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Old 12th January 2013, 02:36 PM   #1551
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Has the EDN 11.10.94 issue for an oscillator design which has THD below 1 ppm been tried by someone we know? authored by Jeff Smith at Analog devices.
As far as I know that's the one Scott Wurcer has co-designed...

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I'm wondering if we could drop the distortion in the notch filter more by using a multiplier with current output in place of the phase controlling LDR. AD has one that has 50 nV/rootHz voltage noise. The 633 I think would be too noisy at 0.8 uV/rootHz.
Careful with too early conclusions; while the AD835 (which is the part you think of I presume) has lower output noise than the AD633, it also has much lower output voltage swing--about 10x lower. So in the end, the usable dynamic range of both parts is pretty similar. For a more detailed comparison you'd need to compare distortion (at an equivalent level above the noise floor) too. Can't predict the exact result, but in any case the THAT2181 multiplier I've posted earlier in this thread will be much better.

Samuel
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Old 12th January 2013, 05:02 PM   #1552
davada is offline davada  Canada
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Originally Posted by Samuel Groner View Post
As far as I know that's the one Scott Wurcer has co-designed...



Careful with too early conclusions; while the AD835 (which is the part you think of I presume) has lower output noise than the AD633, it also has much lower output voltage swing--about 10x lower. So in the end, the usable dynamic range of both parts is pretty similar. For a more detailed comparison you'd need to compare distortion (at an equivalent level above the noise floor) too. Can't predict the exact result, but in any case the THAT2181 multiplier I've posted earlier in this thread will be much better.

Samuel
Okay. x10 we end up with about the same amount of noise after amplifying to restore the DR. The supply is chopped as well from +/-18V to +/-5V

I'll look at the THAT part again.
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Old 12th January 2013, 06:07 PM   #1553
RNMarsh is offline RNMarsh  United States
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Originally Posted by dennismiller55 View Post
For all the discussion on the HP339 over the last month I am confused as to what mods have been done and which ones resulted in beneficial improvements. Before everyone abandons this part of the topic, can someone please outline these mods up to this point?

I have been looking for a deal on an HP339. When I finally land one I am sure I would like to make these improvements. Even though the theory behind some of the mods is over my head, I feel that I am capable of implementing any of the improvement modifications if they are clearly defined.

I do want to thank everyone for this discussion. I did pick up some knowledge and enjoyed following it.

Thanks!
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Old 12th January 2013, 06:17 PM   #1554
RNMarsh is offline RNMarsh  United States
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Default Summary -

For all those thinking of using an HP339A and want to improve it:
I just looked at a similar project by Dick Moore. He copied the 339A oscillator circuit and put it into another existing chassis. Didnt use the 339A analyzer section. If you go to his site, you will get a well written, detailed summary of what to do on the oscillator ... it is the same excercise I/we did with same findings. The idea to use an existing chassis helps a lot in the building of the beast.

Then do similar changes with IC's in the analyzer section as we described in this forum plus upgrade trimmers/ electro type caps as I did and the analyzer will be good for another 20dB+ or to well under .001%.
[ D.Moore includes plenty of FFT distortion plots to show the progress. www.moorepage.net/IG-18-3.html ]

Enjoy !

-RNMarsh

Last edited by RNMarsh; 12th January 2013 at 06:34 PM.
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Old 13th January 2013, 04:49 AM   #1555
Simon B is offline Simon B  United Kingdom
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Very interesting, thanks for posting the url.

Dick Moore has worked on four different IG-18 oscillators, and put up details of each of them. They make an interesting set, his index page is at Home -- article index

Count your blessings for having had Heathkit. Swingeing import duties in post-war britain made them very expensive on this side of the pond, and they're very rare indeed now.
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Old 13th January 2013, 04:54 AM   #1556
richiem is offline richiem  United States
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@Simon B -- My former boss, mentor, and friend Paul Klipsch used to quote the same dictum, using two dollars and two hundred -- Does the current exchanger rate make that come out about even?
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Old 13th January 2013, 07:17 AM   #1557
davada is offline davada  Canada
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@Simon B -- My former boss, mentor, and friend Paul Klipsch used to quote the same dictum, using two dollars and two hundred -- Does the current exchanger rate make that come out about even?

LOL.

I think the Brits have us beat. Even the fools are doing better.
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Old 13th January 2013, 09:56 PM   #1558
DDB is offline DDB  United States
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Does anyone know the distortion of Victor's oscillators at 1Khz and also at 10Khz? Demian did you test yours with the Shibasoku or spectrum analyzer? Larry
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Old 13th January 2013, 10:06 PM   #1559
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Victor's oscillators have proved to be as specced or better.
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Old 13th January 2013, 10:37 PM   #1560
1audio is offline 1audio  United States
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Victor's oscillators measure as specified or better. For a fixed frequency it is by far the best choice. You can't get the parts for the price.
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