Zach's 700B Thread

Zach C.

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On Joe's board that is a 2.7 ohm that floats the board above chassis ground. that is not external to the board.
That's a strange explanation, considering that resistor's placement in Marks diagram, but I can live with it. "Not needed" is sort of what I thought.

I have no luck with the search features on these boards. For example, "R2L" is not a valid search. Is there somewhere that the WO 2.7r (R2) and it's function is discussed on here?

Thanks.

Zach
 
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laatsch55

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Yes go to the PLWO archives. Check for the release notes for Rev "C" board. I'll find it and post a link. The R2's were discussed at lenght
 

Zach C.

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It's buried in one of the 1000 post threads and I'll have to root it out.
It must be. I just looked at the "Rev C" thread, and it's not there as far as I can tell. It's only got 8 posts.

If you can remember where it is, that would be great, but I don't expect you to spend a bunch of time looking.

Zach
 

Zach C.

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Beins I wrote most of it I should remember it.
and...?

Is this like a game of how do you keep an asshole in suspense?

:mrgreen:

Any other guesses which thread it might be in? I don't mind digging a bit, but it's a pretty big haystack.

Zach

p.s. No work on the 700B today. It's the little ladies birthday...I'd better get a move on though, since spring break is almost over and it turns out I need to take an 8 week I forgot about to graduate this semester. Doh!
 

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Star ground details for PL700B, the following wires attach to the copper bus bar "star point" ground (these connections are effectively CHASSIS GROUND in the PL700B):

1. Main transformer center taps (generally 2 wires)
2. B+ 9800uF cap, negative post
3. B- 9800uF cap, positive post
4. Left channel speaker negative binding post (black binding post, note connect both negative binding posts together with short copper bus wire)
5. Right channel speaker negative binding post (black binding post, note connect both negative binding posts together with short copper bus wire)
6. Ground wire to Light Board
7. Ground wire to the center terminal of the two 3 terminal barrier strips mounted on amp back wall. DO NOT connect the far right barrier strip center terminal to anything to the left. The original wiring had it connected this way and is a mistake.
8. Ground wire to pad 5L on White Oak Audio PL14_20 control board

No other connections should exist to the star point ground.

Other SIGNAL GROUND connections are made as follows:

1. Right channel RCA input shell to pad 2R on White Oak Audio PL14_20 control board, this is usually the shield ground in the shielded cable (note that this RCA jack shell and the copper metal plate MUST be isolated from CHASSIS GROUND).
2. Left channel RCA input shell to pad 2L on White Oak Audio PL14_20 control board, this is usually the shield ground in the shielded cable (note that this RCA jack shell and the copper metal plate MUST be isolated from CHASSIS GROUND).
3. There are generally 2-220K resistors from the input tip connection of both RCA input jacks to ground right as the signals come into the amp. The ground for these resistors must be SIGNAL GROUND, not CHASSIS GROUND. A picture of the recommended wiring for the input switch is shown below.

DSCN0002.jpg
 
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Gepetto

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Let me know if any questions, I am back and catching up on order backlog from being in Asia for 15 days.
 

Gepetto

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That's a strange explanation, considering that resistor's placement in Marks diagram, but I can live with it. "Not needed" is sort of what I thought.

I have no luck with the search features on these boards. For example, "R2L" is not a valid search. Is there somewhere that the WO 2.7r (R2) and it's function is discussed on here?

Thanks.

Zach
Zach
Mark's diagram is a schematic representation of the connection between CHASSIS GROUND (the star point ground) and SIGNAL GROUND. This 2.7 ohm connection occurs in the White Oak PL14_20 board assembly via R2L and R2R.
 

Zach C.

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Star ground details for PL700B, the following wires attach to the copper bus bar "star point" ground (these connections are effectively CHASSIS GROUND in the PL700B):

1. Main transformer center taps (generally 2 wires)
2. B+ 9800uF cap, negative post
3. B- 9800uF cap, positive post
4. Left channel speaker negative binding post (black binding post, note connect both negative binding posts together with short copper bus wire)
5. Right channel speaker negative binding post (black binding post, note connect both negative binding posts together with short copper bus wire)
6. Ground wire to Light Board
7. Ground wire to the center terminal of the two 3 terminal barrier strips mounted on amp back wall. DO NOT connect the far right barrier strip center terminal to anything to the left. The original wiring had it connected this way and is a mistake.
8. Ground wire to pad 5L on White Oak Audio PL14_20 control board

No other connections should exist to the star point ground.

