Star Point Ground Scheme for PL700B Amplifiers

Gepetto

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#1
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 further to the right of this point. 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. These resistors provide a bleed path across the input coupling caps to keep them discharged if you are using the amp in Normal mode switch setting.



Notes:
1. The original PL700B amp wiring had the speaker negative binding posts attached to the copper input plate and by virtue of that to the input RCA jack shells as well as the DIRECT-NORMAL switch frame. These connections MUST be removed, they are a big problem for a single point ground.
2. The SIGNAL GROUND is connected to the CHASSIS GROUND on the White Oak Audio PL14_20 board through a 2.7 ohm resistor in locations R2L and R2R.
 
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Gepetto

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#5
It provides a bleed path across the input coupling caps to keep them discharged if you are using the amp in Normal mode switch setting.
 

laatsch55

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#8
Engineering terms and antonyms that I know and understand I can count on one finger.....
 

Gepetto

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#9
Random symbols I grabbed out of the library to make the schematic...

Rev D coming up.
 

marcok

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#15
Hi Gepetto ( in Italian Mastro Geppetto ) and all,
I have looked around the diagram and ,if I have understood well, the star point now is the rectifier .
Is it correct ?
Anyways my question was simpler :
Why PL 400 and 700 have the AC power cord with the ground ?
U.S. safety rules ? In my opinion is a nonsense from noise point of view to connect the chassis to house ground .
Carver 400a has no ground connection , for instance .
Infact 35 years ago in my father's PL 400 the ground pin was cut also in order to use the switched outlet of
PL 4000 . It's only a my curiosity .
Another question ( better to say curiosity )
I added two 510 Ohm 5W resistors at the output of PL 400 ,according PL service manual in
order to avoid " bump" at power up on Infinity RSii b and the bump desappeared .
Are there any effect on sound ? For me no .
Ciao
Marco
 

P.L.F.

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#16
Why PL 400 and 700 have the AC power cord with the ground ?
Not sure about PL Series I, but Series II originally had 2 prong ac power cable. Better to maintain the star point grounding approach also for your entire audio system. Mine is the C-4000 pre-amp. Any attempt to ground the power amp caused buzzing due to the ground loop created...
 

laatsch55

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#17
Hi Gepetto ( in Italian Mastro Geppetto ) and all,
I have looked around the diagram and ,if I have understood well, the star point now is the rectifier .
Is it correct ?
Anyways my question was simpler :
Why PL 400 and 700 have the AC power cord with the ground ?
U.S. safety rules ? In my opinion is a nonsense from noise point of view to connect the chassis to house ground .
Carver 400a has no ground connection , for instance .
Infact 35 years ago in my father's PL 400 the ground pin was cut also in order to use the switched outlet of
PL 4000 . It's only a my curiosity .
Another question ( better to say curiosity )
I added two 510 Ohm 5W resistors at the output of PL 400 ,according PL service manual in
order to avoid " bump" at power up on Infinity RSii b and the bump desappeared .
Are there any effect on sound ? For me no .
Ciao
Marco
Marco, the star point ground is now the copper bus bar between the power supply caps....I have fixed a few 400's and 700's and I have only seen 1, 3 prong cord, and that was added by someone besides the factory...are the 510 ohm resistors in series or parallel with the outputs?
 

laatsch55

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#18
Not sure about PL Series I, but Series II originally had 2 prong ac power cable. Better to maintain the star point grounding approach also for your entire audio system. Mine is the C-4000 pre-amp. Any attempt to ground the power amp caused buzzing due to the ground loop created...

Yep, but within the amp chassis itself the grounding as Joe has drawn it should be maintained for lowest noise. On the 2nd to the last 700 I did, I got down to 237 microvolts umweighted for residual noise.....
 

marcok

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#19
Hi Laatsch and all,
1) the ground star connection now is clear for me
2) the 3 prong cord was original factory in my sample . It was sold new .
Recently I have also seen a PL 1000 with the same cord and on ebay .com
you can see some pictures related to PL 400 with 3 prong cord .
3) The 510 ohm resistors are connected in parallel . This tip is recommended
by the factory for Infinity Quantum line series , but it works with Reference
Standard series , too . See PL 700b service manual .
A curiosity : if you see PL 400 service manual the factory suggests to
use 150 Ohm 10W resistors with Infinity Watkins woofers.
Ciao
Marco
 

laatsch55

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#20
So besides the Zoebel network you also have a 510 ohm accross the same posts as the Zoebel?
 
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