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From: "Edward Rawde" <invalid@invalid.invalid>
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 12:22:51 -0500
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"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.
>