<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto">did you try to remove the LED from the LFO? I think it eats current like hell<br><br><div dir="ltr">http://www.florian-anwander.de <div><br></div></div><div dir="ltr"><br><blockquote type="cite">Am 19.02.2023 um 17:26 schrieb A.M. Barrio via Synth-diy <synth-diy@synth-diy.org>:<br><br></blockquote></div><blockquote type="cite"><div dir="ltr"><div dir="ltr">
<div>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">pata@ieee.org</a> and <a href="mailto:mbryant@futurehorizons.com" target="_blank">mbryant@futurehorizons.com</a>, thank you for your replies, I have taken them into account :-)<br><div><div><table cellpadding="0"><tbody><tr><td><table cellpadding="0"><tbody><tr><td><br></td></tr></tbody></table></td></tr></tbody></table></div></div></div><div>------------------------------------<br></div><div><br></div><div>Hello,<br></div><div>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:</div><div><br></div><div>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. <br></div><div><br></div><div>That would be: <b>without connecting the clock or the LFO anywhere</b>,
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.</div><div><br></div><div>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:</div><div><br></div><div><ul><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></ul><div>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.</div><div><br></div><div>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.</div><div><br></div><div><br><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 href="https://drive.google.com/file/d/1ts1WGcyl2y1Ypp5eP79Ptb5fHXawetZh/view?usp=drive_web" target="_blank" style="display:inline-block;overflow:hidden;text-overflow:ellipsis;white-space:nowrap;text-decoration:none;padding:1px 0px;border:medium none;width:100%" aria-label="LFO (square).jpg"><img style="vertical-align: bottom; border: none;" src="https://drive-thirdparty.googleusercontent.com/16/type/image/png" data-unique-identifier=""> <span dir="ltr" style="color:#15c;text-decoration:none;vertical-align:bottom">LFO (square).jpg</span></a></div><br><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 href="https://drive.google.com/file/d/1RrUNX_Of_RGLAwn2CyV7I5fxRrlHvfHL/view?usp=drive_web" target="_blank" style="display:inline-block;overflow:hidden;text-overflow:ellipsis;white-space:nowrap;text-decoration:none;padding:1px 0px;border:medium none;width:100%" 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" data-unique-identifier=""> <span dir="ltr" style="color:#15c;text-decoration:none;vertical-align:bottom">VCO stutter.mp3</span></a></div><br></div><div><br></div><div>In case you have any idea what could be wrong, your reply will be greatly appreciated. Thanks beforehand!</div><div><br></div><div>Kind regards,</div><div><br></div><div>A.M. Barrio.<br></div><div><br></div><div>
------------------------------------
</div><div><br></div><div>In response to pata and Mike Bryant: <br></div><div><ul><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></ul></div></div>
</div>
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