Another realization of Bob Cordell's THD Analyzer - diyAudio
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Old 19th April 2010, 12:18 PM   #1
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Default Another realization of Bob Cordell's THD Analyzer

Hi all,
I started the adventure to build Bob's THD Analyzer.
I made new PCB for my implementation.
They are: one for Sine Generator and Output Attenuator with the connector for the switch capacitors range board.
The cap sw PCB for Sine Gen, and Filter range (two equal for both).
One for Filter, Amp and Freq Detect.
One for Output Filter with connector for the Meter
One (little) for Meter circuits. Mount AD536AH for RMS conversion
One for Input Attenuator/Amplifier
I still have not decided how to switch the resistance of the frequency, probably Optofet or Photoresistors but they latter have serious problems of thermal drift.

....le first photos
Attached Images
File Type: jpg THD SINE PCB (Small).JPG (63.5 KB, 930 views)
File Type: jpg CAP SW PCB (Small).JPG (62.0 KB, 887 views)
File Type: jpg THD FILTER AMP FREQ DETECT PCB (Small).JPG (70.5 KB, 877 views)
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Old 19th April 2010, 12:25 PM   #2
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Sine Generator and SW CAP board fitted
Attached Images
File Type: jpg CIMG2787 (Small).JPG (57.2 KB, 867 views)
File Type: jpg THD SW CAP MOUNT (Small).JPG (50.6 KB, 845 views)
File Type: jpg THD SINE CAP SW ON BOARD (Small).JPG (48.2 KB, 290 views)
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Old 19th April 2010, 12:42 PM   #3
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These output levels at various frequencies.
(The 200KHZ is the same level )

Note that with the 200pF Wima (in the photos) the generator was unable to go beyond 70kHz. Now I replaced them with Silver Mica and it reaches up to 250kHz without problems and with the same output level!

Test of distortion was done with Hameg HM8027 but it reveals nothing! (Long life to Bob).
...to be continued


Giuliano
Attached Images
File Type: jpg CIMG2786 (Small).JPG (45.3 KB, 335 views)
File Type: jpg CIMG2782 (Small).JPG (47.1 KB, 215 views)
File Type: jpg CIMG2785 (Small).JPG (50.1 KB, 168 views)
File Type: jpg CIMG2778 (Small).JPG (40.9 KB, 243 views)
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Old 19th April 2010, 05:38 PM   #4
tomchr is offline tomchr  United States
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Location: Greater Seattle Area
Nice work!
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Old 22nd April 2010, 11:42 PM   #5
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Thanks tomchr.
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Old 23rd April 2010, 06:15 PM   #6
carpin is offline carpin  Netherlands
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Interesting project, good looking pcb's.
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Old 23rd April 2010, 07:15 PM   #7
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This is the, tested, Voltage-controlled bandpass filter with on-board caps-switch pcb.
The empty sockets of the IC refers to the amplitude and frequency detector and LED tuning frequency, in progress.
To be continued.
Hello
Attached Images
File Type: jpg CIMG2978 (Medium).JPG (112.0 KB, 256 views)
File Type: jpg CIMG2983 (Medium).JPG (103.7 KB, 171 views)
File Type: jpg CIMG2985 (Medium).JPG (85.1 KB, 179 views)
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Old 21st July 2010, 04:11 PM   #8
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The circuit does not oscillate in the range of 200 kHz if resistors (E) - (F) connections are longer than 2 / 3 inches. It is even worse if I use shielded cable.
If increase the value of C (LN) only (470pF i.e.), then the circuit takes to oscillate (frequency appropriate to the capacity added) and by bypass cap resistors series.
I do not think the PCB tracks are longer than the original circuit wiring.
Which is the reason for that?
Resistors (F)-(E) values are 10 binary connecting so as to obtain intermediate frequency values.
1024 steps provide hertz fractions for low ranges and up to 175 Hz in the highest range.
Attached Images
File Type: jpg THD binary res.JPG (66.3 KB, 213 views)
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Old 21st July 2010, 04:12 PM   #9
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Product Amp and Level Set board.
Attached Images
File Type: jpg THD Prod Amp Lev Set.JPG (67.3 KB, 200 views)
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Old 21st July 2010, 04:13 PM   #10
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Fixed Filter and meter board with AD536 RMS converter.
To simplify the implementation I preferred, for now, build the output fixed filter.
The main PCB provides the tracking filter components.
To be continued…
Attached Images
File Type: jpg THD Output Filter RMS Conv.JPG (58.1 KB, 153 views)
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