Jer's PLWO to be... (Jer vs the 700, Round 2... it's "Personal" this time)

Thank you, Jim-Dude!

Well, got it all done... That was a lot of soldering, but it was good fun. Now just waiting til tomorrow when the rest of the parts are coming...

IMG_9921.jpg
 
Thanks Mark! Hmmm.... just thinking out loud now.

The parts (outputs, caps, DCP) are coming tomorrow, but should I go ahead and work on swapping it out with the old one tonight? Can it still drive the original RCA/XPL outputs with no issue? At the very least, what I'm thinking is that by going ahead, I know the main outputs are "ok" as in they won't blow anything up - So I'm thinking that with them I can verify the WOPL installation is good or not? Thoughts, anyone?

Ahh... also... my favorite subject... remember that this 700 ser I is fully "stock", including the input scheme with the dual DC coupled/Cap coupled inputs. Obviously I do want to go with the DC inputs here. But also with the pots in line so I can adjust the input levels. Since those are only (right now) applied with the cap coupled input, what's the best idea? The last I remember was this below. Should this be how I do it? Should I just wire the two gnd tabs on the rca's direct to cap/star ground... or just the signal returns on the PLWO board.. or both? (or neither?)

SignalGroundOptions.jpg
 
jbeckva said:
Thanks Mark! Hmmm.... just thinking out loud now.

The parts (outputs, caps, DCP) are coming tomorrow, but should I go ahead and work on swapping it out with the old one tonight? Can it still drive the original RCA/XPL outputs with no issue? At the very least, what I'm thinking is that by going ahead, I know the main outputs are "ok" as in they won't blow anything up - So I'm thinking that with them I can verify the WOPL installation is good or not? Thoughts, anyone?

Ahh... also... my favorite subject... remember that this 700 ser I is fully "stock", including the input scheme with the dual DC coupled/Cap coupled inputs. Obviously I do want to go with the DC inputs here. But also with the pots in line so I can adjust the input levels. Since those are only (right now) applied with the cap coupled input, what's the best idea? The last I remember was this below. Should this be how I do it? Should I just wire the two gnd tabs on the rca's direct to cap/star ground... or just the signal returns on the PLWO board.. or both? (or neither?)

View attachment 6464
Click to expand...

Or heck.. wait a min..

Now on these rev "c"'s I don't recall seeing another ground option.. which is labeled as "channel ground" aka 5L and 5R.

So now you have the inputs (1R/1L)... "ground" ground (2R/2L)... and then "channel" ground (5R/5L).

Joe.. I need a pic drawn.. heheh.. What is the best way to wire these up with DC coupling and the front panel pots still in play?
 
Hi Jer
Wire as you have shown in your diagram but DO NOT connect 2L/R or the pad that connects the 2 RCA barrel grounds to the star ground. Wire 5L/R on the board to star ground only (or either one of them since you have the backside jumper installed). The 2.7 ohm resistors in location R2L/R take care of the ground for the signal grounds in the amp.

Follow the wiring diagram that I sent you that has the PL700B installation wiring.

And yes you can use this board with the existing outputs and predrivers.
 
Gepetto said:
Hi Jer
Wire as you have shown in your diagram but DO NOT connect 2L/R or the pad that connects the 2 RCA barrel grounds to the star ground. Wire 5L/R on the board to star ground only (or either one of them since you have the backside jumper installed). The 2.7 ohm resistors in location R2L/R take care of the ground for the signal grounds in the amp.

Follow the wiring diagram that I sent you that has the PL700B installation wiring.

And yes you can use this board with the existing outputs and predrivers.
Click to expand...

Ok, so this instead, correct? (and .. dernit... gotta wait til tomorrow anyway... the chassis mount bias trannies are coming too!)

SignalGroundPerJoe.jpg
 
Or hmmm.. should the pots be rewired "rheostat" style? Just wondering about that extension of the ground to the "low" side of the pots from the RCA's.
 
Jer,
It's your call but I like to remove the input "DC/Normal" switch and the series DC blocking capacitor (.47/100V) because the switches are old and they can cause trouble. Of course, I verify that my preamp has a DC blocking capacitor on each channel of the output, I think that is where those DC blocking capacitors belong. As long as you are quite sure you will not have any DC going into you WOPL amp, you will be fine. Lee sometime leaves these alone to keep the amp "stock"; it's your call and if everything works like it should you can leave it stock. Just never move the switch with the amp running, it could cause a transient that will damage your speakers.

The switch/cap input circuit is independent of the volume controls. These should be 100K pots and you should measure them before you connect the inputs, they get mis-marked sometimes. Your board connections to the pots are correct in your first picture. Like Joe says, the two input wires for each channel (use small coaxial cable or twist the two wires of each channel tightly) only go directly to the board from the RCA jacks or from the pots, nowhere else. Also make sure your RCA jacks are not grounded to the chassis, that adds a lot of noise.

You still have to connect 2R and 2L like you had it before.
 
