ShibaSoku Automatic Distortion Analyzer

[PChi]

I thought that it was time to start a new thread for the ShibaSoku Distortion Analyzer. I have reverse engineered part of an AD725C and have attached some schematics. I am in work at the moment so time is limited which is my excuse for the messy schematics. I can't guarantee the accuracy.
The equipment is old school and I think that a better way to go is to use a Sound Card preceeded by a Notch Filter as recommended elsewhere.

 

[31697B]

I thought that it was time to start a new thread for the ShibaSoku Distortion Analyzer. I have reverse engineered part of an AD725C and have attached some schematics. I am in work at the moment so time is limited which is my excuse for the messy schematics. I can't guarantee the accuracy.
The equipment is old school and I think that a better way to go is to use a Sound Card preceeded by a Notch Filter as recommended elsewhere.

So far, I have found most of the old school analyzers and source gen have excellent topology and are easily improved by selective replacement of the opamps with new low noise/low distortion opamps.

I am following the adc/pc/notch filter saga as well. Right now, the limit has been noise floor and poor ADC's with limited dynamic range to about 90dB - artifact free. But with the notch, that -90Db and FFT can see very low harmonics. But its still a cludge of bits and pieces and integrating hardware and software isnt quit There, yet IMO.
For fast testing, Plug N Play still is better with existing hardware. But I am making an active notch filter now and have a B&K passive notch filter also. But then you need another cludge -- to limit input level from power amps etc. it wont be long until a complete integrated package is made just for testing - such as the QA400 but taking it further and without usb driver bugs.

The ShibaSoku, upgraded, could be astonishing. The same opamp mods done in other instruments with similar old opamps has made 20 dB and more improvements.

Thank you for the sketches.... they help A LOT. Now I can go and look at them some more and start changing out selected opamps and see what happens to this analyzer.

Thank you,
Richard Marsh

 

[31697B]

I am looking at the drawings..... they seem to have changed the board numbers on mine... for example board A5 is S340076B-3. A3 is a Twin-T circuit... so it says on the pcb.
Do you have the analyzer monitor output circuit schematic?

Thx-RNMarsh

 

[1audio]

Richard:
I think they did a major rework between this unit and my unit and your much newer unit. The fundamental design is probably the same but many of the circuits may have been changed to deal with parts availability and different features. Yours has two inputs and balanced interface and GPIB. Mine has a single unbalanced input and parallel remote control. Very different at that level. Similar ultimate performance but different surroundings.

 

[31697B]

yes, after more investigating... they are sufficiently different that I cant use the drawings. :-(
I need to get hold of an actual service manual. Until then, all is on hold.

Thx-RNMarsh

 

[PChi]

I am looking at the drawings..... they seem to have changed the board numbers on mine... for example board A5 is S340076B-3. A3 is a Twin-T circuit... so it says on the pcb.
Do you have the analyzer monitor output circuit schematic?

Thx-RNMarsh

Unfortunately I haven't reverse engineered the analyzer monitor output schematic.
Like 1audio's unit mine only has a single ended input and guessing from the IC date codes was manufactured around 1990. I have attached a photograph of board A5 which is one of the bridged T stages.

 

[31697B]

Revamped -

It seems to be completly revamped. A5 is nothing like your A5.
:-(



[Also, I think yours is a Bridge-T and this one is a Twin-T osc.]

Lets try to find a manual/copy for each.

Thx-RNMarsh

 

[PChi]

Thanks for the picture. As you say the 725D has been completely revamped. My guess is that your A5 Board has the distortion residual HPF and LPF filters and RMS to DC Converter which on the 725C is Board A6 which again looks different apart from the collection of capacitors in the bottom right of the board and the metal can TO-100 package. Even the mother board is different with the 725C using PCB edge connectors and the 725D a dedicated connector.
I did an internet search for a 725C manual but was unsuccessful. ShibaSoku have kept a very low profile in the UK. I had never heard of them before visiting this forum.

 

[31697B]

I'll keep looking. You are correct about my A5 board... filters. I'll replace them with quieter opamps. I hope someone will be able to point me/us in the right direction as to where we can obtain the service manual.

Thx-RNmarsh

 

[31697B]

Still looking for schematics... took a break to try the AD797 opamp as an oscillator. Got mixed results.
-RNM

 

[31697B]

An alternative analyzer might be the Panasonic brand (National) model VP-7725. Claims thd below .0001%... It includes the generator with the analyzer and it comes up on eBay every so often. As does their other models. Worth a look.
I picked up a VP-7722 yesterday and will check and compare and see what potential it has. It specs .0005% thd or less.

Thx-RNMarsh

 

[simon7000]

Please PM me the results well before you post so I can buy one before the price goes up.
ES

 

[31697B]

I picked up a VP-7722 yesterday and will check and compare and see what potential it has. It specs .0005% thd or less.

Thx-RNMarsh

Its a VP-7723A

 

[31697B]

I later found and bought a VP-7722. Excellent machine!

-RNMarsh

 

[RM]

VP-7722

I can attest to that Richard. I had one for more than 15 years. Truly excellent machine. I ultimately replaced it with a R&S UPV.

RMalmin

 

[31697B]

The VP-77xx series are all now available on ebay and other places at prices of a used Audio-Precision SYS ONE. It is better than the older A-P by far. However, those nice PC FFT graphs are seductive.

I loaned (gave?) away my SYS One Dual Domain with every option and use either the Panasonic or ShibaShoku now.... But, I just got an A-P 2722 with options. But, I wont give up the ShibaShuko nor the Panasonic.

How do you like the R&S UPV ?

Thx-Richard

 

[RM]

I still miss the Panasonic though. Very handy for the workbench and quick glances at at signal.

The UPV, however, is a veritable Pandoras box of opportunities measurewise. In one word, superb. But as it is built on a computer platform, it does require some time to initialize after turn on, I use it mostly for R&D.

The Panasonic can measure, separately, down to the fifth harmonic. The UPV, on the other hand, can simultaneously display down to the tenth. Very handy for the likes of adjusting quiesent current, verifying operating points etc.

Roar

 

[PChi]

I bought the ShibaSoku AD725C Automatic Distortion Analyzer last year via Ebay for £150 including carriage. It was useful to test my Oscillator design but am now not using it.
It weighs about 17 kgs so I would prefer not to have to pack and ship it. I can demonstrate operation so if anyone would like the AD725C and can collect from Staines upon Thames they are welcome to it for £150.
I am in no hurry so I guess the best way is if anyone is interested please send a private message.

 

[1audio]

If I were on that side of the pond I would be over immediately (not that i need a second unit). I hope it goes to a good home. Thanks for your reverse engineering efforts.

 

[31697B]

Do you have the 725C analog input stage amplifier drawn? Curious what the circuit looks like.

Thx-RM