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Old 21 December 2021, 16:28   #18
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Join Date: Jan 2008
Location: United Kingdom
Age: 44
Posts: 726
Originally Posted by ugrnm View Post
Some measurements with a scope, using the 500Hz sine wave from AmigaTestKit. No clipping, offset, weirdness was visible.

At the exit of C334:
  • Vpp 1/R + 2/R 5.64-5.68
  • Vpp 1/R 3.12-3.16
  • Vpp 2/R 3.08-3.12

At the exit of C324:
  • Vpp 0/L + 3/L 5.84-5.88
  • Vpp 0/L 3.04-3.08
  • Vpp 3/L 3.24-3.28

Not sure if it's worth investigating but 0/L and 3/L are not as balanced as 1/R and 2/R. I should probably not loose sleep over it...

At the exit of CN3
  • Vpp 1/R + 2/R 1.66-1.68
  • Vpp 1/R 1.00-1.02
  • Vpp 2/R 1.00-1.02

At the exit of CN4
  • Vpp 0/L + 3/L 1.74-1.76
  • Vpp 0/L 0.98-1.00
  • Vpp 3/L 1.04-1.06

So as far as I understand my stock A600 1.3, and yours pandy71, are a bit louder than the standard for consumer line level (0.894).

And if my math is correct, I would just have to replace R335 and R325 with 1.5K resistors or maybe 1.4K to be on the safe side? Vpp of pro line level is 3.472.
I wouldn't fiddle with R335/R325 if I were you. A typical measurement accuracy of an oscilloscope is +/- 2.5% +0.2 division, your readings are within the margin of error. If you have a true RMS 5.5 digit or better, DMM, you could get a more accurate reading.

The audio circuit uses 5% tolerance resistors, a typical worst case RSS error could be a +/-8.66% variation in the signal amplitude due to the resistors. alone. I'll spare you the pain of tolerance analysis calculations, what you have now is about right and good enough.
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