Mike's PL400 rebuild (or, Mark's WOPL III!)

Wheel-right

Wheel-right

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#23
Gepetto said:
On purpose Mark. Been to this rodeo before and it is more expeditious to put them in the kit than to deal with a request later on to send a replacement set.
Click to expand...
Gepetto, you are on top of it and making it so much easier to keep these PLs going forever. Thank you for all the thinking ahead, the work and effort you put in!
 
laatsch55

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Amen, Joe's the shit!!

Fred, when Joe came out with the back planes I bought 200 picos..
 
MarkWComer

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The fat lady sings... and sings quite nicely!

Haven’t put her face on just yet, burning her in, and don’t wanna risk damage to the meters.

Nice! Smooth! Detailed bass, wonderfully clear vocals.

BUT- left channel had .1mv DC offset, right had absolutely zero! Is this from the G1 driver board? MARVELOUS!
38C6282C-0F4E-4D42-A647-F8447C17EE33.jpeg
 
Gepetto

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#32
MarkWComer said:
The fat lady sings... and sings quite nicely!

Haven’t put her face on just yet, burning her in, and don’t wanna risk damage to the meters.

Nice! Smooth! Detailed bass, wonderfully clear vocals.

BUT- left channel had .1mv DC offset, right had absolutely zero! Is this from the G1 driver board? MARVELOUS!
View attachment 37170
Click to expand...
Good stuff Mark, you made short work of that... Gets the official "that's purdy"
 
Gepetto

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#34
You may have to rotate your cap hold down plate 180 degrees Mark to clear meters. Some are close and some have plenty of clearance. The plate is designed to accommodate either situation. Pictures attached to show you it did happen :) Like so... IMG_0882.JPG
 
laatsch55

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#36
The OPA 2134 has been responsible for the low offset.

iT TOOK A L;OT OF TYRANSISTOR MATCHING OF THE DIFF INPUT PAIR TO GET IT BEL;OW 10 MV...
 
Gepetto

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#37
When you have +/- 0.5mv typical specified offset and only 5 picoamps of bias current, you can achieve closed loop offsets such as this. That type of performance can be achieved with a MOSFET front end, very hard to achieve with a bipolar front end without adjusting it out (introducing another pot and another failure and noise injection point).
 
MarkWComer

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#38
laatsch55 said:
The OPA 2134 has been responsible for the low offset.

iT TOOK A L;OT OF TYRANSISTOR MATCHING OF THE DIFF INPUT PAIR TO GET IT BEL;OW 10 MV...
Click to expand...
Gepetto said:
When you have +/- 0.5mv typical specified offset and only 5 picoamps of bias current, you can achieve closed loop offsets such as this. That type of performance can be achieved with a MOSFET front end, very hard to achieve with a bipolar front end without adjusting it out (introducing another pot and another failure and noise injection point).
Click to expand...
Just sayin’...

When I checked the offset I thought something was wrong. Surprise!
 
Wheel-right

Wheel-right

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#39
Gepetto said:
You may have to rotate your cap hold down plate 180 degrees Mark to clear meters. Some are close and some have plenty of clearance. The plate is designed to accommodate either situation. Pictures attached to show you it did happen :) Like so... View attachment 37171
Click to expand...
Had to do this when I put them in my 400, all good after that. Great job there Mark it looks fantastic. Now get back to the 700, hoping to get started on mine soon.
 
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