<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><br><div><div><br><blockquote type="cite"><div>On 14 Nov 2023, at 9:49 am, Tom Wiltshire <tom@electricdruid.net> wrote:</div><br class="Apple-interchange-newline"><div><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">Yeah, I did a deep dive on the DR-110 a while back:<div><br></div><div><a href="https://electricdruid.net/analogue-drums-boss-dr-110-drum-machine/">https://electricdruid.net/analogue-drums-boss-dr-110-drum-machine/</a></div><div><br></div><div>Despite what Boss/Roland say about "Interrelations between frequencies are so critical that slight deviation of one frequency can cause beat sound or distortion" in the service manual, I don't believe the frequencies are *that* critical. Shortly after, they mention that the caps need to be 5% tolerance (so *much* tighter than the usual 20%!) but that would give +/-15Hz roughly for even the lowest frequency they list. That's a pretty hefty beat frequency, even before the oscillator you're beating against drifts out by even more in the other direction.</div><div><br></div><div>What I do find interesting is the different ways this "metallic noise" thing has been done. DR-110 uses *four* mixed squarewave sources, bandpass filtered. TR-606 uses *six* squarewave sources, mixed.</div></div></div></blockquote><div><br></div><div><span style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0);">Yes, the CR-8000 is similar, and in addition you get a killer "Rimshot" sound from the lowest 2 oscillators!</span></div><div><font color="#000000"><span style="caret-color: rgb(0, 0, 0);">Mentioned here</span></font></div><div><div style="display: block;"><div style="-webkit-user-select: all; -webkit-user-drag: element; display: inline-block;" class="apple-rich-link" draggable="true" role="link" data-url="https://mezzoauto.blogspot.com/2017/06/roland-cr-8000-compurhythm.html"><a style="border-radius:10px;font-family:-apple-system, Helvetica, Arial, sans-serif;display:block;-webkit-user-select:none;width:300px;user-select:none;-webkit-user-modify:read-only;user-modify:read-only;overflow:hidden;text-decoration:none;" class="lp-rich-link" rel="nofollow" href="https://mezzoauto.blogspot.com/2017/06/roland-cr-8000-compurhythm.html" dir="ltr" role="button" draggable="false" width="300"><table style="table-layout:fixed;border-collapse:collapse;width:300px;background-color:#E5E6E9;font-family:-apple-system, Helvetica, Arial, sans-serif;" class="lp-rich-link-emailBaseTable" cellpadding="0" cellspacing="0" border="0" width="300"><tbody><tr><td vertical-align="center" align="center"><img style="width:300px;filter:brightness(0.97);height:157px;" width="300" height="157" draggable="false" class="lp-rich-link-mediaImage" alt="CR8000profile.jpg" src="cid:B0D66ADE-4809-4EDB-B766-C554CC9870A2"></td></tr><tr><td vertical-align="center"><table bgcolor="#E5E6E9" cellpadding="0" cellspacing="0" width="300" style="font-family:-apple-system, Helvetica, Arial, sans-serif;table-layout:fixed;background-color:rgba(229, 230, 233, 1);" class="lp-rich-link-captionBar"><tbody><tr><td style="padding:8px 0px 8px 0px;" class="lp-rich-link-captionBar-textStackItem"><div style="max-width:100%;margin:0px 16px 0px 16px;overflow:hidden;" class="lp-rich-link-captionBar-textStack"><div style="word-wrap:break-word;font-weight:500;font-size:12px;overflow:hidden;text-overflow:ellipsis;text-align:left;" class="lp-rich-link-captionBar-textStack-topCaption-leading"><a rel="nofollow" href="https://mezzoauto.blogspot.com/2017/06/roland-cr-8000-compurhythm.html" style="text-decoration: none" draggable="false"><font color="#272727" style="color: rgba(0, 0, 0, 0.847059);">Roland CR-8000 CompuRhythm</font></a></div><div style="word-wrap:break-word;font-weight:400;font-size:11px;overflow:hidden;text-overflow:ellipsis;text-align:left;" class="lp-rich-link-captionBar-textStack-bottomCaption-leading"><a rel="nofollow" href="https://mezzoauto.blogspot.com/2017/06/roland-cr-8000-compurhythm.html" style="text-decoration: none" draggable="false"><font color="#808080" style="color: rgba(0, 0, 0, 0.498039);">mezzoauto.blogspot.com</font></a></div></div></td></tr></tbody></table></td></tr></tbody></table></a></div></div></div><div><br></div><div><br></div><div>Economical Roland engineering at work again!</div><div><br></div><div><br></div><div>A</div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><br><blockquote type="cite"><div><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><div> KR-55 uses ring-modulated pairs of six squarewave sources, added together (extra complex!). </div><div><br><div>
<div>Tom</div><br class="Apple-interchange-newline">
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<div><br><blockquote type="cite"><div>On 13 Nov 2023, at 23:08, Adam (synthDIY) <<a href="mailto:synthdiy@adambaby.com">synthdiy@adambaby.com</a>> wrote:</div><br class="Apple-interchange-newline"><div><meta http-equiv="content-type" content="text/html; charset=utf-8"><div style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">Ha, Love it!<div>S'funny, you'd think these frequencies would not be all that critical for what basically is metallic noise, but some schematics suggest otherwise (808, 606, Dr-110)</div><div>This from the Dr-110...</div><div><br></div><div><span id="cid:71BFF9C3-5B10-4CBA-920E-AB5E4C2EF94D"><grab 2023-11-14 at 9.03.25 am.png></span></div><div><br></div><div><br></div><div>A<br><div><br><blockquote type="cite"><div>On 13 Nov 2023, at 11:44 pm, Tom Wiltshire <<a href="mailto:tom@electricdruid.net">tom@electricdruid.net</a>> wrote:</div><br class="Apple-interchange-newline"><div><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><div>Hi All,</div><div><br></div><div>I've been studying old drum machines again. This time, I've been looking at the Korg KR-55.</div><div><br></div><div>I've come up with one quirk or schematic error, and I'd like you to take a look and see if you agree with me.