ADA Preamps > Original MP-1

New (to me) MP-1 and no tube sound

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scole:
So I finally rejoined the ranks of MP-1 owners. While I bought the unit locally, the seller says he bought it off Reverb (original listing here) and I think he may have bought it off an ADA Depot member because there's a website sticker on the top panel. Anyways, The unit is v2.01 and looks to be that way from the factory thanks to the label on the chip. Outside of that, a previous owner had replaced the soldered battery with a newer replaceable battery holder (yay!) and the rear input jack seems to have been replaced since it looks different than the other jacks next to it on the rear panel.

The unit has sound with the S.S. voicing but everytime I switch it to one of the tube voicings, it goes silent (well, there's hiss but no signal otherwise). I wondered if, perhaps, the tubes were blown or bad. I don't have previous experience with tubes but here's what I've done. First, I pulled each tube out and inspected them. They both visually look good with no signs of burning. The front tube is a Mullard 12AX7/ECC83:




The back tube is JJ ECC 83S:




With each tube, I used my multimeter to test continuity from pins 9 to 4/5 and they both were fine & none of the other pins showed continuity. I reinstalled the tubes and then turned the unit on and then took this picture of the tubes after 5 minutes:



I know that it isn't guaranteed that the tubes will glow but neither were in this case. I turned the unit off after this & unplugged it. The tubes themselves were slightly warm to the touch but not hot or scalding. Something was rattling around inside the unit so I took the bottom cover off and found a piece of plastic. It looks like it's part of one of the A/B output jack housings:



I've done pickup & guitar electronic swaps but I'm out of my element with this. Where do I start? Here's a short video where I power up my unit to a patch that uses the S.S voicing. I then edit the patch and try to change it to either of the tube voicings.



Thanks!
Steve

mrguitar:
Hmmm, this is a long shot after watching your video, but make sure the gain settings aren't on zero. I suspect you checked that already. I can't remember if turning them to zero will cause this or not but it's the easiest thing to check first. Set it all to 5. :)

scole:
Hey, thanks for chiming in. Like you thought, I did check that and it made no difference. BUT- I do have great news. I ran down to my local shop today and picked up some new JJs and put them in. Once the unit warmed up, the distortion just faded in. Ahhhhh!  :banana-dance:

Pretty relieved that it was as simple as a tube replacement. I was a little mortified after replacing my tubes because I noticed this red wire that was cut and not connected:



I guess its intentional and I have no idea why its cut but my MP-1 roars. I'll take it!

rnolan:
 :whoohoo!: good to hear it's working  :thumb-up:

MarshallJMP:
It seems the firmware is V2.01 but the hardware is V1. The cut wire is normal on these units, so don't worry about that. You will need to replace those output jacks I guess, but at this stage they are easy to replace. Just take some pliers, heat the holes from the top and gently get them out piece by piece. Then clean the solder from the holes and put some new ones in.

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