PL 700 Pro Build

[derek92994]

VRLA's (valve regulated lead acid) are notorious for thermal runaway. I had a set do that in our battery lab a few months ago. The valve opened on a couple cells and spewed like a geyser. Stunk up the building. Fortunately the rack is on a concrete floor.

Following your advice, I will keep the batteries as a backup to run the fridge and lights only, they are almost at end of life and have done a lot of charge cycles. Power failures are not common here, but its handy to have a backup when they do occur. Lucky nothing bad has happened during charging as they would charge on a timer when I was at work. Now I know the potential of thermal runaway, I can be more careful about it.
I am going to stick to running the stereo setup of that dedicated 15 amp circuit and furman power conditioner. Is there any potential issues that could arise running the preamp and other components off the same circuit, or should they be separated?

 

[George S.]

All the "Pro" amps came with 1/4" mono jacks. These are easily replaced with RCAs, they drop right in. The jacks need insulated from the chassis with the fiber washers. I leave the copper grounding plate out, though others use it.

 

[George S.]

Belden 83284 coax. The outer insulation can be carefully stripped with a razor blade, then the woven braid teased apart with a pointed Xacto blade.
https://catalog.belden.com/index.cfm?event=pd&p=PF_83284&tab=downloads

 

[George S.]

Hmmm, so I have a question I should have asked prior to starting the attenuators.
This amp has 50k ohm pots. My other WOPLs have 100k.
So if I understand the wiring correctly, the preamp should see the entire value of the pot at all times. And of course attenuation changes the value at the amp, but not the value that the preamp sees.
If I have this correct so far, do I need to pull those 50k and replace with 100k?
I do have 4 of the 100k Bourns Pro Audio grade pots if need be.
Thanks all, should have asked this weeks ago.

 

[Gepetto]

Hmmm, so I have a question I should have asked prior to starting the attenuators.
This amp has 50k ohm pots. My other WOPLs have 100k.
So if I understand the wiring correctly, the preamp should see the entire value of the pot at all times. And of course attenuation changes the value at the amp, but not the value that the preamp sees.
If I have this correct so far, do I need to pull those 50k and replace with 100k?
I do have 4 of the 100k Bourns Pro Audio grade pots if need be.
Thanks all, should have asked this weeks ago.

I personally like no pots at all (like the original PL400) because they just add noise and variable phase lag conditions when the pot interacts with the input filter cap of 220pF. If you have to have pots, I prefer 50K, my preamp has an output impedance below 50 ohms so it really doesn't care what it is driving. PL chose 100K likely to allow it to be driven by high impedance tube preamps.

 

[George S.]

I personally like no pots at all (like the original PL400) because they just add noise and variable phase lag conditions when the pot interacts with the input filter cap of 220pF. If you have to have pots, I prefer 50K, my preamp has an output impedance below 50 ohms so it really doesn't care what it is driving. PL chose 100K likely to allow it to be driven by high impedance tube preamps.

Joe, thanks for your thoughts and insight. I'm going to go with the original 50k pots in the 700. If I have issues in a triamp setup with gain, I'll convert the 400s from 100k to 50k. Thanks again.

 

[George S.]

When I WOPLed my two 400s, wiring the attenuators confused the hell out of me. I really didn't understand which end of the coax should go to the control board or RCA jack and why.
Mark Comer made a post last year explaining it in terms I understood. Basically the preamp should not see a change of resistance when the pot is turned. So put the ohm meter between the shield and each center conductor of the each channels coax and turn the pot. The unchanging value should be very close to the pots value, and this coax gets wired to the RCA jack input from the preamp. The ohm reading on the other coax will change from close to zero to close to the value of the pot. This coax goes to the respective channels connection on the control board. Yeah, it's simple, but I didn't understand until Mark C. explained it. Thanks Mark!
I use small pieces of heat shrink to keep the channels straight. The blue shrink designates RCA connection.

 

[George S.]

All wiring completed. Tomorrow I'll double check all the wiring connections, power it up, and adjust the meters.
With the intermediate plate in it's normal position all the wiring lays nice. Later

 

[grapplesaw]

When I WOPLed my two 400s, wiring the attenuators confused the hell out of me. I really didn't understand which end of the coax should go to the control board or RCA jack and why.
Mark Comer made a post last year explaining it in terms I understood. Basically the preamp should not see a change of resistance when the pot is turned. So put the ohm meter between the shield and each center conductor of the each channels coax and turn the pot. The unchanging value should be very close to the pots value, and this coax gets wired to the RCA jack input from the preamp. The ohm reading on the other coax will change from close to zero to close to the value of the pot. This coax goes to the respective channels connection on the control board. Yeah, it's simple, but I didn't understand until Mark C. explained it. Thanks Mark!
I use small pieces of heat shrink to keep the channels straight. The blue shrink designates RCA connection.

George can you post the link to this thread your are referring to
thanks

 

[grapplesaw]

All wiring completed. Tomorrow I'll double check all the wiring connections, power it up, and adjust the meters.
With the intermediate plate in it's normal position all the wiring lays nice. Later

Nice shot. She is all dressed up. Great work

 

[George S.]

George can you post the link to this thread your are referring to
thanks

Glen, I spent about 30 minutes this afternoon searching and couldn't find it.

 

[laatsch55]

It's pretty simple, wiper goes to the board...

 

[grapplesaw]

It's pretty simple, wiper goes to the board...

Well I was wondering if there may be a new twist here but I now see there isn’t
thanks Lee

 

[George S.]

It's pretty simple, wiper goes to the board...

That's it!! Wiper goes to board. Wish I could find that old post where he explains why that matters. Pretty simple when you think about it when you have the phrase "wiper goes to board". Thanks Lee!

 

[derek92994]

She is super tidy, will behave nicely

 

[George S.]

Waiting for the garage door guys to arrive and install the garage door I ordered back in August.
Thought I'd double check the WOAD Cylon wiring and fire her up and let her idle throughout the day until I can calibrate the meters.
Success, 1 red LED illuminated on each meter, yahoo!
Posting a photo from the top.
What are your all thoughts about spacing that control board out a little more from the back planes? Only issue I can think of is it may affect bias transistor temperature.

 

[Gepetto]

Waiting for the garage door guys to arrive and install the garage door I ordered back in August.
Thought I'd double check the WOAD Cylon wiring and fire her up and let her idle throughout the day until I can calibrate the meters.
Success, 1 red LED illuminated on each meter, yahoo!
Posting a photo from the top.
What are your all thoughts about spacing that control board out a little more from the back planes? Only issue I can think of is it may affect bias transistor temperature.

It won't. Ambient is pretty isothermal inside the enclosure cavity once buttoned up. The back wall will obviously heat up as the heat source for that isothermal cavity. Moving the card one way or another won't impact much except for running into other things.

 

[George S.]

It won't. Ambient is pretty isothermal inside the enclosure cavity once buttoned up. The back wall will obviously heat up as the heat source for that isothermal cavity. Moving the card one way or another won't impact much except for running into other things.

Cool, going to find some of those old style brass hexagonal stand offs and bring that control board out some. I built enough slack into the AC run that I can raise it away from the back planes quite a bit more. Thanks Joe.

 

[laatsch55]

George, Glen and I ran some noise tests with different standoff heights years ago, some differences were noted. The further the better. Measure as you go and see what effect your movement has.

 

[George S.]

Thanks Lee, will do.