nelsress begins his WOPL 400 project

[NavLinear]

Thanks Nav, I've always heard about the jolt those big f-in caps can put out, your switch mechanism is a good idea! I might have to build one of those myself for future builds. The alligator clips worked okay this time but I like your idea better. Thanks for stopping in, always good to see your avatar, I mean you.

Always here to help - the avatars are kind on the eye.

 

[laatsch55]

The new one is a wife's example of.........be careful what you wish for....

 

[nelsress]

Now that the B+/Bias+ thing is figured out, when I do my tests again this afternoon and, if I get good readings, I'm assuming that I have to discharge the PS caps after each test prior to installing each new row of transistors, correct?

 

[NavLinear]

Now that the B+/Bias+ thing is figured out, when I do my tests again this afternoon and, if I get good readings, I'm assuming that I have to discharge the PS caps after each test prior to installing each new row of transistors, correct?

The rail voltage ties to the output transistors. As a general rule anytime you put your hands inside you want to make sure the caps are discharged. If you're away from the amp for a while the caps will discharge but it's a good idea to measure the voltage across them.

 

[nelsress]

The rail voltage ties to the output transistors. As a general rule anytime you put your hands inside you want to make sure the caps are discharged. If you're away from the amp for a while the caps will discharge but it's a good idea to measure the voltage across them.

Okay, that's what I was thinking, thanks Nav. Tests indicate +89V and -89V at the B+ (labeled the Bias+) and B- test points, at the rail fuse tips and on the caps themselves. On the outputs I was getting readings of around 0.29V so I'm going to go out and install row number two of transistors and run the tests again.

 

[Gepetto]

Okay, that's what I was thinking, thanks Nav. Tests indicate +89V and -89V at the B+ (labeled the Bias+) and B- test points, at the rail fuse tips and on the caps themselves. On the outputs I was getting readings of around 0.29V so I'm going to go out and install row number two of transistors and run the tests again.

Using miniclip grabbers put a 10K ohm resistor from the output TP to the GND test point and see if that output reading goes from 0.29V to zero or close to it.

 

[nelsress]

Using miniclip grabbers put a 10K ohm resistor from the output TP to the GND test point and see if that output reading goes from 0.29V to zero or close to it.

So to be clear here Joe, you want me to do this with it powered up, right? Thanks. Now I just have to see if I have a 10K ohm resistor. If not, RS probably has some.

 

[Gepetto]

So to be clear here Joe, you want me to do this with it powered up, right? Thanks. Now I just have to see if I have a 10K ohm resistor. If not, RS probably has some.

Please attach the resistor when it is powered down and THEN power it up and take your measurements. 10K is not critical, any value between 8K and 20K will do. The goal is to just put a small load on the output to negate any leakage in the output transistors. In the presence of no resistive load, micro amp type leakage amounts will cause a voltage to be read there.

 

[nelsress]

Please attach the resistor when it is powered down and THEN power it up and take your measurements. 10K is not critical, any value between 8K and 20K will do. The goal is to just put a small load on the output to negate any leakage in the output transistors. In the presence of no resistive load, micro amp type leakage amounts will cause a voltage to be read there.

Understood, will do, thanks Joe.

 

[nelsress]

Bingo

Please attach the resistor when it is powered down and THEN power it up and take your measurements. 10K is not critical, any value between 8K and 20K will do. The goal is to just put a small load on the output to negate any leakage in the output transistors. In the presence of no resistive load, micro amp type leakage amounts will cause a voltage to be read there.

You nailed it Joe, I connected an 8200 ohm resistor with alligator clip leads to left and right channel ground and output test points and powered it up and my readings are now near zero, fluctuating between 0.1 and 0.0. Thanks again buddy. Now I can continue on with the next three rows of transistors, tests between each row of course. Then I think I'll move on to the relay circuit but all the photos in the instructions for that part of the project show it being installed into a PL 400 in its original configuration with the point to point backplane setup so I'll have to figure that out. Thanks again Joe!

 

[nelsress]

Okay Joe, I installed the second row of transistors and powered it up and ran the tests, all values looked good but the output values climbed just a bit to 0.31 V so do I need to do the resistor test again or did the initial test tell you what you needed to know? Thanks.

 

[Gepetto]

Okay Joe, I installed the second row of transistors and powered it up and ran the tests, all values looked good but the output values climbed just a bit to 0.31 V so do I need to do the resistor test again or did the initial test tell you what you needed to know? Thanks.

Do you have the wires to the output binding posts attached? Not sure if you do or not Nelson. If the leads are connected to the binding posts then you can just use the binding posts to connect to the 8200 ohm resistor you have and leave it in place while you install outputs. That is how I accomplish this. I do not know if you have these connected though because I think you are planning on installing a DC protect board.

 

[nelsress]

Do you have the wires to the output binding posts attached? Not sure if you do or not Nelson. If the leads are connected to the binding posts then you can just use the binding posts to connect to the 8200 ohm resistor you have and leave it in place while you install outputs. That is how I accomplish this. I do not know if you have these connected though because I think you are planning on installing a DC protect board.

