Balance LM3886 not working

Ipanema · 7th March 2006, 02:23 AM

Guys,

I have made this balance LM3886 as the schematic attached. The problem is both positve and negative output voltage goes to near VDD upon power ON. Found this schematic from instrumentation amplifier circuit.

What possibly went wrong with this circuit? Pls help.

Thanks.

DcibeL · 7th March 2006, 04:31 AM

Your schematic doesn't have VDD on it. You have used a non-polarized cap for C1?

Some pictures of your project would be helpful, to check the wiring, make sure all the caps are in the right way, no solder bridges, etc.

Ipanema · 7th March 2006, 04:56 AM

Hi Dcibel,

Sorry, the the positive supply is labelled as VCC instead of VDD while the negative suupply is VEE.

C1 (zobel) is Wima MKS2 non-polar.

I 've attached the layout. The red line is my jumper wire. Do you see anything wrong with the layout as well? I'll take picture of the board and post here tomorrow.

Thanks.

Ipanema · 7th March 2006, 04:57 AM

Layout

DcibeL · 7th March 2006, 05:03 PM

My thought is that the small track from pin 1 to pin 5 (VCC) that goes over pin 3 (output) is shorting to pin 3. Can you check this with a multimeter? Also check on your board that the track on pin 8 does not short to pin 9 or 10.

Ipanema · 9th March 2006, 12:37 AM

Hi Dcibel,

I have check through the board and nothing is shorting. Could it be that the the feedback resistor R10 is not physically grounded?

Anyone have tried this circuit before?

Thanks.

DcibeL · 9th March 2006, 01:20 AM

As far as I can tell the circuit should work. When one input is posotive, and the other is negative (balanced input), then the feedback of one chip will be opposite of the feedback of the other, so...I don't know it's hard to explain but it should work. You could test that the circuit works by doing a Spice simulation using a couple of op-amps. That is, provided your circuit design software does Spice simulations.

Normally for a balanced input, you would just apply one signal to the posotive input, and one to the negative. But I guess this way you get a larger output like a bridge configuration.

7th March 2006, 04:31 AM	#2
DcibeL diyAudio Member Join Date: May 2003 Location: Saskatchewan	Your schematic doesn't have VDD on it. You have used a non-polarized cap for C1? Some pictures of your project would be helpful, to check the wiring, make sure all the caps are in the right way, no solder bridges, etc. __________________ The power of Science compels you!

7th March 2006, 05:03 PM	#5
DcibeL diyAudio Member Join Date: May 2003 Location: Saskatchewan	My thought is that the small track from pin 1 to pin 5 (VCC) that goes over pin 3 (output) is shorting to pin 3. Can you check this with a multimeter? Also check on your board that the track on pin 8 does not short to pin 9 or 10. __________________ The power of Science compels you!

9th March 2006, 01:20 AM	#7
DcibeL diyAudio Member Join Date: May 2003 Location: Saskatchewan	As far as I can tell the circuit should work. When one input is posotive, and the other is negative (balanced input), then the feedback of one chip will be opposite of the feedback of the other, so...I don't know it's hard to explain but it should work. You could test that the circuit works by doing a Spice simulation using a couple of op-amps. That is, provided your circuit design software does Spice simulations. Normally for a balanced input, you would just apply one signal to the posotive input, and one to the negative. But I guess this way you get a larger output like a bridge configuration. __________________ The power of Science compels you!

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7th March 2006, 04:56 AM	#3
Ipanema diyAudio Member Join Date: Jun 2004 Location: KL	Hi Dcibel, Sorry, the the positive supply is labelled as VCC instead of VDD while the negative suupply is VEE. C1 (zobel) is Wima MKS2 non-polar. I 've attached the layout. The red line is my jumper wire. Do you see anything wrong with the layout as well? I'll take picture of the board and post here tomorrow. Thanks.

9th March 2006, 12:37 AM	#6
Ipanema diyAudio Member Join Date: Jun 2004 Location: KL	Hi Dcibel, I have check through the board and nothing is shorting. Could it be that the the feedback resistor R10 is not physically grounded? Anyone have tried this circuit before? Thanks.

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