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From: john larkin <jl@glen--canyon.com>
Newsgroups: sci.electronics.design
Subject: Re: The not-all-that-low distortion sine wave oscillator in a faster simulating version
Date: Thu, 19 Dec 2024 14:34:48 -0800
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On Thu, 19 Dec 2024 12:22:51 -0500, "Edward Rawde"
<invalid@invalid.invalid> wrote:

>
>"john larkin" <JL@gct.com> wrote in message news:uoj8mj9t5vc84kl4mdr01n3spqtnra2u6v@4ax.com...
>> On Thu, 19 Dec 2024 09:53:03 -0500, "Edward Rawde"
>> <invalid@invalid.invalid> wrote:
>>
>>>"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vk0ehh$2o9dc$1@dont-email.me...
>>>> On 19/12/2024 2:10 pm, Edward Rawde wrote:
>>>>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vk00um$2i900$1@dont-email.me...
>>>>>> On 19/12/2024 6:00 am, Edward Rawde wrote:
>>>>>>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vjtgnp$24ubg$1@dont-email.me...
>>>>>>>> I've been playing with the circuit, and have got rid of one op amp, which made the simulation run much faster, but didn't 
>>>>>>>> help
>>>>>>>> the
>>>>>>>> distortion performance.
>>>>>>>>
>>>>>>>> Swapping the LT1115 for the LME49710 speeded up the simulation a bit more, but didn't make any difference to the distortion
>>>>>>>> either. A few of the ferrite beads have gone too.
>>>>>>>>
>>>>>>>
>>>>>>> I got a simulation speed of about 30us/s so I didn't wait the nearly 4 days it would take to complete.
>>>>>>> I did an FFT on the first few cycles and it does look 100dB down up to 1.5MHz.
>>>>>>
>>>>>> It rans at 68msec/sec for me and takes a couple of minutes to run the full ten seconds.
>>>>>
>>>>> I used the circuit from your third post. One op amp had to be moved down a bit into position and then I hit simulate.
>>>>> To be sure we're talking about the same circuit I've reposted it below.
>>>>> I'm using LTSpice 24.0.12 with no new model updates available as of this post.
>>>>
>>>> And I'm using LTSpice XVII(x64)(17.0.37.0) up-dated recently.
>>>>
>>>> I finally got your version to work. As you say, U1 had to be moved into place, but I also had to change C10 on the output of U4.
>>>> I'd specified the capacitance as 3.3u. but the "u" symbol had vanished. When I specified the capacitance as 3300n everything
>>>> worked fine.
>>>
>>>C10 is definitely 3.3u here. I tried changing it to 3300n but still less than 30us/s when I start the simulation.
>>>
>>>>
>>>>>>> If building this for real then ten turn trimmers would be used for:
>>>>>>> R14 2.2k
>>>>>>> R3 68 ohm
>>>>>>> R16 100k
>>>>>>> And I'd also want R19 or part of it variable.
>>>>>>
>>>>>> Why a ten turn trimmer?
>>>>>
>>>>> Can be 100 turn if you want. The point is only that fine adjustment would be a good idea.
>>>>
>>>> Lots of turns don't always equate to fine setability.
>>>
>>>Yes I agree. You might easily have the kinds of problems which were solved with anti backlash couplings in the days of drive cords
>>>and tuning capacitors.
>>
>> The long multi-turn trimpots are hard to adjust and expensive, and are
>> no better than single-turns for settability.
>
>Yes particularly if the resistive element is the same length, it may as well be single-turn.
>Single-turn also has the advantage that you can see where it's set before you adjust it.
>Multi-turn is usually enclosed so hard to know where it's set before adjustment.
>
>https://www.google.com/search?&q=multi+turn+trimpots&udm=2
>
>So I'd probably go for good quality open single-turn if I ever build the 120dB circuit.
>
>>
>> Single-turns have much lower HF parasitics too.
>> 
>

The rectangular multi-turn trimpots have a lot of backlash. A good
single is actually more settable. A heap faster too.