preamp noise

[pabse]

Hey guys. (sorry about my english)

I´m having some trouble with a preamp; a noise is comming out from the speakers. When i put the fingers over the BBE chip. It increase. I think the caps are too close the chip.

Use a ne5532, JRC 2150AD (BBE) and LM1876

My older design join to the 1876 works perfectly.

Thanks!!

Older (through hole)

(Smd)

 

[peranders]

A schematic and a parts placement drawing would be useful.

 

[Rick PA Stadel]

Might not be the cause of your noise problem, but C08 and C09 will need their polarity flipped if the 2150 has no negative supply.

I'd also suggest jumpering/removing R7 and R8 -- a direct connection to Gnd eliminates a potential source of noise and oscillation. If their purpose was to match-up the input offsets, there's no need since the amp is AC-coupled In and Out.

Regards,
Rick

 

[pabse]

Hi, thanks for answer.

The polarity of C8 and C9 its now correct.

I remove R7 and R8, but i have no changes.

Near the ic 2150 i still having a noise, like an antenna.

An externally hosted image should be here but it was not working when we last tested it.

 

[Mark Whitney]

Many layout errors. Large loop area and increase inductance on many of the traces caused by the octopus ground. It would have been better if you had used a ground plane on the underside. You should not mix the audio and power grounds.

 

[Zampotech]

Rinse the remaining flux with a mixture of gasoline and ethyl alcohol.
Possible leakage current through the active flux. It is often the cause of increased noise.

 

[Mark Tillotson]

Never use gasoline indoors. Friend of mine never wears shorts due to that mistake.

And for cleaning PCBs use flux cleaner or IPA, not ethyl alcohol or gasoline, that will disolve plastic components!!

 

[Zampotech]

Pure gasoline and pure alcohol does not destroy plastic. Plastic dissolves in the solvent.
Gasoline washes away fat-soluble pollution, alcohol washes away alcohol-soluble and water-soluble pollution. The mixture washes away all kinds of dirt. The flux contains all these types of pollution. Any of these contaminants can cause spurious leakage currents and noise.
I use this mixture for 15 years.
Of course, when working with combustible mixtures should be careful.

On photo net gasoline.

 

[kevinahcc20]

If you want to use a hydrocarbon solvent VM&P Thinner is much safer to work with indoors as it is less volatile than gasoline lacking the lighter C3-C5 components.

 

[Zampotech]

If you want to use a hydrocarbon solvent VM&P Thinner is much safer to work with indoors as it is less volatile than gasoline lacking the lighter C3-C5 components.

If I understand correctly, this is a slightly viscous light yellow liquid with the smell of kerosene?

 

[kevinahcc20]

If I understand correctly, is it a slightly viscous yellow liquid with the smell of kerosene?

No it's a clear liquid with low viscosity composed of middle volatility petroleum distillates, so basically gasoline without the lighter volatiles and without any added alcohols.

 

[Zampotech]

No it's a clear liquid with low viscosity composed of middle volatility petroleum distillates, so basically gasoline without the lighter volatiles and without any added alcohols.

Maybe I know what you're talking about. In Russia it is called the "SOLVENT".
I do not know its effect on plastic, but this liquid dissolves powder paint.

 

[kevinahcc20]

Could be similar, a generic term for it here in the USA is naptha.

 

[Mark Tillotson]

Pure gasoline and pure alcohol does not destroy plastic. Plastic dissolves in the solvent.

Being dissolved sounds like destruction to me.



IPA is the normal solvent used because its safe with nearly everything. More powerful solvents aren't worth the risk unless you know its safe. Electronics is not an internal combustion engine! Using gasoline and similar indoors is a great way to enter for the Darwin awards, but all solvents carry risk.

 

[Zampotech]

I have IPA and many other solvents. But the results of IPA did not impress me at all.
Better than conventional wheat alcohol has not yet come up with anything.

Darwin's award can be received if you do not comply with safety measures.

 

[pabse]

Many layout errors. Large loop area and increase inductance on many of the traces caused by the octopus ground. It would have been better if you had used a ground plane on the underside. You should not mix the audio and power grounds.

Hi, Thanks for the reply.

The problem i have is a hum noise. It could be a ground loop as you say.
What do you think about this layout. What do you mean about separate gnd? Can you show me how to do it.

Thanks!!

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