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<p>I used the same circuit and it works well. I have a 220K for your
R82. That is the only significant difference I see.</p>
<p>--TimR<br>
</p>
<div class="moz-cite-prefix">On 2/6/2019 3:08 PM, Danjel van Tijn
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CACn5rYHF2JnLTU3s5ZvmihZOMjaOe4MUCcyJtJT1uSUa2WRm_Q@mail.gmail.com">
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<div dir="ltr">Here is a link to the schematic block: <a
href="https://ibb.co/njhCcbZ" moz-do-not-send="true">https://ibb.co/njhCcbZ</a>
<div><br>
</div>
<div>Really just a standard Mike Irwin configuration that we
have used on literally thousands of modules. Dave Dixon and
I have tended to use 30k as the standard input resistance to
the VCA cells but on more recent designs we have started using
100k.</div>
<div><br>
</div>
<div>Unfortunately we just built a ton of modules with the
SSI2164 and our factory did not tell me they had switched to
the new chip (from the v2164). We can re-work these by
replacing the three 30k resistors with 100k but I would still
like to understand this better. It also unfortunately means
the SSI2164 is not a blind drop in replacement for the V2164
and I am going to have to test out the rest of our circuits
very carefully before any more manufacturing.</div>
<div><br>
</div>
<div>Hopefully this helps some other folks avoid the same
headache!</div>
<div><br>
</div>
<div><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Wed, Feb 6, 2019 at 3:01 PM
Neil Johnson <<a href="mailto:neil.johnson71@gmail.com"
moz-do-not-send="true">neil.johnson71@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div>Hi Danjel,</div>
<div><br>
</div>
<div>Can you share the circuit you are building? Do you
have some means of pulling the leakage current out of the
summing node? This is usually done with a high-value
resistor. And the issue Matthias raised is that with 30k
you are sending more current into the gain cell, so the
leakage current will be higher (well, it's not really
leakage in the classic sense, but the fact that as this is
a log circuit you can never achieve infinite attenuation,
so *some* current will leak through.</div>
<div><br>
</div>
<div>As to why there is a difference, I would need to make
some measurements on the bench. One difference I do know
is that the SSI2164 has much larger transistors in the
gain cell, giving better log conformance, but they may
exhibit different "off" behaviours.</div>
<div><br>
</div>
<div>The 0.85V you are seeing - that would equate to about
26dB attenuation. In the Irwin linearised circuit an
input CV of 0V would force the VCA CV to very positive
(op-amp output pinned to the +ve rail) as it tries to
attenuate the bias current to 0 with infinite attenuation.<br>
</div>
<div><br>
</div>
<div>Cheers</div>
<div>Neil</div>
<div><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Wed, 6 Feb 2019 at
22:20, Danjel van Tijn <<a
href="mailto:danjel@intellijel.com" target="_blank"
moz-do-not-send="true">danjel@intellijel.com</a>>
wrote:<br>
</div>
</div>
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div dir="ltr">Hi there,
<div><br>
</div>
<div>Has anyone else experienced issues with the SSI2164
used in place of a Coolaudio 2164 in a linearized VCA
configuration?</div>
<div><br>
</div>
<div>With no CV applied to the circuit control pin of
the VCA should be close to 0 (and it is when I swap
back in a coolaudio chip) but with a SSI2164 the
voltage at the control pin is around 0.85V.</div>
<div><br>
</div>
<div>I am using accurate voltage sources for the
negative and positive voltage references (-5 and +5).
and as aforementioned swapping in a coolaudio chip
returns the circuit to working as expected.</div>
<div>Opamp is a TI TL072CPWR.</div>
<div><br>
</div>
<div>The only two differences from the datasheet version
are that we are using 30K for Rin and 510R+560p for
stability; both are within range of acceptable values
according to datasheet.</div>
<div><br>
</div>
<div>Any thoughts? possibly bad batch of ICs? </div>
<div><br>
</div>
<div><br>
</div>
</div>
-- <br>
<div dir="ltr"
class="m_1991626421464980015gmail-m_-9101134765231673121gmail_signature">
<div dir="ltr">cheers,
<div><br>
<div>
<div>Danjel van Tijn<br>
Intellijel Designs Inc.<br>
m. +001 <a href="tel:(604)%20773-2426"
value="+16047732426" target="_blank"
moz-do-not-send="true">604-773-2426</a><br>
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</div>
</div>
</div>
</div>
</blockquote>
</div>
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
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<br clear="all">
<br>
-- <br>
<div dir="ltr" class="m_1991626421464980015gmail_signature"><a
href="http://www.njohnson.co.uk" target="_blank"
moz-do-not-send="true">http://www.njohnson.co.uk</a><br>
</div>
</blockquote>
</div>
-- <br>
<div dir="ltr" class="gmail_signature"
data-smartmail="gmail_signature">
<div dir="ltr">cheers,
<div><br>
<div>
<div>Danjel van Tijn<br>
Intellijel Designs Inc.<br>
m. +001 <a href="tel:(604)%20773-2426"
value="+16047732426" target="_blank"
moz-do-not-send="true">604-773-2426</a><br>
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<br>
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<pre class="moz-quote-pre" wrap="">_______________________________________________
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</blockquote>
<pre class="moz-signature" cols="72">--
--Tim Ressel
Circuit Abbey
<a class="moz-txt-link-abbreviated" href="mailto:timr@circuitabbey.com">timr@circuitabbey.com</a></pre>
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