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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
A VCA of sorts
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gasboss775



Joined: Jan 02, 2016
Posts: 212
Location: Scotland

PostPosted: Tue Apr 11, 2017 5:32 am    Post subject: Reply with quote  Mark this post and the followings unread

I wanted to try out the minimal configuration that would yield usable results. The attached images show the simulation results and schematic for a very basic VCA implementation which seems to work well ( at least on the simulator! )

Only works with Digital Signal Sources

The Pot adjusts the decay time.

The output is highlighted in green, the 2.8 Mohm represents the input impedance of a jfet buffer / mixer.


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gasboss775



Joined: Jan 02, 2016
Posts: 212
Location: Scotland

PostPosted: Tue Apr 11, 2017 11:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Bread-boarded this and it worked well the trigger source was from a 4017 counter. If the trigger source had a bit more muscle ( say from a 555 ) then the first circuit above would probably have sufficed.


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richardc64



Joined: Jun 01, 2006
Posts: 669
Location: NYC
Audio files: 26

PostPosted: Tue Apr 11, 2017 8:28 pm    Post subject: Re: Diode VCA & simple EG Reply with quote  Mark this post and the followings unread

gasboss775 wrote:
I tried this version of the diode VCA today. ( see attached )

R3 was found to be necessary to avoid signal breakthrough.



Without a resistor path to ground at the VCA output -- that is, if it's capacitor coupled -- the right-hand diode can be omitted, as below.


nf_drum.gif
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At +V = 9V, output level was more that adequate to drive my pc Line In without amplification.
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gasboss775



Joined: Jan 02, 2016
Posts: 212
Location: Scotland

PostPosted: Tue Apr 11, 2017 10:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks RichardC64, I was thinking about a drum circuit like that but not sure on component values, I'll definitely give this one a try!
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gagarin



Joined: Mar 17, 2014
Posts: 1
Location: vilnius

PostPosted: Thu Oct 05, 2017 3:46 am    Post subject: Re: Diode VCA & simple EG Reply with quote  Mark this post and the followings unread

richardc64 wrote:
gasboss775 wrote:
I tried this version of the diode VCA today. ( see attached )

R3 was found to be necessary to avoid signal breakthrough.



Without a resistor path to ground at the VCA output -- that is, if it's capacitor coupled -- the right-hand diode can be omitted, as below.


How can I change attack time? What will be if I will use sine or saw as input signal?
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gasboss775



Joined: Jan 02, 2016
Posts: 212
Location: Scotland

PostPosted: Wed Nov 15, 2017 12:55 pm    Post subject: Re: Diode VCA & simple EG Reply with quote  Mark this post and the followings unread

gagarin wrote:
richardc64 wrote:
gasboss775 wrote:
I tried this version of the diode VCA today. ( see attached )

R3 was found to be necessary to avoid signal breakthrough.



Without a resistor path to ground at the VCA output -- that is, if it's capacitor coupled -- the right-hand diode can be omitted, as below.


How ca7n I change attack time? What will be if I will use sine or saw as input signal?


It's easy to add an attack control ( see attached ) this type of VCA can only work with logic / rectangular signals.


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airfrankenstein



Joined: Jan 10, 2010
Posts: 60
Location: france

PostPosted: Tue Apr 16, 2019 1:46 am    Post subject: Re: A VCA of sorts
Subject description: and simple EGs
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Hi there,
So these simple circuits are entirely passive ?









richardc64 wrote:
At some point you'll want to hear the results of interconnecting all these digital circuits, and you'll probably want some dynamic control of the amplitude. The first circuit provides amplitutude control of digital waveforms without resorting to OpAmps, OTAs, or (ugh) cmos in linear mode.

Basically, as CV rises, the rectangular wave from the digital output to be heard "stands up" at the junction of the two diodes and passes through the 100K resistor and the coupling capacitor. This method was used in paia's Stringz-n-Thingz and a similiar technique was used in their Cosmic EGG.

Two simple EGs are shown, which don't really need much explanation. Select pot and cap values for the desired durations. The Gate Inputs should probably be buffered by an AND gate with both inputs tied together. If the output is to be routed many places, it can be buffered by a single-supply OpAmp such as the LM324.
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gabbagabi



Joined: Nov 29, 2008
Posts: 520
Location: will be back soon in Berlin by n8
Audio files: 23

PostPosted: Thu Apr 18, 2019 5:12 am    Post subject: Reply with quote  Mark this post and the followings unread

i was forced to remember something as i saw the simulation screenshot


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Steveg



Joined: Apr 23, 2015
Posts: 107
Location: Perth, Australia

PostPosted: Mon Apr 22, 2019 3:58 pm    Post subject: Re: A VCA of sorts
Subject description: and simple EGs
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airfrankenstein wrote:
Hi there,
So these simple circuits are entirely passive ?


Welcome airfrankenstein,
No, they all have active components such as the transistors.
Passive is usually reserved for circuits that have no powered components.
Cheers,
Steveg
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