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Old 3rd February 2009, 02:52 AM   #21
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The current mirror is not a CCS for the zener, it turns the current around and buffers the load resistor, while still leaving a relatively low impedance in series with the zener for max loop gain. The bandwidth can be inferred from the response data given earlier. I don't know what the output noise is, but according to measurements done by other DIY members, a 30V zener is probably the lowest noise simple reference availabe.
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Old 3rd February 2009, 07:09 AM   #22
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BTW, I have contemplated unbalancing the resistors in the current mirror of my shunt regulator, leaving the 10 ohm in the half in series with the zener, but upping the series resistor on the other half to 50-100 ohms. This would force more current through the zener, lowering its noise and incremental impedance. Right now, the zener is running at ~1 mA quiescent current, which is a little low.
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Old 3rd February 2009, 06:04 PM   #23
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What about feeding the Zener with some 7-8mA ma or more, or less, using a jfet in idss mode, while keeping the CM balanced?
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Old 3rd February 2009, 11:58 PM   #24
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Not necessary - just change the values for the mirror resistors. I simulated the change last night, and the response tightens up, indicating lower output impedance. The results look so-so until you look at the vertical scale...
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Old 4th February 2009, 12:02 AM   #25
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And how many mA you feed that Zener now that the CM got asymmetry?
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Old 4th February 2009, 12:09 AM   #26
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I pushed the values to 4.7 ohms on the zener side and 100 ohms on the other. That gets me 10 mils through the zener and 1 mil on the other side - mind you, that's using my circuit with the extra PNP gain stage. Your mileage may vary.

10 mils is ok for a 1W zener like the 1N4751A. You'd want to push only 5 mils or so through a 500 mW part.
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Old 4th February 2009, 12:13 AM   #27
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True, with your extra gain stage, your approach is wise.

Cool.
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Old 4th February 2009, 12:22 AM   #28
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What is your hunch as to why simple, rather well done shunts are so noticeably better sonically to some of us on any audio application?
Yesterday a friend called me late at night to tell me that his T-Amp doubled its soundstage and fluency and kick in the lows, after he put together a 2.5A simple Mosfet shunt I designed him to try. Can all we be out of our heads? He lives across the south sea, does not listen to my stuff.
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Old 8th February 2009, 02:40 AM   #29
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Attached are left and right response curves for the preamp. The board came up without much trouble using a bench supply. Once I decide what shunt regulator I want to use, I'll build it on perf board and tack it on.
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Old 8th February 2009, 02:47 AM   #30
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Good gain mach between channels. Congrats.
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