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Old 27th April 2004, 04:00 PM   #1
sonu is offline sonu  India
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Default Class D amp

I have made a class D amp based on HIP4080 on a vero board. Modulation frequency set to 150Khz.
But the output is not so clear as compared to the class AB designs. Initially there was a DC offset which I adjusted, but still I am not satisfied with the quality of sound.
There is a little hissing sound and chiirrr__ssiiirrrr type of sound with no input and maybe it increases with the volume. Would it be cause of ringing on the gate of mosfets. There is very nominal heating on the mosfets even at high outputs @4Ohms Load and supply of 25V.
I have used IRF540 mosfets, should I use fast recovery clamping diodes with mosfets.
What else can matter the quality of the output.


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Sonu.
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Old 27th April 2004, 04:02 PM   #2
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Quote:
on a vero board.
This might already be one reason !

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Charles
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Old 27th April 2004, 04:25 PM   #3
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Pcb layout, and a good one is EXTREMELY important for high quality class D amps I think also that 150 kHz is a bit low.
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Old 27th April 2004, 07:10 PM   #4
Pabo is offline Pabo  Sweden
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If a classD amplifier generates audible noise as the ones you describe you most likely have jitter in the power square.

This usually comes from noisy environments causing a threshold to vary from pulse to pulse.
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Old 28th April 2004, 12:52 PM   #5
sonu is offline sonu  India
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Fine..... i have made it on a vero board but layout done has been very perfect as required for high frequency, with good decoupling caps, very short traces.

As I asked earlier would it be cause of ringing on the gates, I have used 10 Ohms Resistors to gate, or what else can be the cause. As per the datasheet 150Khz is the best for efficiency & performance, increasing the modu freq would decrease the efficiency.

Has anyone made and tested this design.

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Old 28th April 2004, 12:54 PM   #6
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Fine..... i have made it on a vero board but layout done has been very perfect as required for high frequency, with good decoupling caps, very short traces.
How about a ground plane or at least an "approximation" of one ???

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Charles
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Old 28th April 2004, 01:19 PM   #7
sonu is offline sonu  India
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As this is my first class D amp, please let me know hints on proper ground plane.

Will single sided PCB work for class D, or do i have to go in for double sided only.
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Old 28th April 2004, 01:23 PM   #8
Alcaid is offline Alcaid  Norway
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Can you post the schematic you're using?
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Old 28th April 2004, 01:31 PM   #9
sonu is offline sonu  India
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Schematic as given by intersil Application note - AN9525
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Old 28th April 2004, 01:31 PM   #10
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While you can actually check if a class-d amp is working in principle by using a Veroboard, you will have to take a double-sided PCB with a good groundplane to get the most out of it.
Have you seen that there is development kit available for this HIP driver ? The layout they use shpuld be available on the WEB.

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Charles
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