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From: JM <sunaecoNoChoppedPork@gmail.com>
Newsgroups: sci.electronics.design
Subject: Re: A variation on my current mirror low distortion sine wave oscillator - 10dB less distortion and much the same number of components
Date: Sun, 16 Feb 2025 15:29:05 +0000
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On Sat, 15 Feb 2025 22:18:09 -0500, "Edward Rawde"
<invalid@invalid.invalid> wrote:

>"JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:gp6vqjl5oma32tga136kspreh7a8182ofg@4ax.com...
>> On Mon, 10 Feb 2025 17:18:01 +1100, Bill Sloman <bill.sloman@ieee.org>
>> wrote:
>>
>>>Basically same idea, but two separate controllable asymmetric current
>>>mirrors, rather than one, and no current steering. The half-wave
>>>rectifier still seems to be the source of the distortion in the
>>>stabilised output.
>>>
>>>C25 and C26 take out as much of it as I can. Increasing them - from 15nF
>>>to 33nF makes the distortion worse. Splitting the resistors into three
>>>rather than two and adding two more capacitors might help, but what this
>>>circuit needs is more insight, rather than more components.
>>
>> What is the point of a push-pull current mirror?  You don't need
>> response at dc.  A "class A" (for want of a better term) mirror with
>> minimal current deviation will have distortion levels orders of
>> magnitude less than the circuit you propose.
>>
>
>Is there any specific reason for the npn Q5?

It's not required here (it's a cut/paste from a different circuit
which uses a different opamp).  

>Replacing it and R25 with a single 100k resistor from U2 to Q1 base seems to work just as well.

That's a bit big, no resistor required unless there's sign of
oscillation at the opamp, and then a few 10/100s ohm.

>2kHz is 141dB down measured with cursors on a zoomed in FFT in LTSPice 24.1.2 
>

That seems a bit high, I measured H2/H3 at about -155/-175 dBc (see
attached).

https://1drv.ms/b/c/1af24d72a509cd48/EZX4RABqnwRPi6QJZuD4r14BXTkKJ_xWLDToBwinfK_qVA?e=2tUakP