| wuffer |
i have just made the gc from http://sound.westhost.com/project19.htm but with the lm3886 instead and this psu http://sound.westhost.com/project04.htm but with 4700 caps instead.. im using a 2*24v 300va trafo
i have no pcb so i have just wired the components together..
the big problem is large noise/hum and a tiny bit of music... :bawling:
i cant see what i have done wrong... can you experts give me a hint what i have done wrong???
sorry about my poor english |
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| jaudio |
Check your wiring,then recheck your wiring espeicially ground.
Check your power supply for correct voltage.
Make sure pin 5 is connected to + power supply |
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| Russ White |
| also make sure you have something like a 10K resistor from the negative rail to the the mute pin. |
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| wuffer |
| thanks all... i will check again and hope i can get it to work :) |
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| wuffer |
i got it to play but some parts went up in smoke:( im not sure wich... but it was very low music...
new parts and then i will see if it works :D |
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| Nuuk |
Wuffer, if it helps to copy a 'tried and tested' design for the LM3886, here is the one that I built. I have not had time yet to write up the full description of the build on Decibel Dungeon.
The orange square is the signal star ground. And note that this was with a snubberized PSU. If you don't want to use that PSU, substitute the 100uF caps on the voltage pins for 1000uF and leave out the big caps at the bottom of the diagram.
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| wuffer |
much closer now... i think the wire i have used is bad.. it influence the sound in a bad direction... not sure what to do...
damn the lm3886 is getting hot. hat hoped that a heatsink from a p4 could be used but no :(
but now there is music coming out of the speaker instead of noise.. now i just have to get the last noise away |
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| macboy |
| quote: | Originally posted by wuffer
much closer now... i think the wire i have used is bad.. |
Unlikely.| quote: | Originally posted by wuffer damn the lm3886 is getting hot. hat hoped that a heatsink from a p4 could be used but no :(
[/B] |
If the 3886 is getting hot, then your amp is probably oscillating badly. I've used heatsinks much smaller than a P4 one, and at low to medium volumes, the chip gets only slightly warm.
Tear it down and start again from the ground up. Nuuk's diagram looks solid; try following that. |
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| wuffer |
| okay thanks.. i will do that later :) |
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| Nuuk |
| Yes, just to second the heat thing. My LM3886's run only slighhtly warm! :att'n: |
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| Nuuk |
Here is something else for you to look at Wuffer. It shows both channels of a 3886 GC and how to connect them together properly. If you follow this carefully, you should have a cool-running, non-oscillating, noise-free and musical GC! ;)
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| wuffer |
| that looks nice :) thanks :cool: |
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| wuffer |
| DC blocker what is that??? i think im going shopping tomorrow :D i want that gc to work.. the 2 on the out, what is that?? the drawing is easy to understand so its going to work... i hope.. i have 10 thumbs |
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| mateo88 |
It's just a capacitor. It is there to only let AC through.
If that drawing is a little difficult to follow, as it is for me, just look at the schematic in the datasheet. Good luck!:) :smash: |
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| Nuuk |
To makes things a little clearer:
The 0R22 resistor on the output should be rated at 3 watts. Many of us are using two 0R47 2 watt carbon film resitors in parallel.
The Zobel is a 100nF capacitor in series with a 2R7 resistor.
As Mateo88 says, the DC blocker is a capacitor (2.2uF-4.7uF) that lets the signal (AC) through but blocks DC.
Looking at a schematic will also be useful but the 'layout' diagrams are useful to show people where the parts go! ;) |
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| wuffer |
| thanks :cool: i think i understand all of it :) |
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| Nuuk |
| quote: | | thanks i think i understand all of it |
If not, don't be afraid to ask. We want to see you succeed. ;) |
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| wuffer |
okay just a last thing before i go out and buy all the parts..
the resistor marked as 47-100K ís that because it dont mean so much if its 50K or 100K?? |
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| boholm |
47 K is a standard value. 50 K is not.
Anything in between is a OK. |
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| wuffer |
| thanks... out to the shop im going :cool: |
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| wuffer |
dosent work here.. the speaker membrane just go in and stays there untill its dead...
i have dobbel tjeck it and cant seem to find anything wrong :bawling:
maybe its ment to be that i should not have i gc :rolleyes: |
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| Nuuk |
| quote: | | dosent work here.. the speaker membrane just go in and stays there untill its dead... |
Did you measure the DC offset before you connected the speakers? |
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| wuffer |
nopz.. im not sure how...
luckly i have some small speakers to test with :)
hmm that is just wrong.. i got full voltage to the speaker :confused: |
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| boholm |
Without anything connected, what are the voltages of input and output?
