What a great idea !
I own a 725D... at Demian's house now. Maybe we can get him to try it. I wonder if I can use it on my A-P 2722 also? It is also very sensitive. Plus the 339A's I have here. And, the Panasonic 7722A et al. They should all do better.... though the Panasonic needs a higher minimum level and therefore isnt as sensitive as the others.
Thx-RNMarsh
I have invested a lot of time in that trick. I ran into limits with the B&K notch. the impedances are too high and limit the resolution with noise. I have been working with Jens notch but have excessive internal distortion so far. I'll sort that out soon as well. The trick does work and you can get much better resolution with it.
I got his oscillator working as well. Its based on this http://www.janascard.cz/PDF/An ultra low distortion oscillator with THD below -140 dB.pdf and demonstrates how good the NSL optocouplers can be when used carefully. In this circuit the CDSe cell has about 10 mV across it. More tuning and tweaking coming for that project as well.
yes, i remember.... I was there.... bought the B&K1607, got a mod for it done and used it to determine how good the QA400 would be... after finding the QA400 became nonlinear below -100dB. Improved it by at least 20dB.
But, I had already gone thru the 339A and others before the T-T.
I just had not gone backward and thought to use the T-T on the others I had set aside when the better analyzers became available. Good to hear they get a boost with additional notching in performance that is significant.
I am always interested in the best possible (T-T) which can be humanly developed. It is nice to work with people with a lot of talent to push things even further without spending a small fortune. Well.... actually I have spent a small fortune... but maybe other's wont have to.
THx-RNMarsh
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You're not alone, Richard -- I've had the stuff sitting here for over two years and just didn't really think about that combination - embarrassing, really. Now, I can see that a few upgrades to the 339 to lower noise and maybe control that spike in 2nd H. could actually be really useful, whereas before, I was put off by the rather limited benefits to the 339 itself.
You'll need to use the notch filter of the AP ahead of the ADC for meaningful low-distortion measurements. I've posted a screenshot of the settings, but can't find the link right now.
Samuel
Would love to see it and try it. I have 4 weeks here at 'the shop' and I'll be back in Asia for 2-3 months. Hope to get some equipment sent over there.... and a T-T, also.
Thx,
RM
Дмитрий, добрый день!
Спасибо Вам за совет. Я проверил таким образом Фильтр на IC2 a\b. Он работает. Но мне не очень понятна эта схема в остальной части. Не будете ли Вы добры хотя бы коротко объяснить назначение остальных каскадов (Т1, Т2 и IC1 a\b ).
Заранее благодарю.
С уважением, Игорь Николаевич.
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Igor, if you post in Russian, please also provide an english translation. I used google translate for the above. 
@Richard
I'm first repairing my B&K 1607.
I replaced the balance pot with a 1K unit.
Wondering if you had to drill out the back of the chassis
to get the 10 turn pot to fit with the venier?
I"ll have to find a longer threaded 10 turn pot
for the through hole chassis fitting as it won't
make it as it. Venier won't work as end of shaft
doesn't quite meet venier set screw either.
However, just having the balance pot in place with
a standard knob on it, doesn't seem to make any difference
with the balance pot. It doesn't seem to lower the notch
or anything.
I assume the pot was to balance either side of the notch when
trying to use the FR option from the FFT?
Can you post pics of the bottom of perf board circuit and straight on
top of the active TT that Gary posted about and you made then put it
in your BK1607?
Hope you have and affordable shipping method to get your
gear over to asia. We used to have to pay for someone to
travel just to lug the gear as it ended up being cheaper for
a person round trip, plus gear, than just shipping the gear.
I'm first repairing my B&K 1607.
I replaced the balance pot with a 1K unit.
Wondering if you had to drill out the back of the chassis
to get the 10 turn pot to fit with the venier?
I"ll have to find a longer threaded 10 turn pot
for the through hole chassis fitting as it won't
make it as it. Venier won't work as end of shaft
doesn't quite meet venier set screw either.
However, just having the balance pot in place with
a standard knob on it, doesn't seem to make any difference
with the balance pot. It doesn't seem to lower the notch
or anything.
I assume the pot was to balance either side of the notch when
trying to use the FR option from the FFT?
Can you post pics of the bottom of perf board circuit and straight on
top of the active TT that Gary posted about and you made then put it
in your BK1607?
Hope you have and affordable shipping method to get your
gear over to asia. We used to have to pay for someone to
travel just to lug the gear as it ended up being cheaper for
a person round trip, plus gear, than just shipping the gear.
hello --- I dont think I can get under the perf board now to take pictures with my camera--- but maybe. The ten turn only replaced the original single turn. It is just to help with finding the deep notch bottom more easily.
I have and will hand carry something over each trip. It is free that way.... even if over the 50# limit, the charge is small compared to usual shipping company.
I sent a small box... about 1 cubic foot in size to a school in remote Nepal.... it had a school microscope and a few other school things in it. All carriers wanted about the same price ---- $500. I'll never do that again! I'll carry it myself, thank you.
-RM
I have and will hand carry something over each trip. It is free that way.... even if over the 50# limit, the charge is small compared to usual shipping company.
I sent a small box... about 1 cubic foot in size to a school in remote Nepal.... it had a school microscope and a few other school things in it. All carriers wanted about the same price ---- $500.
I'll never do that again! I'll carry it myself, thank you.-RM