"The Wire AMP" Class A/AB Power Amplifier based on the LME49830 with Lateral Mosfets

[AKN]

npdot,
It may be out of scope of this thread but my interface will be based on Pete Millet’s interface. His webpage is certainly worth a read: Soundcard Interface
There is a lot of threads about sound car interfaces but please let me know (by PM?) if there is something you want to know about my specific setup.

[npdot]

AP2,

Here are 10KHz and 20KHz--much flatter. I am getting suspicious of my cables because I don't see how it could be the smoothing caps or transformer.

[npdot]

AP2,

150Hz

[AP2]

Originally Posted by npdot

AP2,

150Hz

the angle is now shifted counterclockwise.(as I thought)
I do not understand though, how is it possible to 150Hz, the output Vp is reduced to + /- 15V?

[opc]

Hi Guys,

I performed these measurements in my setup here using an Agilent scope and The Wire connected to a DPS-600 supply.

The load is 8 ohms (WW resistive), and the rails are 65VDC on the mosfets (@400mA bias) and 80V on the LME.

Let's start with the way the waveforms looks at increasing distortion levels:

1. 1kHz waveform at 0.005% THD+N
2. 1kHz waveform at 0.1% THD+N
3. 1kHz waveform at 0.5% THD+N
4. 1kHz waveform at 1.0% THD+N
5. 1kHz waveform at 10.0% THD+N

[opc]

Next up we have zoomed in views of the previous captures. These were done on the positive rail only, and at 10V/div on the output and rail. Looks like I forgot to save the 10% one :S

1. 1kHz waveform at 0.005% THD+N
2. 1kHz waveform at 0.1% THD+N
3. 1kHz waveform at 0.5% THD+N
4. 1kHz waveform at 1.0% THD+N
5. 1kHz waveform at 0.1% THD+N with cursors showing 4.75V peak to rail delta
6. 1kHz waveform at 1.0% THD+N with cursors showing 4.75V peak to rail delta

[opc]

Lastly, I've got waveforms of 10% distortion at different frequencies:

1. 100Hz waveform at 10% THD+N
2. 1kHz waveform at 10% THD+N
3. 10kHz waveform at 10% THD+N

[opc]

My favourite one is the 150Hz 10% measurement as it shows what I suspect is the issue that npdot is seeing with his setup.

Here's my theory for npdot's setup:

Even with a 1kVA toroid and lots of capacitance, the rails will sag significantly under full power load. I get the feeling the cap bank has enough energy stored to maintain rail voltage nearly up to the peak at 1kHz, then starts to pull the rail down as the caps struggle to recharge and maintain the rail voltage, hence the non-flat top of the clipped output wave.

This seems to be further emphasized by the much lower clipping level at 150Hz where the capacitor bank won't do much at all, and the transformer is providing all the power through the peak. The 10kHz waveforms seem to be clipping at much higher voltage levels, further confirming that the huge cap bank is maintaining the rail voltage for the much shorter duration peaks at 10kHz, and the output is actually clipping into a rail that remains relatively stable.

All we need to do to confirm this is to get npdot to put one channel of the scope on the positive supply rail right at the amplifier PCB, and the other channel of the scope on the output right at the amplifier's positive terminal.

This will show us exactly what the supply rail is doing in an instantaneous manner as the output clips.

If it sags down and matches the shape of the clipped waveform, it will be exactly what I suspected above.

It will also be a free advert why regulated supplies are best

Cheers,
Owen

[qusp]

It will also be a free advert why regulated supplies are best

you know when this problem was posted, that was my first cheeky thought, not a wimpy unregulated supply either. great shots to analyze the problem mate! you too npdot! whatever the cause

everyone can see this, but just to be clear

My favourite one is the 100Hz 10% measurement as it shows what I suspect is the issue that npdot is seeing with his setup.

This seems to be further emphasized by the much lower clipping level at 100Hz where the capacitor bank won't do much at all

not 150Hz, you must have had npdot's results on your mind

[AP2]

Hello Owen, good measure! this is a right way of work.
OT:
Unfortunately many do not see these measures with different SMPS Unregulated, especially in a Class D amps.
end:
one test can be put at gnd, pin 8 of lme.