<div dir="ltr">"...the first read only memories ...64 bits"<div><br></div><div>The ProSoloist used the 7488 OTP PROM - made by TI - for instant patch changes. The 7488 had a capacity of 256 bits (not KB or MB!) in an 8x32 matrix - each PROM had 8 control lines for the 30 ProSoloist/ProDGX presets (two addresses were unused "off"), and there were eight of these PROMs in the PS. Access time was a snappy 26ns (compared to 2-300 millisecond access of later 27xxx EPROMs). Jeremy exploited the open collector output feature of those PROMs to enable or disable ProSoloist circuits by shorting control lines to ground through the PROM output when the OC output was a logic '1'. </div><div><br></div><div>I don't think any programmer had a profile for those old PROMs. They last appeared in a 1977 databook, yet ARP kept using them to make Pro/DGXs into 1981...!</div><div><br></div><div>That novel feature was covered in the patent. Other competitors - Moog, Roland, Yamaha, etc - had their preset synths but none lasted as long as the PS, and I don't think any of them could use PROMs for preset control without infringing the patent. I know that the Moog Satellite used a matrix of fixed resistors for preset configuration, which ARP had abandoned with the unreliable Soloist.</div><div><br></div><div>Woe for the 1970s repair tech who had to fix a malfunctioning ProSoloist VCO... few if any understood what made it tick. I asked a tech from those days if he had fixed ARPs - "Woah... Evil..." (sign of the cross) :D</div><div><br></div><div>MC</div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Mon, Jul 6, 2026 at 6:35 PM Tom Wiltshire <<a href="mailto:tom@electricdruid.net">tom@electricdruid.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div style="line-break:after-white-space">Isn't it just the typical adding-up-a-load-of-octave-squarewaves to make a staircase "ramp" waveform? 6 bits in this case, iirc.<div><br></div><div>Ah, yes, here it is, from the service manual:</div><div><br></div><div><img id="m_35478933641289279913458587D-6689-414C-853E-E96F7156B80A" width="387" height="113" src="cid:ii_19f39b8ccce5b83137d1"><br><div><br><blockquote type="cite"><div>On 6 Jul 2026, at 13:01, Mike Bryant <<a href="mailto:mbryant@futurehorizons.com" target="_blank">mbryant@futurehorizons.com</a>> wrote:</div><br><div><div 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;text-decoration:none;font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt">Actually one of the cleverest bits is probably converting the down-scaled squarewaves to sawtooths whilst keeping the levels consistent across the whole frequency range. No mention of how they did they - presumably by programming a constant current source with the key and octave number ?</div><div id="m_3547893364128927991appendonsend" style="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;text-decoration:none"></div><hr style="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;text-decoration:none;display:inline-block;width:609.546875px"><span style="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;text-decoration:none;float:none;display:inline"></span><div id="m_3547893364128927991divRplyFwdMsg" dir="ltr" style="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;text-decoration:none"><font face="Calibri, sans-serif" style="font-size:11pt"><b>From:</b><span> </span>Synth-diy <<a href="mailto:synth-diy-bounces@synth-diy.org" target="_blank">synth-diy-bounces@synth-diy.org</a>> on behalf of Roman Sowa via Synth-diy <<a href="mailto:synth-diy@synth-diy.org" target="_blank">synth-diy@synth-diy.org</a>><br><b>Sent:</b><span> </span>06 July 2026 12:06<br><b>To:</b><span> </span><a href="mailto:synth-diy@synth-diy.org" target="_blank">synth-diy@synth-diy.org</a> <<a href="mailto:synth-diy@synth-diy.org" target="_blank">synth-diy@synth-diy.org</a>><br><b>Subject:</b><span> </span>Re: [sdiy] GRP Genesi</font><div> </div></div><div style="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;text-decoration:none"><font size="2"><span style="font-size:11pt"><div>At first glimpse, just looking at block diagram, it looks like typical<span> </span><br>PLL, but instead of phase comparator it uses F-to-V conversion and<span> </span><br>voltage comparator. Same divider ratio is used in the feedback as in the<span> </span><br>vaweform output, so the VCO works only within 1 octave while overall<span> </span><br>output spans over many octaves.<br><br>Roman<br><br>W dniu 2026-07-05 o 11:26, Neil Johnson via Synth-diy pisze:<br>> Michael E Caloroso wrote:<br>><span> </span><br>> US 3,930,429<br>><span> </span><br>><span> </span><br>> Don did a write-up of it here:<span> </span><br>><span> </span><a href="https://till.com/articles/arp/patents.html#US03930429" target="_blank">https://till.com/articles/arp/patents.html#US03930429</a><span> </span><br>> <<a href="https://till.com/articles/arp/patents.html#US03930429" target="_blank">https://till.com/articles/arp/patents.html#US03930429</a>><br>> Very weird architecture indeed!<br>><span> </span><br>> Neil<br>><span> </span><br>> ________________________________________________________<br>> This is the Synth-diy mailing list<br>> Submit email to: <a href="mailto:Synth-diy@synth-diy.org" target="_blank">Synth-diy@synth-diy.org</a><br>> View archive at:<span> </span><a href="https://synth-diy.org/pipermail/synth-diy/" target="_blank">https://synth-diy.org/pipermail/synth-diy/</a><br>> Check your settings at:<span> </span><a href="https://synth-diy.org/mailman/listinfo/synth-diy" target="_blank">https://synth-diy.org/mailman/listinfo/synth-diy</a><br>> Selling or trading? 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