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From: JM <sunaecoNoChoppedPork@gmail.com>
Newsgroups: sci.electronics.design
Subject: Re: Low distortion sinewave oscillator without big capacitor.
Date: Sat, 05 Apr 2025 21:27:38 +0100
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On Sat, 5 Apr 2025 16:13:27 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:

>"JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:tcl2vjp49q4ga21itrpnmr4u3ts06vqffd@4ax.com...
>> On Fri, 4 Apr 2025 23:55:11 -0400, "Edward Rawde"
>> <invalid@invalid.invalid> wrote:
>>
>>>"JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:uop0vjp3d13t441ujfboi5aeeg08anm1je@4ax.com...
>>>> On Fri, 4 Apr 2025 16:29:27 -0400, "Edward Rawde"
>>>> <invalid@invalid.invalid> wrote:
>>>>
>>>>>"JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:add0vjdh2gcma0n9pfunq76n04cfbkhtnj@4ax.com...
>>>>>> On Fri, 4 Apr 2025 14:25:29 -0400, "Edward Rawde"
>>>>>> <invalid@invalid.invalid> wrote:
>>>>>>
>>>>>>>"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vsnufh$2ou7j$1@dont-email.me...
>>>>>>>> On 4/04/2025 11:33 am, JM wrote:
>>>>>>>>> On Thu, 3 Apr 2025 19:25:33 -0400, "Edward Rawde"
>>>>>>>>> <invalid@invalid.invalid> wrote:
>>>>>>>>>
>>>>>>>>>> "JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:qq8tujlpciqc2jrd0ibljmjr9pd37ip6hi@4ax.com...
>>>>>>>>>>> On Sun, 30 Mar 2025 14:54:56 -0400, "Edward Rawde"
>>>>>>>>>>> <invalid@invalid.invalid> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> Not long ago JM posted a 1KHz sinewave oscillator with very low distortion.
>>>>>>>>>>>> It used a 470uF non polarized capacitor which in practice would probably be made from two 1000uF capacitors.
>>>>>>>>>>>> There's nothing wrong with that but I wanted to see whether I could make a working circuit without needing such a large
>>>>>>>>>>>> capacitor.
>>>>>>>>
>>>>>>>>> You will need to adjust the feedback to suit.  Start with a -5 or -6
>>>>>>>>> gain block after the integrator and adjust it's gain until the startup
>>>>>>>>> is clean (no saturation).
>>>>>>>>
>>>>>>>> Here's my version of John May's variation.
>>>>>>>>
>>>>>>>...
>>>>>>>
>>>>>>>Yes, that works but only 120dB down at 4KHz.
>>>>>>>I put the damping resistor back to 47k since I don't care what happens during the first few seonds as long as it happens.
>>>>>>>If it's necessary to wait one minute for the purest tone, that's fine with me.
>>>>>>>
>>>>>>>>
>>>>>>>> Linewraps are going to be a problem - delete all "\n" from the last few lines
>>>>>>>
>>>>>>>You don't want to remove \n just remove the wraps.
>>>>>>>
>>>>>>>BCM61B does not have two independent transistors.
>>>>>>>
>>>>>>>So you probably want BCM847BS which has two independent matched transistors and a very low price at digikey, so may as well 
>>>>>>>use
>>>>>>>two
>>>>>>>of them as shown below.
>>>>>>>
>>>>>>>I took the model from
>>>>>>>https://github.com/peteut/spice-models/blob/master/nxp/complex_discretes/complex_discretes.txt
>>>>>>>
>>>>>>>It should only be necessary to unwrap the last line of the following.
>>>>>>>Don't remove \n just remove the wraps, you may need to use a horizontal scroll bar.
>>>>>>>
>>>>>>>Version 4.1
>>>>>>
>>>>>>
>>>>>> Best to just offset the integrator output so the amplitude is brought
>>>>>> under control sooner.
>>>>>>
>>>>>
>>>>>Wow. That has much lower distortion too.
>>>>>
>>>>
>>>> If you just replace Q1,2 duals with a simple long tailed pair I think
>>>> you will get better performance.
>>>
>>>I'm not sure I understand how the multiplier could be implemented with just a long tailed pair.
>>>
>>
>> Just modulate the tail current and select how much to steer to the
>> output by directly driving the bases rather than indirectly as in your
>> circuit.  The following link shows one example topology, and a four
>> quadrant differential I/O version.  Compare the linearity of each of
>> them.
>>
>> https://1drv.ms/u/c/1af24d72a509cd48/EWVCUG7-jFJMu7-01VczCRcBzEC9JPHrV45x7TOunN90Gg?e=GXbvX5
>
>Very interesting. Thank you.
>
>>
>> It could be used as shown here.
>>
>> https://1drv.ms/u/c/1af24d72a509cd48/EVmMVrvUD15GutoR5nCJ7QEBSeZsHWpHudqR0b8XtTLMLw?e=HIV74I
>
>Yes that stabilizes, but only 70dB down.

Adjust the maximum timestep.

>
>>
>> For best performance use the multplier circuit with differential I/O.
>> There is already a suitable drive point at U1 in the circuit.
>>
>>>The derived circuit below doesn't seem to have any discernible distortion at all as far as I can tell in an LTSpice FFT.
>>>Not until you get above about 100KHz where it's 160dB down.
>>>
>>
>> Best to use the Hanning windows at these levels if you're not already
>> doing so. 
>