<div dir="ltr"><div>Hello again,</div><div><br></div><div>First off I'd like to show how appreciative I am about all this technical support, I wasn't expecting such extensive and informative answers! (and quick too...). I'll try to answer to everything that's been talked about here:</div><div><br></div><div><ul><li>To David Huss, René Schmitz, Lukas Hazen-Bushbaker: thanks a lot for your thorough explanation on why this is happening. At least I can say I now understand what's going on. David's bucket analogy in particular made it super easy for me to grasp the idea. In the process, though, you also gave me a feeling that these matters might be a little too complicated for me to manage haha! I'm no engineer nor do I have as much knowledge on electronics as I'd like to... I actually do have some, I work as a technician repairing stuff, but the reasons behind my problem and the solutions to it caught me off guard. I was never taught too much on noise issues back when I was studying, I suppose it is explored more deeply in actual EE degrees. As a result I've never been aware of it: there are no 100uF caps anywhere on the entire synth case, my bus board is the crappiest, most DIY thing you can think of and my way-to-go has always been <i>slap in those 100nF caps between rails and go test it!</i> So much for me to learn on this topic.</li></ul><ul><li>To René Schmitz, Roman Sowa: I must note that the schematic I attached on the first email is not the LFO, but the clock, that's my bad again. That's why there's only one LED. However I just noticed that I didn't rectify the signal before plugging it to U1C, so the negative cycles are indeed going nowhere. I will change that in the clock circuit. On the LFO circuit I do have two LEDs per wave, one for positive cycles and one for negative cycles. Took notes about high efficiency LEDs as well, right now I'm using a plain common red LED on the clock and six green (!) LEDs on the LFO, since it has three wave types. I'm still concerned about the LEDs however... a total of 7 LEDs might take around 140mA, would that be correct? Even if I were to correctly bypass all my circuits and properly isolate everything, would the LEDs still suppose an issue in terms of sag/wiggle for a PSU that can supply much more? (all of the PSUs I tried with can supply around 1A max).<br></li></ul></div><div><ul><li>To Mike Beauchamp, Chris McDowell, Roman Sowa: The VCO design comes from Moritz Klein's one. I'm attaching a schematic of the exact circuit I'm implementing. After reading all the responses it is quite obvious to me that it is VERY prone to changes in output frequency: the CV pots are tied directly to the rails, as well as the CD40106 IC in charge of generating the oscillation. Roman, I am taking absolutely no offense from your comment: it is indeed a bad design. I am not willing to improve <i>this</i> particular VCO design as it was just a test and a bad example of me being too excited to have my first panel mounted on my case. Please ignore the wasteful use of the 40106 and the crappy expo converter, much more care will be put into the next VCO I put together. About this: <i>
If you need help deciding which ones those are, post the VCO schematics.</i> Would you mind pointing them out? I mentioned a couple spots above, but I'd like to make sure I cover them all.
That being said, I'd love to hear about the reference voltages. Chris,
thanks for the IC examples, I'll check them out. Besides, I have some
spare 7805 regulators at home. Although they are quite big, would they
do the job for testing before I go ahead and grab some of the examples
you mentioned?
</li></ul></div><div><ul><li>To Ian Fritz: Thanks for welcoming, and that's a good sense of humour you've got :-). I can only show my respect to you guys, you really seem to be very knowledgeable people.</li></ul><div><br></div><div>So, to summarize: I must look for a way to improve my bus board (uh consider spending some money on a proper PSU/bus board). I must plug 100uF to 470uF caps between each rail and GND on every module as well as the bus board. 100nF caps between each IC and GND are recommended. Sensitive parts of circuits should never be tied directly to the power rails, but to a voltage regulator instead. Would these measures remove (or at least notably reduce) the problem I'm facing?</div><div><br></div><div>Thanks a lot beforehand,</div><div><br></div><div>A.M. Barrio.<br></div></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/1EBAwnrlCLTUUEoa8b8sTuSTGzpBY5-kL/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.png"><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.png</span></a></div>
</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, Feb 19, 2023 at 5:21 PM A.M. Barrio <<a href="mailto:albertomunozbarrio@gmail.com">albertomunozbarrio@gmail.com</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 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="m_-7389626369345500697goog_1466379976"></span><span id="m_-7389626369345500697goog_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:rgb(245,245,245);padding:5px;color:rgb(34,34,34);font-family:arial;font-style:normal;font-weight:bold;font-size:13px;border:1px solid rgb(221,221,221);line-height:1"><a href="https://drive.google.com/file/d/1ts1WGcyl2y1Ypp5eP79Ptb5fHXawetZh/view?usp=drive_web" 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" target="_blank"><img style="vertical-align: bottom; border: medium none;" src="https://drive-thirdparty.googleusercontent.com/16/type/image/png"> <span dir="ltr" style="color:rgb(17,85,204);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:rgb(245,245,245);padding:5px;color:rgb(34,34,34);font-family:arial;font-style:normal;font-weight:bold;font-size:13px;border:1px solid rgb(221,221,221);line-height:1"><a href="https://drive.google.com/file/d/1RrUNX_Of_RGLAwn2CyV7I5fxRrlHvfHL/view?usp=drive_web" 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" target="_blank"><img style="vertical-align: bottom; border: medium none;" src="https://ssl.gstatic.com/docs/doclist/images/icon_10_generic_list.png"> <span dir="ltr" style="color:rgb(17,85,204);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>
</blockquote></div>