In fact I did connect the wires to the output binding posts, even though I am intending to install the DC protect circuit because I wasn't sure if it needed to be connected for the test or not. So I can just solder a resistor between the (+) and (-) binding post of each channel, perfect, that's what I'll do, sounds a lot easier, thanks Joe.

 

[Gepetto]

In fact I did connect the wires to the output binding posts, even though I am intending to install the DC protect circuit because I wasn't sure if it needed to be connected for the test or not. So I can just solder a resistor between the (+) and (-) binding post of each channel, perfect, that's what I'll do, sounds a lot easier, thanks Joe.

You don't even have to solder it Nelson. Just use the binding post to hold it from positive to negative.

 

[nelsress]

You don't even have to solder it Nelson. Just use the binding post to hold it from positive to negative.

Okay, easier yet! I'm curious, what does this excess voltage at the output translate to, hum, noise, or?? Thanks again.

 

[Gepetto]

Okay, easier yet! I'm curious, what does this excess voltage at the output translate to, hum, noise, or?? Thanks again.

Nothing, you are essentially just checking each transistor quality as you install each row. A leaky transistor will show up as one that is not compensated by the ~10K resistor. Just a quick check for goodness along the way.

It is far easier to ensure each step is good rather than throw everything together and hope for the best. Very hard to debug it once you have the entire closed loop feedback system up and running. Easier to do it in small steps.

 

[nelsress]

Makes sense

Nothing, you are essentially just checking each transistor quality as you install each row. A leaky transistor will show up as one that is not compensated by the ~10K resistor. Just a quick check for goodness along the way.

It is far easier to ensure each step is good rather than throw everything together and hope for the best. Very hard to debug it once you have the entire closed loop feedback system up and running. Easier to do it in small steps.

This evening I installed the third and fourth rows of transistors and got good test results on each row. Perhaps one of the more challenging things so far from a dexterity standpoint was getting the transistors in those cups. By the last row though I had a feel for it and the last four went in relatively quickly and easily. I'm happy that they're all in and I got good voltage readings and near zero readings on the outputs with the resistors in circuit.

I heard from Don who recommended I finish the amp and make sure it's all working as it should before installing the DC protect relay circuit, basically for the same reason you have us check each row of transistors, to make finding issues, if any arise, easier to locate and fix. Fun stuff, Joe, can't wait to hear it, I'm starting to see an amplifier materialize here!

 

[nelsress]

Hey Joe, RCA jack question...

What is the recommended procedure for the RCA input jacks on the full comp WOPL 400 with the Watts Abundant DC protect relay circuit installed? Don's instructions seem to reuse the copper plate and ground wires in the instructions but the kit comes with new RCA jacks with ground lugs. The latter would make for a neater job but that copper ground bus sure looks to be a more solid ground. What do you and Lee recommend Joe? Thanks.

 

[nelsress]

Control Board

After driving through the flooded back roads the other day from all the snow melting so fast, my wife's car had several warning lights come on in her car. We took it to out mechanic and before dumping too much money in it, he thought with all the water that perhaps just resetting the codes would rectify the problem. Well, it did for a couple hours then the lights came back on. So, I dropped my wife off at her work at 5:45 AM and the shop doesn't open until 7:30 AM so I had some time to kill and decided it would be best used by connecting the control board to the backplane boards, which I did by 7:30.

The next step seems to be setting the bias for this baby, which procedure I'm going to read at least one more time, perhaps more, so it's fresh in my mind. Not that it's that difficult, I just prefer to not be lost during such things. I'm getting really excited and feel like, with a little luck, I'll be testing this baby out before too long now!

I think after I set the bias I'll go ahead and install Don's relay circuit, unless you guys think I shouldn't quite yet. This has really been a fun project, thanks to the attentive assistance from you guys, which is greatly appreciated. Great group here, I must say.

 

[Gepetto]

After driving through the flooded back roads the other day from all the snow melting so fast, my wife's car had several warning lights come on in her car. We took it to out mechanic and before dumping too much money in it, he thought with all the water that perhaps just resetting the codes would rectify the problem. Well, it did for a couple hours then the lights came back on. So, I dropped my wife off at her work at 5:45 AM and the shop doesn't open until 7:30 AM so I had some time to kill and decided it would be best used by connecting the control board to the backplane boards, which I did by 7:30.

The next step seems to be setting the bias for this baby, which procedure I'm going to read at least one more time, perhaps more, so it's fresh in my mind. Not that it's that difficult, I just prefer to not be lost during such things. I'm getting really excited and feel like, with a little luck, I'll be testing this baby out before too long now!

I think after I set the bias I'll go ahead and install Don's relay circuit, unless you guys think I shouldn't quite yet. This has really been a fun project, thanks to the attentive assistance from you guys, which is greatly appreciated. Great group here, I must say.

Seems you are making careful but steady progress Nelson. Make sure you use your DBT for bring up activities until you know that everything checks out properly.