Lm3886 pms!!!

[hannobisschoff@gmail.com]

Yup, you know what PMS stands for.

I built my first gain clone amp and all works well, accept if I unplug the input jack, because then the speaker output's voltage shoots to 32V (I'm using a +35 -35 V rail supply) and burns up my speakers.

THIS IS NOT BECAUSE THE POWER OF THE AMP IS TOO GREAT, because it plays freaking good with an input signal.

It only happens when the input jack is unplugged and not when it is plugged into my mp3 with the volume turned down completely.

 

[hannobisschoff@gmail.com]

Maybe it would help to show you the schematics and layout https://www.electro-tech-online.com/custompdfs/2012/01/ggg_lm3886_amp.pdf

NOTE: I skipped the input pot, and just used a jumper, can that be the problem

 

[4pyros]

You need to check your "DC offset" voltage, thats what kills speakers.
Maybe add a pull-down resister to your input.

Oh and ever connect or disconnect the input to a power amplifier with the power on!
Thats just asking for it.

 

[Nigel Goodwin]

Yup, you know what PMS stands for.

I built my first gain clone amp and all works well, accept if I unplug the input jack, because then the speaker output's voltage shoots to 32V (I'm using a +35 -35 V rail supply) and burns up my speakers.

THIS IS NOT BECAUSE THE POWER OF THE AMP IS TOO GREAT, because it plays freaking good with an input signal.

It only happens when the input jack is unplugged and not when it is plugged into my mp3 with the volume turned down completely.

Presumably you've left out the trimmer gain pot on the input?, that's why unplugging your input causes the problem. If you don't want the pot, then replace it with a 10K resistor.

 

[hannobisschoff@gmail.com]

Ohhh, I see, so it was like a pull-down resistor when set to full input volume. It works now.
It works like a dream.

Don't know why I wanted to buy a car amp IC in the first place when an amp like this was available.

Thanks for the help guys, especially Nigel Goodwin for suggesting this project.

Last question, would a 25-25V 5amp-5amp transformer be enough to power two LM3886 amps?

I'll post pictures of the finished amp later.

Cheerz

 

[Nigel Goodwin]

Ohhh, I see, so it was like a pull-down resistor when set to full input volume. It works now.
It works like a dream.

Don't know why I wanted to buy a car amp IC in the first place when an amp like this was available.

There's usually VERY good reasons for the way things are done - I still own a mains transformer that a friend and I bought back in the early 70's (it was cheap) - I've never found a use for it yet

Last question, would a 25-25V 5amp-5amp transformer be enough to power two LM3886 amps?

That's 250W of Transformer, should be fine.

 

[hannobisschoff@gmail.com]

While testing, my right channel amp output shorted to ground, and now it doesn't work anymore. While on the datasheet it says that it is short-to-ground protected. What could be wrong?

 

[4pyros]

Power down and let it cool down to reset it and try again. you may have to cycle power to reset the protection. Other than that its toast.

 

[hannobisschoff@gmail.com]

Nope ....still nothing. How can they say it's short-protected then?

 

[4pyros]

Its never perfect.

 

[Nigel Goodwin]

Nope, it's just a vague hope.

Did he short out the actual IC pins?, or the actual speaker terminals? - probably the inductor in the output feed would help save it a bit.

 

[hannobisschoff@gmail.com]

I'll go and buy another one tomorrow...

 

[hannobisschoff@gmail.com]

Nope, it's just a vague hope.

Did he short out the actual IC pins?, or the actual speaker terminals? - probably the inductor in the output feed would help save it a bit.

unfortunately the pins.

May I ask you if you have built such an amp before?

 

[Nigel Goodwin]

unfortunately the pins.

That's worse then.

May I ask you if you have built such an amp before?

No, but I have killed plenty of other chips over the years by slipping with a meter probe