API 525C calibration procedure
- Thread starter dogears
- Start date
Help Support GroupDIY Audio Forum:
Posted my set of docs in the Tech Docs section:
https://groupdiy.com/index.php?topic=44738.msg952903#msg952903
https://groupdiy.com/index.php?topic=44738.msg952903#msg952903
Golgoth
Well-known member
Hi,
I am trying to calibrate vintage 525s that got their trim pots replaced.
Modules on the bench have their front panel controls as required on point (3.)
I am considering dBM = dBU here.
I would like to get three questions answered before moving forward:
1. When checking unity gain (4. B.), both my units are around 2dBU hotter on the output than the input (0 dBU in, +2 dBU out). I compared with a modern known-to-be-working 525 and that unit has perfect unity gain. Different opamps had no effect on the gain. Can I proceed forward anyways?
2. I am not sure I understand (4. C.).. What does "Disconnect output lead mean?" Pin 8 being the stereo defeat pin on the original 525 I guess they mean to disconnect the strap between pins 7-8 if they were connected in the first place?
3. Starting from (4. D.) can I assume I should be measuring everything from the output of the module/rack?
Thanks a lot!
I am trying to calibrate vintage 525s that got their trim pots replaced.
Modules on the bench have their front panel controls as required on point (3.)
I am considering dBM = dBU here.
I would like to get three questions answered before moving forward:
1. When checking unity gain (4. B.), both my units are around 2dBU hotter on the output than the input (0 dBU in, +2 dBU out). I compared with a modern known-to-be-working 525 and that unit has perfect unity gain. Different opamps had no effect on the gain. Can I proceed forward anyways?
2. I am not sure I understand (4. C.).. What does "Disconnect output lead mean?" Pin 8 being the stereo defeat pin on the original 525 I guess they mean to disconnect the strap between pins 7-8 if they were connected in the first place?
3. Starting from (4. D.) can I assume I should be measuring everything from the output of the module/rack?
Thanks a lot!
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