PL 700 Pro Build

[Vynuladikt]

You may now be disappointed that the analog needles do not move off of zero at most normal listening levels. All of my customer requests have been how do I make my PL400 needles move more at the levels I listen at? That led to the birth of the LBC light board.

The LED meter has a log amp in it to give you some sizzle at low listening levels while flattening out at higher volume levels. Analog meters don't do that.

Yep, my 400 WOPL barely moves the meters at "normal" listening levels. That would be for the average non PL owner. When it gets to bouncing to -10dB its about 85 to 87 dB at 12-14 ft. , my normal listening position. By the time it is nearing 0 db on the meter we're well into 100+

 

[George S.]

Thanks guys. I really don't care if my meters don't move at normal listening levels. I never look at the amps when they're on as I'm always doing something else when listening to music. And yes, I thought the 400 S1 meters were calibrated at 200 watts, not 100, my mistake.
What's important to me is that the 400s show 200 watts on the meters at 40 VRMS and the 700 shows 350 watts at 53 VRMS.
The PL2000 S2 preamps seem to like the lower value attenuators. Seems like the amps put out more volume at a lower volume setting on the preamp. I wanted to quantify the change with some measurements but was unable to find any information for doing so.

 

[J!m]

Somewhat related-

The meters on my receiver don’t move much either. That are calibrated in watts output. It gets quite loud at 1 watt with most material due to the small room. I assume the Polk speakers are reasonably sensitive as well.

 

[George S.]

Hmmm, is there a good reason to have the 400 S1 WOPL meters show 100 watts at 0db rather than 200? I tend to overlook the obvious quite often. Just seems that calibration of 200 watts at 0 db is the way to go.

 

[Gepetto]

Hmmm, is there a good reason to have the 400 S1 WOPL meters show 100 watts at 0db rather than 200? I tend to overlook the obvious quite often. Just seems that calibration of 200 watts at 0 db is the way to go.

That is just what PL did, and told you so in the service manual. In practice that left another 3dB of power for headroom without going over the rated power. It was likely a compromise on having the needles move with reasonable power output. Like the question I receive often. “How do I get my meters to move more?”

 

[George S.]

Got it Joe, thanks.

 

[J!m]

Put a big ol’ load resistor on the outputs with the speakers?

There was something similar marketed to guitarists to allow them to “crank it” without deafening the town. Get into the “sweet spot” at reasonable volume.

 

[George S.]

I always thought the meters should be accurate like a speedometer on a car.
I do like the meter attenuation switch on the 700 that supposedly matches the 700s meters to a 400s full scale meters. But, you know, I might be wrong about this. I don't know.
Any how, I'll probably put the original resistors back into the 400 S1 so they accurately read 100 watts at the 0 db 100 marking on the meter faces. That's how they designed it, much smarter people than me.

 

[George S.]

Yes indeed. Raise it 1/2” if you can.

Glen was right on the money, 1/2" longer standoffs are perfect. Finally got around to doing this.

 

[Gepetto]

Glen was right on the money, 1/2" longer standoffs are perfect. Finally got around to doing this.

Hi George
While you are in there, you might as well check this out...

First:

It is ESSENTIAL that you have the copper plate installed and connecting the 2 RCA input jacks. This shunts any external ground loops associated with cable connections from entering the amp’s separate signal paths and creating various degrees of ground looping. In other words, it makes the amp INTERNALLY immune to cabling effects from outside the amp. This does not say that you cannot still have external ground looping, it does say that this keeps the amp internals out of the equation. No build I have ever done has removed this copper plate. Remember, the RCA jacks and this copper plate MUST be isolated from the chassis.



Second:

Disconnect and remove the two ground wires running from the backplane pin 5L and 5R which run to the control board pin 5L and 5R Phoenix connector.

Along the bottom, run two new, separate 22AWG wires from a single solder lug on the single point ground copper bus bar to pin 5L and 5R on the control board. The solder lug goes underneath the 10-32 (or M5 if you have our newer caps) screw on the bottom B- bulk cap positive terminal which attaches to the copper bus bar. The wire to 5L is approximately 5” long and the wire to 5R is approximately 10” long, your measurements may be adjusted to suit how you lace these in. You should be able to use one of the #10 solder lugs provided in the White Oak Audio wire kits to accomplish this.



Dress and button up the amp reinstalling all covers.

 

[George S.]

Hi George
While you are in there, you might as well check this out...

First:

It is ESSENTIAL that you have the copper plate installed and connecting the 2 RCA input jacks. This shunts any external ground loops associated with cable connections from entering the amp’s separate signal paths and creating various degrees of ground looping. In other words, it makes the amp INTERNALLY immune to cabling effects from outside the amp. This does not say that you cannot still have external ground looping, it does say that this keeps the amp internals out of the equation. No build I have ever done has removed this copper plate. Remember, the RCA jacks and this copper plate MUST be isolated from the chassis.



Second:

Disconnect and remove the two ground wires running from the backplane pin 5L and 5R which run to the control board pin 5L and 5R Phoenix connector.

Along the bottom, run two new, separate 22AWG wires from a single solder lug on the single point ground copper bus bar to pin 5L and 5R on the control board. The solder lug goes underneath the 10-32 (or M5 if you have our newer caps) screw on the bottom B- bulk cap positive terminal which attaches to the copper bus bar. The wire to 5L is approximately 5” long and the wire to 5R is approximately 10” long, your measurements may be adjusted to suit how you lace these in. You should be able to use one of the #10 solder lugs provided in the White Oak Audio wire kits to accomplish this.



Dress and button up the amp reinstalling all covers.

Joe, I understand and will do. Easy enough as I have Phoenix Contacts Connectors on all 3 amps and still have the copper RCA plates, plenty of wire, unfortunately mostly 16 AWG, it'll have to do.
Was looking for something to do today, looks like "something" found me. I'll get on it after dinner. Thanks!

 

[George S.]

Joe, do the 400s need the ground wire modification or only the 700? All 3 have the Dual Mono control board, the 400s have the backplanes with the pico fuses.
Opening the 700 up now. Had it back downstairs in the system.

 

[Gepetto]

Universal George, 400s and 700s same.

Not urgent, just passing along a further improvement that can be made.

 

[George S.]

Cool! Then it's worth doing. Copper plate was cleaned of old solder with the Hakko 470. Then shined with 00 steel wool. Using the proper toothed washer between the jack ground tab and copper plate. Appropriate fiber insulators of each side of the chassis so the jacks and plate "float" above ground.

 

[George S.]

Wiring completed. #5 R+L jumper removed. Ground wires run from the copper bus bar to Control Board #5 R+L.
Used 16 AWG grey as I have lots of it, follows the existing wire color selections .
Listening to BTO.

 

[Gepetto]

Wiring completed. #5 R+L jumper removed. Ground wires run from the copper bus bar to Control Board #5 R+L.
Used 16 AWG grey as I have lots of it, follows the existing wire color selections .
Listening to BTO.

You should now have an even lower noise floor George.

 

[George S.]

These Hakko 470s do a excellent job. Where most people mess up (I'm included) is turning them up too high. Setting #1 is supposed to be calibrated at 700 deg F.. Go no higher for normal through hole pcb desoldering.
I did these copper plates at setting #4. Awesome.

 

[George S.]

You should now have an even lower noise floor George.

Thanks Joe!

 

[George S.]

The 400 S2 is done. Going to button it up and listen to some music. I'll do the other 400 tomorrow.
Had to drill a extra hole in the buss bar on this one. Put a layer of sticky tape underneath it and drilled. Worked good.

 

[laatsch55]

I can clean up those copper plates with my WES 51, takes about 40 seconds..