PLAN B analog blog

Yes.

Crossfading to nothing will give you an ultra quiet, ultra linear VCA for both CVs and audio signals.  To do this, insert a signal into either the input B or Processor B, making sure there's nothing in the A inject or A Processor inputs and that that offset is at 12 o' clock. use the xcrossfade pots as a manual level and the VC Xfade input as the control voltage input.

Works great.

(we have another non-filtered (non M13 type LPF) VCA coming shortly.  More on that at 
Namm...


If you want an inverted VCA in which the amplitude gets louder as the CV goes lower, then repeat the above but input the signal to the A inject input or A processor.


- P



--- In PLAN_B_analog_blog@yahoogroups.com, John <inform3r@...> wrote:
>
>     So I¹ve never really looked at the M14 closely. I read in Peter¹s post
> that there are some linear VCA¹s in there. Can the M14 be used as a
> conventional VCA?
> 
>     Regards,
>     John
> 
> 
> On 12/13/06 1:32 PM, "(i think you can figure that out)"
> <peter@...> wrote:
> 
> >  
> >  
> >  
> > 
> > 
> > I'm going to answer these based on what I think you may be referring to here.
> > If I'm wrong 
> > please calrify and I will address your questions:
> > 
> > Dead spot - If you're meaning does it have an amplitude drop in center
> > position when 
> > crossfading two audio signals, yes it does, but it's insignificant - only  a
> > half dB - which as
> > you know is inaudible, being about a 1/4 the energy required for the human ear
> > to 
> > recognize a drop in amplitude and well within what's considered equal power
> > transfer.  In 
> > comparison, two crossfaded linear VCAs without the compensation circuitry
> > found in the 
> > M14 will yield a 3dB drop at center.
> > 
> > Accuracy:  If what you're speaking about is in regard to the relative
> > amplitude levels of the
> > A and B inputs when the xfade is at center, then it's completely accurate.
> > The two VCAs 
> > used in the crossfader are ultra linear. When the crossfade pot is at center,
> > it will open the 
> > A and B VCA exactly the same amount, yet both are cheated 2.5 dB positive from
> > about 11 
> > to 1 o' clock (meaning pot position) to remove the audible dead spot (see
> > above).  The 
> > elbow of this cheat circuit is soft - you won't hear a sudden bump in
> > amplitude.  It's a
> > seamless transition.
> > 
> > In order for this to work successfully however, THE SIGNAL LEVELS INTO THE A/B
> > INPUTS 
> > MUST BE THE SAME AMPLITUDE.  Amplitude inequalities between the two inputs
> > will 
> > obviously cause an offset (if your A signal is louder than your B signal going
> > in, then the 
> > mid point crossfade will favor the A side).  If this is the case, you can
> > easily compensate by
> > cheating the pan pot slightly to favor the B side, which is why we decided not
> > to use a 
> > center detent pot for the xfader.
> > 
> > hope this helps -
> > 
> > - P
> > 
> > --- In PLAN_B_analog_blog@yahoogroups.com
> > <mailto:PLAN_B_analog_blog%40yahoogroups.com> , "jalmari3" <jari.jokinen@>
> > wrote:
> >> >
> >>> > > If you hate that, then you'll have to remove of the DC offset by
> >>> > > making sure the offset pot is set to the center positions on both
> >>> > > processors so that both LEDs are unlit WHEN NO SIGNAL IS CONNECTED TO
> >>> > > THE INPUTS.
> >> >
> >>> > > Once you do that there will be no more thump.  A virtual thum-be-gone.
> >> >
> >>> > > - P
> >> >
> >> > How accurately does this work in practice? Does the offset knob have
> >> > a "dead spot" in center position?
> >> >
> >> > I am considering to get a Model 14 to replace two mixers (for CV and
> >> > audio). Of course, it can do other things too.
> >> >
> >> > Best regards
> >> > Jari Jokinen
> >> >
> > 
> > ______________
> > Peter Grenader
> > e: peter@... <mailto:peter%40ear-group.net>
> > p: 866-755-4468 (818 761-9906)
> > w: http://www.ear-group.net
> > 
> >  
> >
>