Hi,
I’m working on a clone BASSFACE class D Type 4 amplifier that was brought in with a burnt-out power supply and a dead output section.
It’s using 10 IRF260Ns for its output.
After fixing the power supply, I noticed the drive waveform on the output had a step on the turn-on, and the low-side FETs were running hot without a load at idle.
I changed the driver transistors from 2316, 916 to 2073, 940 respectively, and doing so solved the problem with the drive waveform. However, the amplifier was getting distortion well before the clipping point. The driver transistors on the low side, especially the 2073, were also running hot when I did this. I switched back to the original drivers to see if the distortion was also present with them fitted, and indeed it was, and it was much worse.
I also tried leaving the 2073, 940 on the high side and the original transistors on the low side, which was somewhat better. I also tried other transistors like 649, 669, and the results were much worse.
Any idea on what is causing this and how I can fix it?
Any help would be greatly appreciated. (I’m kind of new to fixing class D amps 😅)
Also, the rail voltage is 180 peak-to-peak.
I’m working on a clone BASSFACE class D Type 4 amplifier that was brought in with a burnt-out power supply and a dead output section.
It’s using 10 IRF260Ns for its output.
After fixing the power supply, I noticed the drive waveform on the output had a step on the turn-on, and the low-side FETs were running hot without a load at idle.
I changed the driver transistors from 2316, 916 to 2073, 940 respectively, and doing so solved the problem with the drive waveform. However, the amplifier was getting distortion well before the clipping point. The driver transistors on the low side, especially the 2073, were also running hot when I did this. I switched back to the original drivers to see if the distortion was also present with them fitted, and indeed it was, and it was much worse.
I also tried leaving the 2073, 940 on the high side and the original transistors on the low side, which was somewhat better. I also tried other transistors like 649, 669, and the results were much worse.
Any idea on what is causing this and how I can fix it?
Any help would be greatly appreciated. (I’m kind of new to fixing class D amps 😅)
Also, the rail voltage is 180 peak-to-peak.
Update on the Repair
For future reference, I solved the issue by adding a 470nF capacitor to the output of the feedback circuit.
Without the capacitor, it was going into self-oscillation at high duty cycles, resulting in overheating the MOSFETs at high volume. At mid volume, it was generating a high amount of hissing-like distortion with oscillation on the top and bottom of the sine wave.
I also replaced the original driver transistors (A916/sc2316) with A940 / 2073.
For future reference, I solved the issue by adding a 470nF capacitor to the output of the feedback circuit.
Without the capacitor, it was going into self-oscillation at high duty cycles, resulting in overheating the MOSFETs at high volume. At mid volume, it was generating a high amount of hissing-like distortion with oscillation on the top and bottom of the sine wave.
I also replaced the original driver transistors (A916/sc2316) with A940 / 2073.
Hi i have a few years repairing amps , but always came ones with da issues , that give headaches !!! I have one 95% identical , with almost same issue on low side output , low side gate drive distort with output mosfets loaded
Hi,
You can adjust the amount of shoot-through by changing the resistor underneath the glued section near the rail capacitor. Increasing the value of the resistor will decrease the shoot-through.
However, doing so will affect the output signal and may cause distortion.
If it's not getting hot while idling, you can leave it as is, but consider adding a 15V zener diode to prevent overvoltage on the gates. Under heavy load, the voltage may exceed 20V and damage the FETs. Add a 15V zener diode from gate to source on both sides.
I also tried a lower switching frequency, and at 83kHz, it was running much better. However, you should also make some changes to the output filter when doing this.
Last edited:
Thanks , just to be sure the resistor near positive rail cap or the negative ?!.
In idle stay little bit warm , putting signal begin to heat only negative side .
That 15V zener on both sides , gate drive line to mosfet source right ???
In idle stay little bit warm , putting signal begin to heat only negative side .
That 15V zener on both sides , gate drive line to mosfet source right ???
Thanks , i did all that and still the same, Low side Gate drive distort . Any schematic's for this amp ???
Something is distorting de low side loaded .
Power Supply
Positive Rail 102V
Negative Rail 108V
This Amp came to me in Protect , protect circuitry one bad M6 that goes to output drivecard .
Something is distorting de low side loaded .
Power Supply
Positive Rail 102V
Negative Rail 108V
This Amp came to me in Protect , protect circuitry one bad M6 that goes to output drivecard .
The zener was for adding protection to make the output section more reliable.
This is Type 4 amplifier design. the schematics is almost the same between all type 4s:
Send pictures from the gate and drain of the power supply FETs waveforms and probe the rail voltages with AC coupling to see if the ripples is too much.
And maybe one of the rail capacitors gone bad and is leaking.
This is Type 4 amplifier design. the schematics is almost the same between all type 4s:
Send pictures from the gate and drain of the power supply FETs waveforms and probe the rail voltages with AC coupling to see if the ripples is too much.
And maybe one of the rail capacitors gone bad and is leaking.