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Old 4th January 2014, 10:34 PM   #161
1audio is offline 1audio  United States
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For daily use the Panasonic would be my first choice. A PC or tablet in the middle always slows things down. If you are documenting or need to make a complex set of measurements the PC/cloud types of stuff is great. To adjust bias on output transistors the smoke may get out before you know you went too far.

Also the Panasonic won't get damaged if something it wrong. The PC stuff will if it isn't fully protected.
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Old 5th January 2014, 10:23 AM   #162
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Thank you for the advice, soundcard/PC stuff isn't a good choice for a repair shop, but it took me some years to understand that an old Bruel Kjaer 1022 is the **** when you make repair job, also it took me some years to understand that an old good analouge oscilloscope is very useful instead of fiddling with PC display.
I have a lot of good old stuff but it is very frustrating to manage them togehter into a "audio measure station".

The Panasonic VP-7722A, how old are those instruments and it is some hard to get spare parts or parts that I should buy just now.
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Old 5th January 2014, 11:51 AM   #163
RM is offline RM  Norway
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Default VP7722A

I used one of these from approximately -90 to 2005. It is a most competent analyzer, and one that you could probably live with for many years. It can even analyze down to the fifth harmonic just by pressing a button.
I far as I`m aware of it has no particular weakness, so I could`t advise on parts to stock. I still have my original service manual for it, however, where I have it I can`t say. To many relocations the last years.

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Old 5th January 2014, 06:53 PM   #164
RNMarsh is offline RNMarsh  United States
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I have one also and like it very much. It uses the same scheme as the ShibaSoku and thus is quit accurate to -120dB. Plus, it is set up for doing many other types of audio tests.

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Old 19th January 2014, 12:57 PM   #165
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Presados ​​lords

I request to kindly inform me if have for sale a copy of the operating manuals and schematics and calibration devices listed below.
Looking forward to its manifestation
Automatic Distortion Analyzer Shibasoku 725 B
Multichannel TV Sound Signal Generator TA35C
grateful
Alvim
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Old 20th January 2014, 03:12 AM   #166
1audio is offline 1audio  United States
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PM me for a scan of the 725B manual. Calibration and repair are not really covered in the manual. The schematics are in there and some repairs are pretty obvious but alignment is not obvious.
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Old 9th March 2014, 12:59 AM   #167
1audio is offline 1audio  United States
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I made a significant upgrade to my 725. I was bugged by a 2nd harmonic that was pretty strong (-120dB or so). After adjusting the input offset with no effect on the distortion I went to the next stage, the band elimination filter. On that board (A3) I first installed sockets on U1 and U2 and returned the original opamps with no success. At least it wasn't broken.

The I swapped the HA2625 in U1 with an LME49990 I had already mounted on a SOIC to DIP adapter. I was not expecting much but it did the trick. Now, with the Viktor oscillator as a source (the cleanest I have) I get -140 for the 2nd and less for all the others. Schematic for the band elimination filter board below.

The Shibasoku 590AR I have has not lent itself to an easy upgrade the same way. I shuffled the analog multipliers (socketed part) until I got the lowest distortion but I think it has more performance potential with a few parts upgrades. I expect I need to swap the input fets on the amp stages to matched pairs to get it working right. For now it has a limit at around -130 for the harmonics.
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Old 10th March 2014, 07:09 AM   #168
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by 1audio View Post
I made a significant upgrade to my 725. I was bugged by a 2nd harmonic that was pretty strong (-120dB or so). After adjusting the input offset with no effect on the distortion I went to the next stage, the band elimination filter. On that board (A3) I first installed sockets on U1 and U2 and returned the original opamps with no success. At least it wasn't broken.

The I swapped the HA2625 in U1 with an LME49990 I had already mounted on a SOIC to DIP adapter. I was not expecting much but it did the trick. Now, with the Viktor oscillator as a source (the cleanest I have) I get -140 for the 2nd and less for all the others. Schematic for the band elimination filter board below.

.
This is the same opamp used by HP in some of their gear and I found similar improvement when replaced by other newer opamps.

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Old 10th March 2014, 08:09 AM   #169
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30 years ago the Harris opamps were the state of the art. Its only recently on this scale that significanly better opamps have become available. Finding the right one for an application is not simple with many interlocking aspects.
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Old 10th March 2014, 09:17 AM   #170
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It might be worthwhile to point out that the opamp which bootstraps the notch filter (QA2) does contribute to the distortion residual in a non-obvious way. While it does not see significant input or output voltage swing, its output sources significant AC current which in turn causes a distorted voltage to appear at the output terminal. Perhaps biasing the opamp into class A (see e.g. Tek SG505 schematic for a neat way to do this with a '5534) is useful here.

Samuel
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