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Old 6th December 2009, 08:43 PM   #1
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Join Date: Apr 2007
Default Improving the HP-333A distortion analyser ?


Is anyones know any possibles improvements of those circuits or parts ; the impedance converter and the rejection amplifier/bridge balance circuits of my HP-333A distortion analyser ?

I include the HP-333A circuits images, the concerned circuits are in first two images.

Thank you


Attached Images
File Type: gif HP333A-hp334A-63-b.gif (77.4 KB, 215 views)
File Type: gif HP333A-hp334A-66-b.gif (121.5 KB, 204 views)
File Type: gif HP333A-hp334A-69-b.gif (68.8 KB, 199 views)

Last edited by gaetan8888; 6th December 2009 at 08:56 PM.
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Old 6th December 2009, 09:18 PM   #2
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Location: Koskenkorva Land
Hi Gaetan,

I don't have so much to contribute with more than that I had the same idea but with my over 20 years old scope, things I could think of is to get better transistors, especially in the scope case I think there are many more nice RF transistors these days, maybe some better capacitors and replace old dry electrolytic capacitors. Metal film resistors might be a good replacement in case of other types were used in crucial parts of the circuitry.
Did you have any list of what transistors are used or maybe you see it on the packages.

Cheers Michael
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Old 6th December 2009, 09:33 PM   #3
Join Date: Dec 2001
Location: Schaffhausen Switzerland
What makes you think it can be improved? My experience with the hp333A is that it's pretty much perfect as is. In what way could it be improved?

Test equipment isn't like audio, where parts choice makes it sound better - test equipment is designed for a job and it either does that job, or it doesn't. And if it doesn't, then it's faulty and can be repoaired.

And I'm talking from two points of view at once here:

1/ an ex HP service tech who has repaired 333A's

2/ an avid Upgrader and modifier of hi fi equipment.

Regards, Allen
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Old 7th December 2009, 04:44 PM   #4
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The HP-333A do have 80db of rejection of the fundamental frequency, is it possible to improve that ?

Thank you


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Old 7th December 2009, 05:21 PM   #5
SY is offline SY  United States
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At discrete frequencies, yes. A twin-T notch filter will get you 20-30dB more rejection.
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
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Old 7th December 2009, 09:43 PM   #6
Join Date: Dec 2001
Location: Schaffhausen Switzerland
To get more than the standard 80dB notch, the notch's Q will have to be raised a LOT, which means the tuning will be FAR more critical, and drift will become an almost impossible problem.

It is what it is, and I believe any attempts to "improve it" will just screw it up.

It was designed for normal audio usage, not a research project into ultra low distortion levels.

But it can be VERY useful as a front end for a 24 bit computer based spectrum analyser system, the 333A's notch will allow the computer to have a far deeper look into the harmonics. And allow convenient gain changing/attenuation, things often very hard to arrange with a regular sound card and software.

Regards, Allen
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