[sdiy] VCO reference voltages

[Oren Leavitt]

Stewart Pye wrote:
> Hi David,
> 
> You can reduce the value of the coarse tune summing resistor (and tuning 
> pot if necessary to avoid loading by the lower value summing resistor) 
> to get the same tuning range from a lower reference voltage.
> 
> On another note, I've been wondering if it would be acceptable to use an 
> inverting op amp circuit  to generate the negative reference voltage 
> from the positive reference. I guess as long as the offset drift specs 
> for the op amp are suitable then it will be ok...
> 
> Regards,
> Stewart.
> 

Sure - you can use an inverting op-amp to get the negative side.
The datasheet/app notes for your reference IC for should have lots of 
examples.

- Oren

> 
> David G. Dixon wrote:
> 
>> The other downside of regulating rail voltages for the tuning pots is 
>> that,
>> because regulators only regulate to within 1 or 2 volts of the rails, 
>> using
>> regulated voltages for the rails will limit the range of the pots,
>> particularly in a +/-12V system.  This is not necessarily a problem on 
>> the
>> upper end, but it could be on the lower end unless the VCO has an LFO 
>> range
>> switch.
>>
>>   
> 
> 
> 
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