WOPL 400 Build

I got everything soldered up and put back together. I set my bias. I noticed in Mark's video, he takes a DC offset reading. When I take my readings, I get 1.1mV on the right and -.3mV on the left. Did I screw something up?
 
So, after reviewing everything, I think I'm good. In Mark's video, it says the dc offset should be between -.011V and -.017V. I then re-read the control board bring up and it said offset should be 0. -.3 and 1.1mV is about as zero as can be.

I'm just looking for confirmation. I still haven't listened to anything yet.
 
swarmin said:
So, after reviewing everything, I think I'm good. In Mark's video, it says the dc offset should be between -.011V and -.017V. I then re-read the control board bring up and it said offset should be 0. -.3 and 1.1mV is about as zero as can be.

I'm just looking for confirmation. I still haven't listened to anything yet.
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your readings are just fine. The voltages Mark cited were for the predecessor board revision which had higher offset voltages than the rev E board does
 
Gepetto said:
your readings are just fine. The voltages Mark cited were for the predecessor board revision which had higher offset voltages than the rev E board does
Click to expand...

Thank you! How exciting! I'm gonna get my coffee and then have a listen!
 
I've got an audible buzz. I'm guessing it's a grounding issue?

Edit: This is a buzz in both channels without an input and it gets louder with an input plugged in. I'm thinking about it and I didn't ground the shielding going to the front panel. I'm going to open her back up and get that done.

I want to say I read something that said not to. I've always only grounded one side of shielding on interconnects. I'm guessing this is different though.
 
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swarmin said:
I've got an audible buzz. I'm guessing it's a grounding issue?

Edit: This is a buzz in both channels without an input and it gets louder with an input plugged in. I'm thinking about it and I didn't ground the shielding going to the front panel. I'm going to open her back up and get that done.

I want to say I read something that said not to. I've always only grounded one side of shielding on interconnects. I'm guessing this is different though.
Click to expand...

Did you ensure your input RCA connector shells are isolated from the chassis? They should be.

Did you remove the bus wire jumper between the RCA input jack copper plate and the black (negative) speaker binding posts right above the inputs?
 
Gepetto said:
Did you ensure your input RCA connector shells are isolated from the chassis? They should be.

Did you remove the bus wire jumper between the RCA input jack copper plate and the black (negative) speaker binding posts right above the inputs?
Click to expand...

I have the rca ground to chassis. Don't know what I was thinking when I did that...kinda embarrassing. I'm going to solder it up correctly and give her another try. I really appreciate the help.
 
swarmin said:
I have the rca ground to chassis. Don't know what I was thinking when I did that...kinda embarrassing. I'm going to solder it up correctly and give her another try. I really appreciate the help.
Click to expand...

they don’t have the insulating shoulder washers around them?
 
Gepetto said:
your readings are just fine. The voltages Mark cited were for the predecessor board revision which had higher offset voltages than the rev E board does
Click to expand...
Yeah- I noticed that. I bought the E driver for the 700 project before the G driver was available. I decided to go for the G driver for the 700 and put the E driver in my 400- definitely a difference in offset. On the outside job (an 8 fin Series One 400) I took, the customer wanted the G driver since the cost between the two wasn’t much. As I recall, my DVM read zero for the offset.
 
Gepetto said:
they don’t have the insulating shoulder washers around them?
Click to expand...
Hopefully you mean the fiber washers- not the nylon shoulder washers! Omitting those would make instant toast!
 
Gepetto said:
they don’t have the insulating shoulder washers around them?
Click to expand...
They were there, the metal washer was on the chassis. I also had kind of a crappy solder on my grounds. I was trying to do it without cutting any length off the wire leading to the faceplate. I just cut it all off and cleaned it up properly. Buzz is gone. Double checking bias and gonna give her a go!

Don't worry, Mark, no toast or burning flesh!
 
MarkWComer said:
Hopefully you mean the fiber washers- not the nylon shoulder washers! Omitting those would make instant toast!
Click to expand...
Yes the black shoulder washers that are installed on all stock PL amps around the RCA connectors.
 
MarkWComer said:
Yeah- I noticed that. I bought the E driver for the 700 project before the G driver was available. I decided to go for the G driver for the 700 and put the E driver in my 400- definitely a difference in offset. On the outside job (an 8 fin Series One 400) I took, the customer wanted the G driver since the cost between the two wasn’t much. As I recall, my DVM read zero for the offset.
Click to expand...

The revE and RevG1 control boards have identical offset specs since the circuit is identical.

The RevD and earlier boards with bipolar differential pair input transistors had -0.010 to -0.015V offset voltages due to the bias current required by the bipolar transistors.

The RevE and RevG1 boards have FET front end transistors in the op amp which have bias current measured in the low picoamp range which allows those board versions to exhibit extremely low offset voltages, typically 1mV or less.
 
She's singing! Absolutely beautiful! I'm impressed and couldn't be happier!

I'm using a Kyocera R-461 as pre and a pair of heavily modded Klipsch KG4 speakers to test. Sounds amazing. Played 4° by Tool and man did it sound pretty.

Thank you all so much for the help. It feels incredible to pull this off. Pretty much the electronics version of a differential gear swap!
 
swarmin said:
She's singing! Absolutely beautiful! I'm impressed and couldn't be happier!

I'm using a Kyocera R-461 as pre and a pair of heavily modded Klipsch KG4 speakers to test. Sounds amazing. Played 4° by Tool and man did it sound pretty.

Thank you all so much for the help. It feels incredible to pull this off. Pretty much the electronics version of a differential gear swap!
Click to expand...
AND ANOTHER WINNER!
HAVE A CIGAR!
Congratulations!
 
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