[sdiy] Hewlett oscillator

[Grant Richter]

National Semiconductor application note AN-263 "Sine Wave Generation  
Techniques" shows a super low parts count single op-amp section wein  
oscillator. It uses a #327 bulb and dual pot. Dual pots are easy to  
get from Mouser in 22mm.

http://www.national.com/an/AN/AN-263.pdf

If single section pot tuning is important, then Linear Brief LB-16  
"Easily Tuned Sine Wave Oscillators" shows two designs that use a lot  
more parts.

http://www.national.com/ms/LB/LB-16.pdf

The datasheet for the LM837 is here.

http://www.national.com/mpf/LM/LM837.html

The datasheet for the RC4136 is here

http://focus.ti.com/docs/prod/folders/print/rc4136.html

A 741 has around a 45nV/Hz rating. The RC4136 was one of the first  
cheap low noise quad op-amps with an original noise rating of 15 nV/ 
Hz. They have a non-standard pinout. Which is a real pain.

The original low noise op-amp was the NE5534 which has a 3.5nV/Hz  
rating. But compare that a single NE5534 draws 8 ma. While all 4 of  
the LM837 together draw 10 ma.

On Nov 28, 2008, at 1:46 PM, Aaron Lanterman wrote:

>
> On Nov 27, 2008, at 4:42 PM, Grant Richter wrote:
>
>> For an onboard sine source, your best bet would be a single op-amp  
>> Hewlett design with an incandescent lamp for soft limiting.
>> Both the ICL8038 and XR2206 have sine waves with a THDs of 5%,  
>> this is not good.
>> The Hewlett design should have a THD of less than 1%, much better.
>> This sine wave can be normalized to the SIGIN jack, then if you  
>> need voltage control of the carrier frequency, you can patch it  
>> externally.
>>
>> The on-board sine source can then be a simple potentiometer  
>> control. A suggested range is 10 Hz to 1kHz.
>> Adding a wider range is not musically useful, at a 1kHz carrier  
>> frequency everything is shifted so high it's almost inaudible.
>> Th simple sine source should have a panel output also with a 1K  
>> resistor in series.
>
> Some Wiki foo brings me this: http://en.wikipedia.org/wiki/ 
> Wien_bridge_oscillator
>
> The design I see there has two Rs, so I guess I'd need a ganged  
> pot? Or is there a way to work around it to use only a single pot?
>
> - Aaron
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