<div dir="ltr"><span style="color:rgb(0,0,255);font-family:Arial">| 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><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><u></u>
<div>
<div dir="ltr" align="left"><span style="color:rgb(0,0,255);font-family:Arial">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">
<hr>
</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>
<blockquote style="border-left:2px solid rgb(0,0,255);padding-left:5px;margin-left:5px;margin-right:0px" dir="ltr">
<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>
<blockquote style="border-left:2px solid rgb(153,153,153);margin:0px;padding-left:8px" class="gmail-m_-4428784525104293679nh_quote">
<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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