MP-1 v2.01 120hz hum and loss of drive

[guitarmutant]

Hey guys - very new to the site, and first post. I'm sure this issue has been covered somewhere, so I apologize for repeating.

My ADA MP-1 (second version: 2.01, no top switch, instrument level rear jack) has some issues I need to repair. It started with the gain (drive) being noticeably lower. Then within a couple of hours, a loud 120hz hum. While I knew it wouldn't solve a 120hz hum issue, I replaced the tubes just to be safe. It had no effect.

I checked everywhere I could, and in my area, NO ONE will work on these things. I ASSUME the caps in the power supply need to be replaced, but I can only guess. So I'm looking for an expert to chime in and guide me.

The good news (which could also be bad news) is that I know enough to be dangerous. I can build pedals from kits, I know guitar wiring, and have done amp mods when I had a good set of directions. So if anyone has experience with this particular issue, perhaps directions to repair, and any other information, I'm getting kind of desperate as I love this unit and don't want to lose it.

Thanks all!

[rnolan]

Hey guitarmutant, welcome to the depot . 120hz hum I haven't heard of before, 50hz, 60hz (depending on country) sure and that's usually power supply caps or earthing issues.

Ok, so knowing enough to be dangerous, I can relate to LoL.  So  from my experience, you need to be quick and concise and use the right temp setting on your iron so you don't "lift" pads or damage traces when/if you work on these preamps.

Now this could be as simple as some gummy jacks, or maybe more complicated .  So use good contact cleaner and clean all the sockets (and poke a jack in and out to help).

Check all you leads to make sure they are good (I know this is basic stuff but it can "catch" you out).

[MarshallJMP]

Is it only the tube voicings or also the SS voicing?

[Kazinator]

Hey guitarmutant, welcome to the depot . 120hz hum I haven't heard of before, 50hz, 60hz (depending on country) sure and that's usually power supply caps or earthing issues.

When 60Hz AC passes through a full wave bridge rectifier, we get an asymmetric 120 Hz wave. Power supply ripple is 120 Hz, plus harmonics.