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-   -   ShibaSoku Automatic Distortion Analyzer (http://www.diyaudio.com/forums/equipment-tools/231665-shibasoku-automatic-distortion-analyzer.html)

PChi 9th March 2013 12:34 PM

ShibaSoku Automatic Distortion Analyzer
 
1 Attachment(s)
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.

RNMarsh 10th March 2013 05:03 AM

Quote:

Originally Posted by PChi (Post 3402699)
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

RNMarsh 10th March 2013 09:17 AM

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 10th March 2013 05:37 PM

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.

RNMarsh 10th March 2013 06:26 PM

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 10th March 2013 10:41 PM

1 Attachment(s)
Quote:

Originally Posted by RNMarsh (Post 3404010)
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.

RNMarsh 10th March 2013 11:22 PM

Revamped -
 
1 Attachment(s)
It seems to be completly revamped. A5 is nothing like your A5.
:-(

Attachment 335199

[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 11th March 2013 10:00 PM

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.

RNMarsh 11th March 2013 10:39 PM

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

RNMarsh 20th March 2013 06:26 AM

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


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