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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Final final 1kHz oscillator
Date: Sat, 23 Nov 2024 00:12:07 -0500
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"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vhrma8$1io30$2@dont-email.me...
> On 23/11/2024 3:32 am, Edward Rawde wrote:
>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vhp713$12bnt$2@dont-email.me...
>>> On 21/11/2024 1:00 am, Bill Sloman wrote:
>>>> On 20/11/2024 2:03 pm, Edward Rawde wrote:
>>>>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vhjj2v$24eu4$3@dont-email.me...
>>>>>> On 20/11/2024 1:29 pm, Bill Sloman wrote:
>>>>>>> On 20/11/2024 12:59 pm, Edward Rawde wrote:
>>>>>>>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vhibce$1t7v2$1@dont-email.me...
>>>>>>>>> On 18/11/2024 2:58 pm, Edward Rawde wrote:
>>>>>>>>>> "JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:n7iijjdeqecl0kmub0bq5in0dbm60m7qam@4ax.com...
>>>>>>>>>>> On Thu, 14 Nov 2024 11:14:28 -0500, "Edward Rawde"
>>>>>>>>>>> <invalid@invalid.invalid> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> "JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:t5fajjdteskfftvkf84iqsp2vc4b9ta5kj@4ax.com...
>>>>>>>>>>>>> On Fri, 8 Nov 2024 15:43:41 -0500, "Edward Rawde"
>>>>>>>>>>>>> <invalid@invalid.invalid> wrote:
>>>>
>>>> <snip>
>>>>
>>>>>> I've no idea why you are using the LT1994. The circuit doesn't have a common mode problem, so why are you using an op amp
>>>>>> designed
>>>>>> to deal with one?
>>>>>>
>>>>>> This is sci.electronics.design not sci.electronics.incremental-development.
>>>>>>
>>>>>> And the six diode "stabiliser string" is nuts. If you need a 3.6V reference voltage there are lots of ways to do it with more
>>>>>> precision and better temperature stability.
>>>>>
>>>>> In that case please show a circuit with better performance.
>>>>> It may be that some of the circuits JM posted can do better but if so then why are you using a circuit with so many 
>>>>> components?
>>>>> My circuit has far fewer components than yours.
>>>>
>>>> But you don't seem to be able to tell us what they do.
>>>>
>>>> I think I've found my conceptual problem with my circuit. Tweaking the gain around the three-amplifier ring tweaks both 
>>>> amplitude
>>>> and frequency - with more gain a lower frequency signal can still propagate around the ring.
>>>>
>>>> I've got to find a mechanism that will separate amplitude from frequency. My copy of Williams and Taylor on electronic filter
>>>> design may get perused again.
>>>
>>> I found a simpler solution - copy the relevant arrangement in John May's circuit. It did work - after a fashion - but as I got
>>> closer to getting it to a state where it could do what I wanted, the circuit got less and less willing to simulate.
>>>
>>> I suspect an accumulation of typo's in component values - I do try to go the through the schematic to find and purge them. But 
>>> the
>>> last few passes haven't shown up anything. Frustrating. My father's advice in similar situautions was to "drop it in drawer for
>>> six months, then take another look". It has worked in the past.
>
> I found that adding a couple of 14nmH ferrite beads around the transistors and the FETs stopped the simulation dropping out after 
> getting stuck on a too-short time step.
>
> The current version isn't simulating all that fast - I let it run over-night and the amplitude control feed back loop turned out 
> to have been underdamped to the point of instability - it kept on hitting the rails and overshooting back into them. The current 
> version - with more damping - is now on it's second millisecond.

Ok well when you've got a circuit which rivals the one I posted for harmonic distortion and component count let me know.

>
>> I also found a simpler solution. Taking on board advice from JM and others.
>>
>> The circuit below does 0dB into 600 ohms and it only takes about 20 minutes to complete the simulation on my computer.
>>
>> When it's done, select a sample of about 1 second near the end and FFT.
>> Select Use current zoom extent and Blackman-Harris window.
>>
>> It will say all harmonics are more than 120dB down.
>>
>> I'm not saying this level of performance is achievable or measurable in reality so I don't see any point simulating further.
>>
>> The actual distortion in reality will likely be that of the op amps so choose the lowest distortion op amp you can find.
>>
>> Oh and if you need to know the exact function of any of the 21 components in this circuit just ask.
> >
>> I'd feel embarrassed to have produced a circuit using over 70 components which only claims 65dB down on harmonics.
>
> Of course you would. The point of producing the circuit is to find out what it can do, and change it to make it work better. That 
> way you get to understand what the circuit is doing and why it is doing it, which isn't your strong point.

Silly me. I thought that's what I'd been doing all along.

>
>> Does anyone know how to change the default trace in LTSpice?
>
> There isn't one in the version I downloaded. When I start a simulation I get offered a blank display, and have to select a trace 
> to be displayed before I can see anything.

Same here. Therefore it has to be storing alternative behaviour in one of that files it creates.
I have since found that this is a plt file.

>
>> When I click Run/pause it shows the wrong node so then I have to Delete This Trace and click output.
>> How do I make it default to output?
>
> Beats me.

It turns out that the solution to this problem is to delete the plt file.
However I don't know exactly what the circumstances are for this file to be created.


>
> -- 
> Bill Sloman, Sydney
>
>