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<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial>Yes, Mark, it is the same idea. However, it only works
well if the opamp outputs are equal and opposite. If they are unequal,
then the threshold voltages are too sloppy.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial>My circuit is a 9-channel morphing scanner. It is based
on a back-and-forth 2164-based crossfader. For 9 channels, the crossfader
goes from B to A to B to A to B to A to B to A to B. These correspond to
channels 1, 2, 3, 4, 5, 6, 7, 8 and 9. </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial>There are two main parts of the circuit. The first part
turns a -5V to +5V CV signal into a series of truncated triangles which go from
+5 to 0 to +5 to 0 to +5 to 0 to +5 to 0 to +5. This is the control signal
for the linearized 2164 VCA in the crossfader. The actual triangles are
-1V to 6V, but they are clipped at 0V and +5V to give small plateaus where only
one voice is exerted. This part of the circuit works
perfectly.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial>The second part converts the -5V to +5V CV signal to 8 3-bit
codes which control two DG408 8-channel analog muxes. The switching is
done when the control triangles are somewhere on their plateaus, and this
provides a tiny bit of leeway for the actual switching voltages. The
DG408s exert pairs of the input audio signals and send them to the
crossfader. The pattern is:</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial>DG408 A: 1 3 3 5 5 7 7 9</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial>DG408 B: 2 2 4 4 6 6 8 8</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial>In this way, the switching is done in such a way that the same
audio signal is exerted full-strength during the switch, so there is no audible
switching. It's like this: 1 to 2 (switch) 2 to 3 (switch) 3 to 4,
etc. In this way, a single crossfader can process as many voices as you
want.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial>I built a 5-channel version of this and it worked perfectly
(there's a video on Youtube to prove it). The AD in that case was only
2-bit and evidently there was enough slope in the switching voltages such
that all four switches occurred during the control triangle plateaus.
However, the 9-channel version did not work perfectly using the
"rough-and-ready" comparator method. There were one or two audible
switching points, and some of the switches were occurring off of the plateaus,
when more than one voice was being exerted.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial>I don't believe that it would be practical to expand
this design to 17 voices, although that would be cool. 33 voices would be
even cooler, but who has 33 separate audio signals to fade? It would be
possible with a more precise AD converter, like an actual
IC.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=273220800-29112018><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #0000ff 2px solid; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px"
dir=ltr>
<DIV></DIV><FONT color=#0000ff size=2 face=Arial></FONT><FONT color=#0000ff
size=2 face=Arial></FONT><FONT color=#0000ff size=2 face=Arial></FONT><A
href="http://hem.bredband.net/bersyn/VCO/8p2ch VC switch_s.pdf">http://hem.bredband.net/bersyn/VCO/8p2ch%20VC%20switch_s.pdf</A>
<DIV><BR></DIV>
<DIV><BR></DIV>
<DIV>There’s a 3 bit flash converter here, done in the style of John Simonton.
Uses a TL074</DIV>
<DIV><BR></DIV>
<DIV><BR></DIV>
<DIV>Mark</DIV></BLOCKQUOTE></BODY></HTML>