Sorry Rick I quoted the wrong part number. It's the LME49710HA metal can.
I did try a 1468 with the LME49600 and got exactly the same results so I didn't see the point in using the LME buffer and went back to the LME49710HA.
I had the opposite effect of a reduction of 3rd H when changing the level vernier pot to the Bourns cermet from what you found.
If we can't get consistency with these changes then they're are not worth doing.
It is pretty consistent. However, one can trim for lowest H2 or lowest H3 or null on the thd number. I null on THD. But if you null on 1KHz you get higher thd at 10KHz.... but if you had nulled on 10Khz, the distortion is higher at 1Khz ..... Much of this is all about the tolerances of the R and C being switched.... they only used 1% parts... or 2% total deviation when switching decades or range etc. One percent is OK for the frequency but for nulling at -110db and below the trim changes enough. Right now, I dont want to select 0.1% caps and buy 0.1% R's. If I did, the freq changes will stay at lowest trimmed thd value everywhere.
Anyway, the pot change is like the other trimmers and electro cap upgrades... drops distortion some more. -Thx RNMarsh
Anyway, the pot change is like the other trimmers and electro cap upgrades... drops distortion some more. -Thx RNMarsh
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Hi Rick,
The loop gain changes with frequency so the gate voltage and Jfet R has to be changed to compensate this. This is why the distortion is different at 10KHz if the oscillator is tweaked for 1KHz. If you tweak for 10KHz then it's wrong for for 1KHz. Aside from other fundamental reasons like lower open loop gain at higher frequency. No doubt the components contribute to this but not this much. All this was discussed in earlier posts.
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One use of the LME49600 (and BUF634) inside of the feedback loop with an otherwise ordinary opamp is to enable a designer to drive a lower impedance feedback network to reduce total noise. So, not much benefit will be evident by using the buffer in an existing circuit unless the original design was driving an exceptionally low load (ie, it was a bad design).
339A -
I expect some relaxing of the thd spec at higher freq but this is a 100KHz instrument... dont expect to see much at 1/10th that. Phasiness perhaps affecting maintaining deepest null across the board... decades and tenths of the dials. Actually, what I was refering to behaves more like loose tolerance parts. I dont want anyone to get the idea these are big differences -- I can stay under .001% from 100-10KHz. THD+N.
Meanwhile ... today my 339A has crapped out!!!! Puts out a continuous 256Hz rather than 1Khz. Now what?!? Into trouble-shooting mode for awhile. When i get it up and running again, I can try removing some of the protection diodes etc, suggested to take a look-see affects with the ShibaSoku.
Thx-RNMarsh
I expect some relaxing of the thd spec at higher freq but this is a 100KHz instrument... dont expect to see much at 1/10th that. Phasiness perhaps affecting maintaining deepest null across the board... decades and tenths of the dials. Actually, what I was refering to behaves more like loose tolerance parts. I dont want anyone to get the idea these are big differences -- I can stay under .001% from 100-10KHz. THD+N.
Meanwhile ... today my 339A has crapped out!!!! Puts out a continuous 256Hz rather than 1Khz. Now what?!? Into trouble-shooting mode for awhile. When i get it up and running again, I can try removing some of the protection diodes etc, suggested to take a look-see affects with the ShibaSoku.
Thx-RNMarsh
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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 50nV/rootHz voltage noise. The 633 I think would be too noisy at 0.8uV/rootHz.
BTW -- since one can trim for lowest H2 or for lowest H3.... maybe tune for lowest H2 and add a notch for the H3. reason being H3 is further away from fundemental and notch will have least affect on it.
I can measure distortion directly, without calcs and tricks -- -110dB Full Scale..... and easily -20 below that. Direct measurement to below -130. Useable to about -135dB. Then there is the FFT and notch filters to apply. I'll be able to test most oscillators. -RNMarsh
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.
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
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
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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.
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.
