OpenTheremin v3 loosing calibration after minutes

[gianpaolo]

I built the OpenTheremin v3 from the kit provided by gaudi.ch but it is quite unstable. After the first calibration, it worked for some ten minutes, then the sound started to degradate till it did not work anymore. Further calibrations did not reach the working result. After hours, it worked again, but then few minutes later it degraded again. It's the same story each time, it works few minutes then not anymore. And further tentatives to let it calibrate, did not work.

Please can you help me?

I see from the logs that set frequencies are not always in the range, is that wrong? how can I fix it?

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PITCH CALIBRATION

Arudino Freq: 15988545.00

Pitch Set Frequency: 499658
Frequency tuning range: 488401 to 526328

DAC value L: 0 Freq L: -11341
DAC value H: 4095 Freq H: 26677

DAC value L: 4095 Freq L: 26664
DAC value H: 1222 Freq H: -5021

DAC value L: 1222 Freq L: -5008
DAC value H: 1677 Freq H: 1790

DAC value L: 1677 Freq L: 1788
DAC value H: 1558 Freq H: 59

DAC value L: 1558 Freq L: 58
DAC value H: 1554 Freq H: 1

DAC value L: 1554 Freq L: 1
DAC value H: 1554 Freq H: 1

VOLUME CALIBRATION

Volume Set Frequency: 460395
Frequency tuning range: 455623 to 485872

DAC value L: 0 Freq L: -4781
DAC value H: 4095 Freq H: 25475

DAC value L: 4095 Freq L: 25451
DAC value H: 648 Freq H: -3158

DAC value L: 648 Freq L: -3155
DAC value H: 1028 Freq H: -2027

DAC value L: 1028 Freq L: -2046
DAC value H: 1710 Freq H: 815

DAC value L: 1710 Freq L: 802
DAC value H: 1516 Freq H: -220

DAC value L: 1516 Freq L: -236
DAC value H: 1557 Freq H: -24

DAC value L: 1557 Freq L: -23
DAC value H: 1561 Freq H: -3

DAC value L: 1561 Freq L: -13
DAC value H: 1561 Freq H: -3

CALIBRATION COMPLETED

PITCH CALIBRATION

Arudino Freq: 15988638.00

Pitch Set Frequency: 499655
Frequency tuning range: 482584 to 518827

DAC value L: 0 Freq L: -16912
DAC value H: 4095 Freq H: 19279

DAC value L: 4095 Freq L: 19265
DAC value H: 1914 Freq H: -670

DAC value L: 1914 Freq L: -691
DAC value H: 1987 Freq H: 100

DAC value L: 1987 Freq L: 157
DAC value H: 1978 Freq H: 97

DAC value L: 1978 Freq L: 103
DAC value H: 1964 Freq H: -97

DAC value L: 1964 Freq L: -260
DAC value H: 1970 Freq H: -202

DAC value L: 1970 Freq L: -131
DAC value H: 1990 Freq H: 213

DAC value L: 1990 Freq L: 234
DAC value H: 1978 Freq H: 95

DAC value L: 1978 Freq L: 102
DAC value H: 1970 Freq H: 8

DAC value L: 1970 Freq L: 2
DAC value H: 1970 Freq H: 9

VOLUME CALIBRATION

Volume Set Frequency: 460392
Frequency tuning range: 450529 to 479715

DAC value L: 0 Freq L: -9869
DAC value H: 4095 Freq H: 19359

DAC value L: 4095 Freq L: 19348
DAC value H: 1383 Freq H: -5963

DAC value L: 1383 Freq L: -5969
DAC value H: 2021 Freq H: -1010

DAC value L: 2021 Freq L: -1017
DAC value H: 2150 Freq H: 644

DAC value L: 2150 Freq L: 635
DAC value H: 2100 Freq H: 12

DAC value L: 2100 Freq L: -7
DAC value H: 2100 Freq H: 12

DAC value L: 2100 Freq L: 12
DAC value H: 2100 Freq H: 18

CALIBRATION COMPLETED

[petespaco]

I will bet that there are others watching this post, just waiting for someone to jump in, so here goes:
I am no expert about this device, (I have never even built one using semiconductors), but it appears to me that your problem is NOT one of calibration.
Something is wrong with the circuit.
Since it fails after it has been on for a while, it sounds like something could be heating up.  A short somewhere?
Maybe a capacitance is building up due to a missing parallel resistance?
Maybe a defective capacitor or other component?
Bad solder joint?
Power supply issue?
I'd start by measuring some stuff when it is "cold" and then again when it  fails to see what has changed.

[futurist]

Hi

Did you try grounding the theremin? I built several opentheremins v3 but had no issues whatsoever, maybe Gaudi could help?

[gianpaolo]

Thanks for the suggestions, will try.
Unfortunately I don't have an oscilloscope.

I will bet that there are others watching this post, just waiting for someone to jump in, so here goes:
I am no expert about this device, (I have never even built one using semiconductors), but it appears to me that your problem is NOT one of calibration.
Something is wrong with the circuit.
Since it fails after it has been on for a while, it sounds like something could be heating up.  A short somewhere?
Maybe a capacitance is building up due to a missing parallel resistance?
Maybe a defective capacitor or other component?
Bad solder joint?
Power supply issue?
I'd start by measuring some stuff when it is "cold" and then again when it  fails to see what has changed.

[gianpaolo]

Yes I did, but no change with or without grounding.

Did you try grounding the theremin? I built several opentheremins v3 but had no issues whatsoever, maybe Gaudi could help?