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Old 5th October 2012, 05:16 PM   #1541
qusp is offline qusp  Australia
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Quote:
Originally Posted by BFNY View Post
This circuit is shown here, and discussed close to the end of the Audio Xpress interview with Walt Jung

WaltsBlog

Probably off topic here, but worth a new thread in the right place...
yeah I know, seen it, thats why I mentioned it there is already a thread here
which strangely hasnt gotten much attention, given the shunt anything, anytime, at any cost whether there is benefit or not trend that seems taking DIYA by storm. I just thought it might be interesting to bring it up so the 2 could be explored. if indeed we need very good regulation, it would seem to be pretty suitable for the voltages and currents involved.

but yes maybe keep conversation of the reg itself in the thread.
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Old 5th October 2012, 05:24 PM   #1542
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OK I was talking about the post #1380 circuit. Here's a plot of PSRR (at the output) at 20K vs source impedance when the feedback network is 1k,9k (20dB gain). Notice the suckout at exact source resistance match in the un-cascoded case.

This is with and without the J111 or depletion mode MOSFET cascode on just the two input devices. So without you need better supplies. The two devices I now would consider essential.

Does this make our results line up?
Attached Images
File Type: jpg psrr.JPG (63.7 KB, 321 views)
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Last edited by scott wurcer; 5th October 2012 at 05:27 PM.
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Old 5th October 2012, 05:53 PM   #1543
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Apologies Brad - dadod's sim in post 1455 references the complementary version of the circuit in post 1397. His were both done at G=21.

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Originally Posted by stinius View Post
PSRR

This is what I'm getting when simulating Scott's BF862 circuit with the buffer.
I have also attached the schematic I'm using, showing how I do the PSRR simulation. Maybe I'm doing it wrong?

Stein

G=1 does change it a bit but the cascodes appear to make all the difference.

And much like your post 1542 Scott, the pseudo complementary front end is better than the complementary version for PSRR. Looks just as flat in LTSpice, but even more optimistic for rejection.

Dave
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File Type: jpg SW-DOA pseudocomp_casc_negPSRR.jpg (144.7 KB, 302 views)
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Old 5th October 2012, 05:56 PM   #1544
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Quote:
Originally Posted by scott wurcer View Post
OK I was talking about the post #1380 circuit. Here's a plot of PSRR (at the output) at 20K vs source impedance when the feedback network is 1k,9k (20dB gain). Notice the suckout at exact source resistance match in the un-cascoded case.

This is with and without the J111 or depletion mode MOSFET cascode on just the two input devices. So without you need better supplies. The two devices I now would consider essential.

Does this make our results line up?
I was just about to ask about the effects of impedance match at the two inputs, for which this confirms the importance.
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Old 5th October 2012, 06:26 PM   #1545
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I've hit a little snag. It seems the external power device models don't work well in my simulator. It looks like a quasi-sat issue since the dynamic base currents have impossibly fast discontinuities. They look fine in LTSPICE but that means I have to use a personal computer to verify any high power circuits.
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Old 5th October 2012, 08:52 PM   #1546
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Quote:
General appeal: could people please reference a post # when referring to a design? It would burden things unduly to attach the schematic each time, but at least we can use the number and go back and confirm what we're talking about.
Yes PLEASE!

Quote:
SW BF862 with buffer.pdf (34.6 KB, 20 views)
Isn't this from #1380 which Scott has deprecated in favour of #1397 and also has missing traces?

Quote:
OK I was talking about the post #1380 circuit. (duu.uuh!) Here's a plot of PSRR (at the output) at 20K vs source impedance when the feedback network is 1k,9k (20dB gain). Notice the suckout at exact source resistance match in the un-cascoded case.

This is with and without the J111 or depletion mode MOSFET cascode on just the two input devices. So without you need better supplies. The two devices I now would consider essential.
Isn't this a consequence of using big geometry FETs on the i/p LTP?

You have similar effects with BJT LTP i/ps but much smaller ... especially if you use NPNs. I found this in a low feedback Power Amp design.

I'd still like to know why we are using FET i/ps.
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Old 5th October 2012, 10:44 PM   #1547
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Quote:
Originally Posted by kgrlee View Post
Yes PLEASE!

Isn't this from #1380 which Scott has deprecated in favour of #1397 and also has missing traces?

i/ps.
I just can't seem to stop confusing people. There are three circuits that simply display three common input stages. The rest of the circuit is the same. I had a problem with JPEG and noticed that the second one had all the connections intact, I hoped folks could connect the dots. My comment was just to point this out.

The #1380 circuit uses no hard to find parts and probably does everything needed. I need to add the cascodes and make a new definitive version. The second and third circuit have very high slew rates if that appeals to someone as important. Just trying to show how versitle some simple ideas can be.
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Old 5th October 2012, 11:04 PM   #1548
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Originally Posted by kgrlee View Post
I'd still like to know why we are using FET i/ps.

FET's simply have a much larger linear input range for the same gm (hence noise level). The GBW vs slew rate is also much more favorable with FET's.
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Old 5th October 2012, 11:37 PM   #1549
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Originally Posted by scott wurcer View Post
I just can't seem to stop confusing people. There are three circuits that simply display three common input stages. The rest of the circuit is the same. I had a problem with JPEG and noticed that the second one had all the connections intact, I hoped folks could connect the dots.
Anyone have a fully corrected version of #1380 with missing traces re-instated? Maybe even an LTSpice model. It appears Scott is concentrating on developing this version.

Also of #1397 please?

Those of us with small brains have difficulty with connect the dots.
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Old 6th October 2012, 12:06 AM   #1550
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OK, I'm doing a version of the n FET version in #1380 right now, for LTspice. Working, but some funnies with the bipolars so far; give me a chance to check a few things first ...

I'll be calling that version SW-OPAn, the other SW-OPAc, unless someone has a better thought ...

Frank

Last edited by fas42; 6th October 2012 at 12:10 AM.
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