losing streak, ggg lm3886 woes

[PurpleTheory]

I don't mean to whine, but the last 3 projects i have built i cannot for the life of me get to work.  :x  I tried to build ggg lm3886 amp with the bipolar ps both on the same board, I was careful to follow instructions, I've rechecked the caps to make sure they were put in correctly, I thought there might be tiny invisible traces messing it up (had that problem before) but couldn't find any. I've never built an amp before (other than ruby/little gem) so I'm sure I'm doing something wrong. Has anyone run into problems with this project, or can think of any common mistakes that could be made? One thing that I have noticed is that the negative voltage regulator gets really hot, but the positive doesn't. Don't know if it will help at all, but here are a couple photos of the board.
http://home.comcast.net/~knowitallrocks/temp_images/3886_1.jpg
http://home.comcast.net/~knowitallrocks/temp_images/3886_2.jpg
http://home.comcast.net/~knowitallrocks/temp_images/3886_3.jpg
Thanks for any help,
Matt

[ninoman123]

What are the specs of your power supply? Did you prehaps fry one of the chips while soldering? Which power supply layout did you use?

[PurpleTheory]

here is the power supply layout from ggg:
http://www.generalguitargadgets.com/pdf/ggg_bipolar_ps.pdf
the transformer is 24v 1A. I guess I could have fried one of the chips, how hard is it to ruin a voltage regulator? I was pretty careful with the 3886 chip, but you never know, how sensitive are they?

[MartyB]

I haven't looked at the whole thing carefully but it looks to me like you've got a cap in backwards - center of the board - both of those electrolytics should have their neg side pointing the same way (to the right in the photo orientation) if I read the traces correctly from the underboard shot.

HTH
MartyB

[ninoman123]

What are those other wires coming from the PT? Maybe you have a leaky capacitor in the power supply. It is possible to fry the voltage regulator if there is a misconnection that could somehow cause a short and make them over heat. Take a DMM to your power supply. Red probe to the -v and black to ground. Do the same with the otherside.

Also...and I just caught this, but it looks like you have C4 in the wrong way. Flip that around. And now that I look at it some more...it looks like you have C5 the wrong way too.

The negative leg of a cap should always go to the connection with less voltage. Since both of these go to ground. The negative leg should be connected to ground. Im pretty sure you have these two flipped around the wrong way.

Edit: It looks like GGG's amp schematic shows some of the caps with + side going to ground. This should never be...of course unless its positive ground circuit, which this one isnt.

Double edit: Err wait...Im not too sure about bipolar supplies...maybe someone else could check this...

[ninoman123]

Heh Marty we posted at the same time. But look at the schematic some of those caps are part of the negative voltage part of the amp. Im pretty sure that negatives should always go to ground but Im not sure if this still holds true for negative voltage...

[Nasse]

????? LM3886 is a high current device, I think it is not happy with such low amperes regulated power supply, and all heat sinks look way too small I believe, if you want to have all the power the amp can deliver ?????

But it should give some sound at low volume I believe if the circit is ok perhaps there is some small error somewhre, do double and triple check everything

I think it would sound better without regulated pwr supply, when you get it working

[PurpleTheory]

the extra leads on the transformer are taps for different voltages, i just put shrink tubing on the ends and rolled them up so they would be out of the way. I checked the voltages on the ps, the + is 18.1v, but the - isn't working, I take it that it must be ruined. Do I have the - regulator oriented the right way? Also are C4 and C5 in backwards for sure? Could it be like that due to the bipolar ps?

[Nasse]

http://koti.mbnet.fi/~huhtama/ele/index.php?si=ml13.sis&pa=j

There´s a good picture of 78xx and 79xx pins, notice they have different pin order

[ninoman123]

That power supply layout looks completely wrong to me.

It doesnt seem right to me that the outter leg goes to ground...can anyone verify this? The + regulator shows the middle leg of the regulator as going to GND. I think the left most leg and the middle left of the - voltage regulator should be switched. Try that...

Edit: Yes the pinout is different. See Nasse's post...try switching the legs of the negative regulator...you probably have the wrong one...

[PurpleTheory]

I'll try switching the regulator legs, that might be all that it needs. I'll let you know what happens. I appreciate the help guys.

[Johan]

if one of the regulators gets hot and the other doesnt, it usualy means no current is flowing through the one that doesnt get hot. or that the other one is shorted.

looking at the last of the three pictures, is it possibly the negative one that doesnt work?...I think you might have it mounted backwards. it looks like you might have the output leg to ground and the ground-leg to the output..

johan

[PurpleTheory]

halleluja! the neg voltage regulator was in backwards, so it's actually working now! thanks guys for all your help. the only drawback is that it's not very loud at all, probably about as loud as my ruby. guess i need a different transformer. the one i'm currently using 24v 1A, my question is, how high can I go without ruining something. I could get diodes rated for 3A, but I think the voltage regulators can only handle 1.5A. So if i were to a transformer that was 30v 1A, would that make any difference? Would it even make any difference as it's coming out 18v in the end? what would be the ideal transformer specs? anyone know a good place to find transformers?

thanks again,
matt

[PurpleTheory]

what if i used 24v regulators, would that make any difference?

[ninoman123]

I think most voltage regulators can only regulate up to 31 volts or something weird like that. You CAN get the variable voltage regulators. They require some math and you wouldnt be able to use the layout you have now but they would get you more voltage. Then of course you would need a different transformer.

Your best bet might be going with a center tapped transformer and then use this schematic to build a bipolar supply.

Also read This thread.

According to it you need around 35 volts to get about 56 watts from your amp. You would need a completely different power tranny and you couldnt use that power supply layout you have there now. BUT you will get much more volume from your amp.

So with a bridge recto you would lose around 4 volts so in order to get 35 +- volts you would need about a 40 volt tranny. If you want the FULL 68 watts from the chip you would need about a 50 volt tranny using the same bipolar circuit that I posted above.

I always wanted to build one of these solid state amps and I was going to for awhile until I decided that a 36 watt tube amp would be much more fun, but about 100x more expensive lol.

Glad it works though, its weird that GGG would use two different types of voltage regulators for their supply.

[PurpleTheory]

cool, thanks for the tips and the links. i was also wondering, how much does amperage affect the overall volume? is voltage most important?