PLAN B analog blog

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, "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@ear-group.net
p: 866-755-4468 (818 761-9906)
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