Jerry's "Gonna Rebuild me PLWO 1000" thread

[soundude]

Ok the wiper needs to go to board input, this is the norm. way to hook up, the other connection which would be the entire pot resistance goes to input jack and the shields tie together at the oppisite side of pot. The wiper is always the gain input so that at min. setting the inputs are shorted to ground. with the full 100k refrence to the board and the wiper on the input jack resistance is very high so it becomes open loop and no refrence to ground. with the board not on the wiper you have 100k across signal input and so the resistance is high and will pick up noise.

 

[soundude]

Also like lee said I have encountered noise induced to pots when faceplate is seperated from chassis, connect test lead to star ground and clip on matel body of pot the bleed of any rf noise.
Temopary though when you connect the face back to chassis you should need the connection anymore.
But rewire those pots the right way...looking at the pots with the shaft facing you the shields connect to the left term. the board signal in, on center, (wiper), and input jack signal to right terminal.

 

[soundude]

Lee and Jer have great day going for motorcycle ride meet friends for lunch and drinks, checkin when I get back...

 

[jbeckva]

Ok the wiper needs to go to board input, this is the norm. way to hook up, the other connection which would be the entire pot resistance goes to input jack and the shields tie together at the oppisite side of pot. The wiper is always the gain input so that at min. setting the inputs are shorted to ground. with the full 100k refrence to the board and the wiper on the input jack resistance is very high so it becomes open loop and no refrence to ground. with the board not on the wiper you have 100k across signal input and so the resistance is high and will pick up noise.

Yep, that's how I have it, I believe... Here's a quick drawin...

[attachment=0:al3fzpa7]cplwoinput.jpg[/attachment:al3fzpa7]

 

[soundude]

yep exactly, try grounding the casing of the pots, especially if they are flappin in the breeze...

 

[jbeckva]

Yeah I might... but now Lee's comment about the weird 2.7/56 ohm mismatch I got on the driver board and how it does cause a gain imbalance has me thinking. The reason why I wanted to put the pots back in (I had 'em out for a few) is exactly that... I noticed a channel gain imbalance!

Sooo.. maybe I might take 'em out and go "direct". If I do, THEN I need the 47K's across the RCA's, right? Here's a proposed pic so there's no question of what I'm saying... Just showing one channel. The key here is there is NO additional jumping to any ground - straight into the WO input connections. And on the WO board, the two ground connections for the board itself go right to star-ground on the caps.

[attachment=0:1fbmgszz]StraightInput.jpg[/attachment:1fbmgszz]

 

[laatsch55]

I think that might do it Jer. AND you will be the first one to do that because I haven't on any of the ones I've done.

 

[Gibsonian]

So Lee, on Cathy would you recommend that I put these resistors across the inputs as well? You have data from your new gizmo that says this is better (quieter)?

 

[mlucitt]

Joe can jump in here but the PL 400 has no volume controls and takes the input from the RCA jacks directly into the WOA board very well. Some people on this board say the PL 400 is actually cleaner and it may be for this reason. I don't think an additional 47K resistor across the inputs is necessary. A SPICE run will prove if the resistor is helpful or not, if Joe is so incluned to run the simulation.

 

[speakerman1]

What kind of cap? I am trying to figure this out.

larry

 

[laatsch55]

Not a cap Larrt, a 47K resistor.

 

[laatsch55]

So Lee, on Cathy would you recommend that I put these resistors across the inputs as well? You have data from your new gizmo that says this is better (quieter)?

I'll know later on today. I was going to button it up and check it then.

 

[laatsch55]

Scott, do you get some noise that is greater in amplitude if you turn off the pre before Cathy??

 

[speakerman1]

Not a cap Larrt, a 47K resistor.

I thought I had it wrong. Was confused why you would put something in the circuit that could cause noise if it isn't needed. So I put cap.

Larry

 

[Gibsonian]

Scott, do you get some noise that is greater in amplitude if you turn off the pre before Cathy??

Well I haven't heard an amp that wouldn't amplify the shutoff of a preamp Lee. It's generally a nono to turn off the pre first. I can do it but why wouldn't the PLWO amplify the shutdown noise of a preamp? It should, very accurately I might add, amplify that noise.

 

[speakerman1]

Scott, do you get some noise that is greater in amplitude if you turn off the pre before Cathy??

Well I haven't heard an amp that wouldn't amplify the shutoff of a preamp Lee. It's generally a nono to turn off the pre first. I can do it but why wouldn't the PLWO amplify the shutdown noise of a preamp? It should, very accurately I might add, amplify that noise.

HUH?

Larry

 

[laatsch55]

True Scott if the pre-amp doesn't have off-muting, the Spec 1 does. But what I meant was turn on the amp with the pre off and tell me if the noise floor is worse.

 

[speakerman1]

I turn down my preamp and shut it down by my power supply. I have never heard anything. Even when I turn off my pre I never hear anything. I better not or Houston we have a problem. I use to get a pop in one channel on the PL. That wasn't the preamp it was the amp. And we had a problem. Unless I am missing something here. My amp switch is always on.

Larry

 

[soundude]

What the 47K does is it shunts the amp for the open loop, I don't have a PL400 schematic but there has to be some sort of resistor or r/c network across the inputs so there is no buzz or rf injected to the amp.
Do this remove the inputs from the amp and turn amp on if you hear any buzzing or hiss of radio the inputs are open and there in no refrence to ground. Shouldn't hear anything, I also took a bias reading with open loop and its all over the place, as soon as I add the 47k bias is stablize. To me that seems to be a indication of noise. I tried different size resistors and 47K worked the best..

 

[jbeckva]

Ok, so to recap here...

1. 2.7 ohms.. make sure both R2L and R2R are 2.7 ohms
2. I am going with a straight run.. bypassing the level controls
3. Do not tie the grounds together at the RCA's
4. Put 47K resistors at the RCA connectors, from signal to ground / shield connection
5. Wire other side of shielded cables directly to input pins on WO driver board
6. Attach "main" ground pins on WO driver board directly to cap/star ground

Is this "the plan"?