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<DIV dir=ltr align=left><SPAN class=780350520-14122018><FONT color=#0000ff
size=2 face=Arial>I never have problems with analog electronics. In the
case of this scanner, for example, I designed the analog part so that
there are plateaus in the control voltage when switching occurs, which
gives me about 200mV of slop in the CV for switching. This circuit
worked the very first time (even though I've rebuilt it three times).
The problem here was all digital.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=780350520-14122018><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=780350520-14122018><FONT color=#0000ff
size=2 face=Arial>Later today, I'm ordering some DG444 and DG445, and also some
single SPST switches (don't know the DG number yet) and I'm going to rebuild
this thing Roman's way (with a few minor modifiations). The analog part is
perfect and won't have to change at all.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=780350520-14122018><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=780350520-14122018><FONT color=#0000ff
size=2 face=Arial>On the digital side, I'm worried about the fact that the
LM3914 comparators do not have built-in hysteresis, and there is no way to
install it, so I'm worried that the comparators will oscillate. I'm going
to stick with LM339, fully rigged for hysteresis (about 10mV worth) as this
worked well. Does anyone here have any experience with oscillating
LM3914?</FONT></SPAN></DIV><BR>
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<FONT size=2 face=Tahoma><B>From:</B> Rutger Vlek
[mailto:rutgervlek@gmail.com] <BR><B>Sent:</B> Friday, December 14, 2018 5:36
AM<BR><B>To:</B> David G Dixon; SDIY List<BR><B>Subject:</B> Re: [sdiy] Help,
I'm Desperate! (Charge Injection with DG408)<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV dir=ltr><SPAN style="FONT-FAMILY: Arial; COLOR: rgb(0,0,255)">| It just
shouldn't be this hard.</SPAN>
<DIV><BR></DIV>
<DIV>Ha, I totally agree! I once explored an approach to ring-modulation using
a single VCA and an inverting switch. It seemed like a nice, cost-effective,
approach (especially since I wanted to use a discrete VCA that would be too
bulky for another approach). After two prototypes of this circuit, I simply
gave up. In the analog domain it was simply too difficult to trigger the
switch exactly at the point where the VCA was fully closed, due to circuit
accuracy and noise. It was a hard lesson in the reality of analog electronics.
I went down the route of simply duplicating the discrete circuit for the
negative quadrants, and it works extremely well albeit not super-linear, but
that was a deliberate choice.</DIV>
<DIV><BR></DIV>
<DIV>Regards,<BR></DIV>
<DIV><BR></DIV>
<DIV>Rutger</DIV>
<DIV><BR></DIV>
<DIV>
<DIV class=gmail_quote>
<DIV dir=ltr>Op wo 12 dec. 2018 om 03:56 schreef David G Dixon <<A
href="mailto:dixon@mail.ubc.ca">dixon@mail.ubc.ca</A>>:<BR></DIV>
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<DIV>
<DIV dir=ltr align=left><SPAN
style="FONT-FAMILY: Arial; COLOR: rgb(0,0,255)">It just shouldn't be this
hard.</SPAN><BR></DIV>
<DIV dir=ltr align=left><SPAN
class=gmail-m_-4428784525104293679608281300-12122018><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN
class=gmail-m_-4428784525104293679608281300-12122018><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left>
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</DIV>
<DIV dir=ltr align=left><FONT size=2 face=Tahoma><B>From:</B> Synth-diy
[mailto:<A href="mailto:synth-diy-bounces@synth-diy.org"
target=_blank>synth-diy-bounces@synth-diy.org</A>] <B>On Behalf Of
</B>Roman<BR><B>Sent:</B> Tuesday, December 11, 2018 1:20 PM<BR><B>To:</B>
<A href="mailto:synth-diy@synth-diy.org"
target=_blank>synth-diy@synth-diy.org</A><BR><B>Subject:</B> Re: [sdiy]
Help, I'm Desperate! (Charge Injection with DG408)<BR></FONT><BR></DIV>
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<DIV></DIV>
<DIV>I know it's too late, as the circuit at this stage has already gone
slightly different path, and I already gave up, but couldn't help drawing
this little schemo that explains my idea of using single switches with
that obsoleted chip. Switches should be DG444 or similar (0=closed,
1=open), or replace diodes with NAND gates and use any regular dirt cheap
switch like 4066.<BR></DIV>
<DIV>There's no switching happening while VCA is open, provided that VCA
control triangles match the edges of LM3914 stages. The only switched
channels are the ones routed to muted VCA, so in theory there should be no
clicking audible.<BR></DIV>
<DIV>Basicaly this is just the circuit that makes this input switching
sequence:<BR></DIV>
<DIV>VCA-A:12233445566..<BR></DIV>
<DIV>VCA-B:11223344556...<BR></DIV>
<DIV>by creating one step overlap between stages. Only 6 inputs in this
example, but can be extended to any other number.<BR></DIV>
<DIV><A href="http://www.synthdiy.eu/files/scanner.png"
target=_blank>http://www.synthdiy.eu/files/scanner.png</A><BR></DIV>
<DIV><BR></DIV>
<DIV>IMHO switching active channel will always produce some clicking for
many reasons: not matched channels, difference between transistion times
H->L and L->H as Ingo said, break-before-make feature of DG407, slow
response of 4532, and who knows if not also charge injection.<BR></DIV>
<DIV><BR></DIV>
<DIV>Roman<BR></DIV>
<DIV class=gmail-m_-4428784525104293679nh_extra>
<P>Dnia 11 grudnia 2018 18:24 Ingo Debus <<A
href="mailto:igg.debus@gmail.com"
target=_blank>igg.debus@gmail.com</A>> napisał(a):<BR></P>
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<DIV id=gmail-m_-4428784525104293679gwpdccd74d0>
<BLOCKQUOTE>
<DIV>Am 11.12.2018 um 08:10 schrieb David G Dixon <<A
href="mailto:dixon@mail.ubc.ca"
target=_blank>dixon@mail.ubc.ca</A>>:<BR></DIV>
<DIV><BR></DIV>
<DIV>There is now<BR></DIV>
<DIV>only one tiny problem: There is still an almost imperceptible
click when the<BR></DIV>
<DIV>CV crosses 0V (and the logic control voltage crosses 2.5V) in the
positive<BR></DIV>
<DIV>direction. This is when the logic switches from 011 to 100
(i.e., all three<BR></DIV>
<DIV>bits change). Interestingly, I don't hear the click at all
when the CV goes<BR></DIV>
<DIV>in the other direction (100 to 011).<BR></DIV></BLOCKQUOTE>
<DIV><BR></DIV>
<DIV>Couldn’t this still be caused by a very brief „forbidden state“
during the transition from 011 to 100? In your case, the forbidden state
would be 000 (MSBit changes slower that the other two) or 111 (MSBit
changes faster). Probably just a difference between rising and falling
slope. Can you check with a scope?<BR></DIV>
<DIV><BR></DIV>
<DIV>Ingo<BR></DIV>
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