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Old 14th January 2008, 08:57 PM   #41
CBS240 is offline CBS240  United States
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OK

Now for a few latest waveforms...

The top left is a 300KHz square wave at 10Vp per phase. bottom left is a 400KHz sine wave, Ch 2 is inverted and added to Ch 1 so this is what you see across the speaker. Top right is 100KHz both phases and bottom left is the same, just showing the sum across the load.
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Old 14th January 2008, 09:01 PM   #42
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This one I like. Check out the low frequency responce...well into the sub-sonic. This is a 20 cycle square wave. The top is the input, and the bottom is the output, 2.5A. Notice how little degeneration the signal suffers.
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Old 14th January 2008, 09:07 PM   #43
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This is a larger scale of the 20 Hz square wave. This is 20V peak on 8 Ohms. I nearly burned up the resistor I used to test this one, and with the 300KHz square wave, left it on too long and kinda burned my finger. Next I will test the 20 Hz square wave with a speaker and see what the reactive load throws into the mix.
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Old 15th January 2008, 08:08 PM   #44
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It was too late yesterday to crank out up a speaker with low tones, but here is 18 Hz square wave driving a 4 Ohm sub, 10V peak. The time base is 10mS, so the shutter of the camera caught a double trace, But you can see the shape well. There is a little bit of overshoot, but man, that cone was movin'. It sounded like a badly muffled car engine.

I think the amp would drive a lower impedance as is, with a more beefy power supply. The problem is there are only 4 TO-220 outputs. They are quite rugged for their size, but I doubt they could do much more than 100W RMS due to SOA, even with an oversized heat sink. However, I see no reason why I can't use larger devices. This way I won't have to match mosfet transistors. It is nice to be able to just take one out of the package, slap it in the circuit and it works perfectly because the circuit operation is not dependent on specific parameters of a particular device. Since they are essentially in series, they require no matching.

That bit about not having to use a speaker relay is quite step. I would never have expected this circuit would have no DC output misbalance to the speaker when the power is switched on or off. A completely accidental discovery. I was planning to use a couple of UPC1237's or equivalent to drive a relay, which I would still have to find and experiment with. This puts me much closer to making the PCB a reality.
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Old 1st February 2008, 08:05 AM   #45
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Complicated? Naw, ....well maybe just a wee bit. The output's are for TO-220 OR TO-3P. The pads at B+/B- (25V) are for fuse holders. Was thinking of the 3557-2

TO-126 horizontal parts are the Vbe multipliers/EC.
The TO-126 vertical parts are the drivers, and the ones with 2 leads are Caddock resistors as output source resistors. It looks like it all runs together, but there are actually seperate circuit sections, somewhat symetrical.
My rules for the 201 size SMD resistors are, no more than 20V and no more than 20mW. There are many here but most are just a few mW. I derate the SOT-563 parts to 100mW although it is less in this circuit. I think there are two that are at 50mW, the rest are less. These things are great for CCS, among other things because they take very little space for two descrete transistors. The whole circuit will use no more than 30mA, excluding the channels of the output mosfets. If it works as good as the Frankenstien circuit I have now, all the hours spent will have been worth it. Still many design checks to make yet...


EDIT:

TOP
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Old 1st February 2008, 08:14 AM   #46
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The outputs are on the bottom side and will mount to a bracket, just like the Frankinstien circuit does.





BOTTOM
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Old 1st February 2008, 08:20 AM   #47
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BOTH
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Old 5th February 2008, 09:41 PM   #48
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Default Triangle and clipping

Here are some triangle waveforms along with hard and soft clipping on the load at 50KHz. At hard clipping, the output stage(s) actually decrease bias into class B operation, so there is some crossover components, but it has to be continously driven into hard clipping for this to happen. In spite of the complexity, this seems to be the most stable amplifier I've made yet.
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Old 5th February 2008, 09:44 PM   #49
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And 100KHz triangle...



Now, if I can only scrape together the funds to finish the PCB.
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Old 5th February 2008, 10:21 PM   #50
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Default Interesting... very interesting!


thank you to keep us informed related your researches.

regards,

Carlos
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