Jerry's "Gonna Rebuild me PLWO 1000" thread

[laatsch55]

This is getting ridiculous. I have contacted Jer about a separate forum that will be called "White Oak Notes". It will be a section right under the DIY forum so we can copy posts that are pertinent and apply to mthe White Oak conversions. I will go through these mostrosity threads and glean all qualifying posts and copy them to the new section. It will be nice to have a reference to White Oak info withoput having to wade through a 500 post monster.

 

[Gepetto]

Mark here is a bit of the prior dialog on better grounding within the PL400 amp.
Here is what I did to achieve this.
1. Removed the white 22AWG chassis ground wire that runs from the copper bus pad between the input RCA jacks to the White Oak PL14_20 PCB, pin 5R.
2. Removed the 16AWG bus wire jumper that Phase normally installs between this same copper bus pad and the right channel speaker ground binding post.
3. I left the 2 signal grounds in the signal twisted pairs that originate at this copper bus pad between the input RCA jacks that run to the White Oak PL14_20 pin 2R and 2L respectively.
4. I added an 18AWG tinned solid copper bus wire jumper between the right and left channel ground (black) speaker binding posts.
5. I added a #10 ring lug with 2 white 20AWG wired into the ring lug on one end and into the White Oak PL14_20 PCB pin 5R and 5L respectively. The #10 ring lug was attached under one of the large bulk capacitor ground bus bar screws that connect the 2 bulk caps together.
6. I changed R2L from 56 ohms to 2.7 ohms.

This makes the large ground bus bar between the 2 bulk caps into the Single Point Ground for the entire amplifier. This wiring scheme eliminates the common mode noise from the large speaker ground from entering and affecting the low level input and low level ground reference on the White Oak PL14_20 PCB (caused by the bus wire jumper that Phase Linear installed between the right speaker negative binding post and the copper pad at the input RCA jacks)

Hope this is clear what I did. I will try to document in a diagram later on.

 

[jbeckva]

Ok, something killing me here... Since I have already put on the connectors, I probably have covered up the labels on the connections. So what is 5L and 5R? Because if I were to take that literally as the 5th pin from the left, then something really was screwed up here to begin with - THAT pin connects with a brown wire, that goes to the emitter of Q12.. not exactly "ground" or "signal", by any stretch..

Pics appreciated... diagrams better...

 

[Gepetto]

Jer
Looking at the board from the front and starting at the left side of board the numbering goes 12L through 3L then a skip location then 2L and 1L. Continuing just to the right side of the mounting post is 12R through 3R then a skip location then 2R and 1R.

Both sides of the board are identical in regards to pinout.

The wiring chart is attached if you do not have this already.

Joe

 

[jbeckva]

This is getting ridiculous. I have contacted Jer about a separate forum that will be called "White Oak Notes". It will be a section right under the DIY forum so we can copy posts that are pertinent and apply to mthe White Oak conversions. I will go through these mostrosity threads and glean all qualifying posts and copy them to the new section. It will be nice to have a reference to White Oak info withoput having to wade through a 500 post monster.

There's yer forum, ya WOOKIE!

http://forums.phxaudiotape.com/plwo-tips-and-archive-f61.html

 

[jbeckva]

Mark here is a bit of the prior dialog on better grounding within the PL400 amp.
Here is what I did to achieve this.
1. Removed the white 22AWG chassis ground wire that runs from the copper bus pad between the input RCA jacks to the White Oak PL14_20 PCB, pin 5R.
2. Removed the 16AWG bus wire jumper that Phase normally installs between this same copper bus pad and the right channel speaker ground binding post.
3. I left the 2 signal grounds in the signal twisted pairs that originate at this copper bus pad between the input RCA jacks that run to the White Oak PL14_20 pin 2R and 2L respectively.
4. I added an 18AWG tinned solid copper bus wire jumper between the right and left channel ground (black) speaker binding posts.
5. I added a #10 ring lug with 2 white 20AWG wired into the ring lug on one end and into the White Oak PL14_20 PCB pin 5R and 5L respectively. The #10 ring lug was attached under one of the large bulk capacitor ground bus bar screws that connect the 2 bulk caps together.
6. I changed R2L from 56 ohms to 2.7 ohms.

This makes the large ground bus bar between the 2 bulk caps into the Single Point Ground for the entire amplifier. This wiring scheme eliminates the common mode noise from the large speaker ground from entering and affecting the low level input and low level ground reference on the White Oak PL14_20 PCB (caused by the bus wire jumper that Phase Linear installed between the right speaker negative binding post and the copper pad at the input RCA jacks)

Hope this is clear what I did. I will try to document in a diagram later on.

In number 2 above, you say that you left the 2 signal grounds connected to 2L/2R. That tells me that the signal grounds are also still connected to one side of the R2's. At that point, the signal ground connections are only to the 2L/2R pins on the main PCB - You are NOT also running a wire from the copper bus pad (between the 2 rca jacks) to star ground, AND.. since you disconnected the buss pad from the speaker grounds, NOTHING is connected on the RCA jack side, correct?

So in essence, the "ground" on the signal wires at the shields is that floating ground.. with R2 between IT and the main / star ground at the caps (via the connections on 5L/5R). Is this correct?

I think Lee's method contradicts, tho.. he (I think) is saying connect the buss pad at the RCA jacks to star/cap ground directly, do not connect the buss pad to speaker grounds, and leave 2L/2R disconnected at the main PCB. Obviously either way works, but I"m just making sure it's 100 percent accurate on what I *think* both of you are saying.

