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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Random thoughts on sinewave oscillators
Date: Thu, 17 Oct 2024 21:29:51 -0400
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"piglet" <erichpwagner@hotmail.com> wrote in message news:ver5b2$2p6tm$1@dont-email.me...
> On 17/10/2024 12:32 pm, piglet wrote:
>> On 16/10/2024 9:55 pm, Edward Rawde wrote:
>>> Is the reason why this doesn't produce a better looking sinewave because the amplifier slew rate is faster going down than it is
>>> going up or some other reason?
>>>
....
>>>
>>>
>>

Thank you for taking the time to look at this piglet.

>> I assume this is an intellectual challenge and not a real project?

Yes I'm not likely to be building it any time soon.
There was talk of sinewave oscillators here recently so I decided to see how easy or difficult it would be to make a sinewave 
oscillator without using lamps or thermistors.
I think it might be easier if I used standard op amps.

>> I  suspect the jfet gate-channel is forward biased so the amplitude control section is my first place to look?
>>
>> piglet
>>
>
> Hmm, that forward biased gate only happens during startup. Some other ideas:
>
> The amp input bias R6 loads the Wien network too much - try lowering the Wien network impedance?

It has been lowered in the circuit below.

>
> Replace R7 with constant current sink if you think slew rate is the issue?

Done

>
> Rectifier load is too heavy on the follower - increase R22?

Added separate follower.

When trying other suggestions, it's hard to get a stable amplitude control loop.

The circuit below produces a reasonable looking sinewave but the rise time still seems to be slower than the fall time.
It may be that the amplifier in use is not ideal for this.

>
> Q5 base reference is not stiff enough - lower R26-27-28?
>
> Q4 base current flows through rectifier - reference D1 instead to +12 rail?
>
> Maybe later I will find time to explore...
>
> piglet
>

Circuit version 2 follows.

Version 4
SHEET 1 2888 1280
WIRE 112 -144 -304 -144
WIRE 352 -144 112 -144
WIRE 640 -144 352 -144
WIRE 880 -144 640 -144
WIRE 1008 -144 880 -144
WIRE 1808 -144 1008 -144
WIRE 2080 -144 1808 -144
WIRE 2416 -144 2080 -144
WIRE 352 -128 352 -144
WIRE 112 -112 112 -144
WIRE 640 -112 640 -144
WIRE 2416 -96 2416 -144
WIRE 1008 -80 1008 -144
WIRE 2080 -80 2080 -144
WIRE 1808 -64 1808 -144
WIRE 352 -16 352 -48
WIRE 352 -16 256 -16
WIRE 112 0 112 -32
WIRE 112 0 0 0
WIRE 352 0 352 -16
WIRE 640 16 640 -32
WIRE 768 16 640 16
WIRE 880 16 880 -144
WIRE 2416 16 2416 -16
WIRE 2528 16 2416 16
WIRE 112 32 112 0
WIRE 256 32 256 -16
WIRE 2080 32 2080 0
WIRE 2080 32 1984 32
WIRE 2240 32 2080 32
WIRE 0 48 0 0
WIRE 768 64 768 16
WIRE 1008 64 1008 0
WIRE 1136 64 1008 64
WIRE 1808 64 1808 16
WIRE 1808 64 1712 64
WIRE 2528 64 2528 16
WIRE 640 80 640 16
WIRE 1136 80 1136 64
WIRE 1984 80 1984 32
WIRE 2240 80 2240 32
WIRE 352 128 352 80
WIRE 576 128 352 128
WIRE 1808 128 1808 64
WIRE 1920 128 1808 128
WIRE 2336 128 2304 128
WIRE 2416 128 2416 16
WIRE 256 144 256 96
WIRE 0 160 0 112
WIRE 112 160 112 112
WIRE 208 160 112 160
WIRE 768 176 768 128
WIRE 1136 176 1136 144
WIRE 1712 176 1712 64
WIRE 1808 176 1808 128
WIRE 2528 176 2528 128
WIRE 112 192 112 160
WIRE 208 192 208 160
WIRE 1008 192 1008 64
WIRE 400 208 256 208
WIRE 640 208 640 176
WIRE 640 208 464 208
WIRE 640 240 640 208
WIRE 704 240 640 240
WIRE 944 240 784 240
WIRE -304 256 -304 -144
WIRE 352 256 352 128
WIRE 112 304 112 272
WIRE 256 304 256 208
WIRE 256 304 112 304
WIRE 288 304 256 304
WIRE 1008 320 1008 288
WIRE 1104 320 1008 320
WIRE 1248 320 1184 320
WIRE 1376 320 1312 320
WIRE 1408 320 1376 320
WIRE 1504 320 1472 320
WIRE 1536 320 1504 320
WIRE 1664 320 1616 320
WIRE 1712 320 1712 240
WIRE 1712 320 1664 320
WIRE 1808 320 1808 256
WIRE 1808 320 1712 320
WIRE 2336 320 2336 128
WIRE 2416 320 2416 208
WIRE 2416 320 2336 320
WIRE 112 352 112 304
WIRE 2240 352 2240 176
WIRE 2240 352 2096 352
WIRE 208 384 208 256
WIRE 352 384 352 352
WIRE 352 384 208 384
WIRE -32 400 -144 400
WIRE 32 400 -32 400
WIRE 48 400 32 400
WIRE 352 400 352 384
WIRE 2416 432 2416 320
WIRE 2544 432 2416 432
WIRE -144 448 -144 400
WIRE 640 480 640 240
WIRE 656 480 640 480
WIRE 736 480 720 480
WIRE 1200 480 816 480
WIRE 1312 480 1200 480
WIRE 1504 480 1504 320
WIRE 112 496 112 448
WIRE 144 496 112 496
WIRE 448 496 144 496
WIRE 544 496 512 496
WIRE 640 496 640 480
WIRE 640 496 624 496
WIRE -32 512 -32 400
WIRE 16 512 -32 512
WIRE 112 512 112 496
WIRE 112 512 80 512
WIRE -32 528 -32 512
WIRE 112 528 112 512
WIRE 208 528 112 528
WIRE 352 528 352 480
========== REMAINDER OF ARTICLE TRUNCATED ==========