<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Ah, adding a resistor on the opamp output is a nice trick to save some current! The SSI has a 10k impedance so the benefits with their chip is lessened, but still very cool.<div class=""><br class=""></div><div class="">Thanks,</div><div class=""><br class=""></div><div class="">epk</div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Jul 15, 2019, at 10:00 PM, David G Dixon <<a href="mailto:dixon@mail.ubc.ca" class="">dixon@mail.ubc.ca</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><o:smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="PostalCode" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><o:smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="City" class=""><o:smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="country-region" class=""><o:smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="place" class=""><div class="Section1" style="page: Section1;"><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman';" class=""><font size="2" color="navy" face="Arial" class=""><span style="font-size: 10pt; font-family: Arial; color: navy;" class="">To further add to Neil’s comment, in an Irwin cell, the 2164s really heat up when the VCA is off – i.e., when the control voltage is 0V. I have two tricks I always apply to these VCAs: 1) I put -5V to the CV summer through a 10M resistor to ensure that the VCA actually goes off completely at a CV of 0V (to compensate for opamp offset voltage – my beloved TL07Xs can have enough offset voltage to keep the VCA slightly on at 0V), and 2) I put a 4.7k resistor between the output of the CV summer and the 2164 control pins to limit the current into those pins. In the Irwin circuit, when the CV is 0V, the CV summer actually hits the positive rail. Given the 5k input impedance of the V2164 (I know it’s different for the SSI 2164, but I can’t remember what it is), this will put a current of about 2.7mA into both VC pins, or 5.4mA total into the chip. If the unit is a dual VCA, and they are both off, then the 2164 is getting nearly 11mA into its VC pins – it heats up in a hurry. The 4.7k resistor limits the voltage at the VC pins to about 4.7V (coincidentally), and the total current into the chip is only about 0.9mA per pin – about three times less. With that resistor in place, the 2164 doesn’t heat up at all, it has no effect whatsoever on linearity, and 4.7V is still enough to shut the VCAs off pretty hard.<o:p class=""></o:p></span></font></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman';" class=""><font size="2" color="navy" face="Arial" class=""><span style="font-size: 10pt; font-family: Arial; color: navy;" class=""><o:p class=""> </o:p></span></font></div><div class=""><div class="MsoNormal" align="center" style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; text-align: center;"><font size="3" face="Times New Roman" class=""><span style="font-size: 12pt;" class=""><hr size="2" width="100%" align="center" tabindex="-1" class=""></span></font></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman';" class=""><b class=""><font size="2" face="Tahoma" class=""><span style="font-size: 10pt; font-family: Tahoma; font-weight: bold;" class="">From:</span></font></b><font size="2" face="Tahoma" class=""><span style="font-size: 10pt; font-family: Tahoma;" class=""><span class="Apple-converted-space"> </span>Synth-diy [<a href="mailto:synth-diy-bounces@synth-diy.org" class="">mailto:synth-diy-bounces@synth-diy.org</a>]<span class="Apple-converted-space"> </span><b class=""><span style="font-weight: bold;" class="">On Behalf Of<span class="Apple-converted-space"> </span></span></b>Neil Johnson<br class=""><b class=""><span style="font-weight: bold;" class="">Sent:</span></b><span class="Apple-converted-space"> </span>Monday, July 15, 2019 12:14 PM<br class=""><b class=""><span style="font-weight: bold;" class="">To:</span></b><span class="Apple-converted-space"> </span>electronicpresskit<br class=""><b class=""><span style="font-weight: bold;" class="">Cc:</span></b><span class="Apple-converted-space"> </span>SDIY List<br class=""><b class=""><span style="font-weight: bold;" class="">Subject:</span></b><span class="Apple-converted-space"> </span>Re: [sdiy] Difficult 2164 behaviour between different sections.