor that you have to wrangle on. Repeat this step for R37.
When it is finished, your eyes should be as blurry as this picture. You should get the idea…
STEP 4: Put it back together and test it! (…some prayer might help at this time. Consult whatever electronic God you choose to dialog with.)
I tested mine, and NO MORE VOLUME DROP! Hopefully this helps everyone.