Back from the dead!

[Shibiwan]

I've had an MP-2 in my parts pile for over 15 years, and by parts pile, I meant literally "in parts". Never got around to putting it back together until a couple weeks ago when I was cleaning out my storage closet and came across the parts. It helped that I had another MP-2 main board in the pile to salvage parts off, and also did the regular maintenance mods (modded noise mod, also put in a battery holder)

Thanks to the resources and people (especially MarshallJMP) in this forum that have kept this info alive for so long, I managed to put it all together and have finally gotten it working very nicely.

Here's some pics of the rebuild:



Battery holder mod (CR2032)


Almost there...


IT'S ALIVE!!!

[rnolan]

Very cool, nice to see it come together.  Did you get to replace R913 yet and, if so, did it get rid of the hum.

[Shibiwan]

R913 was the issue. The one I pulled out was dead - literally an open circuit. This allowed the HV line to float without feedback/regulation and thus rose to 245VDC, also causing the hum.

Posted the noise mod updates here:
https://adadepot.com/index.php?topic=1014.msg30024#msg30024

[rnolan]

  :thumb-up:

[Shibiwan]

:thumb-up:

Hmmm. Perhaps I spoke too soon.

I was giving it a more thorough test after installing the missing XLR jacks (bought some new Neutrik ones) today. Noticing that there's still a some low 50hz hum in voicings 8/9/10 when I turn off the noise gate or set it to fader...same hum even if nothing's connected. It's silent with the noise gate on and isn't noticable at all when playing.

Is this normal due to the high gain of these voicings?

[Harley Hexxe]

Hey Shibiwan,

     The higher the gain settings on the MP-2, the more noise it makes, just like any high gain capable guitar amp, (within reason). If the noise is too much, (above a normal level), then it could possibly be a faulty circuit. I'm not a tech, but that would be my guess since these ADA units are getting old, they probably need a complete cap job to help quiet them down.

Harley 8)

[Shibiwan]

Yes, I understand the gain vs noise part...I used to be a tech. :D

I had just completed rebuilding the MP-2 and replaced the old caps as well as the bad R913. Not knowing how the MP-2 sounded like before piecing it together, made me curious about the hum.

...... but silly me, it turns out it was an external power supply transformer (Digitech Studio Quad that I had been working on) that was exacerbating the hum. Moved it off my test bench and the hum went down by a ton.

[rnolan]

That's good to hear.  Even when my MP-2 was brand new I had to use the gate (fader) on the high gain voices.  These days I tend to use voice 5 which doesn't need a gate and still has plenty of dist for how I'm playing now.

[Harley Hexxe]

That must have been one hell of a hum :facepalm:

[Shibiwan]

That must have been one hell of a hum :facepalm:

Off brand Chinese made replacement Digitech power supply (AC to AC). Not surprised at all at the lack of transformer shielding.

[Harley Hexxe]

I don't know if you remember when Radio Shack was around, but they used to sell a wall-wart adapter with selectable voltages at one time. I bought one...once.
It buzzed like a hornet's nest :facepalm:

Harley 8)

[Shibiwan]

I don't know if you remember when Radio Shack was around, but they used to sell a wall-wart adapter with selectable voltages at one time. I bought one...once.
It buzzed like a hornet's nest :facepalm:

Harley 8)

Guess what? That Chinese piece of crap quietly burnt out this evening. Let's see how the replacement from Amazon goes.

[Harley Hexxe]

I hope that works out for you

Harley 8)