Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Jan Panteltje <pNaonStpealmtje@yahoo.com>
Newsgroups: sci.electronics.design
Subject: Re: How 3-capacitor sine generator works =?UTF-8?B?cmVhbGx5Pw==?=
Date: Fri, 03 May 2024 07:51:23 GMT
Organization: A noiseless patient Spider
Lines: 48
Message-ID: <v1251t$e0t0$1@dont-email.me>
References: <804485177e123558699ce859cc4d496a@www.novabbs.com>
MIME-Version: 1.0
Content-Type: text/plain; ISO-8859-15
Content-Transfer-Encoding: 8bit
Injection-Date: Fri, 03 May 2024 09:51:25 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="f64e6fb25cbe316221ca4ff0e0eace5b";
	logging-data="459680"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX18/a84vpwQDu111bLJzh3xtr2T/ghNQIXQ="
User-Agent: NewsFleX-1.5.7.5 (Linux-5.15.32-v7l+)
Cancel-Lock: sha1:jyOOI0kJr35neq1HLOzz3aU1Szs=
X-Newsreader-location: NewsFleX-1.5.7.5 (c) 'LIGHTSPEED' off line news reader for the Linux platform
 NewsFleX homepage: http://www.panteltje.nl/panteltje/newsflex/ and ftp download ftp://sunsite.unc.edu/pub/linux/system/news/readers/ 
Bytes: 3346

On a sunny day (Fri, 3 May 2024 06:14:54 +0000) it happened RodionGork
<rodiongork@github.com> wrote in
<804485177e123558699ce859cc4d496a@www.novabbs.com>:

>Hi Friends!
>
>Schematic / simulation in "Falstad online simulator":
>https://tinyurl.com/23hcg8np
>
>This is probably very old and widely known schematic of single-transistor
>generator which
>requires no inductance, but instead uses three capacitors - actually it
>seems a chain
>of high-pass single-stage filters with transistor serving as feedback from
>output to input.
>
>One can find it, for example, in classic stylophone schematic (the part
>creating low-frequency
>oscillations for "vibratto" effect).
>
>I teach it to my pupils for years probably and I always thought I less or
>more understood what
>is happening inside - each filter stage gives shift in phase and hence when
>amplifying feedback
>is added there happen harmonic oscillations.
>
>However on the schematic given above I added 4 scopes over the length of
>the filter (potentials
>at the points A, B, C, D according to labels - here A and B are potentials
>at points between capacitors, C is at the base and D at collector) - I
>suddenly found that intermediate voltages are
>not pretty harmonic! They could be distorted by the current drawn into
>transistor base though. And
>I'm not sure the output is exactly sine now. Though probably it is a matter
>of adding some resistor  to improve input impedance of transistor cascade?
>
>Regretfully I can't find any thorough explanation of the schematic
>(probably due to keywords being too general and I don't know if this design
>has fancy proper name). So I would be grateful either
>for links or for verbal clarifications.

For oscillation you need to put the output back in phase to the input.
The tansistor gives 180 degrees phese shift
(when base goes up the collector goes down)
the RC networks that follow give together an other 180 degrees at some specific frequency.
so at the base now the feedback is in phase
and as gain is >1 it wil oscillate at that frequency set by the R and C values.