[sdiy] Weird MFOS VCO max CV problem

[Travis Thatcher]

Right. I figured I'd swap it just in case, but I was thinking the same
thing.  I tried the circuit with both an LM394 and SSM2210 for U3 and
no change.

On Mon, Apr 9, 2012 at 11:21 PM, mark verbos <mverbos at earthlink.net> wrote:
> 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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>>
>>
>>
>> --
>> http://www.travisthatcher.com
>> http://www.soundcloud.com/travisthatcher
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