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Old 14th March 2009, 12:11 AM   #221
Salas is offline Salas  Greece
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See about C1
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Old 14th March 2009, 03:56 AM   #222
jwb is offline jwb  United States
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Regarding again post #214, I find the performance to be measurably superior with the 2k resistor instead of J2. With a triangular 600Hz ripple on the input, the ripple rejection is 65dB with the JFET and 71dB with the resistor. This is measured, not simulated.

Note that this compares unfavorably with LM317. The performance deficit could be chalked up to breadboarding technique, perhaps. Frankly I'm surprised the patient even survived

Wideband output noise is impossible for me to measure. In simulation it's about 1nV/rthz.

Here's what happens when a fast glitch come in on the input rail. It passes right through with some ringing.
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Old 14th March 2009, 04:07 AM   #223
jwb is offline jwb  United States
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OK actually that ringing was an artifact of my probe. Here it is with a real probe.
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Old 14th March 2009, 04:09 AM   #224
Bonsai is offline Bonsai  Taiwan
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Have you tried removing C1 and then repeating the experiment? I get the feeling that there is some inter dependance between the value of R4, C1 and J2 - i.e. the values have to be selected carefully. I read Jung's notes - I would not have guessed adding th e cap would have improved performance - looks counter intuitive, but, you can not argue with his measured results.

J1 and J5 are also interesting features on this circuit. What is the function of J1, rather than a higher value for R5?
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Old 14th March 2009, 04:25 AM   #225
jwb is offline jwb  United States
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I don't think J1/R5 is a good idea. I'm using a 2-terminal 1.4mA current source there instead.

As for C1, I don't understand it either. In practice it makes ripple rejection worse (e.g. 4dB worse at 30Hz).
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Old 14th March 2009, 05:08 AM   #226
iko is offline iko  Canada
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Quote:
Originally posted by jwb
Regarding again post #214, I find the performance to be measurably superior with the 2k resistor instead of J2. With a triangular 600Hz ripple on the input, the ripple rejection is 65dB with the JFET and 71dB with the resistor. This is measured, not simulated.
We're very fortunate to get real results like these. I'm curious though, how do they compare in the critical region of 50 to, say, 180Hz? For those in North America 60 and 120 Hz will be very important, as is 50 and 100 for those how get that on the utility line.

Quote:


Note that this compares unfavorably with LM317.
This would be surprising and disturbing, because the lm317 does not come anywhere near this regulator, as I have it working here. Perhaps I made a mistake somewhere when using the lm317.
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Old 14th March 2009, 05:11 AM   #227
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Quote:
Originally posted by jwb
OK actually that ringing was an artifact of my probe. Here it is with a real probe.
I'm a bit confused. Is the upper trace the one with the resistor, or the one with the jfet?
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Old 14th March 2009, 05:29 AM   #228
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Quote:
We're very fortunate to get real results like these. I'm curious though, how do they compare in the critical region of 50 to, say, 180Hz? For those in North America 60 and 120 Hz will be very important, as is 50 and 100 for those how get that on the utility line.
Unfortunately because of the way I am generating the ripple with a 555 timer, I'm not at liberty to dictate the ripple frequency. The closest I can come is 160Hz, where the rejection appears to be 75dB (400mV RMS ripple on the input, 70uV RMS ripple on the output.)

Quote:
I'm a bit confused. Is the upper trace the one with the resistor, or the one with the jfet?
In both scope pictures, the upper trace is the output at 50mV/div and the lower trace is the input at 500mV/div. Both circuits were using the resistor rather than the JFET.
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Old 14th March 2009, 05:34 AM   #229
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Coincidentally, it is also a Theremin.
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Old 14th March 2009, 05:48 AM   #230
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Quote:
Originally posted by jwb


Unfortunately because of the way I am generating the ripple with a 555 timer, I'm not at liberty to dictate the ripple frequency. The closest I can come is 160Hz, where the rejection appears to be 75dB
160Hz ok. If I understand correctly, the 75dB is for the resistor version. If it's not too much trouble, would you please try this with a jfet (best of 7-8 mA Idss)? I need to know if I should throw the simulator in the garbage. I'd try this test, but I can't yet measure uV


Are you using the Dennis Colins noise amp for measuring uV?
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