WOPL 700B Has more output on the left channel.

I am closely following Peters's "faraday cage" experiment What are your thoughts about the shield itself and the idea of running the AC across the middle ,and away from the OP amps ?

M
 
I do not run a shield but maybe I have lucked out with transformers that are very quiet.

In the PL700, I run the AC across the backplane boards midships, just south of the thermal cutout switches.

The white (neutral) and black (hot) run across the entire span of both backplane boards. The neutral hops to/from the thermal cutout switches are very short.

On the left side of the right channel backplane, the jacketed wires running to the bottom of the amp between the left and right backplane are the black wire runs to the front panel AC switch. I find this orientation to be the shortest overall run to the power switch by doing it like this. I also keep that sheathed pair separate from the remaining bundles of wires.

Then the run is across the left channel backplane to the right hand side of the transformer where the AC leads turn south and run to the bottom of the transformer, then across the bottom and then up to the AC junction block. Again, the neutral hops to the thermal cutout switches are very short.

All AC wire is M22759/11-18. It lays cleanly and neatly.

All this wiring lays neatly right on the backplanes and crosses critical input traces on the board at 90 degrees. Neatness and careful wire dress counts to having a quiet amp.
 
Joe in regards to your previous post does that a/c wiring plan apply to a 700b with the original backplanes? Where would that particular wire be available from?
 
Steve K said:
Joe in regards to your previous post does that a/c wiring plan apply to a 700b with the original backplanes? Where would that particular wire be available from?
Click to expand...

Can apply to the 700B and 700S2 equally. I think Navo has that wire type. It is my 'go to' wire type because it is thin, high voltage, high temperature and stays put with no solder shrink back. That does not make it cheap :-).


Remember, YMMV and I may be lucky in having quiet transformers.
 
Mohawk said:
I am closely following Peters's "faraday cage" experiment What are your thoughts about the shield itself and the idea of running the AC across the middle ,and away from the OP amps ?

M
Click to expand...


Don't follow that cludge.... It's unneeded
 
Update...

With the 700 running once again I measured 1.5mv AC on the left channel and 4.3 mv AC on the right. ( RCA inputs disconnected )
To the ear this is a distinct low level " buzz" on the right....
I decided to reroute the AC mains across the center of the backplanes just below the thermal switches.... "Thanks Joe !"
The resulted in 0.6 mv left and 1.2 mv right ! Dramatic reduction in noise !

With your ear against the cone on the left (0.6mv) no perceivable noise at all ..... I need to reduce the right side down to that level !
Could there be any RFI issues with Don's protect relays ? What is unique to the right side of the chassis ?

Thoughts before I try Peter's mod ?


M
 
Last edited:
Mohawk said:
Update...

With the 700 running once again I measured 1.5mv AC on the left channel and 4.3 mv AC on the right. ( RCA inputs disconnected )
To the ear this is a distinct low level " buzz" on the right....
I decided to reroute the AC mains across the center of the backplanes just below the thermal switches.... "Thanks Joe !"
The resulted in 0.6 mv left and 1.2 mv right ! Dramatic reduction in noise !

With your ear against the cone on the left (0.6mv) no perceivable noise at all ..... I need to reduce the right side down to that level !
Could there be any RFI issues with Don's protect relays ? What is unique to the right side of the chassis ?

Thoughts before I try Peter's mod ?


M
Click to expand...


Usually the left is worse than the right due to stray flux that the transformer creates. I would check the dress of the AC wiring as it enters the amp and routes to the fuse and fan outlet. Seems like that piece of your amp may not be fully optimized.

This is how I route that section. You can also see the midships routing of AC across the backplane and into the thermal cut out. Make sure you keep things short and sweet like the photo shows.


IMG_2034.JPG
 
Mine is near a perfect copy of yours..... I did however take hot (black) along the case with the neutral and to the fan outlet

Trace in red is where I have it routed.....

1584629897368.png
 
A/C reroute & "Faraday Cage" experiment ...
 

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I think I'm close to closing this up... ! Can we quickly debate the best bias voltage setting ?
It's sitting at .360mv right now.... Any reason to drop it back to .350mv.... Do I hear .375 ?...
Going, going..... Sold ?

M
 
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