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Dual Rectifier - complete gain and volume drop on channels 2 & 3 HELP!

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  • Dual Rectifier - complete gain and volume drop on channels 2 & 3 HELP!

    Hi, Im new to the forum, I live in Panama City (Central America) and recently bought a half working 2000 Dual Rectifier Solo from my bandmate for a reasonable price ($500 with an ATA case). No store sells Mesa in Panama but still I went on to buy the amp thinking it was a great deal and could probably get it fixed at some point. I know for a fact my bandmate took it to 3 different amp techs in Panama but none really figured out the problem, I found a promising tech that has fixed other tube amps (no Mesa though) so I decided to give it a shot. As usual, the first thing people blame any problem on tubes amps are the tubes, so I went on and bought all the tubes new (preamp, power tubes, etc., think it was 11 in total), all I could get down here were Russian Electro Harmonix which the tech said would do the job just fine, the guy changed the tubes and gave back the amp saying it was working. I tried the amp back at the studio and at first it was fine but then after 15-20 min the problem came back. So now in detail the problem:

    Clean Channel 1 seems to work fine all the time, Channel 2 & 3 worked perfect for the first 15-20min and then it started to drop half the volume and all the gain. The problem first happened when switching from the clean channel 1 to either channel 2 or 3, what it does is that it drops the volume and gain to half and it sounds like a filtered bright slight OD, like when you have a bad cable connection that some signal slightly goes by. At first Channel 2 or 3 would flake out when switching channles only and then come back fine in 2 seconds or if I switched back and forth the channels then it would get fixed 1 out of 3 times. If I left it in Channel 2 or 3 alone it didnt really do the volume and gain drop, although after 5-10 minutes of having this problem it was almost impossible to get the distortion channels to work properly. This is the same problem my bandmate had before with the amp as well, so i guess its not the tubes. My bandmate bought this amp in Miami in the year 2000-2001 and then he moved to Panama in 2004 and in 2005 the amp started having this problem. Back then he called Mesa and got the schematics send to him but it seems the techs find this amp to complicated down here, for them its like a Lamborghini and they are used to Toyotas.

    To ship this amp to Mesa directly and get it fixed would be the best solution but an expensive one, my best chance is for someone to point out what the problem could be so that my tech works on it here or worst case scenario I can take the amp to Indianapolis on December when I go visit my brother. I found in the Mesa Boogie website 2 authorized repair shops in Indianapolis and could leave it there and have my bro bring it back at some point. Are those authorized shop as good as the Mesa factory? otherwise I would ask my brother to send it to Mesa in California, I really want to fix the amp and would prefer Mesa to check it directly gladly but if theres a simple solution for this I would prefer to just fix it here and save time and shipping expenses. I read something about LDR but I just play guitar, dont know anything about amp electronics parts.

    Anyone has any idea what it could be? maybe someone with a similar problem that got it fixed. Your replies, comments, and any guidance at all would be greatly appreciated.

  • #2
    Hi,

    I would check for these things:

    1/ Muting FETs (for muting the channels during switching to avoid pops from relays). Check out the whole switching/muting circuit. Make sure all FETs have the proper voltages at their gates.
    2/ If the amp has LDRs they all need to be checked as well because they can go bad with the time.
    3/ Loose connections, cold solder points etc.

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    • #3
      Thanx for the reply Gainfreak.... I gave the amp back to the tech and so far nothing, he changed a gain pot that he thought was the issue, re-soldered some spots that looked sketchy...but the amp is still failing with the same issue...he says he has measured the parts of the amp (whatever that means) and that they all seem fine, they even look new.... it sucks, I hope he finds whats causing the problem

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