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Digital Distortion Compensation for Measurement Setup
Digital Distortion Compensation for Measurement Setup
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Old 6th April 2020, 06:02 AM   #371
jan.didden is offline jan.didden  Europe
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That's impressive.
You've got PM.

Jan
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Old 6th April 2020, 03:12 PM   #372
Bonsai is offline Bonsai  Europe
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Just read thru some of this thread. Some seriously good stuff here Pavel.

I salute you!
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Old 6th April 2020, 03:49 PM   #373
kipman725 is online now kipman725  United Kingdom
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very cool work
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Old 6th April 2020, 07:31 PM   #374
phofman is offline phofman  Czech Republic
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Thank you all for the words of support. The project is taking much longer than initially intended but I still hope it was not wasted time...
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Old 13th April 2020, 04:26 PM   #375
phofman is offline phofman  Czech Republic
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Adapter Mk2 with two calibration potentiometers, OPA1656 output buffer, powered from USB 5V by +/-12V isolated DC/DC convertor. Gerbers off to JLCPCB tomorrow.

Each calibration path (low-pass filters 1&2, voltage divider 1, voltage divider 2) is enclosed in a shielded compartment made in the top cover. This time I want to try the conductive paint instead of the copper tape.
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Old 13th April 2020, 07:17 PM   #376
1audio is online now 1audio  United States
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Digital Distortion Compensation for Measurement Setup
There are a hold lot of these type of products that work well and are pretty cheap: BMI-S-102 Laird Technologies EMI | RF/IF and RFID | DigiKey No opportunity to 3D print but being solid metal they will work.
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Old 13th April 2020, 09:10 PM   #377
phofman is offline phofman  Czech Republic
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Demian, thank you for the link.

The fact is I would like to stay with plastic parts as I can design every detail in CAD. For now I am 3D printing, but for small batches I am looking at options for SLA-printed mold and injection molding. The SLA-printed molds can cut low-batch injection molding price drastically.

Nickel-based conducting paint for plastic PHC05 (IMO the type E-MU use in their USB soundcard enclusures since it is gray too) costs 50USD/kg + shipping from China e.g. China PHC05 Universal Nickel Shielding Conductive Paint Electromagnetic Shielding Anti-static paints | supplier & manufacturer | Shenzhen PH functional materials Co., Ltd.
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Old 1st May 2020, 07:35 PM   #378
phofman is offline phofman  Czech Republic
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CleanSine v2.0 has two steppers/pots to avoid re-tuning the voltage divider between split-sides calibration of DAC (tuned to LPF level) and ADC-side calibration (tuned to DUT output level).

An illuminated pushbutton allows fast calibration - short press runs ADC-side calibration, long press rstarts split-sides calibration of the DAC. The pushbutton LED - solid green light = connected to the software, slow blinking - ADC calibration running, fast blinking - DAC calibration running. Solid red light = no single or dual tone fundamental detected on any side.

Green LEDs show status of OUT and IN - solid light = enabled, blinking = enabled and distortion-compensating that side.

Still the copper shield, the conducting paint has not arrived yet.
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Last edited by phofman; 1st May 2020 at 07:37 PM.
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Old 1st May 2020, 07:50 PM   #379
phofman is offline phofman  Czech Republic
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The two pots must be minimum-distorting. They are easy to measure - switching to a soldered resistor divider as DUT (basically zero distortion) must not raise the pot-calibrated distortions. Not all pots made the test, only 50% success so far. One had slightly elevated H2, the other was plain bad. I will see what the stats will do with the next batch waiting in transport.

These are DAC-side distortions calculated from combined distortions and LPF transfers measured with pot 1 and pot 2 (those with same distortion as the soldered divider, used in the adapter).
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Old 1st May 2020, 08:11 PM   #380
phofman is offline phofman  Czech Republic
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Remeasured opamps, comparison with previous adapter version (the same pot was used for ADC-side calibration). This time the opamp adapter was powered from a linear +/-12V transformer PSU, connected to mains via an isolation transformer (primary/secondary shielded) to lower the capacitive coupling. The +/- supply voltage was 11.7V (last time the SLA batteries fetched 12.7V). The order sorted by THD has not changed, the distortion profiles are very similar to previous measurements Digital Distortion Compensation for Measurement Setup

1) Direct VD - calibration

2) OP1656

3) LM4562 piece 1

4) LM4562 piece 2

5) NE5532

6) OPA2134 piece 1

7) OPA2134 piece 2
Attached Images
File Type: png direct-VD.png (137.4 KB, 66 views)
File Type: png OP1656.png (137.9 KB, 67 views)
File Type: png LM4562-1.png (133.4 KB, 60 views)
File Type: png LM4562-2.png (133.6 KB, 51 views)
File Type: png NE5532.png (133.7 KB, 54 views)
File Type: png OPA2134-1.png (138.3 KB, 54 views)
File Type: png OPA2134-2.png (128.5 KB, 55 views)

Last edited by phofman; 1st May 2020 at 08:16 PM.
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