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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 13:11:15 -0500
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"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vhs1ea$1kbt4$1@dont-email.me...
> On 23/11/2024 4:12 pm, Edward Rawde wrote:
>> "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.
>
> Component count isn't all that important. If you can replace an expensive or hard to get component with a couple of cheap ones, 
> that's a win.

I've worked in plenty of places where using four times as many components as you could have used (and hence four times the cost) 
would not be seen as a win.

>
> Alternative ways of doing much the same job are also interesting -

Sure. There are plenty of examples of that, such as make it a beam tetrode instead of a pentode.

> patent evasion used to be a popular sport. Once the patentable details are buried inside a programmable device it's less 
> worthwhile.
>
> Lawyers don't like going into technical detail - RCA won a colour TV patent case against EMI in a US Court because the judges 
> couldn't be persuaded that quadrature modulation was exactly the same thing as sine/cosine modulation.

Sony didn't care about the PAL patents. They just put a hue control on their early sets.

>
>>>> 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.
>
> Perhaps.
>
>>>> 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
>
>