Low frequency analog VCO with sinewave output?

On Wed, 24 Aug 2011 14:18:46 -0700 (PDT), davew <david.wooff@gmail.com>
wrote:

>
>> If you cough up answers to my questions on what you really need, folks
>> will be able to give you more specific help.
>>
>> I understand not wanting to break the digital barrier -- I tend to =
cross
>> that particular Rubicon with ease, yet I have circuits out there that =
are
>> all analog, or that only use "digital" parts in an analog way.
>
>I'm deliberately trying to make an all analogue design in this case so
>it's not that I'm particularly averse to taking a digital approach as
>such.
>
>>> * What frequency range does it need to run in? * How good does it =
have
>>> to be?
>LF to MF audio band probably 70Hz - 3KHz
>
>>>   * How quiet does it need to be?
>>>   How close to a sine does it need to be?
>Not sure really, I would have thought 2% THD+N would be good enough
>but I find it difficult to be accurate without having performed any
>experimentation yet.
>
>>>   * How linear does the command voltage vs. frequency need to be? *
>I can only answer "nominally" linear.  Definitely not log.
>
>>> * Temperature range?
>10 - 30 degC
>
>>> * what other questions did I leave out?
>Well I suppose the amplitude needs to be reasonably stable with
>frequency but again only to within say 10%.
>
>I think the XR2206 looks promising so far.  I've not yet had enough
>time to look at your other suggestions but will do.  I particularly
>like the idea of a Wien-bridge if it's easy enough to tune because
>there is no digital switching going on internally, so should be
>inherently more quiet.
>
>Many thanks to all.

You may be able to get the tuning range with a parallel-T oscillator and =
4
semi-matched lamp and photoresistor units.  It will produce a decent sine
wave as well.

?-)

On Sat, 27 Aug 2011 19:42:59 -0700 RST Engineering <jweir43@gmail.com>
wrote in Message id: <4paj571ar6cemvmugf7jr4hf48uptasu4h@4ax.com>:

>For[snip]