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This is actually quite a common issue. The advice given so far is sound; bypass capacitors are certainly a must, but not sufficient solution. A comprehensive approach must be taken for any Eurorack case (which tends to be far noisier than standalone equipment) to become noise-free.
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Proper filtering requires a good, low impedance ground path. This includes the module circuitry (proper PCB layout practices), power distribution bus boards, power supply and of course the wall socket ground! Many folks don't even consider the latter.
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Here's a great white paper by Genus Modu to give you some idea:
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<a href="http://www.genusmodu.com/products/libb-wp-01.html">http://www.genusmodu.com/products/libb-wp-01.html</a>
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I'm not proposing you run out and buy their busboards, although I can attest to their performance.
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The PSU may or may not be a factor, but you won't really know until you've created a low impedance ground path from the module back to the PSU.
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Best of luck,
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Peter Knoot
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14197 N Hidden Arroyo Pass
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Marana, AZ 85658-4995
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USA
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650-759-2101
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<a href="http://www.synquanon.com">www.synquanon.com</a>
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On 02/19/2023 9:21 AM MST A.M. Barrio via Synth-diy <synth-diy@synth-diy.org> wrote:
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This is the complete email I wanted to send. There's another thread where the attached files and additional info is missing. My bad, pressed CTRL + Enter by mistake whoops. Please ignore that one! <a href="mailto:pata@ieee.org" target="_blank" rel="noopener">pata@ieee.org</a> and <a href="mailto:mbryant@futurehorizons.com" target="_blank" rel="noopener">mbryant@futurehorizons.com</a>, thank you for your replies, I have taken them into account :-)
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Hello,
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I'm having an issue where the frequency of my VCO is being affected by the operation of other modules. I'll give a broader explanation:
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I'm a beginner on synth DIY, right now I have my home made case, a PSU, two VCOs, an LFO, a clock module and an amplifier/speaker (built in the case, not externally). Everything has been arranged by me, I haven't purchased any module yet. The clock and the LFO are the latest modules I have built (pretty much both at the same time), and when I tested them on their own, they worked just fine. However I noticed that when they are powered, the frequency of the VCO would stutter following the operation of the clock and the LFO.
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That would be: <strong>without connecting the clock or the LFO anywhere</strong>, just having them powered up, whenever the clock is up or down, or the waves generated by the LFO reset, the frequency of the VCO varies a tiny bit. It gets more noticeable the higher the pitch of the VCO.
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After some head scratching I've realised that the signals generated by any of the modules I have (both VCOs, the clock and the LFO) are somehow leaking into the +12 and -12 rails of my PSU. Measuring any of the rails on my scope (on AC mode, so only the noise is shown), I can see that the waves generated by the modules I mentioned above are there as well in the form of noise (around 20mVpp each of them). That explains the little variations in frequency of the VCO. However I have no idea why this is happening or how to fix it. I have tried with different PSUs I have around:
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<li>11V 0.750A SMPS into DCDC to get +12 and -12</li>
<li>Two 12V 1A SMPS together to get +12 and -12</li>
<li>Linear PSU with 7812 and 7912</li>
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I have the same problem<span id="goog_1466379976"></span><span id="goog_1466379977"></span> with all of them. I'm positive there's an issue somewhere with a lack of filtering, but I don't know where, or why.
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I'm attaching a sample of the VCO output where the stutter can be heard and the schematic of the LFO. The way the LFO is set up in terms of caps and isolation can be extrapolated to every other circuit I have made, I always place those 100nF caps between each rail and ground.
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<div class="gmail_chip gmail_drive_chip" style="width: 396px; height: 18px; max-height: 18px; background-color: #f5f5f5; padding: 5px; color: #222; font-family: arial; font-style: normal; font-weight: bold; font-size: 13px; border: 1px solid #ddd; line-height: 1;">
<a style="display: inline-block; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; text-decoration: none; padding: 1px 0px; width: 100%;" href="https://drive.google.com/file/d/1ts1WGcyl2y1Ypp5eP79Ptb5fHXawetZh/view?usp=drive_web" target="_blank" rel="noopener" aria-label="LFO (square).jpg"><img style="vertical-align: bottom; border: none;" src="https://drive-thirdparty.googleusercontent.com/16/type/image/png"> <span dir="ltr" style="color: #15c; text-decoration: none; vertical-align: bottom;">LFO (square).jpg</span></a>
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<div class="gmail_chip gmail_drive_chip" style="width: 396px; height: 18px; max-height: 18px; background-color: #f5f5f5; padding: 5px; color: #222; font-family: arial; font-style: normal; font-weight: bold; font-size: 13px; border: 1px solid #ddd; line-height: 1;">
<a style="display: inline-block; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; text-decoration: none; padding: 1px 0px; width: 100%;" href="https://drive.google.com/file/d/1RrUNX_Of_RGLAwn2CyV7I5fxRrlHvfHL/view?usp=drive_web" target="_blank" rel="noopener" aria-label="VCO stutter.mp3"><img style="vertical-align: bottom; border: none;" src="https://ssl.gstatic.com/docs/doclist/images/icon_10_generic_list.png"> <span dir="ltr" style="color: #15c; text-decoration: none; vertical-align: bottom;">VCO stutter.mp3</span></a>
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In case you have any idea what could be wrong, your reply will be greatly appreciated. Thanks beforehand!
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Kind regards,
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A.M. Barrio.
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In response to pata and Mike Bryant:
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<li>Yes, the current PSU I'm using can provide 8W in total. I'm only powering one VCO and one LFO with some LEDs, power shouldn't be the issue in this case.</li>
<li>I always place 100nF caps between each rail and GND on every circuit/board. However I hadn't heard of placing caps on each IC. I suppose it should be between their power pins and GND? I will have a look at capacitance multipliers as well as I haven't heard about them before.</li>
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