Sutton's Phase Linear, White Oak 500

[Skratch]

LEE what do you think about cutting the ground between the negative speaker terminal and the input and running 2 wires from the copper ground bar 1 to the input and the other for the ground on the PL14b board

 

[laatsch55]

PLEASE cut the ground from between the speaker posts and the input RCA grounds. Run a separate wire FOR EACH back to the star ground point. (that being between the PS caps). Then run the driver board ground in a separate run to the same place. When you get the DC protect relay he's gonna have you run ANOTHER separate wire to the star ground point for it also. DO NOT run it to the solder tabs between the outputs. This really has a marked improvement in the signal to noise ratio. Just separating the low signal inputs from the hi-output speaker posts is a godsend.

 

[laatsch55]

Cleaning out the thermal grease that is everywhere. Whoever put the outputs in this one must have used a gallon. What do people use to clean this stuff out.

WD-40 works as well as anything, still takes some elbow grease, AND if it wasn't such a bitch it would not do it's job as well either.

 

[mlucitt]

Good to see that Mark hooked up with you Lee. This started as a reply to a post in the DIY Adio forum. I was trying to get Mark a PLWOA board but he wants to explore all options. I was going to send him one of my newly acquired P14B boards but it sounds like he may be able to fix the one he already has.

 

[laatsch55]

Nope, I sent him the one out of the recently purchased "double the power" mons. A very good lookin boad actually.trosity

 

[mlucitt]

Skratch, there is a school of thought that the input ground should not be tied directly to the output ground, something about reflected emf and conducted RF back into the inputs. Anyway, you can lift the input ground above master/star ground by installing a 2 or 2.2 Ohm resistor on the isolated ground tabs of the RCA input jacks. The PL14B has a 2.7 Ohm resistor on the Right Channel and a 56 Ohm resistor on the Left Channel to accomplish this. We are not sure why the input grounds are not equal but bringing pin 2 on the board to the star ground is not the same as bringing pin 5 to the star ground. You probably have already considered this.

 

[laatsch55]

Why, to prevent said bad things from just running in a circle back to the speaker outpu grounds??

 

[mlucitt]

Yeah, I think there is some of that but mostly the article I read said that some of the output voltage is reflected back "from" the coils of the speakers out of phase with the signal going "to" the speakers. If the grounds are connected together the path allows some of the voltage to flow back to the inputs. Because the inputs are more sensitive, this out of phase signal mixes with the input to cause distortion.

The signal grounds on the PLWOA boards are better than the original PL14B boards but tying the grounds together can defeat the 2.7/56 Ohm resstors on the input grounds if not done correctly.

 

[laatsch55]

Ahhhhhhhh...............

 

[Skratch]

Finally got all the heat transfer grease off. Took 2 hours. Installed all new resistors and diodes on the output section and 40 amp bridge. Ran new grounds and inputs. Should be ready for the board when I get it. when it is finished, off to the frat house.Wonder how long before the campus police arrive.

 

[Gepetto]

The ground improvements described are to create a true single point ground (at the bulk cap bus bar ground) system within the amp for all the critical audio paths. Phase Linear did not adhere to this and it introduced some assymetrical behavior between the L and R channels. The White Oak Audio grounding scheme fixes this assymetry and makes both channels operate identically (within the component tolerances of course)

 

[Skratch]

Was wondering by grounding the inputs back to the copper bus and cutting the ground between the negative speaker terminal and the inputs if I should make R2 the same?

 

[mlucitt]

The process Lee and I are using is to make R2 the same if using Joe's new main board, which has a better grounding scheme. If using the Phase Linear board, Lee and I leave the R2's as they were. We imagined this was an attempt to keep the amp more stable by seperating the channels a bit at startup. But that is only a guess at what they were thinking back in 1972.

 

[laatsch55]

Ed Blackwood had talked to Dean and Bob Carver about the R2 conondrum and Ed told me that Dean had told him that Bob had been putzing around with the design and informed folks that R2 in the left would be 56 ohms because that helped the distortion numbers. No shit. Don't know if it accomplished that or not.

 

[laatsch55]

Skratch ( I would call you Mark, but in this thread it might get confusing), if you do the back to back 1N4148's on the PL 14a or B board you can , with no worries of positive rail latchup, convert the 56ohm R2 to 2.7. That does not guarantee it will not oscillate, but chances are REAL slim it will. Keeping both at 2.7 will, as Joe has explained elsewhere that both channels will exhibit identical gain.

 

[laatsch55]

Finally got all the heat transfer grease off. Took 2 hours. Installed all new resistors and diodes on the output section and 40 amp bridge. Ran new grounds and inputs. Should be ready for the board when I get it. when it is finished, off to the frat house.Wonder how long before the campus police arrive.

Anything above Mach 6 should get em a runnin'!!

 

[Skratch]

I am going to put XPL909 that were all the same numbers in this one. Probably going to upgrade my original 400 with a White Oak board. What do you find that works the best with White oak board for drivers and outputs. I have a 40 amp bridge and 30000uf Filter caps and blue LED from Joe in it already.

 

[mlucitt]

Skratch, I am running RCA 410 transistors in the driver positions and XPL909 transistors as outputs in my 700B. I think it is a good combination because many of these amps were set up that way. My amp originally had the SJ2741 driver transistors and they cross to the current MJ15024 transistors. I stayed with the RCA 410 transistors because I thought they sounded good in my Phase Linear 200 and I already had them. My outputs are all date coded the same and they measured very close in gain, so I did not upgrade. My upgrade of choice for the outputs would be the MJ21196G. Lee can chime in here too.

 

[laatsch55]

MJ 15024's as drivers and MJ 2`1`194's asa outputs in the 400's, and 21196's as outpts in the 700's. There are some here that will argue the 15024's are overkill for the drivers and that the RCA-410's sound better, and they may well sound better, I have not done a comparison YET!!

 

[laatsch55]

I guess Lee did chime in here. Youmust have been posting at the same time!!