WOPL 400 Build

swarmin · Mar 24, 2020

Hello everyone,

With the current pandemic, I have found myself with plenty of free time on my hands. I am (was?) a line cook, but I've been into repairing speakers, recapping, restoring, built phone pre-amp kits, etc for about 10 years now. I had a side hustle selling silver plated oxygen free copper interconnects and speaker cables for a while on audiokarma.

I'm by no means a professional, but I feel I'm pretty handy when it comes to this sort of stuff. I am having some trouble with putting this kit together and I think it stems from there being too much information available.

I am doing the back plane board kit, the control board and wattsabundant relay. I have a few questions:

1: how do I avoid using the Zoebel network on the Watts relay?

2: The Q6 Bias transistor is soldered to the board, correct? I found some documentation saying it should be attached directly to the chassis, but then found a bunch of pictures with it on the board.

3: what process should I follow with bring up? Pl14_20 first? Back plane? Kinda confused where I should start.

Thank you for your help

MarkWComer · Mar 24, 2020

1: Remove the Zoebel. I don’t have the schematic handy, but identify two resistors with leads twisted together and a capacitor located nearby. There is one arrangement each for left and right channel. Clip the leads, or as I did, desolder and remove. (Member Wattsabundant can give you more details...)

2: Q6 is affixed to a stud via a “P” shaped aluminum thermal clamp, and of course, the leads have to connect to the backplanes with sufficient length for the body of the transistor to be within the square outline on the board. When you install the backplane, put a small drop of superglue to the round top, slide on the “P” clamp, and tighten with a #4 lockwasher and nut.

3: For initial startup, the backplane leads to the PL14 aren’t connected, Initial startup is mainly to check that the power supply has no issues. Do this with the bottom row of output transistors installed. After successful initial startup, its okay to connect the backplane wires to the driver board (PL14).

Right! I was confused by this as well, but with a little hand holding from other members, I made it through.

GOOD LUCK!

MarkWComer · Mar 24, 2020

On the 400 DCP: Remove R1, R2, C3*, C9.

*- I think C3, it’s just next to C9. I have a video on the installation, but there’s too much motion blur. The video details installation into a quasi comp with the old point-to-point backwall.

I removed the resistors, not the capacitors...

Wheel-right · Mar 24, 2020

I think this might help,

https://forums.phxaudiotape.com/threads/resurrected-a-customized-wopl-400.7541/page-11 post 201, 202

swarmin · Mar 24, 2020

Excellent. Thank you very much for the quick replies! I'll get the Zoebel desoldered and get her wired up.

Wheel-right · Mar 24, 2020

Your welcome, I may not have done my 400/700 yet but I've read tons here to get ready and remember some of it. Mark's videos on YouTube are excellent help too besides being entertaining.

Gepetto · Mar 24, 2020

swarmin said:

Hello everyone,

With the current pandemic, I have found myself with plenty of free time on my hands. I am (was?) a line cook, but I've been into repairing speakers, recapping, restoring, built phone pre-amp kits, etc for about 10 years now. I had a side hustle selling silver plated oxygen free copper interconnects and speaker cables for a while on audiokarma.

I'm by no means a professional, but I feel I'm pretty handy when it comes to this sort of stuff. I am having some trouble with putting this kit together and I think it stems from there being too much information available.

I am doing the back plane board kit, the control board and wattsabundant relay. I have a few questions:

1: how do I avoid using the Zoebel network on the Watts relay?

2: The Q6 Bias transistor is soldered to the board, correct? I found some documentation saying it should be attached directly to the chassis, but then found a bunch of pictures with it on the board.

3: what process should I follow with bring up? Pl14_20 first? Back plane? Kinda confused where I should start.

Thank you for your help

Very sorry for TMI (too much information). I respond to not knowing how to do something by creating yet more documentation to explain how to do this or that. After a while it gets to be a large amount of info to go through.

swarmin · Mar 24, 2020

Gepetto said:

No worries at all. It appears just asking here is the best way to go when my brain starts to hurt! I'm really impressed with the quick replies and helpfulness. You guys are great!

MarkWComer · Mar 24, 2020

swarmin said:

I think everyone here knows the frustration of being at an impasse for not understanding instructions clearly. Nothing more frustrating than being on a roll with something and getting stuck! We cover for each other here, I’ve gotten answers quickly myself. By no stretch of the imagination am I an expert- just a hobbyist- and glad to help if I know how.

It’s a good crew here...

laatsch55 · Mar 24, 2020

Damn straight, and proud of it...

swarmin · Mar 25, 2020

Rectifier caps? Not sure. I've see them on multiple builds now. Is this a thing of the past, or should I be concerned?

So, when I run the first bring up (if I'm reading this correctly) I'm supposed to have the backplane boards not connected to the chassis with the help of the nylon washers. Is this correct?

MarkWComer · Mar 25, 2020

swarmin said:

Have a look at this video, maybe it will help. The bottom studs hold your bias transistors, the top left stud is your chassis ground, the top right stud holds the right board in place (all four of these studs serve to help hold the boards in place). The screws through your transistor collectors securely hold the boards in place.

So, yes- the backplane should be secured to the chassis by these four studs, and the bottom row of transistors for the initial startup.

The little capacitors on the rectifier aren’t absolutely necessary, but desirable. They reduce/eliminate switching noise from the rectifier.

Gepetto · Mar 25, 2020

Here is a picture of the PL700B or S2 configuration but the intent is the same regardless of the amp. Components in the assembly aid package are intended for the initial hold down purpose. 6-32 socket head cap screw, #6 flat metal washer, #6 flat nylon washer, heatsink, chassis, thread into backplane board PEM nut. Hope this helps you understand the purpose.

swarmin · Mar 25, 2020

Excellent. Thank you. I've been checking out your videos Mark, very helpful. That was the next one to watch. Guess I should just sit down and watch them through.

MarkWComer · Mar 25, 2020

swarmin said:

They’re guaranteed to cure insomnia...

swarmin · Mar 25, 2020

I just realized the variable transformer I bought is only 5A. I guess this build is on hold until I get back to work...

laatsch55 · Mar 26, 2020

That's plenty to power up. If you are not loading up the amp, should be plenty..

mlucitt · Mar 26, 2020

swarmin said:

Your 5A variable transformer will work fine for checking the circuit initially. The first power up is with the dim bulb and none of the outputs installed, so the current is low. There is no startup surge because you are slowly bringing the AC voltage up.
True, when you want to troubleshoot the fully-assembled amp with a 4 Ohm or 8 Ohm load bank at full power, you may want a 10A or 15A variable transformer.

Lee, you beat me to it by 4 minutes.

wattsabundant · Mar 26, 2020

swarmin said:

Do you have the dim bulb test set for powering up? It prevents damage where a variac won't. I live by it. Material cost is $10 or so. you probably already have most of what's needed.

swarmin · Mar 26, 2020

Ok, cool. I've got a dim bulb for the initial, but when adding the transistors row by row, 5a will do the job?

WOPL 400 Build

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