With input grounded what is the voltage of output? |
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| wuffer |
0,3 on the input and 34,5 on the output :hot: without anything connected
voltage is the same with and without the ground |
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| Nuuk |
OK, you should ahve the same voltage on the positive and negative rail!
So you have a problem in the PSU somewhere. :att'n:
I just completed a new GC this morning. I tested the voltage from the rectifiers before I connected up the regulators, then I tested the input voltages on the regulator and the output voltages. Only when I saw that they were correct did I connect the chips and even though this is a GC that I have used before, I still checked the DC offset! And even though the offset readings were 19mV and 20mV, I still connected my old test speaker and played music through each channel before connecting my 'good' speakers.
Testing for DC offset is described on Decibel Dungeon so it's 'back to school' for you Mr Wuffer! ;) |
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| wuffer |
the psu is just like this one..
but i will read som more... |
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| Nuuk |
| quote: | | the psu is just like this one.. |
And do you have +35 volts on one side and -35 volts on the other?
And have you connected one negative rail to the positive rail on the other 'side'?
When you measure the voltage on your chips, you should measure between the voltage pin (positive or minus) and the power ground star which is at 9or should be at) zero volts.
Have you connected pin 5 to the positive suply? |
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| wuffer |
1. yes i got that
2+3 im not sure i understand that.. my brain is on weekend :rolleyes:
4. yes |
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| Nuuk |
| quote: | | 2+3 im not sure i understand that.. my brain is on weekend |
Is you power supply connected exactly as it is shown in the diagram?
If so you should have three (not four) wires coming from it - positive voltage, negative voltage and zero volts. :att'n: |
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| Nuuk |
So, when we say measure the voltages on the pins, we mean that you should measure between the positive wire (where it joins the chip) and the zero volt wire (where it joins the power ground star. And likewise for the negative rail. |
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| wuffer |
+35 and - 35 volt..
just stop for today... |
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| Nuuk |
| quote: | | just stop for today... |
That's very wise! ;) When having problems, a break can make all the difference in spotting what is wrong! :att'n: |
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| wuffer |
| looked at it again.. cant seem to find any errors... looking at it again tomorrow.. there must be an error :confused: |
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| Nuuk |
| quote: | | looked at it again.. cant seem to find any errors.. |
I think we have all thought that we have checked everything, only to find something wrong later. Sleep on it and don't worry. ;) |
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| wuffer |
| i just looked at it again... the -v is connected on pin 3 but in http://cache.national.com/ds/LM/LM3886.pdf it should be on 4.. and on yor website Nuuk its connected under the 1000 caps and on the other diagram its pin 3... im confused.. |
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| jaudio |
| For the lm3886 chip pin 3 is output and pin4 is -v. |
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| Nuuk |
My apologies Wuffer. I had got it wrong and have now corrected those diagrams. :xeye:
I hope that this is the only 'problem' and that you will now have a working GC! ;) |
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| wuffer |
| now it only play little music with a discman connected.. when i connect anything larger it just come with noise... maybee i should just order a pcb some where |
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| Nuuk |
| quote: | | now it only play little music with a discman connected.. when i connect anything larger it just come with noise... maybee i should just order a pcb some where |
Do you connect through a volume control or preamp?
What sort of noise? |
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| wuffer |
both preamp.. xbox direct without a preamp...
its dificult to explain wich kind of noise its is.. |
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| wuffer |
| i think the problem is in the input... when i dont have anything connected then it's silent.. but im not sure... |
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| Nuuk |
| quote: | | i think the problem is in the input... when i dont have anything connected then it's silent.. but im not sure... |
It sounds like some sort of ground loop. Are you getting a humming noise? |
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| wuffer |
| not sure but i think that can be the problem... |
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| wuffer |
looked at it again and cant find any errors after the drawing.. but i got 26v on the output
anyone got pics off any lm3886 designs???... |
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| wuffer |
:yes: (there was no dancing smilies)..
just looked at it again and put it all together for the 117 time..
the speaker was quiet. could that be it?? plug'd music to it and there was music :cool: :cool:
its alive :D
now i need to finish the other channel and hook it op to my proac clones to see what they can..
thanks for all your help
last question from me this time... is there a lot of different in using a ordenary psu and a snubberized psu?? |
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| Nordic |
I am so with the feeling... just blew the first 3875 chip... luckily have 5 spare... now first to repair the trace on the PSU which burnt through...
Did A real good job of the blowout, chip basicaly split in half...
Wait I'm not finished venting.. been at it since I woke up this morning... man I'm so depressed right now... |
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