</span></font><o:p class=""></o:p></div></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman';" class=""><font size="3" face="Times New Roman" class=""><span style="font-size: 12pt;" class=""><o:p class=""> </o:p></span></font></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman';" class=""><font size="3" face="Times New Roman" class=""><span style="font-size: 12pt;" class="">The 2164 is quite temperature sensitive - there is a reason the data sheet mentions a warm up time as part of the device spec. <o:p class=""></o:p></span></font></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman';" class=""><font size="3" face="Times New Roman" class=""><span style="font-size: 12pt;" class=""><o:p class=""> </o:p></span></font></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman';" class=""><font size="3" face="Times New Roman" class=""><span style="font-size: 12pt;" class="">It is also why<span class="Apple-converted-space"> </span><a href="http://temp.co/" style="color: blue; text-decoration: underline;" class="">temp.co</a><span class="Apple-converted-space"> </span>schemes work quite well, and also why it is the cardinal rule that any compensation gain cell is on the same silicon as the cell it is compensating. The same goes for the Irwin linearised VCA.<o:p class=""></o:p></span></font></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman';" class=""><font size="3" face="Times New Roman" class=""><span style="font-size: 12pt;" class=""><o:p class=""> </o:p></span></font></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman';" class=""><font size="3" face="Times New Roman" class=""><span style="font-size: 12pt;" class="">It is worth bearing in mind that any control voltage more than a couple of volts is going to have a noticeable heating effect on the silicon and that will affect the gain coefficient of the surrounding cells.<o:p class=""></o:p></span></font></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman';" class=""><font size="3" face="Times New Roman" class=""><span style="font-size: 12pt;" class=""><o:p class=""> </o:p></span></font></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman';" class=""><font size="3" face="Times New Roman" class=""><span style="font-size: 12pt;" class="">Neil<o:p class=""></o:p></span></font></div></div></div><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman';" class=""><font size="3" face="Times New Roman" class=""><span style="font-size: 12pt;" class=""><o:p class=""> </o:p></span></font></div><div class=""><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman';" class=""><font size="3" face="Times New Roman" class=""><span style="font-size: 12pt;" class="">On Mon, 15 Jul 2019, 19:39 Erik Dower, <<a href="mailto:electronicpresskit@gmail.com" style="color: blue; text-decoration: underline;" class="">electronicpresskit@gmail.com</a>> wrote:<o:p class=""></o:p></span></font></div></div><blockquote style="border-style: none none none solid; border-left-color: rgb(204, 204, 204); border-left-width: 1pt; padding: 0in 0in 0in 6pt; margin-left: 4.8pt; margin-right: 0in;" class="" type="cite"><div style="margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: 'Times New Roman';" class=""><font size="3" face="Times New Roman" class=""><span style="font-size: 12pt;" class="">I was thinking that might be the way to go. On my circuit, there is a very small amount of fm happening when the gain cell is attenuating, but a very distinct jump in frequency once it starts amplifying.<br class=""><br class="">epk<br class=""><br class="">> On Jul 15, 2019, at 4:57 PM, Tom Bugs <<a href="mailto:admin@bugbrand.co.uk" target="_blank" style="color: blue; text-decoration: underline;" class="">admin@bugbrand.co.uk</a>> wrote:<br class="">><span class="Apple-converted-space"> </span><br class="">> I didn't exactly - I rejigged things so that different sections were used for the critical parts.<br class="">><span class="Apple-converted-space"> </span><br class="">> Best, Tom<br class="">><span class="Apple-converted-space"> </span><br class="">> On 14/07/2019 21:05, Erik Dower wrote:<br class="">>> Hi Tom,<br class="">>><span class="Apple-converted-space"> </span><br class="">>> Did you ever resolve this issue? Unfortunately I find myself in a similar situation.<br class="">>><span class="Apple-converted-space"> </span><br class="">>> Thanks,<br class="">>><span class="Apple-converted-space"> </span><br class="">>> epk<br class="">>><span class="Apple-converted-space"> </span><br class="">>>> On May 30, 2018, at 10:29 PM, Tom Bugs <<a href="mailto:admin@bugbrand.co.uk" target="_blank" style="color: blue; text-decoration: underline;" class="">admin@bugbrand.co.uk</a>> wrote:<br class="">>>><span class="Apple-converted-space"> </span><br class="">>>> Thanks all.<br class="">>>><span class="Apple-converted-space"> </span><br class="">>>> Beefing up the 0V is something I tried on another point of the circuit, but I don't think I tried it on the 0V pin itself - good point!<br class="">>>><span class="Apple-converted-space"> </span><br class="">>>> I will try Rbias some more for sure.