[sdiy] Re: reset circuit for LFO

Mon Oct 19 20:22:35 CEST 2009

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If you're using bipolar power=2C and shorting the cap to ground=2C you=20
should be getting the desired effect (the reset LFO starts over at=20
zero).=A0 If you've only got one supply rail=2C you should short the=20
cap to a buffered Vcc/2 circuit.

That actually raises an interesting question for me: if you're=20
simply grounding this capacitor and=A0 resetting the LFO to its
center value=2C isn't the "direction" of the LFO now the same as it
was before it was reset?=A0 If you want the phase to be predictable=2C
the comparator needs to be reset as well.=A0=20

----------------------------------------
> Date: Mon=2C 19 Oct 2009 10:53:05 -0700
> Subject: Re: [sdiy] Re: reset circuit for LFO
> From: danjel at gmail.com
> To: synth-diy at dropmix.xs4all.nl
>
> Here is another issue (and it may have to do with the point I picked
> to ground the CAP)
>
> Every time the reset pulse is high=2C the CV value of the LFO is held
> high. On normal LFOs when you reset the phase of the waveform seems to
> be held at the zero point. So if I was using an LFO to modulate an
> Oscillators pitch=2C at reset point there would be no modulation.
> In my circuit the reset point creates a higher pitched beep (higher
> than the max point of the modulation waveform). Now that I have
> stretched out the pulses a bit that beep is fairly long and
> significant. It kind of sounds cool since it creates a rhythmic melody
> but it is not the desired effect.
>
> On the LFO pcb there are two timing caps which are for the two
> different rate ranges (Hi/lo) these connect to a switch which selects
> between the two caps and it is at this point that I am trying the
> grounding.
>
> So first should I just try a smaller cap size for the pulse
> stretching? (22pF is already pretty small)? Should I try some other
> type of trigger processing?
>
>
>
> On Mon=2C Oct 19=2C 2009 at 10:25 AM=2C Danjel van Tijn  wrote:
>> ok I put a 22pF cap to stretch out the pulse and this is working great
>> when feeding a pulse signal from the Elf LFO. I also put a diode in
>> series for protecting against negative voltage.
>>
>> However=2C my midi2cv converter clock and gate (which have no problem
>> triggering things like the doepfer A160/161 or doepfer envelopes) are
>> not triggering it at all.
>>
>> This goes back to my question on if I am powering the cd4053 at 12V
>> does it matter that the gates/clk are 5V?
>>
>>
>>
>> cheers=2C
>> Danjel
>>
>>
>>
>>
>>
>>
>> On Mon=2C Oct 19=2C 2009 at 10:06 AM=2C Danjel van Tijn  wrote:
>>> oops not a diode to ground=2C a diode inline!
>>>
>>>> Is it as simple as putting a small cap between signal and ground of my
>>>> reset jack?
>>>>
>>>> Should I also be putting a diode to ground to protect the CMOS chip
>>>> from any negative voltage?
>>>>
>>>> cheers=2C
>>>>   Danjel
>>>>
>>>>>
>>>>> You might try a "pulse stretcher" circuit essentially adding a small
>>>>> something picofarad cap
>>>>> to lag the incoming clock a bit... (would be simpler than adding a
>>>>> comparator and pulse
>>>>> conditioning circuit with debouncing etc?
>>>>>
>>>>> Best Wishes!
>>>>>
>>>>>
>>>>> Cynthia
>>>>>
>>>>>
>>>>>
>>>>> Danjel van Tijn wrote:
>>>>>>
>>>>>> Someone suggested using the circuit that Ken Stone used on the clock
>>>>>> input here: http://www.cgs.synth.net/modules/cgs13v2_gated_comparato=
r.html
>>>>>>
>>>>>> A comparator with a diode like this might help me out.
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Mon=2C Oct 19=2C 2009 at 8:16 AM=2C Danjel van Tijn  wrote:
>>>>>>
>>>>>>>
>>>>>>> A while ago I posted asking for advice on modding a Livewire Vulcan
>>>>>>> lfo so that it could be reset.
>>>>>>> Amos suggested using a CD4053 switch to control the timing cap bein=
g
>>>>>>> shorted to ground temporarily to cause a reset.
>>>>>>>
>>>>>>> As first experiment I had two wires: one to the timing cap and one =
to
>>>>>>> ground. Whenever I connected these together temporarily it
>>>>>>> successfully reset the LFO.
>>>>>>>
>>>>>>> Next step was  wiring up a little board with the switch circuit. Th=
e
>>>>>>> reset jack was connected to one of the control inputs of the cd4053=
 so
>>>>>>> that a short pulse would temporarily connect the LFO timing cap to
>>>>>>> ground.
>>>>>>>
>>>>>>> So far it kind of works but not well:  If I feed at an LFO squarewa=
ve
>>>>>>> from a Plan B ELF LFO  it holds the Vulcan in reset while it is hig=
h
>>>>>>> and then allows it to cycle when it is low. However when I switch t=
o
>>>>>>> the alternative narrow pulse square waveform the pulses seem to be =
too
>>>>>>> short to cause a reset.
>>>>>>> Also when I connect a midi2cv converter and generate clock pulses o=
r
>>>>>>> gate signals they are unable to cause a trigger.
>>>>>>>
>>>>>>> Right now the 4053 is being powered by the 12V rail... should I be
>>>>>>> using a lower voltage so that the logic signals from other devices
>>>>>>> like my midi2cv can actually drive the 40530 controls? i.e. Should =
I
>>>>>>> run it at 5V instead?
>>>>>>>
>>>>>>> Do I need any kind of trigger conditioning off of the reset jack?
>>>>>>> e.g. filter? schmitt trigger?
>>>>>>>
>>>>>>> cheers=2C
>>>>>>> Danjel
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> Synth-diy mailing list
>>>>>> Synth-diy at dropmix.xs4all.nl
>>>>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
>>>
>>
>
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