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Old 26th October 2009, 03:47 PM   #1
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Default is it possible to replace mosfet on my amplifier for better sound

Hi everybody

I have an amplifier sinus live classD mono on my subwoofer ground zero
since 2 or 3 months my amp have is led blown, "who indicate is power on"

The amplifier works but it has less power than before i don't know why

So i would like to change the 8 mos-fets IRF640N who are in the amplifier stage "not in the power supply"

But i don't know what mos-fets can i use ?

If you can explain me how to to choose mos-fets with technical specificity, to have the better sound?

Thanks in advance
best regards
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Old 26th October 2009, 04:26 PM   #2
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The output transistors in an amplifier have VERY little to do with the sound quality.

If this is a class D amp, you need to use exact replacements. Many class D amps are sensitive to changes in the outputs. Changing them to a different part can cause all sorts of problems. If you want to experiment with different parts, you should get it working properly with the original replacement part and then try different parts.

Are you sure the amp is at fault and not the speakers? Many times an open voice coil in a woofer (that has 2 or more voice coils) can make the output less but the woofer continues to produce bass.
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Old 26th October 2009, 05:36 PM   #3
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Hi Perry Babin

Thanks a lot for your advices

Yes i'm sure that the amp is defect because i test the subwoofer on a different amplifier and it works great

my subwoofer have 2 voices coil of 4 ohms

i use it on the amp with voice coil in série so 8 ohms, because i prefer to have more damping factor and BL.

But one day i have listened a noise "like a little a small banger"

The amp isn't power on when i listen this noise, and i don't see any things like smoke or other things it's really strange

And the amp works with less power

Do you thind there is a defect capacitor

i have an other problem since i have bought this amplifier, when i turn it on there is a noise in the amp like a switch who do "on, off" rappidely with a "ploc" in the sub

All my Connections are good.


Thanks in advance
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Old 26th October 2009, 05:50 PM   #4
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Does the woofer cone push out or pull in and remain in or out (from the point of rest) when the amp is powered on?

What model amp?
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Old 26th October 2009, 06:54 PM   #5
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Thanks Perry

For the subwoofer, the cone push out and become again normal with the sound like "ploc"

The amplifier is a sinus live model SL A-1500 V1

Click the image to open in full size.

Thanks for your help
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Old 26th October 2009, 07:19 PM   #6
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One of the outputs may be leaking, or you could have a problem with the drive circuit.

If you want to try to repair the amp, you should pull the output transistors and check them. There should be absolutely no continuity between the first leg and either of the other legs.

You should know that if you have a leaking output and you reinstall it in a different location, the amp could fail.
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Old 26th October 2009, 09:14 PM   #7
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Thanks Perry

It's Verry strange why the amp do not blown the fuse if there is a defect mos-fet is it especially with a class D amplifier ?

That's can explain the less power output ?

I thing the best things to do is to change All Mosfets IRF640N ? the price in euros is 1.72 TTC around 2.16 DOLLARS

I'll test all to see if there is a problem
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Old 26th October 2009, 09:30 PM   #8
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If one is leaking but not badly and the drive circuit can control it, the amp could continue to work (although, maybe not properly).

Check them before ordering replacements.
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Old 26th October 2009, 09:50 PM   #9
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Thanks Perry I'll do it

I'm verry happy do be here on this forum

The only problem is my bad english because i'm french


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