[sdiy] Taylor series and sums and difference tones

[Tom Wiltshire]

On 5 Jun 2009, at 07:10, Dave Manley wrote:

> Dave Manley wrote:
>> Aaron Lanterman wrote:
>>> On Jun 5, 2009, at 1:36 AM, Dave Manley wrote:
>>>
>>>> On a related note, Grant Richter has commented that for the best  
>>>> sounding multiplication (as in a balanced modulator), you want  
>>>> the sine to be very pure, because any components that are not  
>>>> the fundamental will result in, to use Aaron's terms, "all sorts  
>>>> of junk".  Of course, it depends on how many dB down the stray  
>>>> components are.  A sine from a self-oscillating filter is better  
>>>> than any sine from a shaper for use in multiplication for this  
>>>> reason.
>>>
>>> I remember Grant suggesting one that uses the weird properties of  
>>> an incandescent light bulb. (I believe it was the Hewlett-Packard  
>>> design.)
>>>
> Here's a description of the HP circuit: http://en.wikipedia.org/ 
> wiki/Wien_bridge_oscillator

I built one of these when I was about twelve, on my first breadboard.  
I was very intrigued by it, particularly if you set it so that it  
didn't quite oscillate, and then fed other audio through it, or the  
clicks from a 555 timer. It resonated. I had no idea that this would  
be the result at the time and was very excited. It was stuff like  
that that got me into synth diy in the first place.</nostalgia>

But yeah, sticking a lightbulb in to keep it linear was quite a  
common trick with wein bridge oscillators.

T.