Other SIGNAL GROUND connections are made as follows:

1. Right channel RCA input shell to pad 2R on White Oak Audio PL14_20 control board, this is usually the shield ground in the shielded cable (note that this RCA jack shell and the copper metal plate MUST be isolated from CHASSIS GROUND).
2. Left channel RCA input shell to pad 2L on White Oak Audio PL14_20 control board, this is usually the shield ground in the shielded cable (note that this RCA jack shell and the copper metal plate MUST be isolated from CHASSIS GROUND).
3. There are generally 2-220K resistors from the input tip connection of both RCA input jacks to ground right as the signals come into the amp. The ground for these resistors must be SIGNAL GROUND, not CHASSIS GROUND. A picture of the recommended wiring for the input switch is shown below.

View attachment 8056
Excellent. Step by step instructions I can slavishly follow. Step 7 of the chassis ground portion is the only thing that's not perfectly clear to me, but I'm not in front of the amp right this second. I'm sure it will make sense when I am looking at it. The pic is very helpful.

Thanks.

Zach
 

Zach C.

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Let me know if any questions, I am back and catching up on order backlog from being in Asia for 15 days.
It seems the confusion I have/ had stems from the fact that I thought signal ground usually was circuit common as opposed to chassis/ safety ground. It seems I need to review this.

If you have a chance to explain it at some point, I would appreciate it, but there is no rush or expectation that you should.

I don't need to understand it, but I would like to. Been a long time since I read up on amps...

Thanks

Zach
 

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It seems the confusion I have/ had stems from the fact that I thought signal ground usually was circuit common as opposed to chassis/ safety ground. It seems I need to review this.

If you have a chance to explain it at some point, I would appreciate it, but there is no rush or expectation that you should.

I don't need to understand it, but I would like to. Been a long time since I read up on amps...

Thanks

Zach
Don't get too hung up on nomenclature.

The single point ground is the bus bar between the 2 caps that all the first group of grounds tie to that are in the first list. The connection made in list item 7 ties that single point ground to the chassis via the terminal block connection to the chassis using the screw that mounts that terminal block. That is the only connection to the chassis using the scheme that I detailed in the posting. Most star point ground systems tie the chassis and star point together at one point only.

I call the second grouping SIGNAL GROUND because that chain is only connected to the Star Point or CHASSIS GROUND by the 2.7 ohm resistors on the PL14_20 board.


I could have called CHASSIS GROUND as GROUND1 and SIGNAL GROUND as GROUND2 and the net effect would be the same.
 

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Here is a pic of step 7. In fact if you look carefully, you can see most of the runs described in this list pictured here.
DSCN0005.jpg
 

Zach C.

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Here is a pic of step 7. In fact if you look carefully, you can see most of the runs described in this list pictured here.
View attachment 8057
What is pictured here is what I thought you meant, except that I believe you meant to say "DO NOT connect the far right barrier strip center terminal to anything further to the right."

i.e. don't connect the speaker, input, or coupling switch grounds to this run.

I think?

Zach
 

Zach C.

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Don't get too hung up on nomenclature.

The single point ground is the bus bar between the 2 caps that all the first group of grounds tie to that are in the first list. The connection made in list item 7 ties that single point ground to the chassis via the terminal block connection to the chassis using the screw that mounts that terminal block. That is the only connection to the chassis using the scheme that I detailed in the posting. Most star point ground systems tie the chassis and star point together at one point only.

I call the second grouping SIGNAL GROUND because that chain is only connected to the Star Point or CHASSIS GROUND by the 2.7 ohm resistors on the PL14_20 board.


I could have called CHASSIS GROUND as GROUND1 and SIGNAL GROUND as GROUND2 and the net effect would be the same.
OK. The question I really meant to ask, but was unclear about is, why is "signal ground" lifted above circuit common. I thought these were usually the same.

Thanks

Zach
 

Gepetto

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What is pictured here is what I thought you meant, except that I believe you meant to say "DO NOT connect the far right barrier strip center terminal to anything further to the right."

i.e. don't connect the speaker, input, or coupling switch grounds to this run.

I think?

Zach
Your understanding is correct Zach, the original PL700B had this connected in from the right which is not correct for a star point ground. Sever the wiring that used to exit to the right and connect it to the left hand starpoint as I show in the photograph. It is fairly evident.
 

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OK. The question I really meant to ask, but was unclear about is, why is "signal ground" lifted above circuit common. I thought these were usually the same.

Thanks

Zach
It is not lifted Zach, the sensitive section on the PL14_20 board is separated from the higher power sections on the circuit board (power supply decoupling currents) on purpose. They are bonded together by means of the low valued 2.7 ohm resistor. The small ohmic separation ensures that the ground currents in the slightly higher power section do not take any sneak paths through the very low level circuitry and ground paths.

Clearer?
 
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