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Hi Mark,

I'd like to go DC coupled and with the level pots still in circuit. I do plan on simplifying at the back input panel by stripping it down to a single set, but exactly wired as the last diagram above - no caps and just relying on the PLWO's input circuitry for the input impedance.

But hmm... I still wonder about that having the signal "across" the pot with a return through the shield being terminated at the RCA with the "ground wire" I plan on running to cap/star ground. That's why I am thinking of taking out the connection through the shield from the RCA "ground" tabs to the low side of the pot, and instead converting the pot to a rheostat. That way it is strictly variable resistance (0 to 100K, audio tapered) between the high side input and the 1R/1L input on the board.
 
The way you have it wired, with the input "across" the pot (input + at the top and input - at the bottom) is exactly how the engineers at PL designed the amp. It shows that wiring plan in the schematic. However, they grounded the input to the board and the board was grounded to the chassis by a 2.7 Ohm resistor on the Right channel and a 56 Ohm resistor on the Left channel. We're not sure why but we think it helped to keep the amp from latching up when power was applied.

Joe has made the fix that eliminates the possibility of a latch-up. Therefore, the inputs are now balanced in reference to ground. Connecting another wire from the RCA jacks to the chassis or the STAR ground defeats the balanced input ground scheme. Bring your input to the pots as shown, lead the input off the pot wiper and the shield connected to the "bottom" of the pot and bring this pair directly to the WOA board at 1L/2L and 1R/2R. The inputs are then "lifted" slightly above ground by R2R and R2L, a pair of 2.7 Ohm resistors. You will be very happy with the results.

Also, do not connect the inputs together.

In your picture above, "Rheostat mode" this is bad. Think of yourself as the preamp. You are looking at the amp with the volume turned all the way down, you are "seeing" a 100K input impedance. Now imagine the volume is halfway up, your input impedance is now 50K and the loading of your preamp section is reduced by half so the frequency response is trying to compensate due to phase shifting while the damping ratio just fell by 50%. At full volume, your preamp has no load on the output and the transistors are looking at 39K of resistance due to R3L and R3R. It is unlikely to sound good this way.
 
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I just read your post again and caught something. The pots work regardless of the "DC/Normal" switch position. You want to keep the pots, I got that. The switch can remain in place, like mine (I don't want a big hole in the back) but it is not wired to anything. You can leave it wired up if you want, but you will want to run the amp in the DC position to keep the cap out of the signal path.
 
Ok.. let me see..

1. Don't connect L/R RCA grounds to anything but the shield going to the pot.
2. Connect the RCA inputs "across" the pot, with the shield continuing on to 2L/2R with the pot's wiper connected to 1L/1R.
3. Connect star ground to 5R (or 5L since we have a jumper between).
4. Keep L and R ground/shields at the RCA "separate" (don't join the two ground tabs).

Is this right?
 
Your list is correct.

This is the only picture I have of the inputs after I finished. You can barely see how clean it looks in the upper right hand corner. And the sound is awesome.

One of the first things I leaned in electronic school was not to connect the inputs to the outputs. In the PL the output grounds go to the STAR, the input grounds "float" above the chassis and the chassis goes to STAR. This really keeps the noise floor low. Extraneous voltage is bled by the 2.7 Ohm resistors on the WOPL board.
 

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Thing is...

I just looked at the RCA's from the other end. Seems to me that all four share a large square ground plate? Everything appears to be originating from that. I'm assuming that is the "stock" equipment there, right?

(I'd take a picture, but the battery's dead on the camera... ).
 
Got the goods! Thanks Lee-dude!!

Be working on it later... I also picked up a pair of panel mount RCA's because like I was saying above - the 4 "stock" RCA's are all grounded already (I think??) to the chassis via a copper "square". Well.. ya gotta see it to get my drift, so pics later of it too...
 
Ditch the copper square and isolate the jacks from the chassis. The copper plate was PL's grounding method in the early 1970's and we know better now. Grounding the inputs together creates ground loops that act like a directional antenna for hum. Depending on the orientation of your input cables the shields will pick up 60Hz hum from your house, the transmission wires outside, or the toaster in the kitchen, etc.
 
mlucitt said:
Ditch the copper square and isolate the jacks from the chassis. The copper plate was PL's grounding method in the early 1970's and we know better now. Grounding the inputs together creates ground loops that act like a directional antenna for hum. Depending on the orientation of your input cables the shields will pick up 60Hz hum from your house, the transmission wires outside, or the toaster in the kitchen, etc.
Click to expand...

I figured that.. good thing I did pick those connectors up! Thanks for the tip, Mark!
 
Ahh, another dilemna.. Hey guys - does a 700 series 1 have those speaker output posts on the backside that are *shorter* than the 700B? Seems I'm going to have to do the "jer's standoff" again with the DCP... the posts on the speaker outputs don't clear the fuse holders.

(pics later.. eat now.. sammy time... )
 
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