Hi there !
I'm new here, I'm from belgium so please excuse my English![Smile](https://music-electronics-forum.com/core/images/smilies/smile.png)
A Costumer brought me a MarkBass 250 BlackLine that has a constant "hissing" sound in the power amp.
It comes from the power supply.... It's kind of a ripple smps sound.
First I've checked all the filter caps --> Good. Coupling cap between power transistor and transformer (C68) --> Good
Checked the oscillator resistors and caps (R74, C52, C51,...) All good
So I've tried to replace the oscillator (21531D) just in case --> It's changes the frequency sound but still there.
The thing is, when I unplug the Fan (+18v), the sound change a little bit too... strange.
I'm not a noobie but I don't have a lot of experience in SMPS and class D amp so... Do you have any ideas for me ?
In this profession, all opinions, advice and experiences are good to take to evolve![Big Grin](https://music-electronics-forum.com/core/images/smilies/biggrin.png)
Thanks a lot !!
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I'm new here, I'm from belgium so please excuse my English
![Smile](https://music-electronics-forum.com/core/images/smilies/smile.png)
A Costumer brought me a MarkBass 250 BlackLine that has a constant "hissing" sound in the power amp.
It comes from the power supply.... It's kind of a ripple smps sound.
First I've checked all the filter caps --> Good. Coupling cap between power transistor and transformer (C68) --> Good
Checked the oscillator resistors and caps (R74, C52, C51,...) All good
So I've tried to replace the oscillator (21531D) just in case --> It's changes the frequency sound but still there.
The thing is, when I unplug the Fan (+18v), the sound change a little bit too... strange.
I'm not a noobie but I don't have a lot of experience in SMPS and class D amp so... Do you have any ideas for me ?
In this profession, all opinions, advice and experiences are good to take to evolve
![Big Grin](https://music-electronics-forum.com/core/images/smilies/biggrin.png)
Thanks a lot !!
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