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Old 2nd January 2013, 09:08 PM   #1441
davada is offline davada  Canada
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Quote:
Originally Posted by Samuel Groner View Post
Have you tried it? Even with several percent amplitude mismatch output ripple is likely still much lower than for an average or RMS detector (with the same filtering). And you can easily trim the amplitude match for each range.

The S & H peak detector is cleary better, but also more difficult to implement right.

Samuel
I have a pair of AD RMS detectors coming from Scott. The output ripple from these IC's is the square of the input. If I use one on the output and one on a quadrature output I can sum the two together and null the ripple. This can be done with the currents before filtering so no
summing amplifier is required, then follow it with the internal buffer(s). This should be interesting to try.
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Old 2nd January 2013, 09:15 PM   #1442
davada is offline davada  Canada
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This is the output of the RMS detector for the auto set level in the 339A.
1KHz input at 1Vrms and 1Vdc output.

I can live with this but it not as good at lower frequencies.
This can be corrected with more filtering.
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Old 2nd January 2013, 11:37 PM   #1443
RNMarsh is offline RNMarsh  United States
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Lets do more filtering first and see what happens. Thx-RNM
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Old 3rd January 2013, 12:38 AM   #1444
davada is offline davada  Canada
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Lets do more filtering first and see what happens. Thx-RNM
Sure. But with two of these I can really go to town.
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Old 3rd January 2013, 02:09 AM   #1445
davada is offline davada  Canada
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This is the same frequency and voltages as with the optical sensor.
This is with an LDR.

Worse than the optical sensor.

I think I'll move on.
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Old 3rd January 2013, 08:01 PM   #1446
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OK just confirmed that the cap is necessary with the photovoltaic/JFET method and was able to trim the seconds into the noise with it (.033uF). I am using a bridge technique comparing a perfect resistor attenuator to one with the FET. I'm nulling a J310 against 100 Ohms with about .5V p-p across the FET (I assume this is too much). What are good numbers to take a measurement at?
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Old 4th January 2013, 12:15 AM   #1447
davada is offline davada  Canada
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Originally Posted by scott wurcer View Post
OK just confirmed that the cap is necessary with the photovoltaic/JFET method and was able to trim the seconds into the noise with it (.033uF). I am using a bridge technique comparing a perfect resistor attenuator to one with the FET. I'm nulling a J310 against 100 Ohms with about .5V p-p across the FET (I assume this is too much). What are good numbers to take a measurement at?
Hi Scott,

The 339A Jfet has about 50mVpp Vds.
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Old 4th January 2013, 05:29 AM   #1448
RNMarsh is offline RNMarsh  United States
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davada -- pls give source and make/model/part number info for that level control pot (10K) you replaced -- repaired. Mine has some worn spots in it that cause thd to rise when you hit them. Thx-RNM
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Old 4th January 2013, 02:16 PM   #1449
davada is offline davada  Canada
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davada -- pls give source and make/model/part number info for that level control pot (10K) you replaced -- repaired. Mine has some worn spots in it that cause thd to rise when you hit them. Thx-RNM
51SAD-U25-A15L-ND

Digikey
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Old 4th January 2013, 02:59 PM   #1450
davada is offline davada  Canada
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51SAD-U25-A15L-ND

Digikey
This pot is very smooth and quiet.
You will have to cut the shaft down.
I loosened the coupler for the shaft extender of the 339a osc and spun the nut off the old pot
to get it out. No need to remove the knob.

Cheers,
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