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Old 17th June 2011, 02:25 AM   #11
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ok this is the newer one that is stock split chassis

the biggest change was the pots and thier linkage as they were plastic.

the grey caps in the preamp side need replacement.

these caps have a history of being cooked by the neighboring heat sink. Replace them with high temp caps.

remove the wima caps and install orange drop caps as wima caps are really low quality (regaurdless what others might want you to think. maybe because they are red who knows)
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Old 17th June 2011, 02:26 AM   #12
240z4u is offline 240z4u  United States
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Sorry, those photos are old. There aren't any original electrolytic caps left in there at all. Thanks for the headsup on the wimas. Let me take some updated photos right now though.
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Old 17th June 2011, 02:58 AM   #13
240z4u is offline 240z4u  United States
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Here are the newest pictures.

You can see the janky diode work.

Also, why did he cut the resistor off of the balanced output? He said it increased the output of the preamp or something? I don't know what exactly he did that for.

Evan
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Old 17th June 2011, 03:07 AM   #14
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I would clean up the area around those diodes - and preferably replace them with one of the appropriate rating (as other point out). Clean up the board with some flux cleaner. If you don't have any, start with isopropyl alcohol (rubbing alcohol) on a cotton swab. If that doesn't clean the brown flux stuff off, use acetone (careful around plastic parts!!)

The purpose of flux is to clean the solder joint during the soldering process. Once, the parts are soldered on, there's no use for the flux. But it does tend to absorb water and cause electrical leakage issues that could result in hum.

It looks like the resistors on the XLR inputs connected one signal lead to GND through the resistor. The "tech" cut the resistors as he suspected a ground loop problem. Try connecting ONE of those resistors.

~Tom

Last edited by tomchr; 17th June 2011 at 03:10 AM.
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Old 17th June 2011, 03:09 AM   #15
240z4u is offline 240z4u  United States
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Can do Tom. I think that diode situation needs to be rectified. I may actually have some appropriate ones here that I can use.
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Old 17th June 2011, 05:35 AM   #16
tomchr is offline tomchr  United States
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Quote:
Originally Posted by 240z4u View Post
Can do Tom. I think that diode situation needs to be rectified. I may actually have some appropriate ones here that I can use.
Read the type number on the diodes already there. Probably 1N.... Then we can figure out what a suitable replacement would be -- unless you have a schematic that shows what it's supposed to be.

~Tom
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Old 17th June 2011, 01:26 PM   #17
240z4u is offline 240z4u  United States
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Tom, Will do. I am leaving town for the weekend for a wedding. Will update on Sunday.

Thanks.
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Old 18th June 2011, 04:27 PM   #18
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Originally Posted by tomchr View Post
I would clean up the area around those diodes - and preferably replace them with one of the appropriate rating (as other point out). Clean up the board with some flux cleaner. If you don't have any, start with isopropyl alcohol (rubbing alcohol) on a cotton swab. If that doesn't clean the brown flux stuff off, use acetone (careful around plastic parts!!)
also, be sure if you get a white residue after cleaning, clean this as this is really conductive.

remove the blue twisted wire, and the white twisted wire as those I don't remember them being there.
0 ohm fusing resistor goes on pin1 to ground but can be left open (nothing on pin 1)
positive signal to pin 2
inverted signal to pin 3

Last edited by DavesNotHere; 18th June 2011 at 04:44 PM.
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Old 19th June 2011, 12:15 AM   #19
tomchr is offline tomchr  United States
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remove the wima caps and install orange drop caps as wima caps are really low quality (regaurdless what others might want you to think. maybe because they are red who knows)
I'm not sure where you get that from. The Wima MKP are polypropylene caps. That's one of the lowest loss dielectrics and the one that contributes the least to distortion.

The hum is not caused by these caps. Fix the hum. Then upgrade to boutique caps if you have too much money burning holes in your pockets.

~Tom
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Old 20th June 2011, 12:59 AM   #20
240z4u is offline 240z4u  United States
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12b2 is the diode number. I had to cut one out to read it... so I don't want to power it up until I get the proper diode installed.

The white and blue twisted wires are original (or were like that when I got the preamp), but not the same color as the factory installed wire. He replaced a length of wire that was too short with that. I can try disconnecting that after I get that diode swapped. I want to do one thing at a time so I know what I did if something crazy happens.

Thanks guys.
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