 

[laatsch55]

Thanks Jer!!!!!

 

[Gepetto]

Hi Jer
Yes you have it correct. The RCA jacks are isolated from the chassis by virtue of the insulating washers that Phase uses but tied to the small copper pad that joins them and the signal grounds.

To avoid ground looping, these should connect to the board only at pins 2L/R. The board in turn ties to star point ground via connections from 5L/R to the star point.

The speakers independently tie to the star point ground via the 2 heavy gauge white wires. I also tie these 2 speaker grounds together right at the speaker binding posts. This doubles up the ground return from the speakers to the star point.

The chassis is also tied to the star point using the existing Phase connection which goes to the center post of the two 3 terminal solder strips that are mounted in between the output transistors.

Hope this helps to clarify.

 

[mlucitt]

I think there might be an electrical difference (more than an esthetic difference) between these two methods:
1) The RCA jacks outer shields are connected together as they enter the amp via a copper buss, then two wires from that buss lead to the right and left input shield connections on the main board at 2L and 2R.

2) The RCA jacks are independent from each other (copper buss removed) and the two outer shield wires lead to the right and left input shield connections on the main board at 2L and 2R.

This assumes that the main board is properly grounded from terminals 5L or 5R (not both - unless each side is powered separately with no jumpers on the back as Lee does) to the Star ground. This also assumes that the inputs are isolated from the chassis; you have to check because I have seen two amps with missing plastic washers.

I mention this because tying the input shields together could cause a ground loop from the preamp interconnect into the amp, across the copper buss, and back out of the amp on the other interconnect. This also puts the 2.7 Ohm R2L and R2R resistors in parallel, which gives 1.35 Ohms instead of the 2.7 Ohms of float above chassis ground, less than optimum.

Thoughts?

 

[jbeckva]

I think there might be an electrical difference (more than an esthetic difference) between these two methods:
1) The RCA jacks outer shields are connected together as they enter the amp via a copper buss, then two wires from that buss lead to the right and left input shield connections on the main board at 2L and 2R.

2) The RCA jacks are independent from each other (copper buss removed) and the two outer shield wires lead to the right and left input shield connections on the main board at 2L and 2R.

This assumes that the main board is properly grounded from terminals 5L or 5R (not both - unless each side is powered separately with no jumpers on the back as Lee does) to the Star ground. This also assumes that the inputs are isolated from the chassis; you have to check because I have seen two amps with missing plastic washers.

I mention this because tying the input shields together could cause a ground loop from the preamp interconnect into the amp, across the copper buss, and back out of the amp on the other interconnect. This also puts the 2.7 Ohm R2L and R2R resistors in parallel, which gives 1.35 Ohms instead of the 2.7 Ohms of float above chassis ground, less than optimum.

Thoughts?

I see what you mean. Yeah.. that's definitely something to take into consideration. So basically split the input shield straps... connect both independently, and only to the 2L/2R pins, then make sure the 5L/5R's are properly grounded to star ground.

Ahh.. but here's something weird (hate the change of subject, BUT...). Can someone tell me about these two lil beauties (diodes) I found as I was stripping off the Z networks??

 

[mlucitt]

That is funky, never seen anything like that. Lee?

It looks like you can back that mess out easily.

 

[Gepetto]

Static discharge diodes. Since the grounds are floating from the chassis, the static discharge path from your body or from another piece of floating preamp gear when connecting cables is through the control board front end. These diodes do not allow the signal ground to get any higher in potential than one forward diode drop above the chassis.

Mark didn't you add a similar circuit to one of your recent rebuilds?

 

[jbeckva]

Gotcha.. diodes out.

Here's the reroute I did of the AC and fuse. I really didn't see a very good place for the fuse holder to come in from the outside, so I had to think "inside" the box... Yeah, the electrical tape... got a little messy with the drill bit and nicked up the cap.. ugh.. but it'll live. Sporting a nice new cord and plug too!

 

[jbeckva]

Now.. here's another mystery.. I am pretty sure the fuse is NOT on the same side of the AC main as the switch. Traced it out a few times and came to the same conclusion. Should I just follow the schematic and wire it up "to specs"??

 

[laatsch55]

Yep.

 

[laatsch55]

Now I'm confused, kinda.... I was wrong in my previous post.. Flyback diodes would be terminated on the speaker posts right? I thought D1, D2 took care of this. Course that's on a 700B. This amp originally had a 0171 board and I can't find my schematic for it.

 

[laatsch55]

Not a bad place to put the fuse Jer. 'cept ya take off covers when it blows.

 

[jbeckva]

Not a bad place to put the fuse Jer. 'cept ya take off covers when it blows.

Yeah I know heheh.... I'll just not take it up to Mach 8 like "someone I know" too often..

 

[laatsch55]

Mach 8 don't do it, sine wave testing both loaded up and clipping does.

 

[jbeckva]

Heheh... yup

HEY... You know, I"m looking at the DCP wiring diagram right? And am I seeing this right? Basically if the DCP ever tripped, it would shunt both outputs right to ground?? Yipe!!??

Did I see that right? So if that happens, aint we going to toast a few things.. maybe even on the channel that didn't have a problem too??

Edited to add.. no.. that's not right... I'm seeing things now - must be those flux boogers again.