[sdiy] discrete/no-OTA VCO

[Tony Rolando]

harrybissell at wowway.com wrote:
> There is a triangle wave VCO that uses two opamps and one
> transistor. The CV is input to the first opamp (an inverting
> integrator) through two resistors, one to inverting and one to non-inverting.
> A transistor shunts the non-inverting side to ground. Unequal
> resistors make the ramps equal in time. The other opamp is a schmitt
> trigger.
>
> Classic circuit suffers from relatively small tuning range (maybe 10-20:1)
> because eventually the control voltage must get really large to get the
> current in.  Current controlled oscillators have much wider range.
>
> I think this is in the National Semiconductor Linear Apps databook...
> but I can't find it right now.
>
>   

It is in that databook. I designed a variation of this circuit into a 
small noise instrument I built for somebody. They work great for sound 
design and noise, but definitely are not able to be tuned to 1V/oct or 
any standard that I recognized.

TOny

> H^) harry
>
>
>
> On Mon, 29 Dec 2008 08:45:02 -0500, DAF wrote
>   
>> thanks for all of the suggestions thus far - I am particularly 
>> intrigued by the UJT voltage-controlled relaxation osc. especially 
>> because of the low parts count, but I am wondering if the UJT is 
>> also going the way of the dodo bird, and also is the control of 
>> frequency linear over a wide enough range (I see it used in synths 
>> that use octave divider schemes)?
>>
>> In that Ray Wilson schematic, he says for a VCLFO, leave out the 
>> parts in RED; are you to join the resulting gaps together on the 
>> wires shown remaining?
>>
>> Dave
>>
>> ----- Original Message ----- 
>> From: "Simon Brouwer" <simon.oo.o at xs4all.nl>
>> To: "sdiy" <synth-diy at dropmix.xs4all.nl>
>> Sent: Monday, December 29, 2008 3:13 AM
>> Subject: Re: [sdiy] discrete/no-OTA VCO
>>
>>     
>>> Here is one:
>>>
>>> http://www.elby-designs.com/asm-2/lfo/lfo1-asm2-cct.pdf
>>>
>>>
>>> DAF schreef:
>>>       
>>>> Hello - can someone point me to a circuit for a  voltage-controlled
>>>> lfo that uses discrete or other easy to source parts.  I have used an
>>>> OTA-based design in the past, but I want to design around more generic
>>>> parts.  I seem to remember a vco that used a discrete JFET?  I don't
>>>> neet expo response or temp compensation.  I am looking for about a 2
>>>> to 10 Hz response range.  I don't want to use any specialty chips or
>>>> OTA's, just discrete transistors and op-amps.   Any help greatly
>>>> appreciated.
>>>>
>>>> thanks,
>>>> Dave
>>>>         
>>> -- 
>>> Vriendelijke groet,
>>> Simon Brouwer.
>>>
>>> | http://nl.openoffice.org | http://www.opentaal.org |
>>>
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>
>
> Harry Bissell & Nora Abdullah 4eva
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