[sil0nt]

I have been slowly assembling a meta for the past couple weeks, and last night I came close to finishing it. The problem I seem to have is I am getting DC everywhere. Im getting 9v on pins 1, 4, and 5 of the opamp and 1.5v on pin 2. Im getting about 9v on the output. I using two 9v batteries in series as my ps with the standard power supply (rail splitter, buffer, etc). I've thoroughly checked my pcb for poorly soldered joints, but everything is fine. I even cleaned up a few questionalbe joints, just to be sure. I've done a fair share of soldering in the past month (a few cmoy's, fully modded art di/o), and I have never run into something such as this, without an explanation.

something else ive noticed is that if i check each ps cap, i get -9v on the two negative caps, but only .5v on the two positive caps. ive taken many readings at many different locations along the ps path, but i never get readings that make sense. i even removed some components just to be sure i didnt add too much unecessary complexity during my testing phase.

can anyone offer some ideas of how i can continue to troubleshoot my meta? at this point i am sort of at a brick wall.. my soldering skills and understanding of electronics are mediocre, but my troubleshooting skills are pretty much nonexistant.

also, i can take some hires photo's of the board if people think they can help me out. i may just post those later on if i get bored.

thanks
brian

 

[TaffyGuy]

do the photos. make sure it's well lit so you don't have to flash and glare out everything (thats what i always do)

for reference, the square's are plus and the circles are minus

seriously i'd check just your battery connection. are you sure you didn't ground + instead of +ing it? does the LED light up? thats been my first test. hope your electrolytics are pointed the right direction...

i just assembled my first meta 2 nights ago. luckily it worked =). i started with cmoys about a month ago as well.

picture will probably be a givaway for meta pros like tangent and eric, as long as everything is visible. oh did you do the diode part right? that confused me to death, until i pulled my act together. (it was 2am, okay?)

 

[Gariver]

Brian:

Make sure your ground connections are OK! BTW, are you using a star ground system? Maybe some of your connections are not too good.

Here's a cut/paste from another thread...

Jon Risch says: "Solder only has about 10-15% conductivity compared to copper, so a good solder joint is a bad connection anyway, a bad solder joint is a REALLY bad connection!"

Knowing this, I always make sure of a good mechanical connection before I apply solder. I mean, I try to "power squeeze" the wires with my small needle-nose pliers. Why? Well, I want the best possible conductivity at every joint. Solder alone will not give me an optimum connection. Thus, to get the maximum possible conductivity you must squeeeeeze!

Thus, make sure ALL your connections are the best they can be, esp the ground connections. Right now, I think your grounds are causing your problems.

Another thing: Read the other thread on debugging a META42 by finleyville. There's plenty of guidance there.

Good luck to you!

 

[sil0nt]

Ok, i believe you may be onto something gariver. Can someone explicity explain the proper ways to setup grounding on the meta? Or, can someone tell me where to find out about proper grounding? I've read tangent's site inside and out, but i suppose it is possible that im not reading thoroughly.

thanks,
brian

 

[Gariver]

I remember posting a great link for "star grounding." I tried to find with a search, but I could not find it. Give it a try yourself.

http://headwize.powerpill.org/ubb/forums.php?fdays=20

I will try again later. Right now I've got a client on the phone.

 

[Gariver]

I'm back. Try this link...

http://www.aikenamps.com/StarGround.html

I got this link by searching with Goggle.com for "star ground." Also try "star grounding" for slightly different results. Anyway, you should read all you can on this grounding system. It's the best, and it is rather easy to implement.

Remember: Without proper grounding, your amp REVOLTS! Ha! Notice the word "volt" in there! It fits so neatly! Anyway, without proper grounding, your volt readings get really whacky and wild!

Furthermore, I believe that the META42, with its multi-loop design, is more susceptible to ground problems than a CMoy pocket amp. So a good star-ground system is a must to get it to sound good!

I don't remember reading much about grounds and grounding in Tangent's site. So I will try to give you a quick overview. Here we go...

Star Ground System....
In your mind, picture a tree branch. Secondly, imagine the small, outer branches joining the tree's larger branches. Finally, these large branches join the tree's trunk. Well, the star ground system is similar to a tree and its branches.

In a small META42, what are good wires to use for grounding? For the branches, I would use 20 to 22 gauge solid copper wire. For the trunk, I would use heavy-gauge house-wiring, say 10 to 12 gauge solid copper wire (from Home Depot).

In one small amp, I made a closed loop with 12 gauge solid copper wire (width of the loop is about 1/2"). I flattened the ends with a hammer. Then I drilled holes at the ends to hook-up my smaller wires to it. Finally, I applied Cardas eutectic solder to the joints. Overdone? Sure, it's overdone, but it works very, very well. I will be doing the same type of star-grounding in my META42!

