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Old 11th January 2011, 02:57 AM   #1
GlenW is offline GlenW  Canada
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Default Help with a JC2

I have a Levinson JC2 in which several line (3 out of 4) modules have developed a fault. They all have become noisy. They still amplify but they hiss, snap, crackle and pop. One of the faulty 3 is an original module, the other two are replacements bought from Madrigal who used to own the brand. The 4th works noise free. Can anyone offer any wisdom on what's going on in these modules? Any similar experiences?
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Old 11th January 2011, 04:34 AM   #2
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This would be a good project for DIY audio. The original circuits can be improved slightly, over their original design, just because we have learned a little more over the decades.
Also, an IC based plug-in module could be made, but it would not be as good sonically (in my opinion), however, it certainly would be cheaper, and have slightly better specs. This might be more practical, and more appropriate for this level of preamp performance.
The main premise is to use the hybrid circuit pin-out and spacing that was universal, many decades ago, so that the modules could be plugged in and out.
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Old 11th January 2011, 08:06 AM   #3
gk7 is offline gk7
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Hi GlenW,
two modules are line, the other two are the phono stages. I have already built replacement line modules (and will built phono replacement modules too). The thread is here: Need to build JC 2 preamp
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Old 11th January 2011, 09:12 AM   #4
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Quote:
Originally Posted by GlenW View Post
I have a Levinson JC2 in which several line (3 out of 4) modules have developed a fault. They all have become noisy. They still amplify but they hiss, snap, crackle and pop. One of the faulty 3 is an original module, the other two are replacements bought from Madrigal who used to own the brand. The 4th works noise free. Can anyone offer any wisdom on what's going on in these modules? Any similar experiences?
Eventually all those line modules fail! Did you check your power supply? The phono modules seldom fail...
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Old 11th January 2011, 10:05 AM   #5
gk7 is offline gk7
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Quote:
Originally Posted by QSerraTico_Tico View Post
Eventually all those line modules fail! Did you check your power supply? The phono modules seldom fail...
In post #1 it was already said that one module works without problems, this would indicate that the power supply is o.k. (a faulty power supply would affect both channels phono and line).

If I remember correctly John once posted that the problem is the material used for filling the potted modules. It contains chemicals which destroy the semiconductors plastic cases after several years.
(Please correct me if Im wrong). If this is the case, it would be the same for line and phono modules.
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Old 11th January 2011, 02:56 PM   #6
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Actually it was the EPOXY that made the cases for the jfets that was the primary culprit, but the filler epoxy was probably not perfect either.
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Old 11th January 2011, 04:28 PM   #7
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While 'Need to build JC-2 preamp' can be helpful and impressive, it would be better to source the hybrid connectors that are pre-fab, and would fit in at least the line stage of the JC-2 itself, directly. The phono is slightly different, but we MIGHT be able to modify a line state hybrid connector to work. I will have to check.

Last edited by john curl; 11th January 2011 at 04:44 PM.
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Old 11th January 2011, 04:58 PM   #8
AndrewT is offline AndrewT  Scotland
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Is there a chemical that will dissolve the epoxy filling without damaging the pin out cradle?
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regards Andrew T.
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Old 11th January 2011, 06:32 PM   #9
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I don't know.
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Old 12th January 2011, 02:50 AM   #10
GlenW is offline GlenW  Canada
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Thanks for your responses. Some more details: The phono modules are fine, the power supply is also fine. In a couple of cases, the modules are quiet on switch on but become noisy after warm up sounding like a dry joint.

The replacement modules from Madrigal worked fine at first (several years) but later became noisy. The really irritating thing is that they amplify perfectly (to my ears; no measurements taken).

Is it the general consensus that the epoxy cannot be successfully removed?
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