I have a number of MA 2400s of varying vintage, plus some K2 amplifiers, and the oldest MA 2400 is giving me some trouble. Hopefully someone will have seen this problem before and might have a solution, or can suggest where to start with it.
The amp in question has the date code 8069 (so from 1989?) and is branded an amcron MA2400.
The problem is that the level on channel 1 is consistently around 6dB lower than that of channel 2, regardless of sensitivity switch setting. The sensitivity switch has 2 settings; .775 and 2.2 volts.
The problem exists even if both input attenuators are set at full/12 o clock position/ etc.
The problem also still exists regardless of whether the XLRs on the pip module are used or the TRS inputs are used. (so it's not the soldering of the XLRs or the pip connections I assume)
When turning the amp on, the green signal led on the affected channel fades out noticeably quicker than on the good channel, and when switching the amp off, there is a very noticeable turn off transient (like a deflating or discharging noise possibly) from the bad channel.
I have already re-soldered the switch contacts for the sensitivity switch and the ground lift switch, and worked them both as the amp was quite dusty inside. It is from a generation that came without the foam at the air intake, just a metal grid.
So, if anyone has any ideas, I would love to hear them. I'm getting quite fast at macrotech disassembly at this stage...
Many Thanks and Best Regards,