Least I forget, I use Velcro to keep things in place in my small amps. It's the best way to keep that 12 gauge wire from moving around. Velcro is great for this. Just apply a little bit of UHU model airplane glue on the back of the hooks, and then on the back of the loops. Velcro's big advantage is removability! You can remove any item you secure with Velcro. I think that's just marvelous and very convenient!

BTW, Velcro is really good for holding caps in place. The larger the cap, the better the Velcro works. Why? Well, movement tends to weaken soldered joints. So Velcro does a great job in minimizing any type of movement in a portable amp. It also does a good job of dampening vibrations in the caps and the board.

More recommendations....
--Use the best possible eutectic solder (I use Cardas).
--Power squeeze your wire connections with long-nose pliers.
--After you have a good mechanical connection, apply solder.
--Make sure your solder joints shine like polished silver.

Good luck with this info! I hope it helps you overcome your problems.

 

[orl2222]

Ok, let me try and understand this. ive ordered parts for a meta. Please forgive my ignorance. I do understand about the "virtual" ground, and using a rail splitter, as far as voltage is concerned. Now, if i were to put my board in a say hammond case, I would:

A. use a common ground(the actual case)?

B. hook up the input and output jacks grounds to this common ground?(by passing the hookup points on the board)?

C. solder all the input and output hook ups to the board, then use on of the many "ground points" around the board itself to attach to my "case common ground"?

D. also ground my pot to the case or chasis" commond ground"?

E. using a regulated wall wart of say 12v 800ma, Using the virtual ground rail splitter, just hook up the wires from say a input jack to the + and - points on the board?(I plan to use both C1 postions, regardless of power supply otions 2 9V or a regualated wall wart)

F. If using a ad8620 op amp, and connecting (2) 9V batteries in series, just use the + and - points on the board using D1, and the rail spliter?


I know to all of you these may seem like "idiot" questions, but coming from a automotive background, a "ground point" always meant a chasis ground. I was hoping for some clarification here. thanks!

 

[Gariver]

You don't have to ground your Hammond case. Use the Velcro method I explained above. What you are doing is getting the ground electricity away from the amp's circuit. That is usually good enough. Sometimes, though, even the jacks (in and out) have to be grounded.

The ground in a portable amp can be...
--a thick, 10 to 12 gauge wire.
--a small copper plate.

Grounds in an automobile can be tricky, esp with amps. So I know what you are talking about.

Great day in San Juan, PR...
Today I saw the current 2002 Miss Universe, Oxana Fedorova (Russia) and last year's 2001 Miss Universe, Denisse Quinones (Puerto Rico). Believe me, they are both very, very beautiful and very, very charming! Hmm...I think I'm in love! Maybe in my dreams I'll get lucky!

 

[orl2222]

Ok, then I understand that, so would you reccomend hooking everything up to the board, and using one of the ground points along the permiter of the board as a common ground?

 

[tangent]

I wish I'd caught this thread earlier...

Yes, a star ground is good and wonderful and righteous, but when it comes to the META42 or any other printed circuit board, the ground is what it is -- you don't want to go modifying the board just to turn it into the ground scheme you want.

The ground scheme on the META42 board is not, strictly speaking, a star ground. It's similar, in that the ring is like the center point of a star ground and there are branches off of this. But, there is indeed a small amount of resistance between the base parts of any branches off of that ground, which makes it not quite the same as a true star ground. HOWEVER: there have been many META42s made so far, and no one has yet shown that there is a problem with the existing ground scheme. If the lack of a star ground was the problem here, wouldn't all META42s exhibit these wild DC voltage levels, Gariver?

Now to drag this discussion back to the original problem:

First it would be helpful if you said what voltage your power supply is. When you talk about 9V it would be helpful if I knew that the power supply is 9V or 18V, or something else entirely.

I am guessing that all of these voltages you're measuring are relative to virtual ground. And, when measuring against virtual ground, it's helpful to measure from vground to the two pins on your power supply. If vground isn't almost exactly between these two, any further measurements you make aren't going to make much sense.

I'm also assuming that when you talk about "pins" on the op-amp that you're using the board's pin numbers. If you have a pair of single-channel op-amps on an adapter and you're giving the pin numbers of the chips on the adapter, for example, you need to say so.

DC on pin 1: this is normal if you've got some kind of class A bias hooked up.

Small voltage on Pin 2: expected, and also due to the class A. The feedback loop sends an attenuated version of the output voltage to the inverting input, which is pin 2.

Pin 4: This is V-, and is expected.

Pin 5: If you're numbering the pins counterclockwise, this is the right channel input, so there shouldn't be any voltage here. If you're numbering the pins in columns (which is incorrect) then this is V+, which is again expected.

I have no idea what's going on with your power caps, but I'll leave the problem here. Given what I've said above, you may find that you're not testing what you think you are and re-do the test and find that it's okay after all.

