<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">It's cancelling the variable offset introduced by the first one, in order to make a bipolar MDAC instead of a unipolar one.<div class=""><br class=""></div><div class="">Tom</div><div class=""><br class=""><div class="">
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<div><br class=""><blockquote type="cite" class=""><div class="">On 21 Mar 2023, at 10:42, Mike Bryant <<a href="mailto:mbryant@futurehorizons.com" class="">mbryant@futurehorizons.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="elementToProof" style="font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; background-color: rgb(255, 255, 255);">I think you mean to say any R/2R based DAC with external reference. Plenty of delta-sigmas have an external reference but won't work like that.</div><div class="elementToProof" style="font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; background-color: rgb(255, 255, 255);"><br class=""></div><div class="elementToProof" style="font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; background-color: rgb(255, 255, 255);">So what exactly is the second DAC in your scheme doing ?</div><div class="elementToProof" style="font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; background-color: rgb(255, 255, 255);"><br class=""></div><div id="appendonsend" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""></div><hr tabindex="-1" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; display: inline-block; width: 760.46875px;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class=""></span><div id="divRplyFwdMsg" dir="ltr" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><font face="Calibri, sans-serif" style="font-size: 11pt;" class=""><b class="">From:</b><span class="Apple-converted-space"> </span>Synth-diy <<a href="mailto:synth-diy-bounces@synth-diy.org" class="">synth-diy-bounces@synth-diy.org</a>> on behalf of Roman Sowa <<a href="mailto:modular@go2.pl" class="">modular@go2.pl</a>><br class=""><b class="">Sent:</b><span class="Apple-converted-space"> </span>21 March 2023 10:25<br class=""><b class="">To:</b><span class="Apple-converted-space"> </span>Paul Perry <<a href="mailto:pfperry@melbpc.org.au" class="">pfperry@melbpc.org.au</a>>; <a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a> <<a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a>><br class=""><b class="">Subject:</b><span class="Apple-converted-space"> </span>Re: [sdiy] Niche ACM-1 how's this thing work?</font><div class=""> </div></div><div class="BodyFragment" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><font size="2" class=""><span style="font-size: 11pt;" class=""><div class="PlainText">You can make multiplying DAC out of 2 any DACs with external reference<span class="Apple-converted-space"> </span><br class="">input. Both DACs must be controlled by the same SPI. The Vref of 1st DAC<span class="Apple-converted-space"> </span><br class="">is driven with your input of interest, say mxer's channel audio, but<span class="Apple-converted-space"> </span><br class="">with added voltage offset to midscale so the signal fits within DAC's<span class="Apple-converted-space"> </span><br class="">ratings. The Vref of 2nd DAC takes only the offset itself. Then the<span class="Apple-converted-space"> </span><br class="">output of 2nd DAC is reversed and added to the output of 1st DAC.<br class="">Despite the hassle and complexity it's still cheaper than "real"<span class="Apple-converted-space"> </span><br class="">multiplying DAC.<br class=""><br class="">Roman<br class=""><br class=""><br class=""><br class="">W dniu 2023-03-20 o 23:29, Paul Perry via Synth-diy pisze:<br class="">> This reminds me that I can't seem to find any cheap available<span class="Apple-converted-space"> </span><br class="">> multiplying DACs. Any suggestions? Are they abandoned technology?