Dx Blame MKIII-Hx - Builder's thread

[a.wayne]

Martin,

It appears he is saying his has no sticking and he is running different gate stopper values from you and it looks like no diode ..

Did you try with different gate stopper value on the bench or sim ...

[canonnica]

Look at his scope traces, sticking is visible. Stop-resistor value changes nothing on sticking at the bottom or "denting" the downward slope at clipping in the simulator. Stop-resistor only prevents the positive-side ringing.
Martin.

[bonfis]

Originally Posted by canonnica

Look at his scope traces, sticking is visible. Stop-resistor value changes nothing on sticking at the bottom or "denting" the downward slope at clipping in the simulator. Stop-resistor only prevents the positive-side ringing.
Martin.

Martin is correct. I have sticking although it looks less dramatic than his. I accept that this probably has little to do with the stopper resistors. My version has other differences from the original MK III including a larger feedback factor and different input stage degeneration resistors. I don't know if these differences are likely to be relevant to the current problem. Perhaps one of our more technically astute thread watchers could weigh in on that issue.
Steve

[canonnica]

As suggested by Vostro, I've clamped the Miller cap and now rail sticking is gone. Here are some scope traces that shows some nice curves under normal conditions as well as during clipping and hard clipping.

Frequency and amplitudes are shown on the graphs. Don't worry about the ripples visible on the traces, I think I have a parasitic problem into the scope...

For thse who doesn't like the square waves, note that these tests have been made at 40v p-p.

Even under hard clipping, never the amp has gone into oscillations, so that's good. I also join the exact schematic of the amp tested. The load was a 6r/300W resistor. The bias was set at 16mV between two output resistors.

BTW, I burned my speaker protection relay, under heavy clipping at 20KHz, the speaker-prot has triggered... and the contacts went into smoke (D'UH).

Enjoy!

[destroyer X]

Clamping diode...good...i am glad to know.

regards,

Carlos

[Vostro]

Originally Posted by Vostro

If you not satisfied, then try to add C9 as in my drawing

Hi Canonnica, if you dont mind would you try the 1nF capacitor too,
I'd like to know if it affects the positive slope behaviour,

Again, I'm not sure, but interested .

Regards

[canonnica]

Vostro, I tried multiple values and it changed nothing in the simultator. sorry, I don't have any clue about it. A lot of search on forums and a lot of combinations in the simulator led me to nowhere... We'll have to understand by ourselves.

Maybe you're gonna discover what we'll one day call the "Vostro capacitor" or the like, eheheh.

Cheers.

[destroyer X]

"the other side of the fence"...is excellent...will be another "miller" for our lives.

aahahahahahahah!

Carlos

[a.wayne]

Deh 20k squarewave ...err, ahhh, well it looks razor sharp ...


Martin, how is the generator output at 20k ... ?

[canonnica]

...square. It's a 0-2MHz generator