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Help/Ideas for a complementary Mosfet class AB buffer

post #1 of 8
1/5/13 at 7:35am
Thread Starter 

I've spent a fair amount of time over the past week running various simulations with regards to constructing such a buffer with no output blocking caps and I have to say that I'm struggling due to the threshold voltage of mosfets - I haven't got a vbe multiplier to work properly yet.

I chose mosfets as I want a high Zi.

I'm gonna keep at it, but if anyone knows how to design such a thing I'd be grateful for a few pointers.

 

The other idea that I've had is to build a class A source follower and use a dc servo, is this feasible?

 

Any ideas on how to build a high Zi buffer that has no offset would be very welcome,

 

Cheers,

CHris

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post #2 of 8
1/5/13 at 10:14am

lookup the satri circuit which is usually 2 jfets and 2 more jfets, or bipolar, or mosfets.

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post #3 of 8
1/5/13 at 10:24am
Quote:
Originally Posted by kevin gilmore View Post

lookup the satri circuit which is usually 2 jfets and 2 more jfets, or bipolar, or mosfets.


Like this?

 

 

700

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post #4 of 8
1/5/13 at 1:04pm
Thread Starter 

If I were to cut that schematic in half, just before the LEDs and then take the output side, would that be completely idiotic? I simulated it in TINA using BC550/BC560 and if I'm shocked to say that, at 1kHz there's an input impedance of about 6Mohm which seemed surprisingly high, i thought that this was impossibly high for BJTs, so tell me then, where have I screwed up?

 

If i didn't get it wrong then this looks pretty brilliant.

Thanks for your help,

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post #5 of 8
1/5/13 at 5:03pm

http://www.diyaudio.com/forums/analogue-source/154210-mpp-266.html#post2699945

 

just the first stage.

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post #6 of 8
1/5/13 at 6:03pm
Quote:
Originally Posted by kevin gilmore View Post

http://www.diyaudio.com/forums/analogue-source/154210-mpp-266.html#post2699945

 

just the first stage.


Hey, I drew the schematic in post 2654!

 

My how things get around...

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post #7 of 8
1/5/13 at 8:02pm
Look here, too http://diy.ecpaudio.com/2012/11/black-diamond-headphone-amplifier-part-1.html

Part 2, which I hope to post sooner than later, uses JFETs on the input. Replacing the output devices with FETs is trivial.
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post #8 of 8
1/5/13 at 10:38pm

Or just watch the film Dr. Strangelove or: How I Learned to Stop Worrying and Love the Blocking Cap. biggrin.gif

 

se

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