Talk me out of bypassing the PL-700B Input Attenuators

[premiumplus]

I see only benefits from doing this. One of my WOPL 1000s has a flaky input attenuator pot. I always run these wide open, so I think that the next time I open the amp up I'm going to bypass the input pots altogether. My preamp has gain controls and an output attenuator so the ones on the amp are redundant.
I'll just run a short shielded cable from the RCA input jacks to the White Oak driver board input. That will eliminate a couple of feet of wiring inside the amp which is in pretty close proximity to the AC power line...and I think it may lower my noise floor even more.
Of course, I'll leave the attenuators in place. They'll just be disconnected.
Thoughts?

 

[jbeckva]

You won't get me talking you out of that - If I can convince anyone to do it, then I do it for 'em. I also whack the normal/direct stuff while I'm at it.

 

[Northwinds]

If you pull the pots out, they have cool little plastic round inserts that will fill the holes and still look good

 

[premiumplus]

You won't get me talking you out of that - If I can convince anyone to do it, then I do it for 'em. I also whack the normal/direct stuff while I'm at it.

I assume you go direct, right?

 

[jbeckva]

I assume you go direct, right?

Yep. I keep it as simple as it can be. But that's also assuming I'm driving the inputs into a WO PL14-20. Not sure if you have the stock driver board or not, so YMMV.

But if you do have the WO.. what I do there is keep the copper plate (or if I replace the jacks, I just solder the two ground tabs together), and attach the grounds from both downleads to it.. with no other ground connection. Then straight to the inputs on the WO PCB.

 

[laatsch55]

What he said....I've done 5 700's like that so far and my personal one will be like that when and if it gets home..the Direct/normal coupling switch is now superfluous, and the pots will only get worse......that's why we run pre-amps...

 

[Gepetto]

Yep. I keep it as simple as it can be. But that's also assuming I'm driving the inputs into a WO PL14-20. Not sure if you have the stock driver board or not, so YMMV.

But if you do have the WO.. what I do there is keep the copper plate (or if I replace the jacks, I just solder the two ground tabs together), and attach the grounds from both downleads to it.. with no other ground connection. Then straight to the inputs on the WO PCB.

That description above is the proper way of doing it. The PL14_20 provides the input ground, isolated from the single point ground by a 2.7 ohm connection in between these 2 grounds.

 

[Gepetto]

That description above is the proper way of doing it. The PL14_20 provides the input ground, isolated from the single point ground by a 2.7 ohm connection in between these 2 grounds.

And use good quality fully woven braid shield coax cable, not the cheap crap that PL originally used. Preferably Teflon.

 

[premiumplus]

And use good quality fully woven braid shield coax cable, not the cheap crap that PL originally used. Preferably Teflon.

I have the White Oak boards, I did two 700Bs, and the boards were purchased in November and December 2013, so where does the signal ground go, Joe? Same as it is now, right? I followed the installation instructions to the letter.

 

[Gepetto]

I have the White Oak boards, I did two 700Bs, and the boards were purchased in November and December 2013, so where does the signal ground go, Joe? Same as it is now, right? I followed the installation instructions to the letter.

RCA tip to coax center conductor, other coax end to pin 1 of PL14_20 board (signal)
RCA shell to coax shield conductor, other coax end to pin 2 of PL14_20 board (signal ground)

Same for R and L channel. Tie the shields together at the RCA jack end or use the copper plate to do that. Make sure the RCA shells and copper plate are ISOLATED from the chassis.

 

[laatsch55]

And make sure the shield is trimmed back at the control board so no whiskers touch the control board....

 

[premiumplus]

Thanks guys...we're thinkin' alike.

 

[NavLinear]

And make sure the shield is trimmed back at the control board so no whiskers touch the control board....

I always add a little shrink over the outer insulation with about a quater inch or so over the twisted pair - this will prevent the possibility of a short between the shield and whatever it may come in contact with.

 

[Gepetto]

I always add a little shrink over the outer insulation with about a quater inch or so over the twisted pair - this will prevent the possibility of a short between the shield and whatever it may come in contact with.

This wire should be single conductor coax with braid but the same principle applies...

 

[laatsch55]

Now wait a minute......if it's single conductor how do you groind the board with the shield??? When that's a no-no??

 

[Gepetto]

Now wait a minute......if it's single conductor how do you groind the board with the shield??? When that's a no-no??

Yes exactly.

Shield to pin 2 and to RCA shell
Center conductor to pin 1 and RCA tip.

 

[laatsch55]

I'm confused....we started out using 2 conductor shielded and tying the shield to the ground at the RCA shell and just the ground conductor on the board with no shield tied at that end. Now when did that change??

 

[Gepetto]

I'm confused....we started out using 2 conductor shielded and tying the shield to the ground at the RCA shell and just the ground conductor on the board with no shield tied at that end. Now when did that change??

Same exact effect Lee. I have always used Teflon core single conductor coax for all my signal connections and you have been using shielded twisted pair based on your note. Same end result is achieved.

 

[laatsch55]

So the same effect is achieved because the inmput ground plane is no longer grounded so we don't have ground loops possible NOT leaving one end of the shield loose??

 

[laatsch55]

Cause Nav sent SOME REALLY NICE one conductor shielded #20...