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allfet circlotron
allfet circlotron
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Old 22nd May 2016, 04:53 PM   #1
kees52 is offline kees52  Netherlands
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Default allfet circlotron

Hi All


X ask me to post it here, so I do, some ideas behind it because I have simmed it only, but measures nice. distortion test in 4 and 8 ohm.

Maybe nice for a power J-fet .

regards
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Old 22nd May 2016, 05:05 PM   #2
xrk971 is offline xrk971  United States
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allfet circlotron
Thanks Kees!

Can you please give ratings and specs? Bias current, max power, suggested VA rating on power supply, etc?

Also, the schematic looks clipped - can you post full schematic?
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Old 22nd May 2016, 05:47 PM   #3
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Is DC offset a problem? I ask that because there is no DC blocking capacitor is series with R10 feed back loop.
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Old 22nd May 2016, 06:11 PM   #4
kees52 is offline kees52  Netherlands
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hi X

I have not yet build this, with two mosfets IRFP240 I think 100 watts is possible in 8 ohms, there are some things who has to be done, a temp sensitive resistor for the irp 240, I think idle go run away, with 2sk1058 however this is not the case (enhanced).

2 x 65 volts, normally the driver needs 8 volts extra for driving the mosfet output stage as it are source followers, but I think this is not so important with these aready high voltages,

The VA rating is for us diy people not difficult, 2x 65 volts 10/15 amps will do plenty it is just what you need.

But the second schematic without a circlotron is just as good and more save to have no voltage on output as a circlotron has, as a quasy kind amp.

regards
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Old 22nd May 2016, 06:19 PM   #5
kees52 is offline kees52  Netherlands
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Quote:
Originally Posted by JonSnell Electronic View Post
Is DC offset a problem? I ask that because there is no DC blocking capacitor is series with R10 feed back loop.
As with simulation there is not loop, it stays stable.

Have some changes in schematic, the pot on the j fets do setup offset who do nicely. I remove the other feedback loop, do not now precisely of this is really needed tie output together with two resistors give a wrong fase for the feedback and make it a oscillator, (a really good class d).

I do like current feedback more, because of better sound, I go look if it can be implemented with other schematic, do it over again.

regards
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Old 22nd May 2016, 06:25 PM   #6
Ketje is offline Ketje  Belgium
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Well, I think there are problems.
The bias current of the output stage is not stable.
By adjusting R24 the voltage for the gates of the output fet's are jumping from one end to the other.
The 680 ohm resistors probably limit the excursion but is that good ?(big drop in loopgain)
Also missing is an offset adjust.
Using just fet's is amusing but no very practical.
Mona

Last edited by Ketje; 22nd May 2016 at 06:32 PM.
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Old 22nd May 2016, 06:31 PM   #7
xrk971 is offline xrk971  United States
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I think the Circlotron topology - offset is actually what drives the speaker as there is no "ground" on the load. It is floating ground so what offset are you referring to?

I think the goal is balanced outputs from the output stage drivers. Balancing them is balancing the IPS.
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Old 22nd May 2016, 07:07 PM   #8
kees52 is offline kees52  Netherlands
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Quote:
Originally Posted by xrk971 View Post
I think the Circlotron topology - offset is actually what drives the speaker as there is no "ground" on the load. It is floating ground so what offset are you referring to?

I think the goal is balanced outputs from the output stage drivers. Balancing them is balancing the IPS.
Hi X


If there is no ground, do not mean there is not a offset. and for the idle current, yes this can be a problem, special with the vertical mosfet, but maybe also the drivers, so need a correction, maybe a temp resistor of low omage on top of drivers.
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Old 22nd May 2016, 07:22 PM   #9
kees52 is offline kees52  Netherlands
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Quote:
Originally Posted by Ketje View Post
Well, I think there are problems.
The bias current of the output stage is not stable.
By adjusting R24 the voltage for the gates of the output fet's are jumping from one end to the other.
The 680 ohm resistors probably limit the excursion but is that good ?(big drop in loopgain)
Also missing is an offset adjust.
Using just fet's is amusing but no very practical.
Mona
I think also you are quite right, what concerns my math knowledge it do short circuit.

But nice to play, what concerns the 680 ohm resistors, I have to look at if differently I go need to do a circlotron compound like amp, with extra drivers in the circlotron itselfs, the low ohms and a source follower do not work well, but when use a drain follower things change a little, here I need mucho less swing from the driver, but get trouwble with capasitance and miller

The offset I did with a pot between the j fets at input changing balans of them..

regards and thanks for thinking with us.
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Old 22nd May 2016, 11:32 PM   #10
xrk971 is offline xrk971  United States
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allfet circlotron
Kees,
When you are ready, make a PCB design and I will build it. Looks very simple so far.
Thanks,
X

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