 

[Gariver]

I keep forgetting that you guys are building META42s on PCBs. I am doing a Sijosae style META42, which does need a ground.

http://headwize.powerpill.org/ubb/sh...20020817203644

These are like two different animals.

 

[sil0nt]

Ok, I went ahead and took some new measurements, this time a bit more scientifically.

First, I measured distance of each pole on my ps from the virtual ground. I got -9.3 and +9.5. I have to brand new alkaline 9v batteries in series, so this result is expected.

Next, I tested the opamp pins. Since I do not know exactly what pin is what, let me display my results in a table that represents the socket:

-9.3 | +9.5
-1.6 | -9.3
0.0 | -1.5
-9.3 | 0.0

Hopefully the formatting on that comes outs. What I said before is kind of wrong (I think). I got pin 5 and pin 8 confused. Anyway, those are the readings I found.


After the opamp, I measured the ps caps. I have no idea what they should be, or if they should be a particular value, but I got -9.0 on both negative caps and +0.2 on both positive caps.

I do not have an LED hooked up, but there is -9.3 voltage on the negative pad, and 0.0 on the positive pad.

Finally, I measured the left and right output channels. I got -7.2 on both of these.

To clarify my methods, I used my multimeter in 20 DCV mode and put one node on the vground pad in the top righthand corner above the rail splitter. I also measured the distance between the vground and the center tap on my dual 9v power supply, and I got a very unstable +/- 0.1.

After all of this measuring, my only concern is for the -7.2v coming out of my left and right channels. Before I was concerned about my opamp's voltages, but tangent has said this is normal due to class A operation (which I do have installed.)

Thanks for everyone's help so far. I haven't had time to actually do anything besides these measurements, but I do appreciate all of the time that everyone has put in to help me.

brian

 

[tangent]

If there is no op-amp chip in the socket, everything sounds correct, sil0nt, except for the power caps. Because everything else is correct I tend to suspect your measurement method and not an actual problem.

Now, if there is an op-amp on the board, then everything's not okay. I don't know how you could get those voltages with an op-amp in the socket unless both channels had failed in the same way.

You spoke of a rail splitter -- do you mean the place where it would go if you used one, or that you actually used the rail splitter? With that center-tapped battery configuration, you shouldn't be using either the TLE2426 or the 2001G. Ideally, nothing bad will happen, but in reality I think that due to errors in the difference between your center-tap virtual ground and the vground created by the TLE2426, that you'll get problems, most likely uneven battery drain.

If there is no op-amp in the socket and you're just measuring things before putting your precious chip in the socket the first time (good practice) then I think you have nothing to worry about. I think you've got an amplifier, doing exactly what it's supposed to be doing.

On the op-amp pin issue, look at any datasheet -- it will show you how the pins are numbered. Same goes for any chip you use.

 

[sil0nt]

Quote:

Originally posted by tangent If there is no op-amp chip in the socket, everything sounds correct, sil0nt, except for the power caps. Because everything else is correct I tend to suspect your measurement method and not an actual problem.

There is no op-amp chip in the socket.

Quote:

Now, if there is an op-amp on the board, then everything's not okay. I don't know how you could get those voltages with an op-amp in the socket unless both channels had failed in the same way.

So, if I put an op-amp in the socket, the DCV on my output will go away?

Quote:

You spoke of a rail splitter -- do you mean the place where it would go if you used one, or that you actually used the rail splitter? With that center-tapped battery configuration, you shouldn't be using either the TLE2426 or the 2001G. Ideally, nothing bad will happen, but in reality I think that due to errors in the difference between your center-tap virtual ground and the vground created by the TLE2426, that you'll get problems, most likely uneven battery drain.

I do currently have two batteries in series. I do not have the center tap of the batteries connected to anything. I do have a TLE2426 and an EL2001 in the power supply. Should I remove both of these and connect the center tap to the vground?

Thanks,
brian

 

[tangent]

Okay, things are clearing up. Bottom line, I don't think your amp has a problem at all.

To understand why you're seeing DC voltage on the outputs, look at the schematic: through the current source, the op-amp's output is connected to V-. That's why you see roughly -9V on the op-amp's output pins. (1 and 7) The reason you see a lower voltage on each buffer's output (or at the jack, if that's where you're measuring) is because the buffers can't put out voltage clear to the rail -- there's a headroom limitation there, so they cut the V- down by a volt or two.

When you put the op-amp chip in there, it will spend energy "fighting" this drag towards V-, which is the very definition of class A bias: we're making the chip keep certain transistors powered up all the time, when the design of the chip would normally keep these transistors off when they're not being used.

Put the chip in and re-measure it. I'm sure you'll find that the outputs go to 0.

As for your power supply, I recommend that you stick with the rail splitter. You can technically do without it if you run the center tap of your batteries to ground, providing a true dual power supply, but this configuration has problems of its own. Do a seach if you care to read the reasons against this configuration. There was a really good thread on this at Headwize several months ago.