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Old 20th February 2013, 07:50 PM   #1761
FdW is offline FdW  Netherlands
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For me this works
http://measure.feld.cvut.cz/usr/staf...%20TESTING.pdf
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Old 20th February 2013, 08:12 PM   #1762
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by FdW View Post
You can also Google in the title and see it and others.
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Old 21st February 2013, 11:27 PM   #1763
RNMarsh is offline RNMarsh  United States
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I have been searching for a ShibaSoku signal generator to no avail. Meanwhile I picked up an H-Hite 4400A and a 4402B generator.... for IM tests. Might see if they can be lowered in THD also. After I measure them with ShibaSoku 725D analyzer. BTW - before the QA400 left this cold place for somewhere warmer in the universe -- the null used on the 725D appeared to be at least -150dB. !!

Thx-RNMarsh
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Old 21st February 2013, 11:41 PM   #1764
klewis is offline klewis  United States
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Quote:
Originally Posted by RNMarsh View Post
I have been searching for a ShibaSoku signal generator to no avail. Meanwhile I picked up an H-Hite 4400A and a 4402B generator.... for IM tests. Might see if they can be lowered in THD also. After I measure them with ShibaSoku 725D analyzer. BTW - before the QA400 left this cold place for somewhere warmer in the universe -- the null used on the 725D appeared to be at least -150dB. !!

Thx-RNMarsh
I have a kh4402b, manual has a simple proceedure for adjusting/tuning. I would be interested in any improvements beyond tuning. Please keep us posted.

Ken
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Old 21st February 2013, 11:52 PM   #1765
1audio is offline 1audio  United States
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I tweaked mine and got a substantial improvement on the second harmonic. I have been reluctant to change parts since its quite good. The harmonics were all below -110 dB I believe.

I added the injection lock and that really helps the close in phase noise when locked from a clean source. Too much and the harmonics start going up. I'll find the notes I made and post them if anyone is interested.
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Old 22nd February 2013, 12:31 AM   #1766
RNMarsh is offline RNMarsh  United States
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Hi Demian, The stock 4402B specs out as below -120. The 4400 is less... is that the one you modified ?

In either case, it would be good to know how you tweaked the 2H down.

-Richard
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Old 22nd February 2013, 01:16 AM   #1767
richiem is offline richiem  United States
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A quick look at the 4400 and 4402 schematics shows a very low Q tuning filter, so the goodness of low harmonics has to mostly come from the high-gain, but well-bounded JFET AGC system, and good parts. Hard to believe that LM318s can work as well as they seem to do.
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Old 22nd February 2013, 02:31 AM   #1768
1audio is offline 1audio  United States
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All I did was connect it to Shibasoku and adjust the distortion trim. Watching the 2nd H makes it really simple.

The LM318 looks simple but the active load is more than a simple current source. And that is why I did not want to just swap opamps in and out. And it was all working.
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Old 22nd February 2013, 06:00 PM   #1769
RNMarsh is offline RNMarsh  United States
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It appears from the schematic that to get the 318 IC to have its lowest possible thd, it is very lightly loaded.... low currents and light load on the output etc. -RNM
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Old 23rd February 2013, 06:15 AM   #1770
RNMarsh is offline RNMarsh  United States
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Default K-H 4400A

Just for the heck of it, I put in a socket and changed opamps for the oscillator IC in a K-H 4400A. I monitored the output with a 300Mhz scope. Some didnt work well at all.... the LM49710 didnt like the circuit values, i suppose... distortion was much higher than others. BTW - I had to replace the distortion null pot from 500 to 1K Ohms to get the range needed to null some of the other opamps I tried.
The LM318 has pretty low thd across the board but a lot of harmonics.... odd and even. The LT1468 was near the floor of -145dB --- about -130-135 everywhere except a high 3H. [Relatively high at -125dB].

This is a quick way to find out how your favorite opamp looks with its harmonic structure.... Testing is at no load for now -- 1Khz fundamental used. Residual taken from the ShibaSoku 725D (QA400 was doing this fine but it quit on me. I'm back to the analog HP until I can get QA400 working again).

LM318.jpg

LT1468.jpg

Last edited by RNMarsh; 23rd February 2013 at 06:30 AM.
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