[sdiy] VCO comparator's reference voltage - rail OK?

Oren Leavitt obl64 at ix.netcom.com
Mon Mar 29 02:32:32 CEST 2021


Personally I find the least expensive grade of REF02 (5V) works perfect 
for VCOs.

I use the voltage ref to set comparator trip point, the reference 
current to the expo servo, and for any fixed frequency control pots. You 
can basically run the VCO on +/-12V or +/-15V without having to readjust 
anything.


On 3/28/21 4:45 PM, cheater cheater via Synth-diy wrote:
> Sorry, I was thinking of REF01, the 10V one.
>
> Might as well use REF02 or REF03 depending on how you structure your signal.
>
> Is LM4040 just as good? I don't know. The last time we had a voltage
> reference megathread it was decided that REFxx is the best.
>
> On Sun, Mar 28, 2021 at 10:40 PM Tom Bugs <admin at bugbrand.co.uk> wrote:
>> I'm also curious why REF03 - that's the 2.5V one, whereas the REF01 would be a 10V ref.
>> I know many use the REF02 (5V) in euro (is 10V ref ok on +/-12V euro setups?)
>>
>> I use the 10V LM4040 for references & pots for manual control - I like that value as it gives 10oct at 1V/oct, a good sort of range.
>> I find it makes resistor values streamline nicely too.
>>
>> Personally I never really tried AD parts, though note their strong lineage.
>> LM4040s are available in a good range of voltages, accuracies & temp. stability values.
>>
>> On 28/03/2021 21:14, Pete Hartman wrote:
>>
>> What's wrong with the cheaper LM4040's?
>>
>> e.g. https://www.mouser.com/ProductDetail/Diodes-Incorporated/LM4040B25FTA?qs=GWgl%252BsiMZr%2F%252BaZ%252BmKrTIBg%3D%3D
>>
>> On Sun, Mar 28, 2021 at 3:09 PM cheater cheater <cheater00social at gmail.com> wrote:
>>> You want a REF03 voltage reference from AD. That's the easiest and
>>> best way of doing this.
>>>
>>> On Sun, Mar 28, 2021 at 9:42 PM Neil Harper <metadata at gmx.com> wrote:
>>>> so now that I have my own little VCO going on the breadboard, i want to
>>>> do a perfboard module with it for my system. so now I'm thinking about
>>>> how this VCO will remain stable in a system where the rails might be
>>>> fluctuating.
>>>>
>>>> the first issue i see is that my LM311 comparator takes a reference
>>>> voltage drawn from my +15V rail through a resistor to set the trip
>>>> point. if that +15V waivers, so will my trip point.. and so will my
>>>> frequency. so should things like that be derived from an onboard
>>>> reference instead? is this common practice?
>>>>
>>>> I see in schematics like the ENS-76 VCO (
>>>> http://www.synthsource.com/ens76/vcofig6.jpg ) that the comparator
>>>> reference is just taken from the rail (through R13, R14 divider). Same
>>>> with Thomas Henry's VCO-1's, lots of references right off the rails.
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> /// Neil Harper
>>>> /// Every Wave is New Until it Breaks
>>>>
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