[sdiy] Weird MFOS VCO max CV problem

[mark verbos]

Since the 13700 is only the sin shaper, I don't see how that could have anything to do with the problem. 

Mark





On Apr 9, 2012, at 11:07 PM, Travis Thatcher wrote:

> I just replaced the LF442 (found one) and the OPA and still the same behavior.
> 
> On Mon, Apr 9, 2012 at 10:42 PM, Travis Thatcher <recompas at gmail.com> wrote:
>> This is the version, schematics on the page:
>> http://musicfromouterspace.com/analogsynth_new/VCO200604REV01/VCO200604REV01.html
>> 
>> I have some spare lm13700's laying around. I'm probably going to
>> replace that and see what happens. Not sure if i have another lf442
>> though, which is the summing opamp.
>> 
>> T
>> 
>> On Mon, Apr 9, 2012 at 10:06 PM, Olivier Gillet <ol.gillet at gmail.com> wrote:
>>>> There were some discussions about using a TL07x as an inverting integrator  in an OTA filter, many people had hang-up
>>>> issues at power up. Using the same part a voltage follower (with the integtator cap to ground) worked perfectly
>>>> every time...
>>> 
>>> I have seen this problem, but I think it's the other way round: I have
>>> seen frequently a phase reversal "crash" with the "cap to ground +
>>> follower" circuit when signal level was getting too high. Can happen
>>> when self-oscillation is reached, when cutoff is increased (less
>>> high-frequency attenuation -> higher level), or simply when a very hot
>>> external signal is fed into the circuit. I have worked a lot with +/-
>>> 5V so there's not much headroom and it's easy to hit the rails - and
>>> in this context seeing a TL072 with its +ve input not grounded raises
>>> a red flag for me. Neil Johnson has compiled this list of op-amps that
>>> do not phase-reverse:
>>> http://www.milton.arachsys.com/nj71/index.php?menu=2&submenu=2&subsubmenu=2
>>> 
>>> Back to the topic at hand, are there schematics of the offending circuit?
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>> 
>> 
>> 
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> 
> 
> 
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