Hex VC mixer

[bader]

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
> 
>