ADA Preamps > Original MP-1
Lots of noise, changed caps, no bueno
Chris5150:
Hey all, I've recently done a cap job on one of my MP1's and it went well. I changed pretty much all of them on the tube board. I decided to tackle the other one I have that is noisy.
I replaced the 3 big caps on the tube board and the 3 big filter caps on the main board. I figured these were kind of the most important to do, and the soldering went well. Thankfully my MP1 still works after the cap replacement, but the noise is just as bad as it was. It is my newer of the 3, and I've noticed the input jack is of a normal TRS style, but it looks like it has the plastic washer to insulate it. The rear input jack looks different too compared to my other MP1s. I'm kind of puzzled on what to try next, mouser has been easy to find caps and such, but I'm really hoping to order some of the noise mod kits from MJMP once the shipping restrictions end. I'm wondering if I'm missing something else with these noise mods, the other MP1 isn't exactly the quietist either after my cap job, but my noise gates can tame it better then this one. I'm pretty novice when it comes to electronics, but if anyone can point me in the right direction that would be awesome. I saw the thread on the ground loop but some of that stuff in there is way over my head.
I can get some pictures if need be, thank you all for taking a look at this thread. Stay safe out there.
MarshallJMP:
Take some pics so I can have a look at it.
Chris5150:
Hey MJMP, thanks for taking a look. I have a bunch of pictures, but they appear to be too big to be uploaded at the moment. Is there anything in particular you would like to see? I' going to downsize what I have so I can upload, and can take some additional pictures under your guidance. Thank you.
MarshallJMP:
What happends noise wise when you unplug your guitar from the MP-1? Is it better ? Also is it noise, hum or both?
Chris5150:
It seems my room is picking up gnarly EMI interference from somewhere. I don't really get any low end hum from it, it's more like a high pitched whine. When I turn the volume up on the guitar it picks up crazy EMI, way more then the other units. I do happen to have top and bottom covers off and am playing it out of the rack, would this be why?
I definitely don't think it is a ground loop issue though. I recall that is more of a low end 60hz sound. This is just a crazy amount of EMI with a high pitched whine. Unfortunately it happens with all of my guitars, they all have humbuckers too so it's pretty confusing.
Looking at a frequency analyzer, the whine is at 3.5k, with harmonics at 2k, 1k, and a little activity at 125. The guitar feedbacks at those frequencies when I turn the volume up and let it ring out. Testing with my little pre amp pedal, it does not have the same high pitched whine, but definitely has EMI interference, although it is so much worse through the MP1. Plugging back the MP1, you instantly notice the whine and way more EMI. The whine honestly sounds like a b string harmonic at the 5th fret. When I unplug the guitar from the MP1 with the guitar volume off, at the MP1 input, the whine gets quieter, and gets a little louder when I plug in. I wonder if it's the MIDI clock or something?
Anyways, thank you for your help. It's a little difficult to describe, and the EMI seems to be worse at different times of the day. Just a very frustrating experience! It seems my room is located in EMI hell haha. Trying out with my other MP1s, it does not make the same high pitched whine, so this one is unique in that regard, as well in picking up so much EMI. The visible difference I have seen with this one is it is a later version with no top switch, and the instrument input is tied together both front and back. I have attached a picture showing the jack. I've also noticed the transformer is a little different then my other 2. Thanks again!
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