ADA Depot - A Forum To Support Users of ADA Amplification Gear
ADA Preamps => MP-1 Classic => Topic started by: BradS71 on May 11, 2017, 03:21:18 PM
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Hi Guys,
I've been loving my MP1 Classic, but yesterday out of the blue it developed a weird issue. It just started make a low-level crackly, farty sound whenever I play. I fiddled around with it and discovered it only does this on the tube voicings. The solid state presets all sound fine. So I thought bad tube, right? Well, I tried 4 different sets of 12AX7's of various brands and get the exact same results with all. So it doesn't appear to the tubes themselves.
I posted a YouTube video here so you can see/hear the issue:
https://youtu.be/P5i-Hhqy7W4
Any insight/guidance would be very much appreciated.
Thanks,
Brad
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Could be R151, these go bad sometimes and then you can get this.(not always but it can). I'll take some pics tomorrow where to look for it.Do you have a multimeter?
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Hi Brad,
No worries bro, you're in good hands. MJMP answered you in less than a half hour!! whow!
I love my Classic too, and will be watching this thread to see what happens.
Dante
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Wow. You guys are awesome. Yes, I have a multimeter. Really appreciate the help.
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Check this resistor with your multimeter, (do not turn the classic on!!) it should be 180k ohm.
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Check this resistor with your multimeter, (do not turn the classic on!!) it should be 180k ohm.
I'm getting 34.5 MΩ! That's 34million Ohms, right? I checked it multiple times to make sure I wasn't crazy. I'm guessing you've found the problem! :D
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Yeah these go up in value so replace it and it should solve your problem. If not we'll look further !!
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Wow, I hadn't seen a shot of the inside of a classic before, you can see the advance in PCB compared to MP-1/2
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Yeah Richard,
It looks more like the PCB of the MP-2 than the MP-1. I remember posting that a long time ago when Jurrie was still with us.
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It doesn't always looks like that, I attached a pic of my classic pcb.
Downside of the classic pcb's is that they are a b**ch to work on.
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Downside of the classic pcb's is that they are a b**ch to work on.
Yes they are! Which is why I still haven't gotten this done. I'm not quite savvy enough to do this one cleanly and I have a good friend who is an ace with the iron and working in tight spots on PCB's that I would rather have do it...but between his and my travel schedules we have yet to meet up and get this done. I will report back once we do. Thanks again!
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Good thinking, if you're not 100% sure let someone else do it.
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Well...I was finally home for a few days and was able to get the unit over to my buddy's place and work on it. We put in a new 180K resistor in R151 and...Boom! It works perfectly!
Thanks so much for the help. Truly awesome.
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:whoohoo!: great news :thumb-up:
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Sweet! :thumb-up:
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MJMP = Epic Winner! :thumb-up:
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Well that's great news !!! :thumb-up: