Hex VC mixer

[Hairy Harry]

This will ONLY work on an A series (unbuffered) chip.
Trying this on a B series is sure death !!! (chip will overheat)

H^) harry


>From: bader <trip at blackstar.myip.org>
>To: Magnus Danielson <cfmd at swipnet.se>
>CC: synth-diy at node12b53.a2000.nl
>Subject: Re: Hex VC mixer
>Date: Mon, 24 Jul 2000 13:22:16 -0500 (EST)
>
>
>
>While were on the subject of digital logic for analog functions, This
>reminds me of something i saw with a 4011 that made it function
>as a quad op-amp. Connect one of the inputs to vcc, and the extra input
>acts like the negative input on an op-amp. Add your resistors and
>feedback loop, there you go.
>
>I haven't tried this myself, Same idea, maybe?
>
>On a sidenote, maybe you could use the input connected to vcc to toggle it
>between inverting an non inverting. Once again, i haven't tried this.
>
>On Sun, 23 Jul 2000, Magnus Danielson wrote:
>
> > From: "Paul Maddox" <paul.maddox at ndirect.co.uk>
> > Subject: Hex VC mixer
> > Date: Mon, 10 Jul 2000 13:53:35 +0100
> >
> > > Dear all,
> >
> > Dear all,
> >
> > I am just back from 2 weeks of holiday without an Internet connection, 
>so I
> > have a huge backlogg... so I will not even consider checking for a 
>proper
> > reply to this email...
> >
> > >   I remember a while back a schematic for a 4049 based (I think) 
>voltage
> > > controlled
> > > 6 channel mixer..
> > >
> > >   anyone have a link/schematic?
> >
> > No, but I recall the trick.
> >
> > The 4049UB is an hex inverter consisting a N-channel and a P-channel 
>MOSFET
> > transistor. The trick here is to use one of these transistors as an 
>ordinary
> > FET variable resistor (using two resistors), use the common wiring of 
>these
> > interters, namely the powerline as the summation point of the six 
>channels.
> >
> > So, for each channel you feed the CV into the input through an 1 Meg 
>resistor,
> > you hook another 1 Meg resistor from the inverter output to the inverter
> > input. Now, feed your signal into the inverter output (yeah, you heard 
>me!)
> > and use the 4069UB ground as an virtual ground summation point. Wire the
> > Vcc to ground to disable the upper half of the inverter.
> >
> > Its pretty wierd and el-cheapo, but hey! It works! ;)
> >
> > If I recall it correctly this thing was used by no other than Paia ;)
> >
> > Cheers,
> > Magnus
> >
> >
>

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