Got this amp with a weird problem.
While testing with a 2 ohm load, everything looks ok until i pass 100A
then, there is an intermittent noise, that i believe comes from the output
chokes.
Sine wave on the scope looks ok and when this noise comes on, i see a kind of
harmonic swinging on top of the 100Hz signal.
This is a generic type 1 class D amp.
While testing with a 2 ohm load, everything looks ok until i pass 100A
then, there is an intermittent noise, that i believe comes from the output
chokes.
Sine wave on the scope looks ok and when this noise comes on, i see a kind of
harmonic swinging on top of the 100Hz signal.
This is a generic type 1 class D amp.
Attachments
i tried to get a photo but now the problem has changed
when it draws a bit over 70-75A, it goes into protect, shutting down my
power supply.
The very first time i tested this amp, it drew about 152A before making that
noise (output was 50VAC in a 2 ohm load)
I could never repeat that.
The noise started earlier, at around 100A,
and now, it does not make this noise and it just simply shut down.
When i cycle the power of my power supply, it starts the same all over again.
when it draws a bit over 70-75A, it goes into protect, shutting down my
power supply.
The very first time i tested this amp, it drew about 152A before making that
noise (output was 50VAC in a 2 ohm load)
I could never repeat that.
The noise started earlier, at around 100A,
and now, it does not make this noise and it just simply shut down.
When i cycle the power of my power supply, it starts the same all over again.
Look at the waveforms on the input side (non-audio side) of the 4 output filter inductors. When it starts to make the noise, do you see something strange on one of the inductors that isn't there on the other 3 inductors?
Set the scope to 2ms and whatever vertical amp setting it takes to make the waveform fill about 3/4 of the display.
Set the scope to 2ms and whatever vertical amp setting it takes to make the waveform fill about 3/4 of the display.
i had to load the amp with a 4 ohm load, in order to see things easier.
None of the four inductors at the none audio side shows anything different
from the others.
The amp made easily around 1200Wrms at 4 ohm.
But i noticed that as this noise starts and the output becomes low, (as
does the current draw of the amp), the noise "cracks"continue at this
lower level. I am talking about 30-40A.
Also there was a new "crack" sound that i think it was from my 4 ohm
250W resistor getting very hot.
None of the four inductors at the none audio side shows anything different
from the others.
The amp made easily around 1200Wrms at 4 ohm.
But i noticed that as this noise starts and the output becomes low, (as
does the current draw of the amp), the noise "cracks"continue at this
lower level. I am talking about 30-40A.
Also there was a new "crack" sound that i think it was from my 4 ohm
250W resistor getting very hot.
Attachments
things happen so fast, i could only get this photo out of many.
It is strange though, that this noise happens only when i probe one particular choke...
with the rest, everything seems fine. I leave the amp (and my load) to become cold again,
and i test over and over again.
It is strange though, that this noise happens only when i probe one particular choke...
with the rest, everything seems fine. I leave the amp (and my load) to become cold again,
and i test over and over again.
Attachments
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