<br class="">> paul perry Melbourne Australia<br class="">><span class="Apple-converted-space"> </span><br class="">> On Tue, Mar 21, 2023 at 4:12 AM Mike Bryant <<a href="mailto:mbryant@futurehorizons.com" class="">mbryant@futurehorizons.com</a><span class="Apple-converted-space"> </span><br class="">> <<a href="mailto:mbryant@futurehorizons.com" class="">mailto:mbryant@futurehorizons.com</a>>> wrote:<br class="">><span class="Apple-converted-space"> </span><br class="">> That was one of Jim Williams' last app notes for Natsemi before he<br class="">> left for LTC. At the time the DAC1020 family was an improvement on<br class="">> the PMI and ADI devices we used but I recall it was a lot more<br class="">> expensive at the time.<br class="">> ------------------------------------------------------------------------<br class="">> *From:* Ben Stuyts <<a href="mailto:ben@stuyts.nl" class="">ben@stuyts.nl</a> <<a href="mailto:ben@stuyts.nl" class="">mailto:ben@stuyts.nl</a>>><br class="">> *Sent:* 20 March 2023 16:50<br class="">> *To:* Mike Bryant <<a href="mailto:mbryant@futurehorizons.com" class="">mbryant@futurehorizons.com</a><br class="">> <<a href="mailto:mbryant@futurehorizons.com" class="">mailto:mbryant@futurehorizons.com</a>>><br class="">> *Cc:* <a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a> <<a href="mailto:synth-diy@synth-diy.org" class="">mailto:synth-diy@synth-diy.org</a>><br class="">> <<a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a> <<a href="mailto:synth-diy@synth-diy.org" class="">mailto:synth-diy@synth-diy.org</a>>>; mark<br class="">> verbos <<a href="mailto:markverbos@gmail.com" class="">markverbos@gmail.com</a> <<a href="mailto:markverbos@gmail.com" class="">mailto:markverbos@gmail.com</a>>><br class="">> *Subject:* Re: [sdiy] Niche ACM-1 how's this thing work?<br class="">> That reminded me at something I’ve looked at in the past: NatSemi<br class="">> AN-299 uses a multiplying DAC (DAC1020) for this. See page 5<br class="">> (panner/attenuator) and 6 (bandpass filter) of<br class="">> <span class="Apple-converted-space"> </span><a href="https://www.ti.com/lit/an/snva530/snva530.pdf" class="">https://www.ti.com/lit/an/snva530/snva530.pdf</a><br class="">> <<a href="https://www.ti.com/lit/an/snva530/snva530.pdf" class="">https://www.ti.com/lit/an/snva530/snva530.pdf</a>>.<br class="">><span class="Apple-converted-space"> </span><br class="">> Ben<br class="">><span class="Apple-converted-space"> </span><br class="">>> On 20 Mar 2023, at 16:10, Mike Bryant <<a href="mailto:mbryant@futurehorizons.com" class="">mbryant@futurehorizons.com</a><br class="">>> <<a href="mailto:mbryant@futurehorizons.com" class="">mailto:mbryant@futurehorizons.com</a>>> wrote:<br class="">>><br class="">>> The NatSemi LM1973N used to be fairly popular for this<br class="">>> application. Not as good as the dBX chip but a lot cheaper and<br class="">>> smaller. It was three channel, but there were also one and two<br class="">>> channel versions. Maybe they prototyped an 8-channel version but<br class="">>> never released it into volume manufacture.<br class="">>><br class="">>> ------------------------------------------------------------------------<br class="">>> *From:*Synth-diy <<a href="mailto:synth-diy-bounces@synth-diy.org" class="">synth-diy-bounces@synth-diy.org</a><br class="">>> <<a href="mailto:synth-diy-bounces@synth-diy.org" class="">mailto:synth-diy-bounces@synth-diy.org</a>>> on behalf of mark verbos<br class="">>> via Synth-diy <<a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a><br class="">>> <<a href="mailto:synth-diy@synth-diy.org" class="">mailto:synth-diy@synth-diy.org</a>>><br class="">>> *Sent:*20 March 2023 13:55<br class="">>> *To:*<a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a> <<a href="mailto:synth-diy@synth-diy.org" class="">mailto:synth-diy@synth-diy.org</a>><br class="">>> <<a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a> <<a href="mailto:synth-diy@synth-diy.org" class="">mailto:synth-diy@synth-diy.org</a>>><br class="">>> *Subject:*[sdiy] Niche ACM-1 how's this thing work?<br class="">>> Those of us as old as I am might remember this thing from the 90s.<br class="">>> It is patched into the inserts on a mixer and then adds MIDI<br class="">>> controlled automation. All the chatter around is about how it is<br class="">>> passive, so it has “infinite” headroom, 0% distortion, 0% gain. I<br class="">>> got one recently for a low price. I looked inside, eager to know<br class="">>> the trick…. Vactrols? Motorized pots? something I don’t even know<br class="">>> about? Inside the is a big chip 28pins or something with the label<br class="">>> scratched off. Does anyone know what is actually going on in this<br class="">>> thing? Is that an 8 channel digitally controlled pot? Just curious.