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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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I drew up a simple gain stage in LTspice - here:
(Yes I know there are lots of other ways to design a gain stage ... I used this one as it comes from a phono stage - which obviously has a much higher gain!)Anyway, when a low input signal is used (see the relative values of R3 and R15) ... there is a relatively low THD - see here (0.6%):
... whereas, with a much higher input signal level (R3 = 5k and R15 = 45k) ... the THD becomes unacceptably high! (6%!):
My question is: why should a higher input signal entering the gain stage cause there to be a much higher level of THD? Given the higher input signal is only 450mV ptp and the gain is 4x ... we are nowhere near clipping.TIA for any suggestions.
Edits: 08/19/24 08/19/24
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Topic - Can someone explain these THD measurements from LTspice? - andyr 23:16:45 08/18/24 (15)
- RE: With a bit of assistance from here and elsewhere ... I believe I have the answer. ... - andyr 22:11:22 09/05/24 (0)
- Where's all the noise and distortion coming from? - Geoffkait 08:07:36 08/21/24 (0)
- RE: Can someone explain these THD measurements from LTspice? - 13th Duke of Wymbourne 10:27:23 08/19/24 (6)
- RE: Thank you DoW ... - andyr 16:49:40 08/19/24 (1)
- Why? Physics or Maths depending how you view it - 13th Duke of Wymbourne 19:31:25 08/19/24 (0)
- And do what Tom suggests, plot the drain current to be sure the swing is symmetrical - 13th Duke of Wymbourne 10:35:38 08/19/24 (3)
- RE: Sorry - can't quite see how to plot the Drain current ... - andyr 17:05:06 08/19/24 (2)
- RE: Sorry - can't quite see how to plot the Drain current ... - 13th Duke of Wymbourne 19:52:36 08/19/24 (1)
- RE: Yes, that plot *is* the voltage across R1... - andyr 20:00:55 08/19/24 (0)
- RE: Can someone explain these THD measurements from LTspice? - tomservo 10:20:49 08/19/24 (5)
- RE: Thank you, Tom ... - andyr 16:58:42 08/19/24 (4)
- RE: Thank you, Tom ... - tomservo 09:59:12 08/20/24 (3)
- RE: "when you change the resistor values" ... - andyr 15:57:11 08/20/24 (2)
- RE: "when you change the resistor values" ... - tomservo 05:37:21 08/21/24 (1)
- RE: "what do you want to build?" ... - andyr 15:30:30 08/21/24 (0)
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