ADA Preamps > MP-2

old MP2, new problems

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ang3lus:
Hey all,

after fixing my MP1 i got a MP2 which has the "it takes me 10 mins to output sound" problem which i understand is somewhat normal.

other than that i have 2 very strange issues, one of them is having a missing resistor on the board (R398), which looks factory, is it important to have?

2nd one, on the tube patches, i dont get any sound if the Drive or OD are less than 68, and if i increase the master to something more than 25 i get terrible hum, granted the unit appears to be stock, only has the 1.41 eeprom but other than that the capacitors look stock.

engaging the effects loop on Loop A (and also playing with the mix up and down) in any patch results in more hum, even without anything plugged into the input.

wah/compresor/tremolo and all other effects work fine.

Harley Hexxe:
Hey ang3lus,

   I would start with a fresh pair of tubes first of all and see what happens after that. Most of what you're describing sounds like tubes that are almost dead, and since the MP-2 has no solid state voices, you won't get any audio with out good tubes.

Harley 8)

ang3lus:
Tubes are new mesa 12ax7, forgot to mention

Harley Hexxe:
That sound like the tubes aren't getting enough voltage, hopefully it's something minor like cold solder joints or something similar.
Maybe MJMP might have a better idea what's going on with it.

Harley 8)

rnolan:
Hey ang3lus, EPROM v 1.41 is the latest available for the MP2 so your all good there.  Main upgrade was faster midi program switching, you can set it to fast or slow (however slow is close to useless).  The initial MP2 release was very slow (irritatingly) but they issued a new EPROM very quickly to fix it. 

R398 is in the tube area (under V1), on the PCB adjacent to where the tube board attaches to the PCB.  I checked the only internal pic I could find and it's supposed to be there (from what I could see)  MJMP can hopefully advise.  The next row (under V2) has the sometimes problematic (noise at high gains) R913 (replace R913 with 240Kohms 1/2w resistor) see https://adadepot.com/index.php?topic=1066.0 I've attached the MP2 loading chart in case you don't have it. Also attached is the instructions for replacing R611 to eliminate noise gate chatter.  So check that while you have the lid off.

Re no sound with drive or OD less than 68, is the noise gate on? if it is on possibly the gate threshold is set too high (just a guess).  Otherwise there is something wrong.

Master > 25 with lots of hum is not good  :facepalm: , normal master settings are > 60. You may need to do the noise mod and replace the old stock caps, unfortunately the older electrolytic caps go off over time.

Re loop A issues, how is loop B?  does it work ok? It may be loop A jacks need a clean??

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