</div><div><br></div><div>The machine uses eight simple squarewave oscillators to generate two "metallic noise" signals for cymbal synthesis. These are called Ring1 and Ring2, because they're generated using pairs of oscillators "ring modulated" together by 4070 XOR gates. The schematic looks like this:</div><div><br></div><a href="https://electricdruid.net/wp-content/uploads/2023/11/RingGenerator.jpg">https://electricdruid.net/wp-content/uploads/2023/11/RingGenerator.jpg</a><div><br></div><div>The whole thing is here:</div><div><br></div><div><a href="https://www.synthxl.com/wp-content/uploads/2021/10/korg-kr-55-Service-Schematic.pdf">https://www.synthxl.com/wp-content/uploads/2021/10/korg-kr-55-Service-Schematic.pdf</a></div><div><br></div><div>The schematic gives us frequencies for the eight squarewaves. We also know that the general pattern for such oscillators is Freq = k/RC, so it's just a question of working out what k is in this case (using the LM339 on a 5V supply).</div><div>It occurred to me that we can assume the designers wanted the tuning pots roughly in the centre, so if we feed in the required Frequency, with the midpoint R value and the given capacitor, we can work out k. That gives us this:</div><div><br></div><div><table style="margin: auto; width: 1081.1875px; border: 1px solid rgb(102, 102, 102); font-family: -webkit-standard; background-color: rgb(255, 255, 255);"><tbody><tr><th>Required Freq</th><th>R</th><th>C</th><th>K</th></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">272 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">125 KΩ</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">22 nF</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">748000</td></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">8529 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">49 KΩ</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">8.1 nF</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">3385160.1</td></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">633 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">125 KΩ</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">9.1 nF</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">720037.5</td></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">9073 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">49 KΩ</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">1.5 nF</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">666865.5</td></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">1458 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">125 KΩ</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">3.3 nF</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">601425</td></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">13500 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">49 KΩ</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">1 nF</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">661500</td></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">731 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">125 KΩ</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">7.5 nF</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">685312.5</td></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">3946 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">125 KΩ</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">1.5 nF</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">739875</td></tr></tbody></table><div><br></div></div><div>This is all pretty reasonable, with values between 600,000 and 750,000, which is not much of a spread. However, that second row is an exception - it's way out. Working out the average value, excluding 8529Hz, gives us k = 689,002. We can then put that k value back in and see where the tuning pots need to be in theory:</div><div><br></div><div><table style="margin: auto; width: 1081.1875px; border: 1px solid rgb(102, 102, 102); font-family: -webkit-standard; background-color: rgb(255, 255, 255);"><tbody><tr><th>Required Freq</th><th>Required R</th><th>Midpoint R</th></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">272 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">115.1K</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">125 K</td></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">8529 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">10.0K</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">49 K</td></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">633 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">119.6K</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">125 K</td></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">9073 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">50.6K</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">49 K</td></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">1458 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">143.2K</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">125 K</td></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">13500 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">51.0K</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">49 K</td></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">731 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">125.7K</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">125 K</td></tr><tr><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">3946 Hz</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">116.4K</td><td style="text-align: center; border: 1px solid rgb(153, 153, 153);">125 K</td></tr></tbody></table><div><br></div></div><div>As you can see, all the "Required R" values are pretty close to the midpoint R values. The fifth line, 1458Hz, is pushing it a bit - we have 150K as the maximum value from the resistor+trimmer, so that's a bit close to the end, but it's still within, just about.</div><div><br></div><div>The BIG EXCEPTION is that second line, which needs an R value five times smaller than the available 39K+20K trimmer. What's going on? Is this just a mistake on the schematic? Is the frequency wrong, or is it the cap value that is wrong?</div><div><br></div><div>Any thoughts much appreciated.</div><div><br></div><div>Thanks,</div><div>Tom</div><div><br></div><div><div>
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