<br class="">>><br class="">>> Mark<br class="">>><br class="">>><br class="">>><br class="">>> _______________________________________________<br class="">>> Synth-diy mailing list<br class="">>> <a href="mailto:Synth-diy@synth-diy.org" class="">Synth-diy@synth-diy.org</a> <<a href="mailto:Synth-diy@synth-diy.org" class="">mailto:Synth-diy@synth-diy.org</a>><br class="">>> <span class="Apple-converted-space"> </span><a href="http://synth-diy.org/mailman/listinfo/synth-diy" class="">http://synth-diy.org/mailman/listinfo/synth-diy</a><br class="">>> <<a href="http://synth-diy.org/mailman/listinfo/synth-diy" class="">http://synth-diy.org/mailman/listinfo/synth-diy</a>><br class="">>> Selling or trading? Use <a href="mailto:marketplace@synth-diy.org" class="">marketplace@synth-diy.org</a><br class="">>> <<a href="mailto:marketplace@synth-diy.org" class="">mailto:marketplace@synth-diy.org</a>><br class="">>> _______________________________________________<br class="">>> Synth-diy mailing list<br class="">>> <a href="mailto:Synth-diy@synth-diy.org" class="">Synth-diy@synth-diy.org</a> <<a href="mailto:Synth-diy@synth-diy.org" class="">mailto:Synth-diy@synth-diy.org</a>><br class="">>> <span class="Apple-converted-space"> </span><a href="http://synth-diy.org/mailman/listinfo/synth-diy" class="">http://synth-diy.org/mailman/listinfo/synth-diy</a><br class="">>> <<a href="http://synth-diy.org/mailman/listinfo/synth-diy" class="">http://synth-diy.org/mailman/listinfo/synth-diy</a>><br class="">>> Selling or trading? <a href="mailto:Usemarketplace@synth-diy.org" class="">Usemarketplace@synth-diy.org</a><br class="">>> <<a href="mailto:marketplace@synth-diy.org" class="">mailto:marketplace@synth-diy.org</a>><br class="">><span class="Apple-converted-space"> </span><br class="">> _______________________________________________<br class="">> Synth-diy mailing list<br class="">> <a href="mailto:Synth-diy@synth-diy.org" class="">Synth-diy@synth-diy.org</a> <<a href="mailto:Synth-diy@synth-diy.org" class="">mailto:Synth-diy@synth-diy.org</a>><br class="">> <span class="Apple-converted-space"> </span><a href="http://synth-diy.org/mailman/listinfo/synth-diy" class="">http://synth-diy.org/mailman/listinfo/synth-diy</a><br class="">> <<a href="http://synth-diy.org/mailman/listinfo/synth-diy" class="">http://synth-diy.org/mailman/listinfo/synth-diy</a>><br class="">> Selling or trading? Use <a href="mailto:marketplace@synth-diy.org" class="">marketplace@synth-diy.org</a><br class="">> <<a href="mailto:marketplace@synth-diy.org" class="">mailto:marketplace@synth-diy.org</a>><br class="">><span class="Apple-converted-space"> </span><br class="">><span class="Apple-converted-space"> </span><br class="">> _______________________________________________<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="">><span class="Apple-converted-space"> </span><a href="http://synth-diy.org/mailman/listinfo/synth-diy" class="">http://synth-diy.org/mailman/listinfo/synth-diy</a><br class="">> Selling or trading? 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Use marketplace@synth-diy.org<br class=""></div></span></font></div><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">_______________________________________________</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">Synth-diy mailing list</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><a href="mailto:Synth-diy@synth-diy.org" 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-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">Synth-diy@synth-diy.org</a><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><a href="http://synth-diy.org/mailman/listinfo/synth-diy" 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-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">http://synth-diy.org/mailman/listinfo/synth-diy</a><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">Selling or trading? 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