<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Hi , The LM324 is a quad opamp. LM194/LM394 is a matched transistor pair.<div class=""><br class=""></div><div class="">regards,</div><div class=""><br class=""></div><div class="">Terry<br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Nov 3, 2017, at 4:40 PM, <a href="mailto:ijfritz@comcast.net" class="">ijfritz@comcast.net</a> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class=""><font face="Helvetica" class="">Isn't the LM324 a quad opamp? <br class=""><br class=""><br class="">Sent from XFINITY Connect Mobile App<br class=""><br class=""><br class="">------ Original Message ------<br class=""><br class="">From: Ben Bradley<br class="">To: SYNTH<br class="">Sent: November 3, 2017 at 1:45 PM<br class="">Subject: [sdiy] On-chip transistor pairs<br class=""><br class="">The talk of exponential converters on VCAs brings to mind the use of<br class="">transistors for expo conversion, specifically on-chip transistor<br class="">pairs. Was there any use of National's (and later TI until they<br class="">stopped production) LM324 precision dual transistor in a synth expo<br class="">converter? The only product I know of it being used in was the Jensen<br class="">990 discrete op-amp. This tells Jensen's story of going through<br class="">replacements for the LM324:<br class=""><br class=""><a href="http://www.technicalaudio.com/pdf/Jensen_Transformers/Jensen_OpAmps_990_and_related/Jensen_JE-990_opamp_JAES_reprint_1980.pdf" class="">http://www.technicalaudio.com/pdf/Jensen_Transformers/Jensen_OpAmps_990_and_related/Jensen_JE-990_opamp_JAES_reprint_1980.pdf</a><br class=""><br class="">On the first couple pages of text here is Deane Jensen's descriotion<br class="">of the LM324, how it's made with many on-chip transistors wired<br class="">together as two:<br class="">http://www.johnhardyco.com/pdf/990.pdf<br class=""><br class="">I noticed our friends from Latvia are now making an LM324 replacement:<br class="">http://www.alfarzpp.lv/eng/sc/transistors.php<br class=""><br class="">There was also the ua726 self-heating temperature-regulated pair used<br class="">in classic synths that is basically unobtainable now. It would be good<br class="">to have that remade, or perhaps even an LM324 version with an on-chip<br class="">heater/temp regulator.<br class=""><br class="">The newly-remade module-on-a-chip designs are wonderful in having<br class="">everything built in, but I still want to make some "discrete" designs,<br class="">and having these transistor-pair-on-a-chip products available helps a<br class="">lot.<br class="">_______________________________________________<br class="">Synth-diy mailing list<br class="">Synth-diy@synth-diy.org<br class="">http://synth-diy.org/mailman/listinfo/synth-diy<br class=""></font></div>_______________________________________________<br class="">Synth-diy mailing list<br class=""><a href="mailto:Synth-diy@synth-diy.org" class="">Synth-diy@synth-diy.org</a><br class="">http://synth-diy.org/mailman/listinfo/synth-diy<br class=""></div></blockquote></div><br class=""></div></body></html>