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Problem with my audio amplifier
Problem with my audio amplifier
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Old 22nd February 2021, 04:47 PM   #1
Niko58 is offline Niko58  Slovenia
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Default Problem with my audio amplifier

Hello, I recently designed a power amplifier with capabilities of around 120W. The problem came as I connected the speakers and turned it on. What happened was the speaker started moving and making noise without any input signal. I also measured the voltege between speaker terminals and my multimeter showed the same voltage that was on the positive output of the power supply, sience Im using dual polarity type psu.

I hope someone here has some insight on the topic, it would be really helpful.
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Old 22nd February 2021, 05:27 PM   #2
as_audio is offline as_audio
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I am afraid you did not tell us enough to be helpful..
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Old 22nd February 2021, 05:28 PM   #3
Michael Bean is offline Michael Bean  United States
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Is this a guessing game? Seriously, nobody can shed light on a problem without any relevant info. So what's the design (schematic)? How was it built (pictures)? What were the specific test conditions? Etc.
It's the equivalent of "I made this thingamajiggy and it doesn't work...tell me what's wrong" without providing anything to go on.

Mike
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Last edited by Michael Bean; 22nd February 2021 at 05:30 PM.
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Old 22nd February 2021, 05:34 PM   #4
as_audio is offline as_audio
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His second post, so please be patient.
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Old 22nd February 2021, 05:42 PM   #5
Michael Bean is offline Michael Bean  United States
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I was patiently explaining why that post would not get the desired results.

Mike
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Where we have strong emotions, we're liable to fool ourselves...Carl Sagan
They say I'm lazy, but it takes all my time...Joe Walsh (The Musician)
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Old 22nd February 2021, 05:55 PM   #6
rayma is offline rayma  United States
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A new DIY amplifier should always be checked with test equipment first, before connecting speakers to it.
Especially if it is a new design, and not a kit. The speakers can be damaged otherwise.

Last edited by rayma; 22nd February 2021 at 05:58 PM.
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Old 22nd February 2021, 06:00 PM   #7
adason is offline adason  United States
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Quote:
Originally Posted by Niko58 View Post
Hello, I recently designed a power amplifier with capabilities of around 120W. The problem came as I connected the speakers and turned it on. What happened was the speaker started moving and making noise without any input signal. I also measured the voltege between speaker terminals and my multimeter showed the same voltage that was on the positive output of the power supply, sience Im using dual polarity type psu.

I hope someone here has some insight on the topic, it would be really helpful.
dc on the output the same as positive power supply should never be connected to the speaker
its likely some dead transistor
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Old 22nd February 2021, 06:06 PM   #8
as_audio is offline as_audio
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In that case the woofer will be dead.
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Old 22nd February 2021, 07:46 PM   #9
adason is offline adason  United States
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120 watt amp is probably running +/-45 volt supply, or higher, typically
niko58 did not share that with us
that would make woofers membrane jump on the floor

when I test new amp (i do not design any, just copy), I use cheap small fullrange, even that often cap protected

we need pictures, niko58, post lots of pictures
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Old 23rd February 2021, 07:57 AM   #10
Niko58 is offline Niko58  Slovenia
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Its runing on +/- 60V, Im using dummy speakers so no worries about blowing them up. Ive came to the same conclusion that one of the lateral MOSFETs probbably SJ162 is faulty.

Ive measured Source to drain about 200, then I went and measured drain to source and both of the two PMOS Im using started filling up, one of them came to the value of 2000 and then showed an open circuit, however the other one didnt. It just stayed rock solid at just below 2000.

This doesnt seem okay to me, but Im no pro so thats why Im here.

Hope you can tell me something with the data I gave you.
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