<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="">Thanks for the positive feedback on this.<div class=""><br class=""></div><div class="">The PolySix VCF FM modulation:</div><div class="">At first I tried to duplicate Jürgen´s schematics for VCF FM-modulation directly, but it failed for me. Working on version two (which worked better, but not good enough), I understood the general idea better and came up with the solution for the final version, which included a lot more parts than anticipated. As several has mentioned here; you need a complete and separate path for all signals. So for the Polysix I needed 6. In addition I choose to have one CV-control common for all voices, just like on the Prophet-5.</div><div class=""><br class=""></div><div class="">The general path is like this:</div><div class="">- Each VCO output goes to an op-amp, and is then fed to each individual VCF, using the CV-input to the filter</div><div class="">- The amount of modulation is controlled by a pot, which generate a CV that controls each individual path (op-amp). One common control for all six voices. The pot drives an op-amp for this.</div><div class="">- I also added an on-off switch for each VCO-FM-VCF path, which is especially handsome when doing arpeggios to get changing rhythms, or when in unison mode and some voices are modulated and others not</div><div class="">- The Polysix analog board actually has a small diode (D10) on the PCB to indicate if the voice is on (taken directly from the gate signal). I removed these LEDs, and…</div><div class="">- The on-off switches for each voice FM-modulation have a LED on the top of the switches, and the LED-signals from the analog board was routed to these front panel switches, to easily see which voice is being modulated</div><div class=""><br class=""></div><div class="">I had to carefully choose values for the various parts to make it work. There is a limited CV-window where this works from zero to full FM-modulation.</div><div class="">There are also various support circuitry, like CV-smoothing, decoupling, LED-drivers, power etc.</div><div class="">Finding the various input/output points was fairly easy, especially since I first did all the other modifications mentioned.</div><div class="">All the circuitry was put on a veroboard, and fitted on top of the analog voice card inside, close to the edge of the keyboard frame inside. There is enough room between the analog PCB and front panel for this.</div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">Terje Winther</div><div class="">WintherStormer</div><div class=""><br class=""></div><div class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">5. okt. 2025 kl. 15:06 skrev Todd Sines <<a href="mailto:sines_list@scale.la" class="">sines_list@scale.la</a>>:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="content-type" content="text/html; charset=utf-8" class=""><div dir="auto" class="">This demo is otherworldly— can you share more details on how to do this for the PolySix?<div class=""><br class=""></div><div class=""><br id="lineBreakAtBeginningOfSignature" class=""><div dir="ltr" class=""><span style="background-color: rgba(255, 255, 255, 0);" class="">Todd<br class=""></span><div class=""><div class=""><span style="background-color: rgba(255, 255, 255, 0);" class=""><img src="http://scale.la/SCALE_2015.png" class="" data-unique-identifier=""><br class=""></span></div><div class=""><font style="background-color: rgba(255, 255, 255, 0);" class=""></font></div></div></div><div dir="ltr" class=""><br class=""><blockquote type="cite" class="">On Oct 5, 2025, at 7:34 AM, Terje Winther <<a href="mailto:terje.winther@wintherstormer.no" class="">terje.winther@wintherstormer.no</a>> wrote:<br class=""><br class=""></blockquote></div><blockquote type="cite" class=""><div dir="ltr" class=""><meta http-equiv="Content-Type" content="text/html; charset=utf-8" class="">I just want to add….<div class=""><br class=""></div><div class="">Jürgen Haible explained what he did with his Oberheim OB-8 here:</div><div class=""><a href="http://jhaible.com/legacy/hj_pmob8.html" class="">http://jhaible.com/legacy/hj_pmob8.html</a></div><div class=""><br class=""></div><div class="">I used this as a starting point for me doing the same on an Korg Polysix. Sound examples and a snippet of a photo here:</div><div class=""><a href="https://soundcloud.com/terjewinther/polysix-test" class="">https://soundcloud.com/terjewinther/polysix-test</a></div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">Terje Winther<br class=""><div class=""><div class=""><a href="mailto:terje.winther@wintherstormer.no" class="">terje.winther@wintherstormer.no</a><br class=""><a href="http://wintherstormer.no/" class="">http://wintherstormer.no/</a></div><div class=""><br class=""></div><br class="Apple-interchange-newline">
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<div>Terje Winther<br class=""><a href="mailto:terje.winther@wintherstormer.no" class="">terje.winther@wintherstormer.no</a><br class="">http://wintherstormer.no/</div><div class=""><br class=""></div><br class="Apple-interchange-newline">
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