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Old 23rd January 2013, 09:40 PM   #1581
1audio is offline 1audio  United States
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That is exceptional. Looks like you won't need my AG16 for long.

If you have a spectrum analyzer you can connect it to the distortion monitor and see all the harmonics. It doesn't need much dynamic range or frequency range either.
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Last edited by 1audio; 23rd January 2013 at 09:44 PM.
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Old 23rd January 2013, 10:14 PM   #1582
Telstar is offline Telstar  Italy
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Originally Posted by 1audio View Post
I still think Victor's oscillators are the best deal. Contact him here: viccc at ml dot lv Anything else will be a lot of work and probably not as good.
doh! I thought the brand was Chinese

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A QA400 will do a fine job of analyzing and is a real value for the price. However its limited to 1V in and not much more out. I'm working on an interface to make it more useful but got sidetracked by real work.
How much output? Can or cannot produce a 2,83V signal?
I don't remember anything wrt this in their specs...
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Old 23rd January 2013, 11:47 PM   #1583
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Not RMS -- 1VRMS is essentially full output for QA400.
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Old 24th January 2013, 12:43 AM   #1584
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Default Hyper-Tuned

Quote:
Originally Posted by 1audio View Post
That is exceptional. Looks like you won't need my AG16 for long.

If you have a spectrum analyzer you can connect it to the distortion monitor and see all the harmonics. It doesn't need much dynamic range or frequency range either.
Hi Demian --- Do you have a schematic for the AG16 that I could look at?
Working on the FFT part.... Thx-Richard

Last edited by RNMarsh; 24th January 2013 at 12:46 AM.
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Old 24th January 2013, 06:19 AM   #1585
1audio is offline 1audio  United States
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No schematic. Have not found a source. Perhaps we should buy a manual or two.

The FFT requirements are simple since it converts everything to 420 Hz or so, so even the tenth harmonic is only 4 KHz. You could even use an ipod-iphone spectrum analyzer app.
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Old 24th January 2013, 11:21 AM   #1586
Telstar is offline Telstar  Italy
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Originally Posted by richiem View Post
Not RMS -- 1VRMS is essentially full output for QA400.
Looks like I have to look elsewhere, thanks. I need to test power amps with standard input signal (2V or 2.83V).

I followed the thread a bit at the beginning, then got lost and i'm following again... Richard, do you plan to use the spectrum analyzing function of the 339A somehow?
Otherwise my best bet is to go for the 239A and do the mods there, is smaller and cheaper (I have limited bench space). Or should I shell the money for a Krohn-Hite 4400A?

My goals are sub-ppm @50hz, 1khz and 20khz.
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Old 24th January 2013, 12:28 PM   #1587
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I painstakingly worked adjusting my KH4402:

Click the image to open in full size.

I've posted it once before, but misplaced the jpeg.
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Old 24th January 2013, 03:41 PM   #1588
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Default HP339A list of changes

I recall someone stating they would post a detailed list of changes made to the 339A to improve it. Did I miss it?

I suppose I could re-read several hundreds of posts to try and sort it out but a post detailing the oscillator section changes in one place would be useful if it has not been done yet. The oscillator as shown by results of RNMarsh seems finished.

I recall he has said he changed some IC's, filters, trimmers, pots.

Which IC's and with what etc? Did the jfet get changed or anything in the AGC/jfet circuit besides adding a 2ndH nuller?

Did the lo-pass/hi-pass filter IC in the analyzer get changed? Did it help?

Thanks, Larry
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Old 24th January 2013, 05:06 PM   #1589
RNMarsh is offline RNMarsh  United States
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Originally Posted by Telstar View Post
I followed the thread a bit at the beginning, then got lost and i'm following again... Richard, do you plan to use the spectrum analyzing function of the 339A somehow?
Otherwise my best bet is to go for the 239A and do the mods there, is smaller and cheaper (I have limited bench space). Or should I shell the money for a Krohn-Hite 4400A?

My goals are sub-ppm @50hz, 1khz and 20khz.
There are other oscillators that start out very low in harmonics to attempt improvments on (such as the K-H). The 339A has an analyzer included which can have similar things done to it to keep the total unit useful. You can measure THD+N a tad below -100. And, I have used an FFT (HP) with it to see lower... could use any PC-FFT as well to see the individual harmonics levels.

The other route is to buy just an oscillator and use it with a PC, FFT software and an ADC. As Demian has noted, this route often has limited input level acceptance and thus an interface is sometimes needed. He is working on one and will present it here... so add that to the list. The HP accepts up to 300V rms with its built-in attenuator.

I havent had much luck finding ultra low distortion generators at low cost. The exception are the two fixed freq osc. pcb/modules by Victor - sold on eBay. I am sure ultra-low thd osc. can be obtained but they never were wildly popular and now used ones are getting even harder to find. I have been looking for the AG16 from ShibaSoku with no luck. The 339A is not hard to find at low cost.

To get even lower numbers, you need to add notch filters to the osc. 2h and 3H. Also, the oscillator from others have been published and which I showed (single freq) a few dozen pages back will go to a claimed -140 or more. Not avail as a completed product... you'll have to make your own pcb etc.

Thx-RNMarsh

Last edited by RNMarsh; 24th January 2013 at 05:21 PM.
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Old 24th January 2013, 05:09 PM   #1590
RNMarsh is offline RNMarsh  United States
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Originally Posted by jackinnj View Post
I painstakingly worked adjusting my KH4402:

Click the image to open in full size.

I've posted it once before, but misplaced the jpeg.
Very good! Might make a good mod article -- were can one find a used KH4402?
You could notch that '1' digit out with a passive twin-T. :-)

Last edited by RNMarsh; 24th January 2013 at 05:23 PM.
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