Propeller Head Plaza

RE: Thank you, Tom ...

120.146.101.112

andyr

In Reply to: RE: Can someone explain these THD measurements from LTspice? posted by tomservo on August 19, 2024 at 10:20:49

I'm afraid I'm not 100% sure what you meant by "I assume your spice has a scope probe, see if the asymmetry is large enough to see on the hot side of R1 and R4" - but if I get spice to give me the waveform at the join between R1 and R4 ... I get this:

Which seems alright?

Follow Ups:

RE: Thank you, Tom ... - tomservo 09:59:12 08/20/24 (3)
Hi
The 13th is right, it's too small to see without nulling some of the sine.

The reason was perhaps one could identify which direction the non-linearity was in (the upward signal or downward signal voltage) / operation above and below static (0 signal) bias point.

I am not clear on something though, when you change the resistors, are you also changing the input signal to maintain a fixed "voltage out"?.
- RE: "when you change the resistor values" ... - andyr 15:57:11 08/20/24 (2)
  These resistors are there to simulate the effect of having a volume pot ahead of the gain stage - so I can both attenuate the original 500mV pp signal ... and increase it.
  - RE: "when you change the resistor values" ... - tomservo 05:37:21 08/21/24 (1)
    Hi
    My thought was that assuming one kept the output Voltage the same as you changed the input divider ratio, that one would see the distortion is constant with output level- or -it changes according to the input divider even when the output voltage is held constant.
    
    The emitter follower output run class A should not add much distortion, the current source likewise but they ARE part of the circuit and can't be ruled out when tracking something down.
    
    Better question might be what do you want to build?
    This circuit seems like a design for very low level signals?
    
    Tom
    - RE: "what do you want to build?" ... - andyr 15:30:30 08/21/24 (0)
      Very good Qu, Tom.
      
      And you are absolutely right ... the circuit was designed for very low signals (it comes from a phono stage).
      
      I was curious to know whether, by adding a volume pot on the input ... it would be suitable for a preamp.

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