<br class="">>>><span class="Apple-converted-space"> </span><br class="">>>> And agree with many of the points from David - it has been an eye opener & I will have a few more deep sessions with it.<br class="">>>><span class="Apple-converted-space"> </span><br class="">>>> I'll report back..<br class="">>>><span class="Apple-converted-space"> </span><br class="">>>> Cheers - Tom<br class="">>>><span class="Apple-converted-space"> </span><br class="">>>><span class="Apple-converted-space"> </span><br class="">>>> On 30/05/2018 19:41, David G Dixon wrote:<br class="">>>>> That's an excellent idea. I was thinking something similar, because if<br class="">>>>> there is any external impedance at that pin, then those control inputs are<br class="">>>>> going to interact because of those internal 5k impedances. That's probably<br class="">>>>> the issue -- your ground isn't really ground.<br class="">>>>><span class="Apple-converted-space"> </span><br class="">>>>>> -----Original Message-----<br class="">>>>>> From: Synth-diy [mailto:<a href="mailto:synth-diy-bounces@synth-diy.org" target="_blank" style="color: blue; text-decoration: underline;" class="">synth-diy-bounces@synth-diy.org</a>] On<br class="">>>>>> Behalf Of Oakley Sound<br class="">>>>>> Sent: Wednesday, May 30, 2018 9:11 AM<br class="">>>>>> To: Synth DIY<br class="">>>>>> Subject: Re: [sdiy] Difficult 2164 behaviour between<br class="">>>>>> different sections.<br class="">>>>>><span class="Apple-converted-space"> </span><br class="">>>>>> It could well be internal to the 2164 but have you tried<br class="">>>>>> lowering the the resistance to the 0V pin? Temporarily cludge<br class="">>>>>> a ruddy big wire from the PSU's 0V directly to pin 8, in<br class="">>>>>> parallel with what you've already got on the board, and see<br class="">>>>>> what happens.<br class="">>>>>><span class="Apple-converted-space"> </span><br class="">>>>>> Tony<br class="">>>>>><span class="Apple-converted-space"> </span><br class="">>>>>><span class="Apple-converted-space"> </span><a href="http://www.oakleysound.com/" target="_blank" style="color: blue; text-decoration: underline;" class="">www.oakleysound.com</a><br class="">>>>>> _______________________________________________<br class="">>>>>> Synth-diy mailing list<br class="">>>>>><span class="Apple-converted-space"> </span><a href="mailto:Synth-diy@synth-diy.org" target="_blank" style="color: blue; text-decoration: underline;" class="">Synth-diy@synth-diy.org</a><br class="">>>>>><span class="Apple-converted-space"> </span><a href="http://synth-diy.org/mailman/listinfo/synth-diy" target="_blank" style="color: blue; 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text-decoration: underline;" class="">www.bugbrand.co.uk</a><br class="">>>><span class="Apple-converted-space"> </span><br class="">>>><span class="Apple-converted-space"> </span><br class="">>>> ---<br class="">>>> This email has been checked for viruses by AVG.<br class="">>>><span class="Apple-converted-space"> </span><a href="https://www.avg.com/" target="_blank" style="color: blue; text-decoration: underline;" class="">https://www.avg.com</a><br class="">>>><span class="Apple-converted-space"> </span><br class="">>>> _______________________________________________<br class="">>>> Synth-diy mailing list<br class="">>>><span class="Apple-converted-space"> </span><a href="mailto:Synth-diy@synth-diy.org" target="_blank" style="color: blue; text-decoration: underline;" class="">Synth-diy@synth-diy.org</a><br class="">>>><span class="Apple-converted-space"> </span><a href="http://synth-diy.org/mailman/listinfo/synth-diy" target="_blank" style="color: blue; text-decoration: underline;" class="">http://synth-diy.org/mailman/listinfo/synth-diy</a><br class="">>><span class="Apple-converted-space"> </span><br class="">> --<span class="Apple-converted-space"> </span><br class="">> BugBrand LTD<br class="">><span class="Apple-converted-space"> </span><st1:country-region w:st="on" class=""><st1:place w:st="on" class="">UK</st1:place></st1:country-region><span class="Apple-converted-space"> </span>company No. 07199808<br class="">> VAT No. GB 988 2629 57<br class="">> 1 Ninetree Hill<br class="">><span class="Apple-converted-space"> </span><st1:place w:st="on" class=""><st1:city w:st="on" class="">BRISTOL</st1:city><span class="Apple-converted-space"> </span><st1:postalcode w:st="on" class="">BS1 3SB</st1:postalcode></st1:place><br class="">><span class="Apple-converted-space"> </span><st1:country-region w:st="on" class=""><st1:place w:st="on" class="">United Kingdom</st1:place></st1:country-region><br class="">><span class="Apple-converted-space"> </span><a href="http://www.bugbrand.co.uk/" target="_blank" style="color: blue; 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