Gibsonian's Cherry Pl 700 Ser I, soon to be a PLWO-1000

[laatsch55]

Good Man!!! Frequency Response.....

 

[NavLinear]

Good Man!!! Frequency Response.....

Does it get much flatter than that? Damn good!

 

[laatsch55]

Nav, I'm messin with some bypass caps on the 3 terminal strips on the backwall, very interesting....

 

[NavLinear]

Nav, I'm messin with some bypass caps on the 3 terminal strips on the backwall, very interesting....

Cool - as always you're doing some very interesting modifications and I can't wait to read your next post. Always new frontiers!

 

[laatsch55]

More like an idiot savant stumbling around in the dark and gettin lucky once in awhile!!!

 

[laatsch55]

Heck of a place to leave ya wasn't it Scott. Bypass caps are having a huge effect. When polarized wrong they sound like small firecrackers.When right youy can watch the THD & N drop as the caps form. In my excitement I managed to take out a couple outputs on the right side. Why is it always Cathy that appears to take most of the abuse when we're having a breakthrough??

 

[Gibsonian]

Which bypasss caps Lee? How bout a picture of them for us?

 

[laatsch55]

The ones that bypass the output rails to ground. Left out of yous after converting it the first time as I thought it was quiet enough without wem. Had not considered the effect on THD & N. It has enough I'll bypass the rest I do....

The originals on yours were 4uf at 150 volts paper caps. I was trying some 4.7uf at 160 electro's and some 3.3uf at 250volt polypro, and some 2.2uf at 150 volt electro'. .....

 

[laatsch55]

And I got in at 1:00 AM last night, didn't get a damn thing done...

 

[Fairchild]

How about a little sleep, I would consider that an accomplishment at that point.

Jim

 

[laatsch55]

Thanks Jim, I actually got some of that stuff. Slept till 8 this morning and never got up once. 7 straight hours is a rare blessing.

 

[Gibsonian]

yes, 7 hours of uninterrupted sleep would be a wonderful thing, I must agree. You be feeling like a champ today.

 

[mlucitt]

Rail Bypass Caps

Lee, How about a picture? None of the 400 or 700 amps I have originally had those bypass caps. It seems PL stopped installing them after a while. Did you do any comparison tests to get the best noise measurements with various cap values? Is there a best location on the back wall; rail to 3-terminal strip? (need to make sure that center post is well-grounded to the bare aluminum of the chassis). Maybe Joe can weigh in with a formula for the ideal cap value?

Mark

 

[laatsch55]

This is a representaion of how all the series 1 700's that I have had anything to do with have looke. A 4uf 150 volt cap , 1 from the emitter resistor common tie point on the negative rail to the middle terminal-ground., 1 from the ground terminal to the base bus bar on the positive rail.
We really need to pick Joe's brain on this one. It was very strange to see the THD & N numbers drop like a rock in real time as the formed up, prwetty freaky guys.

 

[laatsch55]

The 400's I've seen them on are usually on the left channel only and are .33uf at 100 volt.

 

[Gibsonian]

This is a representaion of how all the series 1 700's that I have had anything to do with have looke. A 4uf 150 volt cap , 1 from the emitter resistor common tie point on the negative rail to the middle terminal-ground., 1 from the ground terminal to the base bus bar on the positive rail.
We really need to pick Joe's brain on this one. It was very strange to see the THD & N numbers drop like a rock in real time as the formed up, prwetty freaky guys.

Mr. Blackwood might have some insight for us on this as well, or his buddy Dean.

 

[laatsch55]

I'm sure Ed culd have some input. What I would like from Joe is how to determine the values of the caps, and where to put them exactly.

 

[Gepetto]

Hi Lee
Got your PM. The place you have them is fine and any small value is fine here, somewhere around 1uF as it is bypassing for the end of the power distribution run.

You will notice a ground string running from the middle leg of each of the 3 position barrier strips in series from the leftmost barrier strip, to the rightmost barrier strip and then on to the amp output binding post ground (the two black binding posts)


2 things that I do recommend:

First, increase the gauge of this wire to 18AWG
Second, tie it to ground at the single point ground at the main bulk caps rather than to the speaker binding post ground. Remove the connection at the speaker binding post end.


The reason this makes a difference is that the main rail distribution wires run from the bulk caps on the left all the way to the right side of the amp and then from the other side of the fuse all the way back to where it started again. This is because of where they chose to put the fuseholders. Maybe this is good from a service standpoint it is not from an engineering perspective. You have those long inductive, single wire runs with no accompanying ground pair for it. The bypass you are installing provides that effective ground return.


Hope this is clear.

Joe

 

[laatsch55]

Have you observed the phenomenon i did when watching on power up with the AP and monitoring THD & N and watching those numbers drop[ as the electro's formed?? Also would polypro be a better cvap in this installation??

 

[Gepetto]

non-polars are better here Lee, either Polyester or Polypropylene. You will notice less forming time with a poly** film type than electrolytics. And the life of the poly** film type is much longer and the high frequency performance is much better than an electrolytic (much lower ESR).